Indoor Air Quality Measurements in Enclosed Spaces Combining Activities with Different Intensity and Environmental Conditions

Ci a ion: U bina-Ga cia, O.;
Fe nandez-Gamiz, U.; Zulue a, E.;
Uga e-Ane o, A.; Po al-Po as, K.
Indoo Ai Quali y Measu emen s in
Enclosed Spaces Combining Ac i i ies
wi h Di e en In ensi y and
En i onmen al Condi ions. Buildings
2024,14, 1007. h ps://doi.o g/
10.3390/buildings14041007
Academic Edi o : Ch is ophe
Yu-Hang Chao
Recei ed: 4 Feb ua y 2024
Re ised: 9 Ma ch 2024
Accep ed: 29 Ma ch 2024
Published: 5 Ap il 2024
Copy igh : © 2024 by he au ho s.
Licensee MDPI, Basel, Swi ze land.
This a icle is an open access a icle
dis ibu ed unde he e ms and
condi ions o he C ea i e Commons
A ibu ion (CC BY) license (h ps://
c ea i ecommons.o g/licenses/by/
4.0/).
buildings
A icle
Indoo Ai Quali y Measu emen s in Enclosed Spaces
Combining Ac i i ies wi h Di e en In ensi y and
En i onmen al Condi ions
Oska U bina-Ga cia 1, Unai Fe nandez-Gamiz 1,* , Ekai z Zulue a 2, Aina a Uga e-Ane o 1
and Koldo Po al-Po as 1
1Nuclea Enginee ing and Fluid Mechanics Depa men , Uni e si y o he Basque Coun y, UPV/EHU,
Nie es Cano 12, 01006 Vi o ia-Gas eiz, A aba, Spain; [email p o ec ed] (O.U.-G.);
[email p o ec ed] (A.U.-A.); [email p o ec ed] (K.P.-P.)
2Sys em Enginee ing and Au oma ion Con ol Depa men , Uni e si y o he Basque Coun y, UPV/EHU,
Nie es Cano 12, 01006 Vi o ia-Gas eiz, A aba, Spain; [email p o ec ed]
*Co espondence: [email p o ec ed]
Abs ac : The impac o he COVID-19 pandemic has caused an inc ease in knowledge in ce ain
ields such as human b ea hing and espi a o y diseases. In he cu en s udy, enclosed-space
cha ac e is ics we e assessed due o he g ea deba e gene a ed because o he pandemic. Tempe a u e,
ela i e humidi y, ca bon dioxide (CO
2
) concen a ion, pa icula e ma e (PM) concen a ion and
cumula i e pa icle concen a ion pe cen age pe size ac ion we e measu ed in h ee buildings
unde he occu ence o ac i i ies wi h di e en in ensi y le els. Fo he measu emen s, A duino
UNO, Sensi on SCD30 and APS-3321 de ices we e used. Na u al en ila ion was con olled ia
windows and/o doo s, and he in luence o ai condi ioning was s udied in one o hese ooms, in
which medium- o high-in ensi y ac i i ies we e conduc ed. All expe imen s e ealed a dec ease
in empe a u e associa ed wi h an inc ease in he ela i e humidi y when CO
2
dec eased. As
a consequence
, d as ic dec eases occu ed a ew minu es a e windows and doo s we e opened. In
no- en ila ion in e als, he obse ed linea inc ease changed in o an asymp o ic end below he
1000 ppm limi ecommended by Sinphonie guidelines. Addi ionally, he opposi e beha io was
obse ed be ween pa icles abo e and below a ce ain size. This expe imen is o in e es o u he
in es iga e c i ical en ila ion a e e sus olume o ai pe indi idual.
Keywo ds: ae odynamic pa icle size; ca bon dioxide concen a ion; enclosed space; na u al en ila ion;
pa icula e ma e
1. In oduc ion
Th ee yea s o unce ain y due o he COVID-19 pandemic esul ed in p oblems
anging om global economic issues o se e e damage o he heal h o indi iduals [
1
].
To comba his i us, se e al accines we e p oduced by pha maceu ical companies. In
s udies on he de elopmen o an e ec i e and sa e accine agains he i us, p o ein
S was conside ed he bes an igen o be included [
2
]. The i us mu a ed as expec ed
a e a ian B.1.1.7 was de ec ed in England and a ian B.1.617.2 iden i ied in India
exhibi ed a di e en beha io o accines [
3
]. Once a ian B1.1.529 eme ged, conce ns
ega ding he e ec i eness o a ailable accines and an ibody-based he apeu ics we e
aised
[4–6]
. A he same ime, qua an ine measu es, es ic ions on anspo o indi iduals,
in e pe sonal dis ancing and mask use we e p o en o be he mos e ec i e measu es o
p e en SARS-CoV-2 ansmission [
7
]. In addi ion, o he measu es mus be moni o ed
while allowing in e ac ion in enclosed spaces unde es ic i e condi ions, i.e., ca bon
dioxide (CO
2
) measu emen and en ila ion [
7
,
8
]. The educ ion in he ansmission
isk in indoo class ooms a schools due o e ec i e CO
2
concen a ion moni o ing and
Buildings 2024,14, 1007. h ps://doi.o g/10.3390/buildings14041007 h ps://www.mdpi.com/jou nal/buildings
Buildings 2024,14, 1007 2 o 28
aking en ila ion ac ions was explained [
8
]. To his mus be added, as he esul s o he
esea ch o Shao e al. [
9
], ha a eliable design o he en ila ion sys em educes he
isk o pa icle accumula ion; con e sely, an un o una e design c ea es an en i onmen
whe e he concen a ion o in ec ion is high. Taking he design o he en ila ion sys em as
an impo an pa ame e ,
William e al. [
10
] concludes ha be ween Con en ional O e head
Dis ibu ion (COHD) and Unde loo Ai Dis ibu ion (UFAD), he la e ca ches be e
ae osols, hus educing he isk o ansmission. Looking o he u u e, Song e al. [
11
]
wo ks on a s udy on he de elopmen o cus om en ila ion in each space and he con ol
o CO
2
concen a ion. Addi ionally, he analysis o he isk o in ec ion by ansmission
o he i us in he ai has been s udied [
12
–
15
]. SARS-CoV-2 ansmission can occu ia
ai bo ne ansmission, espi a o y ae osol d ople s and di ec –indi ec con ac p ocesses
be ween wo indi iduals [
16
]. Howe e , he main sou ce o ansmission in ol es ae osols
o ai bo ne ansmission, as demons a ed by Zhang e al. [
17
]. Rega ding he isk o
SARS-CoV-2 ansmission, enclosed spaces o en i onmen s suppose a highe isk, o
example, c owded esiden ial buildings, public anspo ehicles, en e ainmen enues
and shopping malls [
18
]. To a oid a high ansmission isk in an enclosed en i onmen , i
is c ucial o implemen an e icien en ila ion sys em [
19
]. This is e en mo e impo an
in en i onmen s whe e many people ga he o long pe iods, i.e., wo king in an o ice.
An excessi ely high concen a ion o pa icula e ma e (PM) is usually conside ed o
indica e poo -quali y ai . Ne e heless, ega ding o he quali y o indoo ai , ano he
c i ical componen ha mus be educed ia en ila ion is CO
2
. Enclosed spaces such as
class ooms, which a e ypically ull o people, poo ly en ila ed and o e hea ed, end o
in ensi y his e ec . This could lead o a scena io whe e he ca bon dioxide concen a ion
could ad e sely a ec he heal h o indi iduals, e.g., a concen a ion exceeding 1500 ppm o
a le el lowe han 1000 ppm, acco ding o Schools Indoo Pollu ion and Heal h Obse a o y
Ne wo k in Eu ope (Sinphonie) guidelines [
20
]. Indoo concen a ions o ca bon dioxide
play an impo an ole when examining indoo ai quali y (IAQ) and en ila ion [
21
]. The
ele ance o he measu es o CO
2
concen a ion educ ion, en ila ion con ol and IAQ
s anda ds esides in hei associa ion wi h bio-e luen s and odo s in enclosed spaces and
he en ila ion-pe -indi idual a io le el. Indoo and ou doo co ela ions be ween CO
2
and PM
2.5
a ios we e u he assessed, he eby co ela ing measu ed da a wi h class oom
occupancy and en ila ion a es [
22
]. In addi ion o ha , he Ene gy pe o mance o
buildings—Ven ila ion o buildings EN16798-1 [
23
] is ecognized as a well-known s anda d
o PM
2.5
and PM
10
concen a ion limi s ega ding indoo ai quali y, e.g., conside ing
25 µg/m3
as a limi o bo h pa icle ma e diame e s o accep able IAQ ha should be
aken in o accoun when assessing and designing indoo spaces.
In o de o main ain p ope indoo ai quali y le els in a class oom unde ce ain
pa ame e s, simple ac ions such as p e en ing o e c owding, employing sui able en-
ila ion a es and ins alling en ila ion sys ems including ai cleane s we e highly ec-
ommended [
24
]. The au ho s ecommended p io i izing he use o ai pu i ie s and ai
condi ione s acco ding o il e sys ems. Whene e possible, annual moni o ing o indoo
PM and andom concen a ions could be a good s a egy [
25
]. In addi ion, mo e easible
measu emen s we e p oposed o gain be e IAQ condi ions. Fo ins ance, equipmen
p oducing ola ile o ganic compounds (VOCs) o pa icles should be loca ed ou side,
and he class oom empe a u e should be main ained wi hin he a ge ange wi h he
aid o he mos a s. Dinh e al. [
26
] obse ed he ele ance o CO
2
as an indica o o be
measu ed wi h he in en ion o con olling he indoo ai quali y and measu ing he en-
ila ion e iciency. By con olling en ila ion in enclosed en i onmen s and moni o ing
CO
2
le els, indi iduals could p e en becoming ill, pa icula ly conside ing espi a o y
i al ansmission. CO
2
dioxide concen a ion is a key pa ame e because he con en in
exhaled ai can be co ela ed wi h he isk o in ec ion and he p obabili y o ansmission
h ough he Wells–Riley equa ion [
27
]. Pa icles in gene al, and ca bon dioxide molecules
in pa icula , a e dense han ai . Howe e , in e ms o anspo ia ai low, hey exhibi
he same capabili y as ha o i us pa icles. The e o e, CO
2
concen a ions abo e a ce -
Buildings 2024,14, 1007 3 o 28
ain le el sugges inadequa e en ila ion, and ac ions mus be aken. The displacemen
en ila ion s a egy was p oposed by Bhaga e al. [
28
] as he mos e icien app oach o
educe he isk o exposu e o in ec ion. Once displacemen en ila ion is well designed,
his could aid e ical s a i ica ion and mi iga e he accumula ion o hea ed and pollu ed
ai close o he ceiling. In addi ion, he use o masks is ano he ac ion ha can p oduce
a d as ic dec ease in he amoun o ejec ed o exhaled d ople s and, he e o e, also he
numbe o bioae osols in ai . Fu he mo e, hey sugges ed p e en ing mixed en ila ion
since his could p o oke ai dis ibu ion h oughou he enclosed space and diminish clean
a eas. The easibili y o his en ila ion s a egy in class ooms wi h a hea eco e y pump
was examined by Wang e al. [
29
]. As a esul , he indoo ai quali y was imp o ed, and
a educ ion
in he ene gy consump ion o he school was no ed. Simula ion was pe o med
ia a compu a ional luid dynamics so wa e o echnically p o e he easibili y o his
s a egy. Li e al. [
30
] used an inno a i e en ila o ha eplaced pa o a window ame
wi h a en ila o con aining a c oss low an a he co e. Many o he issues causing poo
en ila ion we e conside ed by Dominguez-Ama illo e al. [
31
]. Buildings wi h low adian
empe a u es as a consequence o hei he mal en elopes p o ide a limi ed pe o mance.
This could ad e sely impac indi iduals, which could esul in o ced en ila ion educ ion,
c ea ing e en iskie condi ions unde con inemen du ing he pandemic, in cold clima es
and du ing longe pe iods o ime. Sa ish e al. [
32
] obse ed ha en ila ion limi a ion
some imes aimed o only educe he consump ion o ene gy, leading o low and ine ec i e
en ila ion a es. Rumche e al. [
33
] s udied loca ions wi h a high a e o po e y and
concluded ha a highe isk o espi a o y diseases could mainly be a ibu ed o he lack
o minimum en ila ion equipmen , e en chimneys and occasionally windows.
The aim o his s udy is o in es iga e indoo ai quali y in enclosed spaces. Th ee
scena ios a e p esen ed: Fi s , a class oom wi h and wi hou s uden s in ol ed in low-
in ensi y ac i i ies was conside ed, deno ed as measu emen s 1 and 2. Secondly, a lib a y
wi h a child en’s a ea, mee ing oom and con e ence oom we e used o da a acquisi ion,
conside ing his a medium-in ensi y scena io, deno ed as measu emen s 3, 4 and 5. Fi-
nally, he hi d scena io included spo s acili ies wi h high-in ensi y ac i i ies, deno ed
as measu emen s 6 and 7. In each expe imen o measu emen , he concen a ion o CO
2
,
ela i e humidi y, empe a u e, pa icle size, pa icle ma e (PM
2.5
, PM
10
and PM
20
) and
he pe cen age o accumula ed pa icle mass concen a ion we e moni o ed and cap u ed
o achie e a comp ehensi e s udy. In addi ion, he analysis o he isk o in ec ion om
ai bo ne i us ansmission was also included as an empi ical s udy. Las ly, ecommenda-
ions o building design and conclusions a e gi en in o de o lowe he isk o in ec ion
and main ain an adequa e IAQ o enclosed spaces.
2. Ma e ials and Me hods
The expe imen al measu emen s p esen ed in his a icle encompassed a o al o se en
e en s moni o ed a h ee loca ions in Vi o ia-Gas eiz ci y be ween
15 Decembe 2021
and
28 Decembe 2021. The i s wo measu emen s occu ed a he Uni e si y o he Basque.
Th ee measu emen s we e ealized a he Ignacio Aldecoa public lib a y. Da a o he
las wo measu emen s we e acqui ed in he Mendizo oza spo s acili ies. Rega ding
he measu emen s inside enclosed spaces, da a acquisi ion was pe o med wi h an ae o-
dynamic pa icle size spec ome e (APS-3321) and wo A duino boa ds connec ed o
wo Sensi on
SCD30 senso s, all o which we e connec ed ia USB o a lap op o da a
collec ion. Ou side wea he condi ions we e ex ac ed om he public and eely accessible
webpage o EUSKALMET conside ing he closes s a ion o he measu emen loca ions,
and he same s a ion was used o h ee o he measu emen s loca ed on he uni e si y
campus o he Facul y o Pha macy.
2.1. Measu emen De ini ion
The du a ion o he expe imen s depended on he du a ion o he ongoing ac i i-
ies, ex a ime was added be o e he expe imen s and once equipmen se up was inal-
Buildings 2024,14, 1007 4 o 28
ized, and a “back o calm” in e al was conside ed a e he expe imen s. The du a ion
o
all expe imen s
anged om 1 h 57 min o 2 h 22 min. The en ila ion me hod in
all he expe imen s
was na u al en ila ion by opening doo s and/o windows. The las
wo expe imen s
we e pe o med in he Mendizo oza spo s acili ies wi h ai condi ion-
ing. Rega ding people, all he expe imen s we e conduc ed in he same way. The enclosed
spaces we e emp y a he s a ing poin , and people en e ed he spaces o a ce ain ac i i y
and le a e hey we e inished. The ac i i y in ensi y le els we e low in measu emen s 1,
2, 4 and 5 since all people a ended a lec u e o mee ing in a si ing and elaxed posi ion.
Measu emen 3 in ol ed he low- o medium-in ensi y ac i i y o singing owa d he end.
Medium-in ensi y gym ac i i ies occu ed in he six h expe imen as people engaged in
exe cise, and high-in ensi y ae obic ac i i ies combined wi h exe cise we e obse ed in
he se en h expe imen . The expe imen s we e all conduc ed wi h pa icipan s wea ing
su gical o clinical masks he en i e ime, excep o he hi d expe imen , in which se e al
child en did no wea masks a all. Table 1p esen s a summa y o he measu emen condi-
ions, and Table 2lis s he physical and na u al en ila ion cha ac e is ics o he enclosed
spaces; in bo h ables, Ven . deno es en ila ion. Measu emen s 1 and 2 we e pe o med
wi h he same indi iduals, s uden s in a 20–22 age ange. Fo measu emen 3, he e we e
14 child en in a 6–10 yea s ange and 26 adul s in a 30–45 ange. Measu emen s 4 and
5 in ol ed indi iduals o mo e han 65 yea s old, and measu emen s 6 and 7 in ol ed
indi iduals in a b oade age ange, om 18 o 55.
Table 1. Measu emen condi ion summa y.
M.
No. Loca ion Day Pe iod Ven .
Sys em
Occupancy
* (Xi-Xm-Xe)
Ac i i y
In ensi y
Le el Mask
1UPV/EHU
A206 class oom 15 Dec 2021 11:07–13:29 na u al 0-15-0 Low YES
2UPV/EHU
A206 class oom 16 Decembe 2021 11:21–13:43 na u al 0-1-0 Low YES
3Lib a y
child en’s a ea 22 Decembe 2021 17:34–19:31 na u al 0-40-0
Low/medium
14 Child en
NO
4Lib a y
assembly hall 23 Decembe 2021 10:53–13:13 na u al 0-49-0 Low YES
5Lib a y
con e ence oom 23 Decembe 2021 17:38–19:56 na u al 0-31-0 Low YES
6Gym
aining oom 27 Decembe 2021 18:01–20:00 na u al
(A/C ON) 0-14-0 Medium YES
7Gym
spinning oom 28 Decembe 2021 18:55–21:15 na u al
(A/C ON) 0-22-0
Medium/high
YES
* Fo Occupancy column in Table 1: Xi-Xm-Xe s ands o numbe o indi iduals X. “Xi” a he ini ia ion o he
measu emen s, “Xm” maximum du ing he measu emen and “Xe” a he end o he measu emen . Typically,
nobody a he s a and a he end o measu emen s.
Table 2. Enclosed space speci ica ions.
M.
No.
Ceiling
Heigh
[m]
Floo
A ea
[m2]
Enclosed
Space
Volume
[m3]
Window
Type
Ven .
A ea
Min.
[m2]
Ven .
A ea
Windows
[m2]
Ven .
A ea
Doo s
[m2]
Ven .
A ea
Max.
[m2]
Floo
A ea pe
Pe son
[m2]
1 4.0 57.2 229 Tu n 0.0 4.2 3.4 7.5 3.8
2 4.0 57.2 229 Tu n 0.0 4.2 3.4 7.5 57.2
3 5.0 315.8 1579 Cen e
Til 0.5 2.4 - 2.4 7.9
4 3.3 305.5 1008 Cen e
Til 0.0 - 1.8 1.8 6.2
5 3.4 79.7 271 Cen e
Til 0.2 0.2 - 0.2 2.6
6 3.3 149.0 492 Bo om
Til 2.4 2.4 2.0 4.3 10.6
7 3.0 116.8 350 Bo om
Til 2.4 0.4 2.4 2.8 5.3
Buildings 2024,14, 1007 5 o 28
The lis o measu emen s in ch onological o de o pe o mance is as ollows:
1. Uni e si y Class oom A206–Scena io 1: Du ing class wi h s uden s.
2. Uni e si y Class oom A206–Scena io 2: Quasi-emp y class.
3. Ignacio Aldecoa Lib a y—Child en’s a ea.
4. Ignacio Aldecoa Lib a y—Assembly Hall
5. Ignacio Aldecoa Lib a y—Con e ence Room.
6. Mendizo oza spo s acili ies—T aining Room
7. Mendizo oza spo s acili ies—Spinning Room
Fo a mo e de ailed iew o he enclosed spaces, please e e o he 2D d awings
included in he Supplemen a y Ma e ial o he cu en a icle. Table 3p esen s he ou side
wea he condi ions du ing he expe imen s collec ed by he Basque me eo ology se ice,
EUSKALMET, om he nea es wea he s a ion loca ed on he uni e si y campus o he
Facul y o Pha macy. Ex ended da a including ou doo en i onmen condi ions can also be
ound in he Supplemen a y Ma e ial.
Table 3. Ou side wea he condi ions.
M.
No.
Closes
Wea he
S a ion
S a ion
Dis ance
[m]
Tempe a u e
[◦C]
Rela i e
Humidi y
[%]
Pa m
[mba ]
Wind Speed
[km/h]
Wind Main
Componen
1 Pha macy 250 2–5 97–90 961 1–2 N
2 Pha macy 250 2–4 94–87 962 1–3 NE
3 Pha macy 500 5–4 88–94 952 2–3 NW
4 Pha macy 500 7–9 82–79 954 3–2 W
5 Pha macy 500 7.5 90–92 951 1–2 NW
6 Pha macy 1250 13 66–63 945 25–28 SW
7 Pha macy 1250 14–13 70–72 954 12–9 SW
2.2. Ins umen a ion and Me hodology
Two Sensi on SCD30 senso s (Sensi ion AG, S ä a, Swi ze land) we e used o da a
collec ion o he CO
2
concen a ion in he ai using NDIR echnology, ela i e humidi y and
empe a u e. Each o hese senso s, he ea e e e ed o as Senso 1 (S1) and Senso 2 (S2),
p o ides he same measu emen abili y. The CO
2
senso moun ed on hese de ices exhibi s
an e o o
±
(30 ppm + %3 MV), and he measu emen alue anges om
400 ppm
o
10,000 ppm. Be ween 0
◦
C and +50
◦
C, he ins alled empe a u e senso exhibi s an e o
o
±
(0.4
◦
C + 0.023
×
(T [
◦
C]
−
25
◦
C)), and he measu emen alue anges om
−
40
◦
C
o +70
◦
C. The associa ed humidi y senso exhibi s an e o o
±
3% RH a 25
◦
C, and he
measu emen alue anges om 0% o 100%. Rega ding he en i onmen al condi ions, he
ca bon dioxide senso exhibi s a limi ed ope a ing ange, a ying be ween 0
◦
C and +50
◦
C
o he empe a u e and below +95% o he humidi y. The SCD30 senso s we e calib a ed
using he Spa kFun SCD30 lib a y wi h de aul pa ame e s and ollowing he ins uc ions
ound in he da ashee p o ided by he ab ican . Each SCD30 senso was connec ed o
an A duino UNO R3 boa d. Da a we e ans e ed om he senso o he A duino boa d
ollowing he I2C p o ocol, as shown in Figu e 1, whe e he pu ple cable is he Vin cable,
o ange is he GND cable, g een is he SCL cable, and blue is he SDA cable. The A duino
p og am was used wi h he Spa kFun lib a y, speci ically concei ed o he SCD30 senso .
Each A duino boa d was connec ed ia USB o he lap op. Da a we e ans e ed om
he A duino boa d o he compu e e e y 6 s ia he se ial po . The ans e ed da a was
p ocessed on a lap op in he MATLAB 9.13 R2022b en i onmen .
An ae odynamic pa icle size (APS) spec ome e was used o measu e he ae osol
mic opa icle size dis ibu ion inside he class oom. The de ice (model APS-3321; TSI,
Sho e iew, MN, USA) uses he echnique whe eby ime-o - ligh alues o indi idual
pa icles a e measu ed in an accele a ing low ield wi h a single, high-speed iming
p ocesso . Coincidence de ec ion was achie ed using a pa en ed, double-c es op ical

Buildings 2024,14, 1007 6 o 28
sys em, and pa icle size binning was based on an in e nally s o ed calib a ion cu e. The
pa icle size anged om 0.5 o 20
µ
m ega ding he ae odynamic size and 0.37 o 20
µ
m in
ega d o op ical de ec ion.
Buildings2024,14,xFORPEERREVIEW6o 31
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°Cand+50°C o  he empe a u eandbelow+95% o  hehumidi y.TheSCD30senso s
we ecalib a edusing heSpa kFunSCD30lib a ywi hde aul pa ame e sand ollow‐
ing heins uc ions oundin heda ashee p o idedby he ab ican .EachSCD30senso 
wasconnec ed oanA duinoUNOR3boa d.Da awe e ans e ed om hesenso  o
heA duinoboa d ollowing heI2Cp o ocol,asshowninFigu e1,whe e hepu ple
cableis heVincable,o angeis heGNDcable,g eenis heSCLcable,andblueis he
SDAcable.TheA duinop og amwasusedwi h heSpa kFunlib a y,speci icallycon‐
cei ed o  heSCD30senso .

Figu e1.Connec ionbe weenA duinoUnoandSCD30.
EachA duinoboa dwasconnec ed iaUSB o helap op.Da awe e ans e ed
om heA duinoboa d o hecompu e e e y6s ia hese ialpo .The ans e edda‐
awasp ocessedonalap opin heMATLAB9.13R2022ben i onmen .
Anae odynamicpa iclesize (APS)spec ome e wasused omeasu e heae osol
mic opa iclesizedis ibu ioninside heclass oom.Thede ice(modelAPS‐3321;TSI,
Sho e iew,MN,USA)uses he echniquewhe eby ime‐o ‐ ligh  alueso indi idual
pa iclesa emeasu edinanaccele a ing low ieldwi hasingle,high‐speed imingp o‐
cesso .Coincidencede ec ionwasachie edusingapa en ed,double‐c es op icalsys‐
em,andpa iclesizebinningwasbasedonanin e nallys o edcalib a ioncu e.The
pa iclesize anged om0.5 o20μm ega ding heae odynamicsizeand0.37 o20μm
in ega d oop icalde ec ion.
TheAPSwassuccess ullyusedbyA amendiae al.[34] o measu ingnebulized
pa iclesizedis ibu ions,p o idinghigh‐ esolu ionmeasu emen s o d ople sbe‐
ween0.5and20μm.P ei e e al.[35]no ed ha  hesizinge o  a elyexceeded10%.
Chene al.[36]desc ibed hema hema icalmodelsusedinAIM12.1so wa e(TSIIn‐
co po a ed) ocalcula e hequan i yo suc ionedpa iclesand hei size.Thespec ome‐
e wasalsoconnec ed iaUSB o helap op,andcollec edda awe eacqui ed,analyzed
ands o edon helap opalongwi hda ameasu edby heSCD30senso s.A ypicallay‐
ou o  hese upisshowninFigu e2.AIMso wa ewasalsoadjus ed ocollec da ae e‐
y6s.Da awe eassessed o PM2.5, e e ed oas inepa icles,i.e.,pa icleswi hadi‐
ame e smalle  han2.5μm,whicha e ela ed oheal hissues.Ne e heless,PM10and
PM20,whicha emo eno ablyassocia edwi hcon aminan ssuspendedin hea mos‐
phe e,we es udied.
Figu e 1. Connec ion be ween A duino Uno and SCD30.
The APS was success ully used by A amendia e al. [
34
] o measu ing nebulized
pa icle size dis ibu ions, p o iding high- esolu ion measu emen s o d ople s be ween
0.5 and 20
µ
m. P ei e e al. [
35
] no ed ha he sizing e o a ely exceeded 10%. Chen
e al. [
36
] desc ibed he ma hema ical models used in AIM 12.1 so wa e (TSI Inco po a ed)
o calcula e he quan i y o suc ioned pa icles and hei size. The spec ome e was also
connec ed ia USB o he lap op, and collec ed da a we e acqui ed, analyzed and s o ed on
he lap op along wi h da a measu ed by he SCD30 senso s. A ypical layou o he se up is
shown in Figu e 2. AIM so wa e was also adjus ed o collec da a e e y 6 s. Da a we e
assessed o PM
2.5
, e e ed o as ine pa icles, i.e., pa icles wi h a diame e smalle han
2.5
µ
m, which a e ela ed o heal h issues. Ne e heless, PM
10
and PM
20
, which a e mo e
no ably associa ed wi h con aminan s suspended in he a mosphe e, we e s udied.
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Figu e2.Exampleins umen layou inUni e si yClass oomA206.S1andS2a e heSCD30sen‐
so s;APSis heae odynamicpa iclesize andlap op(ha dwa e o ins umen da as o age).
2.3.Measu emen Repea eabili yLimi a ions
Ino de  o epea  hemeasu emen spe o med,i shouldbe akenin oaccoun  he
in o ma ionp esen edin hisa icleandin heSupplemen a yIn o ma ion iles,whe e
he eisg aphicdesc ip iono  hespaces, olume,a eas,dimensionsandloca iono 
windows,doo sandins umen son hem.I mus bemen ioned ha ou sideai and
wea he condi ions epea abili ycouldbeimpo an  o  he esul s,bu i hasbeenkep 
ou o  hecu en s udyas heya ehighlydi icul  oob ain.Howe e ,due oamajo 
impac o  heindoo condi ions,i isconside ed obeenough o as a ingpoin o  e‐
pea abili yandcompa ison om u u e esea che s.
3.Resul s
Fo eachmeasu emen desc ibedinSec ion2, h ee igu esa ep esen edin he ol‐
lowingsubsec ionso  hecu en sec ion.Fi s ,Figu es3,6,9,12,15,18and21show he
CO2concen a ion(CO2C)inpa iclespe million(ppm)andpa iclenumbe concen a‐
ion(PNC)in henumbe o pa iclespe cubiccen ime e (pa icles/cm3).Second,Fig‐
u es4,7,10,13,16,19and22show he empe a u e(T)indeg eesCelsius(°C)and ela‐
i ehumidi y(RH)asape cen age(%).Then,Figu es5,8,11,14,17,20and23show he
pa iclemassconcen a iono pa icula ema e (PM)concen a ionunde  h eepa icle
sizesinmic ome e s,includingPM2.5(smalle  han2.5μm),PM10(smalle  han10μm)
andPM20(smalle  han20μm; hemaximumsizede ec edby heAPS),allinmi‐
c og amspe cubicme e (μg/m3).Thesame ablep esen s heae odynamicdiame e 
(Da),whichis hemean alueo  heae odynamicdiame e (μm)o  hepa iclesmeas‐
u edin hesample.Addi ionally, hemassmedianae odynamicdiame e (MMAD)is
p esen ed,whichis heae odynamicdiame e size(μm) ha di ides hesampledis i‐
bu ionmassinhal .No e ha Pa se al’s heo emwasconside ed oa oidlosinge ec s
o in e es  om hecap u edda a.Fou ie  ans o mwaspe o med oelimina ehigh‐
equencysignalnoise.No e ha ,whe eno speci ied, hep esen edT,RHandCO2da a
a e ela ed o heS1senso closes  o heAPS.
3.1.Uni e si yClass oom—Scena io1:Du ingClasswi hS uden s
Figu e3shows heca bondioxideandpa iclenumbe concen a ionsinside he
class oom.Be o es a ing hemeasu emen ,a15min en ila ionp ocesswaspe o med
wi hpeopleinside heclass oom.Assoonas hemeasu emen wass a ed,allwindows
anddoo swe eclosed,and heca bondioxideconcen a ioninc eased om700ppm o
abo e1000ppmwi hin20min,whichis hemaximumle el ecommendedby
Sinphonieguidelines,andi could eachup o1027ppm.Inaddi ion, hePNC aluede‐
c eased om44pa icles/cm3 o34pa icles/cm3.Then,onemo ealumnusen e ed he
Figu e 2. Example ins umen layou in Uni e si y Class oom A206. S1 and S2 a e he SCD30 senso s;
APS is he ae odynamic pa icle size and lap op (ha dwa e o ins umen da a s o age).
2.3. Measu emen Repea eabili y Limi a ions
In o de o epea he measu emen s pe o med, i should be aken in o accoun he
in o ma ion p esen ed in his a icle and in he Supplemen a y In o ma ion iles, whe e
he e is g aphic desc ip ion o he spaces, olume, a eas, dimensions and loca ion o
windows, doo s and ins umen s on hem. I mus be men ioned ha ou side ai and
wea he condi ions epea abili y could be impo an o he esul s, bu i has been kep ou
o he cu en s udy as hey a e highly di icul o ob ain. Howe e , due o a majo impac
Buildings 2024,14, 1007 7 o 28
o he indoo condi ions, i is conside ed o be enough o a s a ing poin o epea abili y
and compa ison om u u e esea che s.
3. Resul s
Fo each measu emen desc ibed in Sec ion 2, h ee igu es a e p esen ed in he
ollowing subsec ions o he cu en sec ion. Fi s , Figu es 3, 6, 9, 12, 15, 18 and 21 show he
CO
2
concen a ion (CO
2
C) in pa icles pe million (ppm) and pa icle numbe concen a ion
(PNC) in he numbe o pa icles pe cubic cen ime e (pa icles/cm
3
). Second, Figu es
4, 7, 10, 13, 16, 19 and 22 show he empe a u e (T) in deg ees Celsius (
◦
C) and ela i e
humidi y (RH) as a pe cen age (%). Then, Figu es 5, 8, 11, 14, 17, 20 and 23 show he
pa icle mass concen a ion o pa icula e ma e (PM) concen a ion unde h ee pa icle
sizes in mic ome e s, including PM
2.5
(smalle han 2.5
µ
m), PM
10
(smalle han 10
µ
m)
and PM
20
(smalle han 20
µ
m; he maximum size de ec ed by he APS), all in mic og ams
pe cubic me e (
µ
g/m
3
). The same able p esen s he ae odynamic diame e (D
a
), which is
he mean alue o he ae odynamic diame e (
µ
m) o he pa icles measu ed in he sample.
Addi ionally, he mass median ae odynamic diame e (MMAD) is p esen ed, which is he
ae odynamic diame e size (
µ
m) ha di ides he sample dis ibu ion mass in hal . No e
ha Pa se al’s heo em was conside ed o a oid losing e ec s o in e es om he cap u ed
da a. Fou ie ans o m was pe o med o elimina e high- equency signal noise. No e ha ,
whe e no speci ied, he p esen ed T, RH and CO2da a a e ela ed o he S1 senso closes
o he APS.
3.1. Uni e si y Class oom—Scena io 1: Du ing Class wi h S uden s
Figu e 3shows he ca bon dioxide and pa icle numbe concen a ions inside he
class oom. Be o e s a ing he measu emen , a 15 min en ila ion p ocess was pe o med
wi h people inside he class oom. As soon as he measu emen was s a ed, all windows
and doo s we e closed, and he ca bon dioxide concen a ion inc eased om 700 ppm o
abo e 1000 ppm wi hin 20 min, which is he maximum le el ecommended by Sinphonie
guidelines, and i could each up o 1027 ppm. In addi ion, he PNC alue dec eased om
44 pa icles/cm3
o 34 pa icles/cm
3
. Then, one mo e alumnus en e ed he oom, and win-
dows we e opened du ing he ollowing 16 min, aising he PNC alue o
88 pa icles/cm3
while ai was enewed, and CO
2
C dec eased o 625 ppm. Once again, all windows and
doo s we e closed o 20 min, and he ca bon dioxide le el inc eased o 969 ppm, while
PNC dec eased o 47 pa icles/cm
3
. A his ime, all windows and doo s we e opened.
App oxima ely 5 min a e his, he PNC alue eached i s maximum o 81 pa icles/cm
3
,
hen dec eased o 60 pa icles/cm
3
a e 7 min. Mo eo e , CO
2
C eached i s minimum
alue o 683 ppm 5 min a e all windows and doo s we e opened, and hen i emained
s able un il all windows and doo s we e again closed a e 7 min. Jus be o e closing, he
al eady men ioned alumni le he oom. Again, du ing he subsequen 20 min in e als a
he all-closed s age, CO
2
C inc eased o 1000 ppm, while PNC dec eased o 50 pa icles/cm
3
.
A e his in e al, only he doo s we e opened un il he end o he class. Du ing his
30 min
in e al, he ca bon dioxide le el g adually dec eased o 847 ppm and hen inc eased o
a 961 ppm
peak, inally declining o he 910 ppm le el, which migh be due o people pass-
ing h ough he hall. No e ha he e was a 5 min lack o cap u ed da a due o disconnec ion
o he senso s, a e which hey we e eini ia ed. Howe e , PNC only inc eased a his
s age, inally eaching 80 pa icles/cm
3
. To inish he measu emen , a back- o-calm s age
was pe o med, and o 25 min a e he class had ended, he measu emen con inued a
he all-closed s age wi h he oom emp y. In his in e al, bo h PNC and CO
2
C sligh ly
and slowly dec eased. The i s pa ame e peaked a 868 ppm, while he second pa ame e
eached a peak o 68 pa icles/cm3.
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oom,andwindowswe eopeneddu ing he ollowing16min, aising hePNC alue o
88pa icles/cm3whileai was enewed,andCO2Cdec eased o625ppm.Onceagain,all
windowsanddoo swe eclosed o 20min,and heca bondioxidele elinc eased o
969ppm,whilePNCdec eased o47pa icles/cm3.A  his ime,allwindowsanddoo s
we eopened.App oxima ely5mina e  his, hePNC alue eachedi smaximumo 81
pa icles/cm3, hendec eased o60pa icles/cm3a e 7min.Mo eo e ,CO2C eachedi s
minimum alueo 683ppm5mina e allwindowsanddoo swe eopened,and heni 
emaineds ableun ilallwindowsanddoo swe eagaincloseda e 7min.Jus be o e
closing, heal eadymen ionedalumnile  he oom.Again,du ing hesubsequen 20
minin e alsa  heall‐closeds age,CO2Cinc eased o1000ppm,whilePNCdec eased
o50pa icles/cm3.A e  hisin e al,only hedoo swe eopenedun il heendo  he
class.Du ing his30minin e al, heca bondioxidele elg aduallydec eased o847
ppmand heninc eased oa961ppmpeak, inallydeclining o he910ppmle el,which
migh bedue opeoplepassing h ough hehall.No e ha  he ewasa5minlacko cap‐
u edda adue odisconnec iono  hesenso s,a e which heywe e eini ia ed.How‐
e e ,PNConlyinc easeda  hiss age, inally eaching80pa icles/cm3.To inish he
measu emen ,aback‐ o‐calms agewaspe o med,and o 25mina e  heclasshad
ended, hemeasu emen con inueda  heall‐closeds agewi h he oomemp y.In his
in e al,bo hPNCandCO2Csligh lyandslowlydec eased.The i s pa ame e peaked
a 868ppm,while hesecondpa ame e  eachedapeako 68pa icles/cm3.

Figu e3.CO2concen a ion[ppm] o S1andS2andpa icleconcen a ion[pa icles/cm3].
Figu e4shows heTandRHinside heclass oom.Assoonas hemeasu emen s a ‐
ed,allwindowsanddoo swe eclosed,andTinc easedwi hin20min om18.5°C o21
°C.Mo eo e ,RH emainedalmos s ablea app oxima ely36%.Then,onemo ealumnus
en e ed he oom,and hewindowswe eopeneddu ing he ollowing16min.A  i s ,RH
dec eased o34.5%and heninc eased o37%.Mo eo e ,Tdec eased o17°C.The ea e ,
andonceagain,allwindowsanddoo swe eclosed o 20min,andTinc eased o21°C,
whileRHdec eased o35.5%.A  his ime,allwindowsanddoo swe eopened.App ox‐
ima ely5mina e wa ds,RH eachedi sminimumo 33%, heninc eased o34%a e 7
min.Inaddi ion,T eachedi sminimum alueo 20°Capp oxima ely5mina e allwin‐
dowsanddoo swe eopened,and heni  emaineds ableun ilallwindowsanddoo s
we eagaincloseda e 7min.Thise ec isdue o hehea ingo  hebuilding,speci ically
o  hehalla ea.Jus be o eclosing, heal eadymen ionedalumnile  he oom.Again,
wi hinano he 20minin e ala  heall‐closeds age,Tinc eased o22°C,whileRH
sligh lyinc eased oalmos 35%.A e  hisin e al,only hedoo swe eopenedun il he
endo  heclass.Du ing his30minin e al,RHg aduallydec eased o33%a  heendo 
hes age,wi hapeako 35.3%a e 15min.Incon as ,Tinc eased o22.5°Ca  heendo 
S1 CO2 [ppm] and S2 CO2 [ppm]
Pa icle Conc [pa icles/cm3]
All closed
Open Windows(+1)
All closed
Open Windows & Doo s
All closed(-1)
Open Doo s
All closed and Emp y
Figu e 3. CO2concen a ion [ppm] o S1 and S2 and pa icle concen a ion [pa icles/cm3].
Figu e 4shows he T and RH inside he class oom. As soon as he measu emen
s a ed, all windows and doo s we e closed, and T inc eased wi hin 20 min om 18.5
◦
C
o 21
◦
C. Mo eo e , RH emained almos s able a app oxima ely 36%. Then, one mo e
alumnus en e ed he oom, and he windows we e opened du ing he ollowing 16 min.
A i s , RH dec eased o 34.5% and hen inc eased o 37%. Mo eo e , T dec eased o
17
◦
C. The ea e , and once again, all windows and doo s we e closed o 20 min, and T
inc eased o 21
◦
C, while RH dec eased o 35.5%. A his ime, all windows and doo s we e
opened. App oxima ely 5 min a e wa ds, RH eached i s minimum o 33%, hen inc eased
o 34% a e 7 min. In addi ion, T eached i s minimum alue o 20
◦
C app oxima ely 5 min
a e all windows and doo s we e opened, and hen i emained s able un il all windows
and doo s we e again closed a e 7 min. This e ec is due o he hea ing o he building,
speci ically o he hall a ea. Jus be o e closing, he al eady men ioned alumni le he oom.
Again, wi hin ano he 20 min in e al a he all-closed s age, T inc eased o 22
◦
C, while RH
sligh ly inc eased o almos 35%. A e his in e al, only he doo s we e opened un il he
end o he class. Du ing his 30 min in e al, RH g adually dec eased o 33% a he end o
he s age, wi h a peak o 35.3% a e 15 min. In con as , T inc eased o 22.5
◦
C a he end o
he s age, wi h a alley o 20.8
◦
C a e 15 min. This al e a ion in alues was no conside ed
in he analysis since his migh be due o he 5 min disconnec ion pe iod o he senso s and
eini ia ion s abiliza ion ime. Ne e heless, o inish he measu emen , he back- o-calm
s age was implemen ed, and o 25 min a e he class ended, he measu emen con inued
a he all-closed s age wi h he oom emp y. In his in e al, T con inued o inc ease o
23.4 ◦C, and RH emained comple ely s able a 33%.
Figu e 5shows he PM
2.5
, PM
10
, PM
20
, D
a
and MMAD inside he class oom. As soon
as he measu emen s a ed, all he windows and doo s we e closed, and wi hin 20 min,
PM
20
luc ua ed be ween 20
µ
g/m
3
and 25
µ
g/m
3
, e en eaching 19
µ
g/m
3
. Mo eo e , D
a
inc eased om 0.78
µ
m o 0.83
µ
m and hen dec eased o 0.81
µ
m. Then, one mo e alumnus
en e ed he oom, and he windows we e opened du ing he ollowing 16 min. PM
20
i s a ied be ween 19
µ
g/m
3
and 33
µ
g/m
3
be o e inc easing o 68
µ
g/m
3
. Mo eo e ,
D
a
dec eased o 0.71
µ
m and hen inc eased o 0.77
µ
m. The ea e , all windows we e
again closed du ing 20 min, and PM
20
again dec eased o 19
µ
g/m
3
and hen inc eased
o
31 µg/m3
. In addi ion, D
a
slowly inc eased o 0.78
µ
m du ing he i s 10 min and hen
apidly inc eased o 1.00
µ
m. A his ime, all windows and doo s we e opened, and PM
20
again dec eased o 7
µ
g/m
3
and hen inc eased o 16
µ
g/m
3
, while D
a
dec eased o
0.70 µm
and hen inc eased o 0.74
µ
m. I was ema kable how pa icles wi h sizes la ge han
10 µm
almos disappea ed a he alley poin s o PM
20
= 7
µ
g/m
3
and D
a
= 0.70
µ
m. Jus
be o e closing, he al eady men ioned alumni le he oom. Du ing he subsequen 20 min
in e al a he all-closed s age, PM
20
again inc eased o 45
µ
g/m
3
and hen dec eased o
37 µg/m3
, while D
a
inc eased o 0.90
µ
m du ing he i s 10 min and hen slowly dec eased
Buildings 2024,14, 1007 9 o 28
o 0.88
µ
m. A e his in e al, only he doo s we e opened un il he end o he class. Du ing
his 30 min in e al, D
a
dec eased o 0.77
µ
m a e 15 min and emained s able un il he
end o he s age. In con as , PM
20
again dec eased o an 18
µ
g/m
3
alue a e 15 min, a e
which i inc eased o 34
µ
g/m
3
a he end o he s age. A he back- o-calm s age, and o
25 min a e he class ended, he measu emen con inued a he all-closed s age wi h he
oom emp y. In his in e al, PM
20
again dec eased o 13
µ
g/m
3
du ing he i s 20 min
and hen inc eased o 21
µ
g/m
3
, while D
a
sligh ly dec eased o 0.74
µ
m du ing he i s
20 min and hen inc eased o 0.78 µm.
Buildings2024,14,xFORPEERREVIEW9o 31

hes age,wi ha alleyo 20.8°Ca e 15min.Thisal e a ionin alueswasno conside ed
in heanalysissince hismigh bedue o he5mindisconnec ionpe iodo  hesenso sand
eini ia ions abiliza ion ime.Ne e heless, o inish hemeasu emen , heback‐ o‐calm
s agewasimplemen ed,and o 25mina e  heclassended, hemeasu emen con inued
a  heall‐closeds agewi h he oomemp y.In hisin e al,Tcon inued oinc ease o23.4
°C,andRH emainedcomple elys ablea 33%.

Figu e4.Tempe a u e[°C]and ela i ehumidi y[%] o S1andS2.
Figu e5shows hePM2.5,PM10,PM20,DaandMMADinside heclass oom.Assoonas
hemeasu emen s a ed,all hewindowsanddoo swe eclosed,andwi hin20min,PM20
luc ua edbe ween20μg/m3and25μg/m3,e en eaching19μg/m3.Mo eo e ,Dain‐
c eased om0.78μm o0.83μmand hendec eased o0.81μm.Then,onemo ealumnus
en e ed he oom,and hewindowswe eopeneddu ing he ollowing16min.PM20 i s 
a iedbe ween19μg/m3and33μg/m3be o einc easing o68μg/m3.Mo eo e ,Dade‐
c eased o0.71μmand heninc eased o0.77μm.The ea e ,allwindowswe eagain
closeddu ing20min,andPM20againdec eased o19μg/m3and heninc eased o31
μg/m3.Inaddi ion,Daslowlyinc eased o0.78μmdu ing he i s 10minand hen apidly
inc eased o1.00μm.A  his ime,allwindowsanddoo swe eopened,andPM20again
dec eased o7μg/m3and heninc eased o16μg/m3,whileDadec eased o0.70μmand
heninc eased o0.74μm.I was ema kablehowpa icleswi hsizesla ge  han10μm
almos disappea eda  he alleypoin so PM20=7μg/m3andDa=0.70μm.Jus be o e
closing, heal eadymen ionedalumnile  he oom.Du ing hesubsequen 20minin e ‐
ala  heall‐closeds age,PM20againinc eased o45μg/m3and hendec eased o37
μg/m3,whileDainc eased o0.90μmdu ing he i s 10minand henslowlydec eased o
0.88μm.A e  hisin e al,only hedoo swe eopenedun il heendo  heclass.Du ing
his30minin e al,Dadec eased o0.77μma e 15minand emaineds ableun il he
endo  hes age.Incon as ,PM20againdec eased oan18μg/m3 aluea e 15min,a e 
whichi inc eased o34μg/m3a  heendo  hes age.A  heback‐ o‐calms age,and o 25
mina e  heclassended, hemeasu emen con inueda  heall‐closeds agewi h he oom
emp y.In hisin e al,PM20againdec eased o13μg/m3du ing he i s 20minand hen
inc eased o21μg/m3,whileDasligh lydec eased o0.74μmdu ing he i s 20minand
heninc eased o0.78μm.
11:30 12:00 12:30 13:00
Time [hh:mm]
14
15
16
17
18
19
20
21
22
23
24
30
31
32
33
34
35
36
37
38
39
40
Figu e 4. Tempe a u e [◦C] and ela i e humidi y [%] o S1 and S2.
Buildings2024,14,xFORPEERREVIEW10o 31


Figu e5.PM2.5,PM10andPM20[μg/m3]wi hDa[μm]andMMAD(median)[μm].
3.2.Uni e si yClass oomA206–Scena io2:Quasi‐Emp yClass
Figu e6shows heca bondioxideandpa iclenumbe concen a ionsinside he
class oom.Be o es a ing hemeasu emen ,a5min en ila ionp ocesswaspe o med
wi h heclass oomemp y.Assoonas hemeasu emen wass a ed,all hewindows
anddoo swe eclosed,and heca bondioxideconcen a ioninc eased om800ppm o
873ppmwi hin1min.Mo eo e ,PNCsligh lydec eased om39pa icles/cm3 o34
pa icles/cm3.Then,onealumnusen e ed he oom,and hewindowswe eopeneddu ‐
ing he ollowing16min, aisingPNC o80pa icles/cm3whileai was enewed,and
CO2Cdec eased o515ppm.Onceagain,all hewindowswe eclosed o 20min,and
heca bondioxidele elinc eased o602ppm,whilePNCdec eased o40pa icles/cm3.
A  his ime,all hewindowsanddoo swe eopened.A e app oxima ely5min,PNC
eachedi smaximumo 63pa icles/cm3,dec easing o51pa icles/cm3a e 7min.
Mo eo e ,CO2C eachedi smaximum alueo 688ppm5mina e allwindowsand
doo swe eopened,and heni sligh lydec eased o662ppm7mina e all hewin‐
dowsanddoo swe eagainclosed.Jus be o eclosing, hesinglealumnusle  he oom.
Again,du ingano he 20minin e ala  heall‐closeds age,CO2Cinc easedwi hin1
min o698ppmand hensligh lydec eased o686ppm,whilePNCdec eased o43pa ‐
icles/cm3, eachingapeako 57pa icles/cm3a e 4min.A e  hisin e al,only he
doo swe eopenedun il heendo  heclass.Du ing his30minin e al, heca bondi‐
oxidele elsmoo hlyinc eased o718ppmand hendec eased o680ppm.Howe e ,
PNConlyinc easeda  hiss age, eaching100pa icles/cm3a  heendo i .To inish he
measu emen ,aback‐ o‐calms agewaspe o med,and o 25mina e  heclasswas
ended, hemeasu emen con inueda  heall‐closeds age.In hisin e al,PNCasymp‐
o icallydec eased o80pa icles/cm3,whileCO2Csligh lyinc eased o694ppmand
hendec eased o eacha inal alueo 681ppm.No e ha  heca bondioxidemaximum
le el ecommendedby heSinphonieguidelineswasno  eached.
11:30 12:00 12:30 13:00
Time [hh:mm]
0
10
20
30
40
50
60
70
80
90
100
0.5
0.6
0.7
0.8
0.9
1
1.1
1.2
1.3
1.4
1.5
Figu e 5. PM2.5, PM10 and PM20 [µg/m3] wi h Da[µm] and MMAD (median) [µm].
3.2. Uni e si y Class oom A206–Scena io 2: Quasi-Emp y Class
Figu e 6shows he ca bon dioxide and pa icle numbe concen a ions inside he
class oom. Be o e s a ing he measu emen , a 5 min en ila ion p ocess was pe o med
wi h he class oom emp y. As soon as he measu emen was s a ed, all he windows
and doo s we e closed, and he ca bon dioxide concen a ion inc eased om 800 ppm
o 873 ppm wi hin 1 min. Mo eo e , PNC sligh ly dec eased om 39 pa icles/cm
3
o
34 pa icles/cm3
. Then, one alumnus en e ed he oom, and he windows we e opened
du ing he ollowing 16 min, aising PNC o 80 pa icles/cm
3
while ai was enewed, and
CO
2
C dec eased o 515 ppm. Once again, all he windows we e closed o 20 min, and he
ca bon dioxide le el inc eased o 602 ppm, while PNC dec eased o 40 pa icles/cm
3
. A
his ime, all he windows and doo s we e opened. A e app oxima ely 5 min, PNC eached
i s maximum o 63 pa icles/cm
3
, dec easing o 51 pa icles/cm
3
a e 7 min. Mo eo e ,
Buildings 2024,14, 1007 16 o 28
whole pe iod. A his ime, 5 pe sons le , and a e 15 min, bo h PM
20
and D
a
sligh ly
inc eased and hen e u ned o hei p e ious alues. Again, a his momen , 4 mo e
pe sons le , and a e 8 min, PM
20
inc eased o 13
µ
g/m
3
, while D
a
inc eased o 0.87
µ
m.
To inish he measu emen , a back- o-calm s age was pe o med, and o 20 min a e he
con e ence had ended, he measu emen con inued as be o e unde he same en ila ion
condi ions. In his in e al, in which people le wi hin a ew minu es, PM
20
i s inc eased
o 21
µ
g/m
3
, hen dec eased o 14
µ
g/m
3
and inally inc eased o 27
µ
g/m
3
a he end o
he measu emen . D
a
i s inc eased o 0.94
µ
m and hen dec eased o 0.86
µ
m a he end. I
should be no ed ha pa icles wi h sizes g ea e han 10
µ
m e u ned o hei ini ial s a e a
his inal s age, simila o he s a ing poin o he measu emen .
Buildings2024,14,xFORPEERREVIEW17o 31
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
Figu e13.CO2Concen a ion[ppm] o S1andS2andpa icleconcen a ion[pa icles/cm3].
Figu e14shows hePM2.5,PM10,PM20,DaandMMADinside heassemblyhall.I 
shouldbemen ioned ha PM2.5wasmain ainedwi hou no able a ia ionbe ween2.5
μg/m3and5μg/m3du ingall hemeasu emen s.Once hemeasu emen s a ed, o 9
min,PM20 anged om28μg/m3 o29μg/m3,e en eachinga33μg/m3peak alue.
Mo eo e ,Dadec eased om0.86μm o0.80μm.A  his ime,11mo epe sonsen e ed
hea ea.Thecon e ences a ed,and hedoo wascloseda  hesame ime.Du ing he
ollowing23min,PM20dec eased o12μg/m3.Da i s inc eased o0.81μmand hende‐
c eased o0.79μm.I was ema kablehowpa icleswi hsizesg ea e  han10μmal‐
mos disappea eda  heendo  hiss age.Then,5mo epe sonsen e ed,anddu ing he
ollowing1hand5mincon e encepe iod, en ila ion emaineds able,andpeople e‐
mainedinside hea ea;PM20dec eased o7.3μg/m3a e 5minand hen emaineds a‐
bleun il heendo  hein e al.Incon as ,Da emaineds ablea 0.80μmdu ing he
wholepe iod.A  his ime,5pe sonsle ,anda e 15min,bo hPM20andDasligh lyin‐
c easedand hen e u ned o hei p e ious alues.Again,a  hismomen ,4mo epe ‐
sonsle ,anda e 8min,PM20inc eased o13μg/m3,whileDainc eased o0.87μm.To
inish hemeasu emen ,aback‐ o‐calms agewaspe o med,and o 20mina e  he
con e encehadended, hemeasu emen con inuedasbe o eunde  hesame en ila ion
condi ions.In hisin e al,inwhichpeoplele wi hina ewminu es,PM20 i s in‐
c eased o21μg/m3, hendec eased o14μg/m3and inallyinc eased o27μg/m3a  he
endo  hemeasu emen .Da i s inc eased o0.94μmand hendec eased o0.86μma 
heend.I shouldbeno ed ha pa icleswi hsizesg ea e  han10μm e u ned o hei 
ini ials a ea  his inals age,simila  o hes a ingpoin o  hemeasu emen .
11:00 11:30 12:00 12:30 13:00
Time [hh:mm]
16
17
18
19
20
21
22
37
38
39
40
41
42
43
44
45
46
Figu e 13. CO2Concen a ion [ppm] o S1 and S2 and pa icle concen a ion [pa icles/cm3].
Buildings2024,14,xFORPEERREVIEW18o 31
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
Figu e14.PM2.5,PM10andPM20[μg/m3]wi hDa[μm]andMMAD(median)[μm].
3.5.IgnacioAldecoaLib a y—Con e enceRoom
Figu e15shows heca bondioxideandpa iclenumbe concen a ionsinside he
con e ence oom.Hal anhou be o es a ing hemeasu emen ,onepe sonwasinside
hea ease ingup heins umen a ion o  hemeasu emen .Thedoo was ully
opened,and hewindowswe eclosed.Once hemeasu emen s a ed, hedoo was
closed, heca bondioxideconcen a iona S1inc easedin4min om553ppm o572
ppm,and ha a S2 emaineds ablea app oxima ely570ppm.Du ing hemeasu e‐
men , heca bondioxidele ela S1clea lys ayedabo e heS2le el.Mo eo e ,PNC
dec eased om14pa icles/cm3 o13pa icles/cm3.A  his ime,4mo epe sonsen e ed
hea ea;du ing he ollowing4min,S1inc eased o595ppm,andS2inc eased o581
ppm.PNC emaineda  hesame alueo 13pa icles/cm3.Then,2mo epe sonsen‐
e ed,and4mina e  wowindowswe epa iallyopened,PNCwasmain aineda 13
pa icles/cm3,whileCO2Cinc eased o733ppma S1and680ppma S2.A  heendo 
hisin e al,5minla e ,i dec eased o660ppma S1and o620ppma S2,whilePNC
inc eased o27pa icles/cm3.A  hismomen ,10mo epeopleen e ed hea ea,anddu ‐
ing henex 10min, heca bondioxidele ela S1inc eased o880ppm,while ha a S2
inc eased o820ppm.PNC eachedapeako 33pa icles/cm3be o ei dec eased o27
pa icles/cm3.Then,15mo epeopleen e ed,and hecon e ences a ed.Du ing he ol‐
lowing1hand25min, hecon e encecon inued o emains ablein e mso  en ila ion
andpeopleinside hea ea.PNCdec eased o20pa icles/cm3in15minandwasmain‐
aineda  ha le el.Du ing his15minin e al,bo hS1andS2hadal eadyexceeded
1000ppm, hemaximumle el ecommendedby heSinphonieguidelines.A  heendo 
hecon e ence,S1inc eased o2002ppm,andS2inc eased o1965ppm.To inish he
measu emen ,a e u n‐ o‐calms agewaspe o med,and o 26mina e  hecon e ence
hadended, hemeasu emen con inuedasbe o e ega ding o en ila ion.In hisin e ‐
al,inwhichpeoplele wi hina ewminu es,PNCinc eased o48pa icles/cm3,anda 
heend,i dec eased o45pa icles/cm3.S1cons an lydec eased o813ppm,whileS2
did hesamebu dec eased o744ppm.
11:00 11:30 12:00 12:30 13:00
Time [hh:mm]
0
10
20
30
40
50
60
70
80
90
100
0.5
0.6
0.7
0.8
0.9
1
1.1
1.2
1.3
1.4
1.5
Figu e 14. PM2.5, PM10 and PM20 [µg/m3] wi h Da[µm] and MMAD (median) [µm].
3.5. Ignacio Aldecoa Lib a y—Con e ence Room
Figu e 15 shows he ca bon dioxide and pa icle numbe concen a ions inside he
con e ence oom. Hal an hou be o e s a ing he measu emen , one pe son was inside
he a ea se ing up he ins umen a ion o he measu emen . The doo was ully opened,
and he windows we e closed. Once he measu emen s a ed, he doo was closed, he
ca bon dioxide concen a ion a S1 inc eased in 4 min om 553 ppm o 572 ppm, and ha
a S2 emained s able a app oxima ely 570 ppm. Du ing he measu emen , he ca bon
dioxide le el a S1 clea ly s ayed abo e he S2 le el. Mo eo e , PNC dec eased om
14 pa icles/cm3
o 13 pa icles/cm
3
. A his ime, 4 mo e pe sons en e ed he a ea; du ing
he ollowing 4 min, S1 inc eased o 595 ppm, and S2 inc eased o 581 ppm. PNC emained

Buildings 2024,14, 1007 17 o 28
a he same alue o 13 pa icles/cm
3
. Then, 2 mo e pe sons en e ed, and 4 min a e wo
windows we e pa ially opened, PNC was main ained a 13 pa icles/cm
3
, while CO
2
C
inc eased o 733 ppm a S1 and 680 ppm a S2. A he end o his in e al, 5 min la e , i
dec eased o 660 ppm a S1 and o 620 ppm a S2, while PNC inc eased o 27 pa icles/cm
3
.
A his momen , 10 mo e people en e ed he a ea, and du ing he nex 10 min, he ca bon
dioxide le el a S1 inc eased o 880 ppm, while ha a S2 inc eased o 820 ppm. PNC
eached a peak o 33 pa icles/cm
3
be o e i dec eased o 27 pa icles/cm
3
. Then, 15 mo e
people en e ed, and he con e ence s a ed. Du ing he ollowing 1 h and 25 min, he
con e ence con inued o emain s able in e ms o en ila ion and people inside he a ea.
PNC dec eased o 20 pa icles/cm
3
in 15 min and was main ained a ha le el. Du ing
his 15 min in e al, bo h S1 and S2 had al eady exceeded 1000 ppm, he maximum le el
ecommended by he Sinphonie guidelines. A he end o he con e ence, S1 inc eased o
2002 ppm, and S2 inc eased o 1965 ppm. To inish he measu emen , a e u n- o-calm s age
was pe o med, and o 26 min a e he con e ence had ended, he measu emen con inued
as be o e ega ding o en ila ion. In his in e al, in which people le wi hin a ew minu es,
PNC inc eased o 48 pa icles/cm
3
, and a he end, i dec eased o 45 pa icles/cm
3
. S1
cons an ly dec eased o 813 ppm, while S2 did he same bu dec eased o 744 ppm.
Buildings2024,14,xFORPEERREVIEW19o 31
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
Figu e15.CO2concen a ion[ppm] o S1andS2andpa icleconcen a ion[pa icles/cm3].
Figu e16shows heTandRHinside hecon e ence oom.Once hemeasu emen 
s a ed, hedoo wasclosed,and o 4min,T1inc eased om20.1°C o20.6°C,while
T2inc eased om19.4°C o19.9°C.RH1sligh lydec eased om43.6% o43%,and
RH2 emaineds ablea app oxima ely41%.I mus beno ed ha T1andRH2 emained
abo eT2andRH1, espec i ely,du ing hewholemeasu emen .A  his ime,4mo e
pe sonsen e ed hea eain4min.Then,2mo epe sonsen e ed,and4mina e  he wo
windowswe epa iallyopened, he empe a u eand ela i ehumidi y alueswe e
main ained.A  heendo  hisin e al,5minla e ,T1dec eased o20°C,whileT2de‐
c eased o19.2°C.RH1inc eased o42.4%,andRH2inc eased o44.4%.A  hismomen ,
10mo epe sonsen e ed hea ea,andin henex 10min,T1inc eased o20.4°C,while
T2inc eased o19.6°C.RH1inc eased o43.5%,andRH2inc eased o45.5%.Then,15
mo epe sonsen e ed,and hecon e ences a ed.Du ing he ollowing1hand25min,
hecon e encecon inued o emains ablein e mso  en ila ionandpeopleinside he
a ea.A e  he i s 15min,T1inc eased o22.2°C,whileT2inc eased o21.2°C.RH1
dec eased o42.3%,andRH2dec eased o44.2%.Howe e ,by heendo  hispe iod,T1
dec eased o22.2°C,whileT2dec eased o21.2°C.RH1inc eased o45.4%,andRH2
inc eased o47.9%.To inish hemeasu emen ,a e u n‐ o‐calms agewaspe o med,
and o 26mina e  hecon e encehadended, hemeasu emen con inuedasbe o e e‐
ga ding en ila ion.In hisin e al,inwhichpeoplequicklyle ,T1dec eased o18.3
°C,whileT2dec eased o17.1°C.RH1inc eased o46.3%,andRH2inc eased o49.6%.

S1 CO2 [ppm] and S2 CO2 [ppm]
Pa icle Conc [pa icles/cm3]
Emp y & All Closed
En e ing (4 inside)
2 windows pa ially opened
(6 inside)
(16 inside)
Con e ence S a (31 inside)
Con e ence End
% People Lea e
17:48 18:00 18:12 18:24 18:36 18:48 19:00 19:12 19:24 19:36 19:48
Time [hh:mm]
17
18
19
20
21
22
23
40
42
44
46
48
50
52
Figu e 15. CO2concen a ion [ppm] o S1 and S2 and pa icle concen a ion [pa icles/cm3].
Figu e 16 shows he T and RH inside he con e ence oom. Once he measu emen
s a ed, he doo was closed, and o 4 min, T1 inc eased om 20.1
◦
C o 20.6
◦
C, while
T2 inc eased om 19.4
◦
C o 19.9
◦
C. RH1 sligh ly dec eased om 43.6% o 43%, and RH2
emained s able a app oxima ely 41%. I mus be no ed ha T1 and RH2 emained abo e
T2 and RH1, espec i ely, du ing he whole measu emen . A his ime, 4 mo e pe sons
en e ed he a ea in 4 min. Then, 2 mo e pe sons en e ed, and 4 min a e he wo windows
we e pa ially opened, he empe a u e and ela i e humidi y alues we e main ained. A
he end o his in e al, 5 min la e , T1 dec eased o 20
◦
C, while T2 dec eased o 19.2
◦
C.
RH1 inc eased o 42.4%, and RH2 inc eased o 44.4%. A his momen , 10 mo e pe sons
en e ed he a ea, and in he nex 10 min, T1 inc eased o 20.4
◦
C, while T2 inc eased o
19.6 ◦C
. RH1 inc eased o 43.5%, and RH2 inc eased o 45.5%. Then, 15 mo e pe sons
en e ed, and he con e ence s a ed. Du ing he ollowing 1 h and 25 min, he con e ence
con inued o emain s able in e ms o en ila ion and people inside he a ea. A e he i s
15 min, T1 inc eased o 22.2
◦
C, while T2 inc eased o 21.2
◦
C. RH1 dec eased o 42.3%, and
RH2 dec eased o 44.2%. Howe e , by he end o his pe iod, T1 dec eased o 22.2
◦
C, while
T2 dec eased o 21.2
◦
C. RH1 inc eased o 45.4%, and RH2 inc eased o 47.9%. To inish he
measu emen , a e u n- o-calm s age was pe o med, and o 26 min a e he con e ence
had ended, he measu emen con inued as be o e ega ding en ila ion. In his in e al,
in which people quickly le , T1 dec eased o 18.3
◦
C, while T2 dec eased o 17.1
◦
C. RH1
inc eased o 46.3%, and RH2 inc eased o 49.6%.
Buildings 2024,14, 1007 18 o 28
Buildings2024,14,xFORPEERREVIEW19o 31


Figu e15.CO2concen a ion[ppm] o S1andS2andpa icleconcen a ion[pa icles/cm3].
Figu e16shows heTandRHinside hecon e ence oom.Once hemeasu emen 
s a ed, hedoo wasclosed,and o 4min,T1inc eased om20.1°C o20.6°C,while
T2inc eased om19.4°C o19.9°C.RH1sligh lydec eased om43.6% o43%,and
RH2 emaineds ablea app oxima ely41%.I mus beno ed ha T1andRH2 emained
abo eT2andRH1, espec i ely,du ing hewholemeasu emen .A  his ime,4mo e
pe sonsen e ed hea eain4min.Then,2mo epe sonsen e ed,and4mina e  he wo
windowswe epa iallyopened, he empe a u eand ela i ehumidi y alueswe e
main ained.A  heendo  hisin e al,5minla e ,T1dec eased o20°C,whileT2de‐
c eased o19.2°C.RH1inc eased o42.4%,andRH2inc eased o44.4%.A  hismomen ,
10mo epe sonsen e ed hea ea,andin henex 10min,T1inc eased o20.4°C,while
T2inc eased o19.6°C.RH1inc eased o43.5%,andRH2inc eased o45.5%.Then,15
mo epe sonsen e ed,and hecon e ences a ed.Du ing he ollowing1hand25min,
hecon e encecon inued o emains ablein e mso  en ila ionandpeopleinside he
a ea.A e  he i s 15min,T1inc eased o22.2°C,whileT2inc eased o21.2°C.RH1
dec eased o42.3%,andRH2dec eased o44.2%.Howe e ,by heendo  hispe iod,T1
dec eased o22.2°C,whileT2dec eased o21.2°C.RH1inc eased o45.4%,andRH2
inc eased o47.9%.To inish hemeasu emen ,a e u n‐ o‐calms agewaspe o med,
and o 26mina e  hecon e encehadended, hemeasu emen con inuedasbe o e e‐
ga ding en ila ion.In hisin e al,inwhichpeoplequicklyle ,T1dec eased o18.3
°C,whileT2dec eased o17.1°C.RH1inc eased o46.3%,andRH2inc eased o49.6%.

S1 CO2 [ppm] and S2 CO2 [ppm]
Pa icle Conc [pa icles/cm3]
Emp y & All Closed
En e ing (4 inside)
2 windows pa ially opened
(6 inside)
(16 inside)
Con e ence S a (31 inside)
Con e ence End
% People Lea e
17:48 18:00 18:12 18:24 18:36 18:48 19:00 19:12 19:24 19:36 19:48
Time [hh:mm]
17
18
19
20
21
22
23
40
42
44
46
48
50
52
Figu e 16. Tempe a u e [◦C] and ela i e humidi y [%] o S1 and S2.
Figu e 17 shows he PM
2.5
, PM
10
, PM
20
, D
a
and MMAD inside he con e ence oom.
I should be men ioned ha PM
2.5
was main ained wi hou no able a ia ion be ween
1.6 µg/m3
and 5
µ
g/m
3
du ing all he measu emen s. Once he measu emen s a ed,
he doo was closed o 4 min. A his ime, 4 mo e pe sons en e ed he a ea in 4 min.
Then, 2 mo e pe sons en e ed, and 4 min a e he wo windows we e pa ially opened,
PM
20
inc eased om 12
µ
g/m
3
o 21
µ
g/m
3
. Mo eo e , D
a
dec eased om 0.75
µ
m o
0.90 µm
. A he end o his in e al, 5 min la e , PM
20
inc eased o 32.5
µ
g/m
3
. Mo eo e ,
D
a
dec eased o 0.81
µ
m. A his momen , 10 mo e pe sons en e ed he a ea, and in he nex
10 min, PM
20
i s inc eased o 43
µ
g/m
3
and hen dec eased o 41
µ
g/m
3
. Mo eo e , D
a
inc eased o 0.85
µ
m. Then, 15 mo e pe sons en e ed, and he con e ence s a ed. Du ing
he ollowing 1 h and 25 min, he con e ence emained s able in e ms o en ila ion and
people inside he a ea. PM
20
dec eased o 18.5
µ
g/m
3
in 15 min, and D
a
i s inc eased o
0.86 µm and hen dec eased o 0.84 µm. I was no ed ha pa icles wi h sizes g ea e han
10
µ
m almos disappea ed a his momen . Du ing he es o he in e al, D
a
con inued
o slowly dec ease o 0.76
µ
m. In con as , PM
20
s abilized a app oxima ely 11
µ
g/m
3
be o e i inc eased o 17
µ
g/m
3
a he end o he s age. To inish he measu emen ,
a e u n
o he calm s age was pe o med, and o 26 min a e he con e ence had ended, he
measu emen con inued as be o e ega ding en ila ion. In his in e al, in which people
quickly le , PM
20
i s in-c eased o 19
µ
g/m
3
and hen dec eased o 10
µ
g/m
3
be o e
inally eaching
a 12 µg/m3
eading alue. D
a
only once dec eased o 0.69
µ
m and hen
inc eased o 0.74 µm a he end.
Buildings2024,14,xFORPEERREVIEW20o 31

Figu e16.Tempe a u e[°C]and ela i ehumidi y[%] o S1andS2.
Figu e17shows hePM2.5,PM10,PM20,DaandMMADinside hecon e ence oom.
I shouldbemen ioned ha PM2.5wasmain ainedwi hou no able a ia ionbe ween1.6
μg/m3and5μg/m3du ingall hemeasu emen s.Once hemeasu emen s a ed, he
doo wasclosed o 4min.A  his ime,4mo epe sonsen e ed hea eain4min.Then,
2mo epe sonsen e ed,and4mina e  he wowindowswe epa iallyopened,PM20
inc eased om12μg/m3 o21μg/m3.Mo eo e ,Dadec eased om0.75μm o0.90μm.
A  heendo  hisin e al,5minla e ,PM20inc eased o32.5μg/m3.Mo eo e ,Dade‐
c eased o0.81μm.A  hismomen ,10mo epe sonsen e ed hea ea,andin henex 10
min,PM20 i s inc eased o43μg/m3and hendec eased o41μg/m3.Mo eo e ,Dain‐
c eased o0.85μm.Then,15mo epe sonsen e ed,and hecon e ences a ed.Du ing
he ollowing1hand25min, hecon e ence emaineds ablein e mso  en ila ionand
peopleinside hea ea.PM20dec eased o18.5μg/m3in15min,andDa i s inc eased o
0.86μmand hendec eased o0.84μm.I wasno ed ha pa icleswi hsizesg ea e 
han10μmalmos disappea eda  hismomen .Du ing he es o  hein e al,Dacon‐
inued oslowlydec ease o0.76μm.Incon as ,PM20s abilizeda app oxima ely11
μg/m3be o ei inc eased o17μg/m3a  heendo  hes age.To inish hemeasu emen ,
a e u n o hecalms agewaspe o med,and o 26mina e  hecon e encehadended,
hemeasu emen con inuedasbe o e ega ding en ila ion.In hisin e al,inwhich
peoplequicklyle ,PM20 i s in‐c eased o19μg/m3and hendec eased o10μg/m3be‐
o e inally eachinga12μg/m3 eading alue.Daonlyoncedec eased o0.69μmand
heninc eased o0.74μma  heend.

Figu e17.PM2.5,PM10andPM20[μg/m3]wi hDa[μm])andMMAD(median)[μm].
3.6.Mendizo ozaSpo sFacili ies—T ainingRoom
Figu e18shows heca bondioxideandpa iclenumbe concen a ionsinside he
aining oom.Hal anhou be o es a ing hemeasu emen , hedoo wasclosed,and
hewindowswe epa iallyopenedwhileonepe sonwasinside hea ease ingup he
ins umen a ion o  hemeasu emen .Du ing hemeasu emen , heca bondioxidele ‐
ela S1gene allys ayedabo e heS2le elbe o e heac i i y.Howe e ,du ing heac‐
i i yandun il heendo  hemeasu emen , his endencyswi chedwi h heS2le el
emainingabo e heS1le el.Du ing hewholemeasu emen ,PNC a iedbe weena10
pa icles/cm3and13pa icles/cm3wi hou no able a ia ion.Theai ‐condi ioningsys em
wasswi chedondu ing hemeasu emen .Once hemeasu emen s a ed, hedoo kep 
openingandclosingeach imepeopleen e ed he oom,and heca bondioxideconcen‐
a iona S1oscilla edin his30minin e al om592ppm o556ppm;i  i s inc eased
o595ppm, hendec eased o541ppmand inally eached582ppm.Mo eo e ,S2 e‐
17:48 18:00 18:12 18:24 18:36 18:48 19:00 19:12 19:24 19:36 19:48
Time [hh:mm]
0
10
20
30
40
50
60
70
80
90
100
0.5
0.6
0.7
0.8
0.9
1
1.1
1.2
1.3
1.4
1.5
Figu e 17. PM2.5, PM10 and PM20 [µg/m3] wi h Da[µm]) and MMAD (median) [µm].
Buildings 2024,14, 1007 19 o 28
3.6. Mendizo oza Spo s Facili ies—T aining Room
Figu e 18 shows he ca bon dioxide and pa icle numbe concen a ions inside he
aining oom. Hal an hou be o e s a ing he measu emen , he doo was closed, and
he windows we e pa ially opened while one pe son was inside he a ea se ing up he
ins umen a ion o he measu emen . Du ing he measu emen , he ca bon dioxide le -el
a S1 gene ally s ayed abo e he S2 le el be o e he ac i i y. Howe e , du ing he ac i i y
and un il he end o he measu emen , his endency swi ched wi h he S2 le el emaining
abo e he S1 le el. Du ing he whole measu emen , PNC a ied be ween a 10 pa icles/cm
3
and 13 pa icles/cm
3
wi hou no able a ia ion. The ai -condi ioning sys em was swi ched
on du ing he measu emen . Once he measu emen s a ed, he doo kep opening and
closing each ime people en e ed he oom, and he ca bon dioxide concen a ion a S1
oscilla ed in his 30 min in e al om 592 ppm o 556 ppm; i i s inc eased o 595 ppm,
hen dec eased o 541 ppm and inally eached 582 ppm. Mo eo e , S2 emained s able
a app oxima ely 580 ppm o he i s hal o his pe iod, a e which i i s inc eased
o
600 ppm
, hen dec eased o 543 ppm and inally eached 581 ppm. A his ime, he
aining class s a ed, and o he ollowing 60 min, he oom emained s able in e ms o
en ila ion and he numbe o people inside he a ea. The dioxide ca bon le els a S1 and
S2 inc eased o 608 ppm o he i s 6 min o wa m-up, he S1 and S2 le els hen inc eased
o 675 ppm
6 min
la e , and he S1 le el oscilla ed be ween 686 ppm and 830 ppm o e he
nex
36 min
and du ing he medium-in ensi y exe cises and pauses be o e s e ching. A
he inal
12 min
s age, i dec eased o 700 ppm. Mo eo e , he S2 le el oscilla ed be ween
656 ppm and 817 ppm be o e e u ning o 700 ppm a he end o his in e al. A his
momen , he class ended, he doo was opened, and people le . Du ing he ollowing
15 min
, S1 and S2 dec eased o 575 ppm. To inish he measu emen , a back- o-calm s age
was pe o med, and o 15 min, he doo was closed, and S1 again dec eased o 550 ppm,
while S2 dec eased o 540 ppm. No e ha he ca bon dioxide maximum le el ecommended
by he Sinphonie guidelines was no eached.
Buildings2024,14,xFORPEERREVIEW21o 31

maineds ablea app oxima ely580ppm o  he i s hal o  hispe iod,a e whichi 
i s inc eased o600ppm, hendec eased o543ppmand inally eached581ppm.A 
his ime, he ainingclasss a ed,and o  he ollowing60min, he oom emained
s ablein e mso  en ila ionand henumbe o peopleinside hea ea.Thedioxideca ‐
bonle elsa S1andS2inc eased o608ppm o  he i s 6mino wa m‐up, heS1and
S2le els heninc eased o675ppm6minla e ,and heS1le eloscilla edbe ween686
ppmand830ppmo e  henex 36minanddu ing hemedium‐in ensi yexe cisesand
pausesbe o es e ching.A  he inal12mins age,i dec eased o700ppm.Mo eo e ,
heS2le eloscilla edbe ween656ppmand817ppmbe o e e u ning o700ppma  he
endo  hisin e al.A  hismomen , heclassended, hedoo wasopened,andpeople
le .Du ing he ollowing15min,S1andS2dec eased o575ppm.To inish hemeas‐
u emen ,aback‐ o‐calms agewaspe o med,and o 15min, hedoo wasclosed,and
S1againdec eased o550ppm,whileS2dec eased o540ppm.No e ha  heca bondi‐
oxidemaximumle el ecommendedby heSinphonieguidelineswasno  eached.

Figu e18.CO2concen a ion[ppm] o S1andS2andpa icleconcen a ion[pa icles/cm3].
Figu e19shows heTandRHinside he aining oom.Du ing hemeasu emen ,
heT2le elgene allys ayedabo e heT1le elbe o es a ing heac i i y.Howe e ,
du ing hemedium‐in ensi yac i i ypa o  heclass, his endencyswi ched,wi h he
T1le els ayingabo e heT2le el.A  hes e chings ageandun il heendo  he
measu emen , heT2le el emainedabo e heT1le el.Rega ding he ela i ehumidi y,
RH2 emainedabo eo a leas ma chedRH1du ing hewholemeasu emen .The e‐
o e,onlyT1andRH2 aluesa ede ailed.Once hemeasu emen s a ed, hedoo kep 
openingandclosingeach imepeopleen e ed he oom,andT1dec eased om19.7°C
o18.6°Cand inallyinc eased o19.2°C.RH2dec eased om52.4% o50.6% o52.3%.
A  his ime, he ainingclasss a ed,and o  he ollowing60min, he oom emained
s ablein e mso  en ila ionand henumbe o peopleinside hea ea.T1inc eased o
20.6°Cand hendec eased o19.4°C.RH2inc eased o57.6%and hendec eased o
53.2%.A  hismomen , heclassended, hedoo wasopened,andpeoplele ;du ing he
ollowing15min,T1inc eased o19.9°C.RH2 i s inc eased o57.6%and hende‐
c eased o50.1%.To inish hemeasu emen ,aback‐ o‐calms agewaspe o med,and
o 15min, hedoo wasclosed,andT1andRH2 e u ned o hep e ious alueso 19.9
°Cand50.1%, espec i ely,a  heendo  hemeasu emen .
S1 CO2 [ppm] and S2 CO2 [ppm]
Pa icle Conc [pa icles/cm3]
Emp y
& Windows pa ially opened
People Inside
TRX Class S a
People Lea e
TRX Class End & Doo Opened
Doo Closed
Figu e 18. CO2concen a ion [ppm] o S1 and S2 and pa icle concen a ion [pa icles/cm3].
Figu e 19 shows he T and RH inside he aining oom. Du ing he measu emen , he
T2 le el gene ally s ayed abo e he T1 le el be o e s a ing he ac i i y. Howe e , du ing
he medium-in ensi y ac i i y pa o he class, his endency swi ched, wi h he T1 le el
s aying abo e he T2 le el. A he s e ching s age and un il he end o he measu emen ,
he T2 le el emained abo e he T1 le el. Rega ding he ela i e humidi y, RH2 emained
abo e o a leas ma ched RH1 du ing he whole measu emen . The e o e, only T1 and
RH2 alues a e de ailed. Once he measu emen s a ed, he doo kep opening and closing
each ime people en e ed he oom, and T1 dec eased om 19.7
◦
C o 18.6
◦
C and inally
inc eased o 19.2
◦
C. RH2 dec eased om 52.4% o 50.6% o 52.3%. A his ime, he
aining class s a ed, and o he ollowing 60 min, he oom emained s able in e ms o
en ila ion and he numbe o people inside he a ea. T1 inc eased o 20.6
◦
C and hen
dec eased o
19.4 ◦C
. RH2 inc eased o 57.6% and hen dec eased o 53.2%. A his momen ,
Buildings 2024,14, 1007 20 o 28
he class ended, he doo was opened, and people le ; du ing he ollowing 15 min, T1
inc eased o 19.9
◦
C. RH2 i s inc eased o 57.6% and hen dec eased o 50.1%. To inish he
measu emen , a back- o-calm s age was pe o med, and o 15 min, he doo was closed,
and T1 and RH2 e u ned o he p e ious alues o 19.9
◦
C and 50.1%, espec i ely, a he
end o he measu emen .
Buildings2024,14,xFORPEERREVIEW22o 31


Figu e19.Tempe a u e[°C]and ela i ehumidi y[%] o S1andS2.
Figu e20shows hePM2.5,PM10,PM20,DaandMMADinside he aining oom.I 
shouldbemen ioned ha PM2.5wasmain ainedbe ween6.6μg/m3and8.6μg/m3wi h‐
ou no able a ia iondu ing heen i emeasu emen pe iod.Once hemeasu emen 
s a ed, hedoo kep openingandclosingeach imepeopleen e ed he oom,andPM20
inc eased om14μg/m3 o20μg/m3.Dainc eased om1.10μm o1.15μm.Sixminu es
be o e heendo  hein e al,almos nopa icleswi hsizesg ea e  han10μmwe e
p esen .A  his ime, he ainingclasss a ed,and o  he ollowing60min, he oom
emaineds ablein e mso  en ila ionand henumbe o peopleinside hea ea.PM20
i s inc eased o22.6μg/m3and hendec eased o11.5μg/m320minbe o e heendo 
hes age,and heni againinc eased o22.4μg/m3.Dadec eased o1.06μm20minbe‐
o e heendo  hes ageand heninc eased o1.15μma  heendo  hes age.I mus al‐
sobemen ioned ha a 20minbe o e heendo  hes age, he alleypoin so bo hPM20
andDacoincidedwi hanabsenceo pa icleswi hsizesg ea e  han10μm.A  his
momen , heclassended, hedoo wasopened,andpeoplele .Du ing he ollowing15
min,PM20dec eased o17.4μg/m3,andDadec eased o1.13μm.To inish hemeasu e‐
men ,a e u n‐ o‐calms agewaspe o med,and o 15min,as hedoo  emained
closed,PM20dec eased o14.5μg/m3,andDadec eased o1.10μm.

Figu e20.Tempe a u e[°C]and ela i ehumidi y[%] o S1andS2.
3.7.Mendizo ozaSpo sFacili ies—SpinningRoom
18:12 18:24 18:36 18:48 19:00 19:12 19:24 19:36 19:48 20:00
Time [hh:mm]
18.5
19
19.5
20
20.5
21
49
50
51
52
53
54
55
56
57
58
18:12 18:24 18:36 18:48 19:00 19:12 19:24 19:36 19:48 20:00
Time [hh:mm]
0
10
20
30
40
50
60
70
80
90
100
0.5
0.6
0.7
0.8
0.9
1
1.1
1.2
1.3
1.4
1.5
Figu e 19. Tempe a u e [◦C] and ela i e humidi y [%] o S1 and S2.
Figu e 20 shows he PM
2.5
, PM
10
, PM
20
, D
a
and MMAD inside he aining oom.
I should be men ioned ha PM
2.5
was main ained be ween 6.6
µ
g/m
3
and 8.6
µ
g/m
3
wi hou no able a ia ion du ing he en i e measu emen pe iod. Once he measu emen
s a ed, he doo kep opening and closing each ime people en e ed he oom, and PM
20
inc eased om 14
µ
g/m
3
o 20
µ
g/m
3
. Da inc eased om 1.10
µ
m o 1.15
µ
m. Six minu es
be o e he end o he in e al, almos no pa icles wi h sizes g ea e han 10
µ
m we e p esen .
A his ime, he aining class s a ed, and o he ollowing 60 min, he oom emained
s able in e ms o en ila ion and he numbe o people inside he a ea. PM
20 i s inc eased
o 22.6
µ
g/m
3
and hen dec eased o 11.5
µ
g/m
3
20 min be o e he end o he s age, and
hen i again inc eased o 22.4
µ
g/m
3
. Da dec eased o 1.06
µ
m 20 min be o e he end o
he s age and hen inc eased o 1.15
µ
m a he end o he s age. I mus also be men ioned
ha a 20 min be o e he end o he s age, he alley poin s o bo h PM
20
and D
a
coincided
wi h an absence o pa icles wi h sizes g ea e han 10
µ
m. A his momen , he class ended,
he doo was opened, and people le . Du ing he ollowing 15 min, PM
20
dec eased o
17.4
µ
g/m
3
, and D
a
dec eased o 1.13
µ
m. To inish he measu emen ,
a e u n- o-calm
s age was pe o med, and o 15 min, as he doo emained closed, PM
20
dec eased o
14.5 µg/m3, and Dadec eased o 1.10 µm.
Buildings2024,14,xFORPEERREVIEW22o 31


Figu e19.Tempe a u e[°C]and ela i ehumidi y[%] o S1andS2.
Figu e20shows hePM2.5,PM10,PM20,DaandMMADinside he aining oom.I 
shouldbemen ioned ha PM2.5wasmain ainedbe ween6.6μg/m3and8.6μg/m3wi h‐
ou no able a ia iondu ing heen i emeasu emen pe iod.Once hemeasu emen 
s a ed, hedoo kep openingandclosingeach imepeopleen e ed he oom,andPM20
inc eased om14μg/m3 o20μg/m3.Dainc eased om1.10μm o1.15μm.Sixminu es
be o e heendo  hein e al,almos nopa icleswi hsizesg ea e  han10μmwe e
p esen .A  his ime, he ainingclasss a ed,and o  he ollowing60min, he oom
emaineds ablein e mso  en ila ionand henumbe o peopleinside hea ea.PM20
i s inc eased o22.6μg/m3and hendec eased o11.5μg/m320minbe o e heendo 
hes age,and heni againinc eased o22.4μg/m3.Dadec eased o1.06μm20minbe‐
o e heendo  hes ageand heninc eased o1.15μma  heendo  hes age.I mus al‐
sobemen ioned ha a 20minbe o e heendo  hes age, he alleypoin so bo hPM20
andDacoincidedwi hanabsenceo pa icleswi hsizesg ea e  han10μm.A  his
momen , heclassended, hedoo wasopened,andpeoplele .Du ing he ollowing15
min,PM20dec eased o17.4μg/m3,andDadec eased o1.13μm.To inish hemeasu e‐
men ,a e u n‐ o‐calms agewaspe o med,and o 15min,as hedoo  emained
closed,PM20dec eased o14.5μg/m3,andDadec eased o1.10μm.

Figu e20.Tempe a u e[°C]and ela i ehumidi y[%] o S1andS2.
3.7.Mendizo ozaSpo sFacili ies—SpinningRoom
18:12 18:24 18:36 18:48 19:00 19:12 19:24 19:36 19:48 20:00
Time [hh:mm]
18.5
19
19.5
20
20.5
21
49
50
51
52
53
54
55
56
57
58
18:12 18:24 18:36 18:48 19:00 19:12 19:24 19:36 19:48 20:00
Time [hh:mm]
0
10
20
30
40
50
60
70
80
90
100
0.5
0.6
0.7
0.8
0.9
1
1.1
1.2
1.3
1.4
1.5
Figu e 20. Tempe a u e [◦C] and ela i e humidi y [%] o S1 and S2.
Buildings 2024,14, 1007 21 o 28
3.7. Mendizo oza Spo s Facili ies—Spinning Room
Figu e 21 shows he ca bon dioxide and pa icle numbe concen a ions inside he
spinning oom. Hal an hou be o e s a ing he measu emen , he doo was opened and he
windows we e closed while one pe son was inside he a ea se ing up he ins umen a ion
o he measu emen . Du ing he measu emen , he ca bon dioxide le el a S2 gene ally
s ayed abo e ha a S1, bu his endency swi ched, wi h ha a S1 s aying abo e he
S2 le el when people le a he las s age o he measu emen . Mo eo e , PNC a ied
be ween 10 pa icles/cm
3
and 13 pa icles/cm
3
wi hou no able a ia ion be o e a window
was pa ially opened. Then, PNC g adually inc eased o 27 pa icles/cm
3
un il he end
o he class, and hen i smoo hly dec eased o 22 pa icles/cm
3
. Ai condi ioning was
applied du ing he measu emen , and he doo was kep open. Once he measu emen
s a ed, people g adually en e ed he oom un il he class s a ed, and he ca bon dioxide
concen a ion a S1 inc eased in his 41 min in e al om 309 ppm o 1161 ppm. Mo eo e ,
he S2 le el inc eased om 618 ppm o 1229 ppm in his 41 min in e al. Bo h S1 and
S2 we e abo e 1000 ppm, he maximum le el ecommended by he Sinphonie guidelines
be o e he class s a ed. A his ime, he aining class s a ed, and du ing he ollowing
41 min, he oom emained s able in e ms o en ila ion and he numbe o people inside
he a ea. Howe e , du ing he 18-min pe iod a e he window was pa ially opened, he
ca bon dioxide le el a S1 a ied be ween 1176 ppm and 1493 ppm du ing he high-in ensi y
exe cise pe iod. Mo eo e , S2 also oscilla ed bu a ied be ween 1176 ppm and 1468 ppm.
A his momen , he class ended, and s e ching occu ed du ing he ollowing 13 min.
S1 and S2 dec eased o 959 ppm and 995 ppm, espec i ely. To inish he measu emen ,
a back- o-calm
s age was pe o med, and wi hin 35 min, S1 dec eased o 714 ppm, while
S2 dec eased o 704 ppm.
Buildings2024,14,xFORPEERREVIEW23o 31

Figu e21shows heca bondioxideandpa iclenumbe concen a ionsinside he
spinning oom.Hal anhou be o es a ing hemeasu emen , hedoo wasopenedand
hewindowswe eclosedwhileonepe sonwasinside hea ease ingup heins umen‐
a ion o  hemeasu emen .Du ing hemeasu emen , heca bondioxidele ela S2
gene allys ayedabo e ha a S1,bu  his endencyswi ched,wi h ha a S1s aying
abo e heS2le elwhenpeoplele a  helas s ageo  hemeasu emen .Mo eo e ,PNC
a iedbe ween10pa icles/cm3and13pa icles/cm3wi hou no able a ia ionbe o ea
windowwaspa iallyopened.Then,PNCg aduallyinc eased o27pa icles/cm3un il
heendo  heclass,and heni smoo hlydec eased o22pa icles/cm3.Ai condi ioning
wasapplieddu ing hemeasu emen ,and hedoo waskep open.Once hemeasu e‐
men s a ed,peopleg aduallyen e ed he oomun il heclasss a ed,and heca bon
dioxideconcen a iona S1inc easedin his41minin e al om309ppm o1161ppm.
Mo eo e , heS2le elinc eased om618ppm o1229ppmin his41minin e al.Bo h
S1andS2we eabo e1000ppm, hemaximumle el ecommendedby heSinphonie
guidelinesbe o e heclasss a ed.A  his ime, he ainingclasss a ed,anddu ing he
ollowing41min, he oom emaineds ablein e mso  en ila ionand henumbe o 
peopleinside hea ea.Howe e ,du ing he18‐minu epe ioda e  hewindowwaspa ‐
iallyopened, heca bondioxidele ela S1 a iedbe ween1176ppmand1493ppm
du ing hehigh‐in ensi yexe cisepe iod.Mo eo e ,S2alsooscilla edbu  a iedbe‐
ween1176ppmand1468ppm.A  hismomen , heclassended,ands e chingoc‐
cu eddu ing he ollowing13min.S1andS2dec eased o959ppmand995ppm, e‐
spec i ely.To inish hemeasu emen ,aback‐ o‐calms agewaspe o med,andwi hin
35min,S1dec eased o714ppm,whileS2dec eased o704ppm.

Figu e21.CO2concen a ion[ppm] o S1andS2andpa icleconcen a ion[pa icles/cm3].
Figu e22shows heTandRHinside hespinning oom.Be o es a ing heac i i y,
heT2le elgene allys ayedsligh lyabo e heT1le el.Howe e ,du ing hehigh‐
in ensi yac i i ypa o  heclass, his endencyswi ched,wi h ha a T1s ayingabo e
heT2le el.Thise ec wasmo eno ablejus a e  hewindowwasopenedandun il
heendo  hemeasu emen .Rega ding he ela i ehumidi y,RH2wasabo eo a leas 
ma chedRH1be o e hewindowwasopened.Once hemeasu emen s a ed,people
g aduallyen e ed he oomun il heclasss a ed.T1andT2inc eased om19.9°C o
20.8°C.RH1inc eased om59% o59.2%,andRH2inc eased om59% o59.5%.A 
his ime, he ainingclasss a ed,anddu ing he ollowing41min, he oom emained
s ablein e mso  en ila ionand henumbe o peopleinside hea ea.Howe e ,du ing
he18‐minu epe ioda e  hewindowwaspa iallyopened,T1inc eased o20.9°C
when hewindowwasopenedand hendec eased o20°C o inally each21°C,while
T2alsoinc eased o20.9°Cwhen hewindowwasopenedand hendec eased o20.6°C
S1 CO2 [ppm] and S2 CO2 [ppm]
Pa icle Conc [pa icles/cm3]
Doo Open (2 inside)
(6 inside)
(10 inside)
(13 inside)
Spinning Class S a
(22 inside)
Pa ially opened window
Spinning Class End
& S e ching S a
S ecching End
& People Lea e
Figu e 21. CO2concen a ion [ppm] o S1 and S2 and pa icle concen a ion [pa icles/cm3].
Figu e 22 shows he T and RH inside he spinning oom. Be o e s a ing he ac i i y,
he T2 le el gene ally s ayed sligh ly abo e he T1 le el. Howe e , du ing he high-in ensi y
ac i i y pa o he class, his endency swi ched, wi h ha a T1 s aying abo e he T2 le el.
This e ec was mo e no able jus a e he window was opened and un il he end o he
measu emen . Rega ding he ela i e humidi y, RH2 was abo e o a leas ma ched RH1
be o e he window was opened. Once he measu emen s a ed, people g adually en e ed
he oom un il he class s a ed. T1 and T2 inc eased om 19.9
◦
C o 20.8
◦
C. RH1 inc eased
om 59% o 59.2%, and RH2 inc eased om 59% o 59.5%. A his ime, he aining class
s a ed, and du ing he ollowing 41 min, he oom emained s able in e ms o en ila ion
and he numbe o people inside he a ea. Howe e , du ing he 18-min pe iod a e he
window was pa ially opened, T1 inc eased o 20.9
◦
C when he window was opened and
hen dec eased o 20
◦
C o inally each 21
◦
C, while T2 also inc eased o 20.9
◦
C when
he window was opened and hen dec eased o 20.6
◦
C o inally each 21.4
◦
C. RH1 and

Buildings 2024,14, 1007 22 o 28
RH2 inc eased o 65% when he window was opened and hen again o 70%. A his
momen , he class ended, and s e ching occu ed o e he nex 13 min. T1 inc eased o
21.4
◦
C, ending a 20.9
◦
C, and T2 inc eased o 21.7
◦
C, ending a 21.4
◦
C. Mo eo e , RH1
inc eased o 74.5%, ending a 73.2%, and RH2 inc eased o 73.3%, ending a 73%. To inish
he measu emen , a back- o-calm s age was pe o med, and wi hin 35 min, T1 dec eased o
20.5
◦
C and T2 inc eased o 20.7
◦
C. Du ing his pe iod, RH1 dec eased o 68%, and RH2
dec eased o 67.4%.
Buildings2024,14,xFORPEERREVIEW24o 31

o inally each21.4°C.RH1andRH2inc eased o65%when hewindowwasopened
and henagain o70%.A  hismomen , heclassended,ands e chingoccu edo e 
henex 13min.T1inc eased o21.4°C,endinga 20.9°C,andT2inc eased o21.7°C,
endinga 21.4°C.Mo eo e ,RH1inc eased o74.5%,endinga 73.2%,andRH2in‐
c eased o73.3%,endinga 73%.To inish hemeasu emen ,aback‐ o‐calms agewas
pe o med,andwi hin35min,T1dec eased o20.5°CandT2inc eased o20.7°C.Du ‐
ing hispe iod,RH1dec eased o68%,andRH2dec eased o67.4%.

Figu e22.Tempe a u e[°C]and ela i ehumidi y[%] o S1andS2.
Figu e23shows hePM2.5,PM10,PM20,DaandMMADinside hespinning oom.I 
shouldbemen ioned ha bo hPM2.5andDadidno no ably a yun il heclassended.
A  heendo  heclass,s e chingoccu ed o  he ollowing13min,andPM20inc eased
om13μg/m3 o29μg/m3and hendec eased o18μg/m3.Da i s inc eased om0.96
μm o0.98μmand hendec eased o0.93μm.To inish hemeasu emen ,a e u n‐ o‐
calms ageoccu ed,andwi hin35min,PM20dec eased o8μg/m3.Mo eo e ,Dade‐
c eased o1.15μm.

Figu e23.PM2.5,PM10andPM20[μg/m3]wi hDa[μm]andMMAD(median)[μm].
4.DiscussionandMeasu emen Compa ison
In hissec ion, hecu en s udyiscompa ed o ha pe o medbyChillone al.
[37].Simila ins umen a ionwasused,and heob ained esul sa ecompa ed o hose
ob ainedin hei measu emen s udyinwhichaclass oomwi hna u al en ila ionwas
S1 T [ºC] and S2 T [ºC]
S1 RH [%] and S2 RH [%]
Doo Open (2 inside)
(6 inside)
(10 inside)
(13 inside)
Spinning Class S a
(22 inside)
Pa ially opened window
Spinning Class End
& S e ching S a
S ecching End
& People Lea e
PM 2.5 / PM10 / PM20 [ g/m3]
MMAD [ m]
Da [ m]
Doo Open (2 inside)
(6 inside)
(10 inside)
(13 inside)
Spinning Class S a
(22 inside)
Pa ially opened window
Spinning Class End
& S e ching S a
S ecching End
& People Lea e
Figu e 22. Tempe a u e [◦C] and ela i e humidi y [%] o S1 and S2.
Figu e 23 shows he PM
2.5
, PM
10
, PM
20
, D
a
and MMAD inside he spinning oom. I
should be men ioned ha bo h PM
2.5
and D
a
did no no ably a y un il he class ended. A
he end o he class, s e ching occu ed o he ollowing 13 min, and PM
20
inc eased om
13
µ
g/m
3
o 29
µ
g/m
3
and hen dec eased o 18
µ
g/m
3
. D
a
i s inc eased om
0.96 µm
o 0.98
µ
m and hen dec eased o 0.93
µ
m. To inish he measu emen , a e u n- o-calm
s age occu ed, and wi hin 35 min, PM
20
dec eased o 8
µ
g/m
3
. Mo eo e , D
a
dec eased o
1.15 µm.
Buildings2024,14,xFORPEERREVIEW24o 31

o inally each21.4°C.RH1andRH2inc eased o65%when hewindowwasopened
and henagain o70%.A  hismomen , heclassended,ands e chingoccu edo e 
henex 13min.T1inc eased o21.4°C,endinga 20.9°C,andT2inc eased o21.7°C,
endinga 21.4°C.Mo eo e ,RH1inc eased o74.5%,endinga 73.2%,andRH2in‐
c eased o73.3%,endinga 73%.To inish hemeasu emen ,aback‐ o‐calms agewas
pe o med,andwi hin35min,T1dec eased o20.5°CandT2inc eased o20.7°C.Du ‐
ing hispe iod,RH1dec eased o68%,andRH2dec eased o67.4%.

Figu e22.Tempe a u e[°C]and ela i ehumidi y[%] o S1andS2.
Figu e23shows hePM2.5,PM10,PM20,DaandMMADinside hespinning oom.I 
shouldbemen ioned ha bo hPM2.5andDadidno no ably a yun il heclassended.
A  heendo  heclass,s e chingoccu ed o  he ollowing13min,andPM20inc eased
om13μg/m3 o29μg/m3and hendec eased o18μg/m3.Da i s inc eased om0.96
μm o0.98μmand hendec eased o0.93μm.To inish hemeasu emen ,a e u n‐ o‐
calms ageoccu ed,andwi hin35min,PM20dec eased o8μg/m3.Mo eo e ,Dade‐
c eased o1.15μm.

Figu e23.PM2.5,PM10andPM20[μg/m3]wi hDa[μm]andMMAD(median)[μm].
4.DiscussionandMeasu emen Compa ison
In hissec ion, hecu en s udyiscompa ed o ha pe o medbyChillone al.
[37].Simila ins umen a ionwasused,and heob ained esul sa ecompa ed o hose
ob ainedin hei measu emen s udyinwhichaclass oomwi hna u al en ila ionwas
S1 T [ºC] and S2 T [ºC]
S1 RH [%] and S2 RH [%]
Doo Open (2 inside)
(6 inside)
(10 inside)
(13 inside)
Spinning Class S a
(22 inside)
Pa ially opened window
Spinning Class End
& S e ching S a
S ecching End
& People Lea e
PM 2.5 / PM10 / PM20 [ g/m3]
MMAD [ m]
Da [ m]
Doo Open (2 inside)
(6 inside)
(10 inside)
(13 inside)
Spinning Class S a
(22 inside)
Pa ially opened window
Spinning Class End
& S e ching S a
S ecching End
& People Lea e
Figu e 23. PM2.5, PM10 and PM20 [µg/m3] wi h Da[µm] and MMAD (median) [µm].
4. Discussion and Measu emen Compa ison
In his sec ion, he cu en s udy is compa ed o ha pe o med by Chillon e al. [
37
].
Simila ins umen a ion was used, and he ob ained esul s a e compa ed o hose ob ained
in hei measu emen s udy in which a class oom wi h na u al en ila ion was in es iga ed
du ing a class wi h s uden s. In bo h s udies, he layou o he class oom was simila
in e ms o dimensions, sys em and a eas o en ila ion, loca ion o windows and doo s,
Buildings 2024,14, 1007 23 o 28
numbe o pe sons in he class oom, mask-wea ing pa e n and p esence o uni e si y s u-
den s o he same age ange. A simila me hod o en ila ion was ollowed in bo h s udies.
The s eps included all windows and doo s closed, only windows opened,
all windows
and doo s closed, windows and doo s opened, and all windows and doo s closed a he
end o he measu emen . No e ha in he cu en s udy, an ex a cycle, consis ing o only
opened doo s ollowed by all windows and doo s closed un il he end, was pe o med.
While Chillon e al. [
37
] used a class oom wi h a su ace a ea o 91.8 m
2
, a heigh o 2.64 m
and a olume equal o 242 m
3
, he cu en s udy occu ed in a class oom wi h a su ace
a ea o 57.2 m
2
, a heigh o 4 m and an inside olume o 229 m
3
. Thei en ila ion a ea
on he window side was 4.83 m
2
, and he alue was 3.12 m
2
o he doo s, wi h a o al
en ila ion a ea o 7.95 m
2
. In he cu en s udy, he window en ila ion a ea was 4.2 m
2
,
he doo en ila ion a ea was 3.4 m
2
, and he o al en ila ion a ea was he e o e 7.5 m
2
.
The cu en s udy occu ed in a class oom wi h a 62% smalle su ace a ea bu only a 6%
smalle olume. A he same ime, he o al en ila ion a ea was 5% smalle , 14% smalle
o he windows and 8% la ge o he doo s. In con as , he same numbe o 15 people
wea ing masks in he class oom du ing bo h measu emen s sugges s a simila olume le el
o human inhala ion and exhala ion. This also indica es e y simila sou ce le els o CO
2
du ing he measu emen s. Rega ding he ou side condi ions, hei measu emen occu ed
a 6
◦
C wi h a 79% ela i e humidi y, while he cu en measu emen was pe o med in
a 2 ◦C o 5 ◦C empe a u e ange and a 97% o 90% ela i e humidi y ange.
In e ms o he PM
2.5
and pa icle concen a ions, signi ican di e ences a e obse ed
be ween bo h s udies. In Chillon e al. [
37
], PM
2.5
anged om 2.5 o 3.7
µ
g/m
3
, and
he pa icle concen a ion anged om 6 o 11.5 pa icles/cm
3
. Howe e , in he cu en
s udy, PM
2.5
anged om 8 o 12
µ
g/m
3
, and he pa icle concen a ion anged om
34 o 88 pa icles/cm3
. No ably, he cu en s udy measu ed h ee imes mo e PM
2.5
and
app oxima ely se en imes mo e pa icles in he class oom ai . Bo h s udies e ealed
simila e ec s ega ding he closed and en ila ion s ages. A he all-closed s age, he e was
an inc ease
in bo h he PM
2.5
and pa icle concen a ions, while he e was a dec ease a he
en ila ion s ages and unde he scena ios wi h only he windows opened o wi h bo h he
windows and doo s opened. Rega ding he CO
2
le els, he opposed beha io o ha o he
PM
2.5
and pa icle concen a ions du ing he all-closed and en ila ion e en s was obse ed
in bo h s udies. E en ually, a simila le el o inc ease in he ca bon dioxide concen a ion
pe minu e was obse ed in bo h s udies and a he all-closed s age. Howe e , in hei
s udy, a maximum le el o 1140 ppm was eached, while a maximum o 1027 ppm was
eached in he cu en s udy. Thus, he same linea end o he inc emen in he ca bon
dioxide le el a he all-closed s age could be de e mined.
The cu en s udy e ealed a linea inc emen o 16.4 ppm/min a he i s all-closed
s age and a 17.2 ppm/min inc emen a he second s age (Figu e 3). These alues a e simila
o hose ob ained by Chillon e al. [
37
], a 18.1 ppm/min and 16.2 ppm/min, espec i ely.
No e ha he ca bon dioxide le el also exhibi ed a e y simila asymp o ic beha io a
bo h he only windows
opened and windows plus doo opened s ages in bo h s udies.
Howe e , he asymp o ic alue o he ca bon dioxide le el di e ed be ween he s udies.
This depends no only on he ini ial le el o ca bon dioxide a he s a o he measu emen s,
which is 700 ppm in he cu en s udy and 904 ppm in hei s udy, bu also depends on he
du a ion o each o he en ila ion s ages. No e ha he du a ion o each s age is di e en .
In he wo k o Chillon e al. [
37
], he i s all-closed s age las ed 13 min, he second s age
wi h only he windows opened las ed 27 min, he hi d s age wi h all he windows and
doo s closed las ed 33 min, and he ou h s age wi h he windows and doo s opened las ed
17 min, o a o al o 90 min. In he cu en s udy, he du a ions o he same ou s ages
we e 20 min, 16 min, 20 min and 12 min, espec i ely, o a o al ime o 68 min.
This s udy is based on expe imen ally measu ed en i onmen s moni o ing wha is
p oduced in di e en ac i i ies o di e en in ensi y le els, wi h di e en olume a ios pe
pe son and wi h di e en en ila ions o ob ain a sample and app ecia e he e ec i eness
o he en ila ions ca ied ou . The moni o ing ime was es ablished based on he du a ion
Buildings 2024,14, 1007 24 o 28
o he ac i i ies and he epicen e o hese measu emen s o moni o wha we ha e ied o
de ine he e as he pe iod o e u n o calm a e he end o he ac i i y wi h he space emp y
o people. In hese measu emen s, he du a ion o he ac i i ies was g ea e han 45 min
and less han 2 h. Typically, due o he pandemic, ai enewal wi h he ou side is ca ied ou
h ough na u al en ila ion p io o and a e he ac i i ies. In addi ion, i is expec ed ha
hese good p ac ices will con inue in he u u e. The e o e, i is use ul o make hem pa
o he s udy, measu ing as hey a e p oduced, wi hou al e ing hei s a e o hei ini ial
and inal condi ions. A he same ime, i has been obse ed when opening windows ha
he ansien s a es ega ding he ca bon dioxide measu emen s las less han 45 min o
30 min
, and in some cases e en less ime. We ha e also obse ed ha he ansien s a e in
all-closed scena ios can ake longe o become s a iona y, i.e., measu emen 3.4, whe e he
s a iona y s a e was es ablished a e app oxima ely 60 min.
An o e all e ec ega ding he heigh o he ca bon dioxide senso s is obse ed. I
indica es ha measu ed alues o CO2 concen a ions a e almos equal when he senso s
a e a he same heigh , namely, o measu emen s l and 2. Fo he es o he measu emen s,
he di e ence in heigh o he loca ion o he used couple o senso s is a cons an alue
o
each measu emen
, since hey a e ixed du ing he measu emen s, and i s alue s ays
be ween 0.45 m and 0.75 m. Howe e , ypically he di e ence in hei measu es is no con-
s an . The only no o ious cases when i is cons an is o he low-in ensi y scena io cap u ed
du ing measu emen s 4 and 5, when he senso loca ed a 1.1 m heigh measu es highe
concen a ions o CO2 compa ed o he senso loca ed a 0.6 m heigh . These measu emen s
we e pe o med wi h people si ing on chai s; he e o e, he 1.1 m heigh senso p esen ed
100–150 ppm highe dioxide ca bon concen a ion le el han he one loca ed a 0.6 m heigh .
These pa icula cases a e low-in ensi y ac i i ies and indi iduals did no mo e du ing
he measu emen s, esul ing in a highe mou h heigh a ound
1.1 m
. The es o he mea-
su emen s wi h di e en heigh loca ions o he senso s we e
measu emen s 3, 6 and 7
. Fo
measu emen 3, wi h low-medium in ensi y, due mainly o he mo emen o he child en,
some pa en s s anding up and si ing down in o de o ge hem back, he e is no cons an
pa e n o he di e ence in he cap u es o bo h senso s. Howe e , he senso a 1.3 m
p esen ed a ound 100 ppm highe le el han he one loca ed a 0.7 m, which could be due
o he mo emen o he child en, who we e a ely alle han 1.4 m. Fo measu emen 6,
wi h medium-in ensi y, due o he ac i i y equi ing mo emen s below 1 m heigh , such
as lying down and squa ed posi ions o some exe cises, he e is no cons an pa e n in
he di e ence, bu he senso a 1 m heigh om he loo cap u ed alues a ound 50 ppm
highe han he o he senso . Fo measu emen 7, wi h high-in ensi y and people si ing on
bikes and wi h hei mou hs ypically abo e 1.75 m, a highe concen a ion le el o a ound
100 ppm was p esen ed by he senso loca ed a 1.75 m heigh in compa ison wi h he one
loca ed a 1.25 m.
As a consequence o he ype o en ila ion in es iga ed, measu emen s 3, 6 and
7 we e excluded om he compa ison o di e en easons. In addi ion, i should be
men ioned ha a ious en ila ion me hods di e in ene gy consump ion. HRV and
ERV sys ems sa e ene gy by p econdi ioning ai , while DCV adjus s based on needs. PV
in eg a ion can u he educe eliance on adi ional ene gy sou ces, as s udied by Kalmá
e al. [
38
]. Table 4p esen s he da a wi h he di e ences om his wo k highligh ed. Du ing
measu emen s 6 and 7, ai condi ioning was applied, and hey in ol ed ac i i ies no o he
low-in ensi y ype. In measu emen 3, no all-closed s age occu ed, and i did no in ol e
low-in ensi y ac i i ies. Measu emen 2 occu ed in an almos emp y oom (one pe son
inside) and con ained one all-closed s age.
Buildings 2024,14, 1007 25 o 28
Table 4. Di e ence summa y o he linea inc emen end o he ca bon dioxide le el a he all-closed
s age du ing measu emen s 1, 2, 4 and 5.
M.
No.
Measu emen
Min
CO2
[ppm]
Max
CO2
[ppm]
Closed
Time
[min]
CO2
Func ion
( ) Type
No. o
Pe sons
Inside
Volume
[m3]
Inside
Volume/Pe son
[m3]
∆
CO
2
/Time
[ppm/min]
(Inside
Volume/Pe son)
/(∆CO2/Time)
[m3·min/ppm]
1 1 700 1027 20 Linea 15 229 15.3 16.4 0.9
2 2 522 605 20 Linea 1 229 229 4.2 55.1
4 4 700 820 23 Linea 49 1008 20.6 5.2 3.9
5 5 700 1200 25 Linea 31 271 8.7 20.0 0.4
Measu emen s 4 and 5 e ealed nonlinea beha io a he all-closed s age, as p esen ed
in Table 4. This should be u he in es iga ed in ega d o enclosed spaces wi hou
en ila ion o main ain he CO
2
concen a ion below he ecommended le el o p e en he
isk o ansmission.
Acco ding o ex ensi e li e a u e on he issue o ai bo ne i us ansmission, he
p obabili y o in ec ion isk is in es iga ed and usually ep esen ed by he well-known
Wells–Riley model [
39
–
41
]. Figu e 24 shows he co esponding p obabili y o in ec ion
isk o all he measu emen s ob ained in his wo k. The exp ession used o ep esen
p obabili y o in ec ion isk (P) is he ollowing Equa ion (1):
P=1−e(−q·Y· )(1)
whe e qis he quan a gene a ion a e (1/h) and in his case is 10, a alue ixed by he
e e enced wo ks [
39
–
41
]. Yis he passi e scala , maximum and minimum le els o CO
2
,
and is he exposu e ime (h).
Buildings2024,14,xFORPEERREVIEW27o 31

Table4.Di e encesumma yo  helinea inc emen  endo  heca bondioxidele ela  heall‐
closeds agedu ingmeasu emen s1,2,4and5.
M.
No.
Measu e‐
men
Min
CO2
[ppm]
Max
CO2
[ppm]
Closed
Time
[min]
CO2
Func ion
( )Type
No.o
Pe sons
Inside
Volume
[m3]
Inside
Vol‐
ume/Pe son
[m3]
ΔCO2/Time
[ppm/min]
(InsideVol‐
ume/Pe son)
/(ΔCO2/Time)
[m3∙min/ppm]
1 1 700 1027 20Linea 15 229 15.3 16.4 0.9
2 2 522 605 20Linea 1 229 229 4.2 55.1
4 4 700 820 23Linea 49 1008 20.6 5.2 3.9
5 5 700 1200 25Linea 31 271 8.7 20.0 0.4
Measu emen s4and5 e ealednonlinea beha io a  heall‐closeds age,asp e‐
sen edinTable4.Thisshouldbe u he in es iga edin ega d oenclosedspaceswi h‐
ou  en ila ion omain ain heCO2concen a ionbelow he ecommendedle el op e‐
en  he isko  ansmission.
Acco ding oex ensi eli e a u eon heissueo ai bo ne i us ansmission, he
p obabili yo in ec ion iskisin es iga edandusually ep esen edby hewell‐known
Wells–Rileymodel[39–41].Figu e24shows heco espondingp obabili yo in ec ion
isk o all hemeasu emen sob ainedin hiswo k.Theexp essionused o ep esen 
p obabili yo in ec ion isk(P)is he ollowingEqua ion(1):
𝑃  1  𝑒󰇛∙∙󰇜(1)
whe eqis hequan agene a ion a e(1/h)andin hiscaseis10,a alue ixedby he e ‐
e encedwo ks[39–41].Yis hepassi escala ,maximumandminimumle elso CO2,
and is heexposu e ime(h).

Figu e24.P obabili yo in ec ion isko  hemeasu emen sinpe cen age.
Figu e24showsadi ec  ela ionshipbe weenhighle elso ca bondioxideand he
p obabili yo in ec ion isk.The eisadi e enceinhowquickly hisinc easeoccu s,as
aconsequenceo  he ela ionshipbe ween hesi ua ionswhen hele elo CO2inc eases
andhowquickly hisoccu s o eachmeasu emen .F ommeasu emen s1and2, he eis
a educ ionin hep obabili yo in ec ion iskwhen en ila ionscena iooccu s.Howe ‐
e , hise ec didno  akeplace o  he es o  hemeasu emen s.Thismeans ha  he
p obabili yo in ec ion iska e alongpe iodo no en ila iono oncei  eaches he
maximum alueba elyp esen sany educ ion.
5.Conclusions
Figu e 24. P obabili y o in ec ion isk o he measu emen s in pe cen age.
Figu e 24 shows a di ec ela ionship be ween high le els o ca bon dioxide and he
p obabili y o in ec ion isk. The e is
a di e ence
in how quickly his inc ease occu s, as
a consequence o he ela ionship be ween he si ua ions when he le el o CO
2
inc eases
and how quickly his occu s o each measu emen . F om measu emen s 1 and 2, he e is
a educ ion
in he p obabili y o in ec ion isk when en ila ion scena io occu s. Howe e ,
his e ec did no ake place o he es o he measu emen s. This means ha he p obabil-
i y o in ec ion isk a e a long pe iod o no en ila ion o once i eaches he maximum
alue ba ely p esen s any educ ion.
5. Conclusions
In he cu en s udy, he empe a u e, ela i e humidi y, ca bon dioxide concen a ion
and pa icle size cumula i e concen a ion and hei ela ionships we e in es iga ed in
se e al enclosed spaces used o ac i i ies wi h low o high in ensi ies unde na u al