In e na ional Jou nal o
En i onmen al Resea ch
and Public Heal h
A icle
Analysis o Alpha Ac i i y Le els and Dependence on
Me eo ological Fac o s o e a Complex Te ain in
No he n Ibe ian Peninsula (2014–2018)
Miguel Ángel He nández-Ceballos 1, Fe nando Lega da 2and Na alia Aleg ía2,*
1Depa men o Physics, Uni e si y o Co doba, 14071 Có doba, Spain; [email p o ec ed]
2Depa men o Ene ge ic Enginee ing, Uni e si y o he Basque Coun y, 48013 Bilbao, Spain;
[email p o ec ed]
*Co espondence: [email p o ec ed]; Tel.: +34-94-601-7279
Recei ed: 18 Sep embe 2020; Accep ed: 28 Oc obe 2020; Published: 29 Oc obe 2020
Abs ac :
Alpha ambien concen a ions in g ound-le el ai we e measu ed weekly in Bilbao (no he n
Spain) by collec ing ae osols in il e s be ween 2014 and 2018. O e his pe iod, he alpha ac i i y
concen a ions in he ae osol’s samples ange om 13.9
µ
Bq/m
3
o 246.5
µ
Bq/m
3
, wi h a mean
o 66.49
±
39.33
µ
Bq/m
3
. The in e -annual and in a-annual (seasonal and mon hly) a ia ions
a e analyzed, wi h he highes ac i i y in au umn mon hs and he lowes one in win e mon hs.
Special a en ion has been paid o alpha peak concen a ions (weekly concen a ions abo e he
90 h pe cen ile) and i s ela ionship wi h egional me eo ological scena ios by means o ai mass
ajec o ies and local me eo ological pa ame e s. The me eo ological analysis o hese high alpha
concen a ions has e ealed wo ai low pa e ns-one om he sou h wi h land o igin and one om he
no h wi h ma i ime o igin-mainly associa ed wi h hese alpha peak concen a ions. Su ace winds
du ing ep esen a i e pe iods o bo h ai low pa e ns a e also analyzed in combina ion wi h
222
Rn
concen a ions, which demons a ed he di e en daily e olu ion associa ed wi h each ai low pa e n.
The p esen esul s a e ele an in unde s anding ends and me eo ological ac o s a ec ing alpha
ac i i y concen a ions in his a ea, and hence, o con ol po en ial a mosphe ic en i onmen al eleases
and ensu e he en i onmen al and public heal h.
Keywo ds: g oss alpha ac i i y; no he n Ibe ian Peninsula; adon; ai low pa e ns; su ace winds
1. In oduc ion
Radioac i i y is na u ally p esen in he ai due o cosmogenic adionuclides (14C, 7Be, and 3H),
cosmic adia ion, and na u al adionuclides p esen in all ocks and soils (
238
U and p ogenies,
232
Th and p ogenies, and
40
K), and i s na u al backg ound is inc eased by an h opogenic sou ces,
such as nuclea / adiological acciden , nuclea weapon es s, o he p oduc ion and applica ion o
phospho us e ilize s [1].
The impac o adioac i i y on he en i onmen and popula ion heal h makes he con ol o
adioac i i y le els necessa y. In his sense, alpha ac i i y concen a ion is usually used as a con ol
indica o o he adioac i i y le els in ai , and i is a common measu emen o de ec ing ac i i y peaks
associa ed wi h adioac i e eleased o he a mosphe e [
2
]. This ac i i y concen a ion can be measu ed
coun ing he numbe o alpha emissions p oduced pe uni o ime and ai olume (g oss alpha),
which a e de e mined om he sampling o a mosphe ic ae osols. The de e mina ion and o ma ion o
adioac i e ae osols in he a mosphe e ai a e analyzed in de ail in Papas e anou [
3
]. In case o alpha
ac i i y concen a ion in ae osols, hei o igin can be na u al due o adon daugh e s [3].
The long- e m moni o ing o g oss alpha ac i i y concen a ions enables us o s udy ends
and pe iodic a ia ions and, in combina ion wi h me eo ological pa ame e s, o iden i y he main
In . J. En i on. Res. Public Heal h 2020,17, 7967; doi:10.3390/ije ph17217967 www.mdpi.com/jou nal/ije ph
In . J. En i on. Res. Public Heal h 2020,17, 7967 2 o 12
me eo ological causes in luencing he spa ial and empo al a iabili y o he en i onmen al adioac i i y
le els [
4
]. The seasonal a ia ion and i s link wi h me eo ological pa ame e s such as ain all,
empe a u e, ela i e humidi y, p essu e, isibili y, wind speed, and wind di ec ion, which in luence
he concen a ion o ae osols adio ace s in he a mosphe e, has been analyzed in se e al si es in Spain.
Dueñas [
5
,
6
] and Piñe o-Ga c
í
a [
7
] in he sou h, Ga c
í
a-Tala e a [
8
] in he wes , and Sa
é
z-Muñoz [
9
] in
he eas p o ide in o ma ion abou he spa ial dis ibu ion and he me eo ological condi ions d i en
g oss alpha concen a ions in su ace ai in Spain. Howe e , in he no he n pa o Spain, he e a e
comple ely di e en me eo ological and clima ic condi ions, and o he au ho s’ knowledge, he e a e
no s udies analyzing alpha concen a ions.
The di ec ele ance o alpha ac i i y on he e ec i e dose causes he need o analyzing and
cha ac e izing hese concen a ions. Depending on he ae osol’s size, in he espi a ion p ocess,
some ae osol se ling occu s in he al eola spaces [
10
], and i he e a e some adionuclides on hem,
in e nal i adia ion is p oduced [
11
]. Due o he inhala ion o he sho -li ed adon decay p oduc s,
his adionuclide deli e s he la ges p opo ion o he na u al adia ion dose o humans [
3
]. The alpha
ene gy eleased by Rn p ogeny is close o 35 GeV/Bq.
In his pape , we analyze he empo al a ia ion o he adioac i e ae osol concen a ions by
measu ing weekly he g oss alpha ac i i y o e i e yea s (2014–2018) a Bilbao (no he n Spain),
and due o he po en ial heal h impac o alpha peak concen a ions, we in es iga ed he me eo ological
ac o s con olling hem. To his end, he link be ween local/ egional me eo ological condi ion and
alpha peak concen a ions a e examined by means o he calcula ion o backwa d ajec o ies ( egional
scale) and he empo al a iabili y o su ace winds and
222
Rn measu ed (local scale). This las analysis
is based on he ac ha , in no mal si ua ions, g oss alpha o igin in ai is mainly explained due
o he p esence o long-li ed daugh e s o gaseous
222
Rn ha a e a ached o ae osols a e clus e
o ma ion [3].
The ollowing esea ch issues a e add essed in he p esen s udy:
1. Analysis o he empo al a ia ion o alpha ac i i y concen a ions in su ace ai ;
2. Dependence o alpha peak ac i i y concen a ions on ai low pa e ns;
3.
Analysis o he daily empo al e olu ion o alpha ac i i y concen a ions by means he link
be ween su ace wind pa e ns and 222Rn concen a ions.
The s uc u e o his pape is he ollowing: Sec ion 2desc ibes he measu emen place,
he adioac i i y measu emen s, and he me eo ological pa ame e s and da a used o he s udy.
Sec ion 3p esen s, in a i s s ep, he s a is ical analysis o he alpha ac i i y concen a ion, while in a
second s ep, he co ela ion o high alpha concen a ions wi h egional and local me eo ological
pa ame e s is in es iga ed. To inalize his esul s sec ion, he dependence o alpha ac i i y
concen a ions, by means o
222
Rn alues, on he su ace wind condi ions is analyzed. In Sec ion 4,
he conclusions a e shown.
2. Ma e ials and Me hods
2.1. S udy A ea
Bilbao Ci y (43.26 N,
−
2.94 W) is placed in he Basque Coun y egion (no he n Spain) (Figu e 1).
Bilbao is abou 16 km away om he sea, in a moun ainous coas al a ea a he Gul o Biscay, and in he
na ow alley o he Ne ion i e . The moun ains su ounding Bilbao ha e low al i ude (300–800 m),
al hough 40 km away he e a e moun ains wi h al i udes o 1500 m.
The clima e in Bilbao is wa m and empe a e, wi h a signi ican amoun o ain all du ing he
yea . Ai masses mainly a i e om he wes and no h o his a ea. In he pe iod co e ed by he
p esen s udy (2014–2018), he empe a u e a e aged 16.0
◦
C, while he p ecipi a ion was abou 980 mm
pe yea .
In . J. En i on. Res. Public Heal h 2020,17, 7967 3 o 12
In . J. En i on. Res. Public Heal h 2020, 17, 7967 3 o 13
Figu e 1. Loca ion o he sampling si e in he no he n a ea o he Ibe ian Peninsula.
2.2. Alpha Ac i i y Concen a ion and Radon Measu emen s.
The concen a ion o adionuclides in soil in his a ea is e y low based on he Eu opean Digi al
A las o Na u al Radia ion [12] ( o
40
K, u anium, ho ium, e c.).
The alpha ac i i y concen a ions we e measu ed in a moni o ing s a ion si ed in Bilbao ci y
(43.26 N, −2.94 W) a 34 m abo e sea le el, on he oo o he Facul y o Enginee ing (Figu e 2).
Figu e 2. The ae osol sample , he me eo ological s a ion and he adon s a ion used in he p esen
analysis.
A mosphe ic ai bo ne ae osols we e collec ed using a low olume sample whose nominal low
a e is 30 L/min. I is impo an o ema k ha he ae osol sampling akes se en days. In a week he
o al olume ci cula ed is abou 300 m
3
. This sample uses a cellulose ni a e memb ane il e
(diame e 47 mm and 0.8 um po e size) which was eplaced weekly. The il e is aken om he
sample and placed in a d ye o six days o allow ho on and adon sho -li ed alpha p ogeny o
decay, and, hen, i is measu ed in a gas low p opo ional coun e . The gas low p opo ional coun e
Figu e 1. Loca ion o he sampling si e in he no he n a ea o he Ibe ian Peninsula.
2.2. Alpha Ac i i y Concen a ion and Radon Measu emen s.
The concen a ion o adionuclides in soil in his a ea is e y low based on he Eu opean Digi al
A las o Na u al Radia ion [12] ( o 40K, u anium, ho ium, e c.).
The alpha ac i i y concen a ions we e measu ed in a moni o ing s a ion si ed in Bilbao ci y
(43.26 N, −2.94 W) a 34 m abo e sea le el, on he oo o he Facul y o Enginee ing (Figu e 2).
In . J. En i on. Res. Public Heal h 2020, 17, 7967 3 o 13
Figu e 1. Loca ion o he sampling si e in he no he n a ea o he Ibe ian Peninsula.
2.2. Alpha Ac i i y Concen a ion and Radon Measu emen s.
The concen a ion o adionuclides in soil in his a ea is e y low based on he Eu opean Digi al
A las o Na u al Radia ion [12] ( o
40
K, u anium, ho ium, e c.).
The alpha ac i i y concen a ions we e measu ed in a moni o ing s a ion si ed in Bilbao ci y
(43.26 N, −2.94 W) a 34 m abo e sea le el, on he oo o he Facul y o Enginee ing (Figu e 2).
Figu e 2. The ae osol sample , he me eo ological s a ion and he adon s a ion used in he p esen
analysis.
A mosphe ic ai bo ne ae osols we e collec ed using a low olume sample whose nominal low
a e is 30 L/min. I is impo an o ema k ha he ae osol sampling akes se en days. In a week he
o al olume ci cula ed is abou 300 m
3
. This sample uses a cellulose ni a e memb ane il e
(diame e 47 mm and 0.8 um po e size) which was eplaced weekly. The il e is aken om he
sample and placed in a d ye o six days o allow ho on and adon sho -li ed alpha p ogeny o
decay, and, hen, i is measu ed in a gas low p opo ional coun e . The gas low p opo ional coun e
Figu e 2.
The ae osol sample , he me eo ological s a ion and he adon s a ion used in he p esen analysis.
A mosphe ic ai bo ne ae osols we e collec ed using a low olume sample whose nominal low
a e is 30 L/min. I is impo an o ema k ha he ae osol sampling akes se en days. In a week he
o al olume ci cula ed is abou 300 m
3
. This sample uses a cellulose ni a e memb ane il e (diame e
47 mm and 0.8 um po e size) which was eplaced weekly. The il e is aken om he sample and
placed in a d ye o six days o allow ho on and adon sho -li ed alpha p ogeny o decay, and,
In . J. En i on. Res. Public Heal h 2020,17, 7967 4 o 12
hen, i is measu ed in a gas low p opo ional coun e . The gas low p opo ional coun e used is
LB 770 10-Channel
α
-
β
Low-Le el Coun e by Be hold Technologies GmbH & Co. KG adema k.
This de ice is equipped wi h 10 de ec o s. The e iciency o he p opo ional coun e calib a ed wi h
241
Am is close o 20%. A calib a ion sou ce was p epa ed ad hoc wi h he same ype o il e as used.
The coun ing ime was 6
×
10
4
seconds, and he de ec ion limi s ob ained we e be ween 9.71
µ
Bq/m
3
and 50.68 µBq/m3and unce ain ies, wi h a co e age ac o k =2, we e be ween 14 ±6.7 µBq/m3.
A high low sample and a adiological s a ion a e loca ed close o his low low sample (Figu e 2).
The adiological s a ion p o ides hou ly adon ac i i y concen a ions in he a mosphe e, which ha e
also been used in his s udy.
2.3. Me eo ology and Backwa d T ajec o ies
Ten-minu e in e als o he ollowing su ace me eo ological pa ame e s, which we e measu ed in
he wea he s a ion placed close o he sampling s a ion (Figu e 2), we e also used in he p esen analysis
o cha ac e ize he impac o local me eo ology on alpha ac i i y concen a ions: ai empe a u e (
◦
C),
ela i e humidi y (%), p essu e (mba ), wind di ec ion (◦), wind speed (m/s), and p ecipi a ion (mm).
Backwa d ajec o ies we e calcula ed and used in he p esen s udy. Fou kinema ic
h ee-dimensional backwa d ajec o ies pe day du ing speci ic sampling pe iods be ween 2014
and 2018, compu ed a 00:00, 06:00, 12:00, and 18:00 UTC, wi h a un ime o 96 hou s and wi h a inal
heigh o 100 m abo e g ound le el, we e calcula ed by using he hyb id single pa icle Lag angian
in eg a ed ajec o y (HYSPLIT) model [
13
]. The Global Da a Assimila ion Sys em Na ional Cen e s o
En i onmen al P edic ion (GDAS-NCEP) model, main ained by he Na ional Oceanic and A mosphe ic
Adminis a ion Ai Resou ces Labo a o y (NOAA/ARL) we e used as me eo ological inpu .
Wo king wi h a la ge numbe o ajec o ies equi es he applica ion o clus e analysis [
14
] o
classi y hem acco ding o hei pa hways, and hence, o iden i y he co esponding ai low pa e ns.
The p esen s udy uses he clus e me hodology implemen ed in he HYSPLIT model and desc ibed
in S unde [
15
]. This mul i a ia e s a is ical echnique g oups ajec o ies wi h simila di ec ion and
leng hs by using he Wa d’s minimum a iance clus e ing me hod o minimize he dissimila i y in he
ajec o ies wi hin each clus e while maximizing he dissimila i y o di e en clus e s.
3. Resul s
3.1. Alpha Ac i i y Concen a ion Cha ac e iza ion: Time Se ies
The alpha ac i i y concen a ion alues, measu ed weekly om 2014 o 2018, a e plo ed in
ch onological o de (Figu e 3a). In o al, he e we e 258 da a, and hey we e a ailable in each yea ,
hus gua an eeing he la ges s a is ical sample. The ac i i y concen a ions in he ae osol’s samples
ange om 246.5
µ
Bq/m
3
o 13.97
µ
Bq/m
3
, wi h a mean o 66.49
±
39.33
µ
Bq/m
3
, whe e he unce ain y
is gi en as he sample s anda d de ia ion. This Figu e 3a sugges s a cyclical a iabili y e e y yea ,
wi h low alues in he i s hal o he yea ollowed by an inc ease and low alues a he end o he
yea . This beha io is only b oken in 2015. These alpha ac i i y concen a ions a e also assessed in a
box-and-whiske plo (Figu e 3b), which shows ha he e is a symme ical dis ibu ion o he alues,
i.e., di e ences be ween P75 and P25 wi h he median (P50) a e simila . The a e age is g ea e han he
P50, which deno es he p e alence o low alpha alues, al hough wi h la ge impac o occasional high
ones. Using he G ubbs es , he exis ence o ou lie s among he egis e ed alues has been assessed,
concluding ha he e a e no ou lie s in he p esen se o da a.
Alpha measu emen s in Figu e 3a cons i u e a ime se ies due o he exis ence o co ela ion
delays o up o 12 weeks be ween da a [
16
,
17
]. The pe iodog am calcula ed o his pe iod is shown in
Figu e 4. A pe iodog am is a help ul ool used o iden i y he dominan cyclical beha io o a ime se ies.
In he Figu e 4, he X-axis ep esen s equency and he Y-axis ep esen s he spec um. Fou main
peaks, i.e., pe iodici ies o alpha concen a ion eco ds, a e iden i ied in Figu e 4. The i s one e eals
a one-yea pe iod a ia ion ( equency 1.93
×
10
−2
week
−1
i.e., 52 weeks), while he second, hi d and
In . J. En i on. Res. Public Heal h 2020,17, 7967 5 o 12
ou h peaks indica e in a-annual a iabili y ( equencies 3.9
×
10
−2
, 6.9
×
10
−2
and
1.6 ×10−1
week
−1
i.e., 25, 12, and six weeks). These esul s highly ag ee wi h he componen s o he
7
Be ime se ies
iden i ied and analyzed in p e ious s udies [4,18]
In . J. En i on. Res. Public Heal h 2020, 17, 7967 5 o 13
Figu e 3. (a) Tempo al a ia ion and (b) box-and-whiske plo o he alpha ac i i y concen a ions
om Janua y 2014 o Decembe 2018 a Bilbao sampling s a ion. In b, he cen e o he box deno es
he 50% (P50), and he bo om and op o he box co espond o he 25% (P25) and 75% (P75) alues,
espec i ely. The squa e indica es he P90 and he ci cle he P10 alues, while he ex emes o he box
ep esen he P95 and P5 alues. The c oss in he box is he a e age alue.
Alpha measu emen s in Figu e 3a cons i u e a ime se ies due o he exis ence o co ela ion
delays o up o 12 weeks be ween da a [16,17]. The pe iodog am calcula ed o his pe iod is shown
in Figu e 4. A pe iodog am is a help ul ool used o iden i y he dominan cyclical beha io o a ime
se ies. In he Figu e 4, he X-axis ep esen s equency and he Y-axis ep esen s he spec um. Fou
main peaks, i.e., pe iodici ies o alpha concen a ion eco ds, a e iden i ied in Figu e 4. The i s one
e eals a one-yea pe iod a ia ion ( equency 1.93 × 10−2 week−1 i.e., 52 weeks), while he second,
hi d and ou h peaks indica e in a-annual a iabili y ( equencies 3.9 × 10−2, 6.9 × 10−2 and 1.6 × 10−1
week−1 i.e., 25, 12, and six weeks). These esul s highly ag ee wi h he componen s o he 7Be ime
se ies iden i ied and analyzed in p e ious s udies [4,18]
Figu e 4. Pe iodog am o Bilbao ime se ies o alpha ac i i y concen a ions om 2014 o 2018.
a)
b)
0
50
100
150
200
250
300
01/01/2014
01/07/2014
01/01/2015
01/07/2015
01/01/2016
01/07/2016
01/01/2017
01/07/2017
01/01/2018
01/07/2018
01/01/2019
Ac i i y concen a ion (µBq/m3)
0
20
40
60
80
100
120
140
160
Bilbao-Alpha
Ac i i y Concen a ion (µBq/m
3
)
Figu e 3.
(
a
) Tempo al a ia ion and (
b
) box-and-whiske plo o he alpha ac i i y concen a ions
om Janua y 2014 o Decembe 2018 a Bilbao sampling s a ion. In
b
, he cen e o he box deno es
he 50% (P50), and he bo om and op o he box co espond o he 25% (P25) and 75% (P75) alues,
espec i ely. The squa e indica es he P90 and he ci cle he P10 alues, while he ex emes o he box
ep esen he P95 and P5 alues. The c oss in he box is he a e age alue.
In . J. En i on. Res. Public Heal h 2020, 17, 7967 5 o 13
Figu e 3. (a) Tempo al a ia ion and (b) box-and-whiske plo o he alpha ac i i y concen a ions
om Janua y 2014 o Decembe 2018 a Bilbao sampling s a ion. In b, he cen e o he box deno es
he 50% (P50), and he bo om and op o he box co espond o he 25% (P25) and 75% (P75) alues,
espec i ely. The squa e indica es he P90 and he ci cle he P10 alues, while he ex emes o he box
ep esen he P95 and P5 alues. The c oss in he box is he a e age alue.
Alpha measu emen s in Figu e 3a cons i u e a ime se ies due o he exis ence o co ela ion
delays o up o 12 weeks be ween da a [16,17]. The pe iodog am calcula ed o his pe iod is shown
in Figu e 4. A pe iodog am is a help ul ool used o iden i y he dominan cyclical beha io o a ime
se ies. In he Figu e 4, he X-axis ep esen s equency and he Y-axis ep esen s he spec um. Fou
main peaks, i.e., pe iodici ies o alpha concen a ion eco ds, a e iden i ied in Figu e 4. The i s one
e eals a one-yea pe iod a ia ion ( equency 1.93 × 10−2 week−1 i.e., 52 weeks), while he second,
hi d and ou h peaks indica e in a-annual a iabili y ( equencies 3.9 × 10−2, 6.9 × 10−2 and 1.6 × 10−1
week−1 i.e., 25, 12, and six weeks). These esul s highly ag ee wi h he componen s o he 7Be ime
se ies iden i ied and analyzed in p e ious s udies [4,18]
Figu e 4. Pe iodog am o Bilbao ime se ies o alpha ac i i y concen a ions om 2014 o 2018.
a)
b)
0
50
100
150
200
250
300
01/01/2014
01/07/2014
01/01/2015
01/07/2015
01/01/2016
01/07/2016
01/01/2017
01/07/2017
01/01/2018
01/07/2018
01/01/2019
Ac i i y concen a ion (µBq/m3)
0
20
40
60
80
100
120
140
160
Bilbao-Alpha
Ac i i y Concen a ion (µBq/m
3
)
Figu e 4. Pe iodog am o Bilbao ime se ies o alpha ac i i y concen a ions om 2014 o 2018.
Figu e 5displays he box-and-whiske plo s o alpha ac i i y concen a ions o e he yea s.
This Figu e 5shows ha he a e age (squa e) and he a iabili y o alpha alues (P75–P25) a e simila
o e he yea s, which can be associa ed wi h he minimal change in he sou ce e m o alpha ac i i y
concen a ions du ing his i e-yea pe iod. The a e ages a e always highe han P50. The a e age
anges om 60.2
µ
Bq/m
3
in 2018 o 72.9
µ
Bq/m
3
in 2015, and he 90 h pe cen ile (P90), which is usually
In . J. En i on. Res. Public Heal h 2020,17, 7967 6 o 12
aken as e e ence o maximum alues [
19
], o a oid he impac o possible ou lie s, anges om
108.1 µBq/m3in 2014 o 117.2 µBq/m3in 2015.
In . J. En i on. Res. Public Heal h 2020, 17, 7967 6 o 13
Figu e 5 displays he box-and-whiske plo s o alpha ac i i y concen a ions o e he yea s. This
Figu e 5 shows ha he a e age (squa e) and he a iabili y o alpha alues (P75–P25) a e simila
o e he yea s, which can be associa ed wi h he minimal change in he sou ce e m o alpha ac i i y
concen a ions du ing his i e-yea pe iod. The a e ages a e always highe han P50. The a e age
anges om 60.2 µBq/m3 in 2018 o 72.9 µBq/m3 in 2015, and he 90 h pe cen ile (P90), which is usually
aken as e e ence o maximum alues [19], o a oid he impac o possible ou lie s, anges om 108.1
µBq/m3 in 2014 o 117.2 µBq/m3 in 2015.
Figu e 5. Box-and-whiske plo o alpha ac i i y concen a ions o e he yea s (2014−2018) a Bilbao.
The meaning o he box plo is he same o Figu e 3b.
The analysis o he in a-annual a iabili y, conside ing win e (Decembe , Janua y, and
Feb ua y), sp ing (Ma ch, Ap il, and May), summe (June, July, and Augus ), and Au umn
(Sep embe , Oc obe , and No embe ), epo s he maximum a e age alue in au umn (Figu e 6a),
conc e ely in Oc obe (110 µBq/m3) (Figu e 6b), while he minimum a e age alue is in win e (Figu e
6a), wi h he mon hly minimum in Feb ua y (40 µBq/m3) (Figu e 6b). These seasonal and mon hly
a iabili y do no ag ee wi h p e ious s udies ca ied ou in Spain [5,8,9], in which he ac i i y
maxima a e egis e ed in summe . This di e ence would poin ou di e ences in sou ce e ms and
in he me eo ological condi ions d i en alpha ac i i y concen a ions du ing he yea s among hese
si es, and hence, he need o analyze he link be ween alpha and me eo ological pa ame e s.
0
20
40
60
80
100
120
140
160
2014 2015 2016 2017 2018
Ac i i y Concen a ion (µBq/m
3
)
Figu e 5.
Box-and-whiske plo o alpha ac i i y concen a ions o e he yea s (2014–2018) a Bilbao.
The meaning o he box plo is he same o Figu e 3b.
The analysis o he in a-annual a iabili y, conside ing win e (Decembe , Janua y, and Feb ua y),
sp ing (Ma ch, Ap il, and May), summe (June, July, and Augus ), and Au umn (Sep embe , Oc obe ,
and No embe ), epo s he maximum a e age alue in au umn (Figu e 6a), conc e ely in Oc obe
(110
µ
Bq/m
3
) (Figu e 6b), while he minimum a e age alue is in win e (Figu e 6a), wi h he mon hly
minimum in Feb ua y (40
µ
Bq/m
3
) (Figu e 6b). These seasonal and mon hly a iabili y do no ag ee
wi h p e ious s udies ca ied ou in Spain [
5
,
8
,
9
], in which he ac i i y maxima a e egis e ed in summe .
This di e ence would poin ou di e ences in sou ce e ms and in he me eo ological condi ions d i en
alpha ac i i y concen a ions du ing he yea s among hese si es, and hence, he need o analyze he
link be ween alpha and me eo ological pa ame e s.
In . J. En i on. Res. Public Heal h 2020, 17, 7967 7 o 13
Figu e 6. (a) S a ional a iabili y and (b) mon hly a e age o alpha ac i i y concen a ions a Bilbao
om 2014 o 2018.
3.2. Me eo ological Cha ac e iza ion o he Alpha Peak Ac i i y Concen a ions
This sec ion p esen s he esul s o s udying he impac o me eo ological pa ame e s on he
highes alpha ac i i y concen a ions egis e ed in Bilbao o he i e yea s analyzed (2014−2018). The
eason o aking he highes alpha ac i i y concen a ions as e e ence is due o heal h haza ds
associa ed wi h he p esence o adionuclides in ai [20].
High alpha su ace concen a ions a e iden i ied as alues exceeding he P90 calcula ed o e
2014−2018 (117.1 µBq/m3 in Figu e 3b). P90 has been p e iously used in o he esea ch as he ex eme
c i e ion [18–21]. The a e age o he 26 high alpha alues iden i ied du ing he pe iod 2014−2018
abo e P90 is 152.0 ± 6.6 µBq/m3, while he highes alpha alue is 246.5 µBq/m3. Seasonal dis ibu ion
o hese alpha peak concen a ions is shown in Figu e 7, as well as he co esponding seasonal mean.
This Figu e 7 epo s he la ges occu ence o hese high alpha concen a ions in au umn (14 ou o
26 pe iods, 53%), and he minimum occu ence in summe ( h ee ou o 26 pe iods, 11.5%). Howe e ,
he maximum seasonal a e age o hese peak concen a ions is egis e ed in sp ing (187.9 µBq/m3),
ollowed by summe (166.7 µBq/m3), and lowe and simila alues in win e (142.4 µBq/m3) and
au umn (144.8 µBq/m3). This seasonal a iabili y o alpha peak concen a ions, mainly explained by
di e ences in a mosphe ic ac o s, is di e en o Figu e 6a bu simila o he seasonal a ia ions
shown in p e ious a icles ca ied ou in Spain, and, a he same ime, i p o ides insigh in o he
la ge impac o occasional high alpha alues du ing he wa m (sp ing/summe ) pe iod o he yea .
The e alua ion o co ela ion be ween weekly alpha peak ac i i y concen a ions and a i hme ic
alues o local me eo ological pa ame e s ( empe a u e, ela i e humidi y, a mosphe ic p essu e,
and wind speed and di ec ion) du ing each sampling pe iod is pe o med a he signi icance le el o
0.05. In he case o p ecipi a ion, he o al amoun du ing each sampling pe iod is used. The
co ela ions ound a e a ound ze o, i.e., he e is no ela ionship be ween he wo a iables used. The
highes is −0.22 wi h p ecipi a ion, which, being nega i e, indica es ha p ecipi a ion ends o educe
alpha ac i i y a he si e as a consequence o sca enging o ai bo ne adionuclides by ain all [22].
b)
0
20
40
60
80
100
120
Jan Feb Ma Ap May Jun Jul Aug Sep Oc No Dec
Ac i i y Concen a ion (µBq/m3)
0
20
40
60
80
100
120
1591317
Ac i i y Concen a ion (µBq/m3)
Wi Sp Su Au Wi Sp Su Au Wi Sp Su Au Wi Sp Su Au Wi Sp Su Au
2014 2015 2016 2017 2018
a)
Figu e 6.
(
a
) S a ional a iabili y and (
b
) mon hly a e age o alpha ac i i y concen a ions a Bilbao
om 2014 o 2018.
3.2. Me eo ological Cha ac e iza ion o he Alpha Peak Ac i i y Concen a ions
This sec ion p esen s he esul s o s udying he impac o me eo ological pa ame e s on he
highes alpha ac i i y concen a ions egis e ed in Bilbao o he i e yea s analyzed (2014–2018).
In . J. En i on. Res. Public Heal h 2020,17, 7967 7 o 12
The eason o aking he highes alpha ac i i y concen a ions as e e ence is due o heal h haza ds
associa ed wi h he p esence o adionuclides in ai [20].
High alpha su ace concen a ions a e iden i ied as alues exceeding he P90 calcula ed o e
2014–2018 (117.1
µ
Bq/m3 in Figu e 3b). P90 has been p e iously used in o he esea ch as he ex eme
c i e ion [
18
–
21
]. The a e age o he 26 high alpha alues iden i ied du ing he pe iod 2014–2018
abo e P90 is 152.0
±
6.6
µ
Bq/m
3
, while he highes alpha alue is 246.5
µ
Bq/m
3
. Seasonal dis ibu ion
o hese alpha peak concen a ions is shown in Figu e 7, as well as he co esponding seasonal mean.
This Figu e 7 epo s he la ges occu ence o hese high alpha concen a ions in au umn (14 ou o
26 pe iods, 53%), and he minimum occu ence in summe ( h ee ou o 26 pe iods, 11.5%). Howe e ,
he maximum seasonal a e age o hese peak concen a ions is egis e ed in sp ing (187.9
µ
Bq/m
3
),
ollowed by summe (166.7
µ
Bq/m
3
), and lowe and simila alues in win e (142.4
µ
Bq/m
3
) and
au umn (144.8
µ
Bq/m
3
). This seasonal a iabili y o alpha peak concen a ions, mainly explained by
di e ences in a mosphe ic ac o s, is di e en o Figu e 6a bu simila o he seasonal a ia ions shown
in p e ious a icles ca ied ou in Spain, and, a he same ime, i p o ides insigh in o he la ge impac
o occasional high alpha alues du ing he wa m (sp ing/summe ) pe iod o he yea .
In . J. En i on. Res. Public Heal h 2020, 17, 7967 8 o 13
These esul s, wi h none o hem signi ican a 0.05, indica e he weakness o he ela ionship be ween
alpha peak concen a ions and each indi idual me eo ological a iable a his weekly empo al scale
le el. The e o e, o he a mosphe ic p ocesses should be included in he p esen analysis aiming a
unde s anding he me eo ological easons o hese high alpha su ace concen a ions in Bilbao.
Figu e 7. A e aged concen a ion in each season conside ing only hose sampling pe iods egis e ing
alpha concen a ions abo e P90 du ing 2014−2018 (in b acke s below he season).
Due o he impac ha ai low pa e ns ha e o e he su ace wea he condi ions and ae osols
empo al dis ibu ion in a gi en a ea and o e a pe iod o ime [23], backwa d ajec o ies in Bilbao
a e calcula ed and a e used o de e mine he in luence o egional me eo ological pa e ns on alpha
peak concen a ions. Figu e 8a shows he mean ajec o ies (clus e ) o Bilbao a 100 m calcula ed
conside ing all he 26 sampling pe iods abo e P90. Se en ai low pa e ns a e iden i ied by applying
he clus e me hodology explained in S unde [15]. Taking in o accoun he pa hways ollowed by
each ai low pa e n as well as he equency (numbe in b acke s) o each one, he a i al o slow
con inen al sou he n (27%, clus e 4) and ma i ime no he n (28%, clus e 1) ai masses domina es
pe iods wi h high alpha concen a ions agains he a i al o as no he n (7%, clus e 6) and
di e en A lan ic ad ec ions om he no hwes (24%, clus e s 2 and 3) and om he wes (14%,
clus e s 5 and 7) (Figu e 8a).
Figu e 8. Back- ajec o y clus e cen e s (cen oids) ob ained a 100 m agl o pe iods wi h alpha
ac i i y concen a ions (a) abo e he 90 h pe cen ile and (b) below he 10 h pe cen ile du ing he
2014−2018 pe iod a Bilbao. The le numbe s in he cen oids a e an iden i ica ion numbe o he
0
20
40
60
80
100
120
140
160
180
200
Win e Sp ing Summe Au umn
Ac i i y concen a ion (µBq/m3)
(5) (4) (3) (14)
Figu e 7.
A e aged concen a ion in each season conside ing only hose sampling pe iods egis e ing
alpha concen a ions abo e P90 du ing 2014–2018 (in b acke s below he season).
The e alua ion o co ela ion be ween weekly alpha peak ac i i y concen a ions and a i hme ic
alues o local me eo ological pa ame e s ( empe a u e, ela i e humidi y, a mosphe ic p essu e,
and wind speed and di ec ion) du ing each sampling pe iod is pe o med a he signi icance le el o
0.05. In he case o p ecipi a ion, he o al amoun du ing each sampling pe iod is used. The co ela ions
ound a e a ound ze o, i.e., he e is no ela ionship be ween he wo a iables used. The highes
is
−
0.22 wi h p ecipi a ion, which, being nega i e, indica es ha p ecipi a ion ends o educe
alpha ac i i y a he si e as a consequence o sca enging o ai bo ne adionuclides by ain all [
22
].
These esul s, wi h none o hem signi ican a 0.05, indica e he weakness o he ela ionship be ween
alpha peak concen a ions and each indi idual me eo ological a iable a his weekly empo al scale
le el. The e o e, o he a mosphe ic p ocesses should be included in he p esen analysis aiming a
unde s anding he me eo ological easons o hese high alpha su ace concen a ions in Bilbao.
Due o he impac ha ai low pa e ns ha e o e he su ace wea he condi ions and ae osols
empo al dis ibu ion in a gi en a ea and o e a pe iod o ime [
23
], backwa d ajec o ies in Bilbao
a e calcula ed and a e used o de e mine he in luence o egional me eo ological pa e ns on alpha
peak concen a ions. Figu e 8a shows he mean ajec o ies (clus e ) o Bilbao a 100 m calcula ed
conside ing all he 26 sampling pe iods abo e P90. Se en ai low pa e ns a e iden i ied by applying
he clus e me hodology explained in S unde [
15
]. Taking in o accoun he pa hways ollowed by
each ai low pa e n as well as he equency (numbe in b acke s) o each one, he a i al o slow
In . J. En i on. Res. Public Heal h 2020,17, 7967 8 o 12
con inen al sou he n (27%, clus e 4) and ma i ime no he n (28%, clus e 1) ai masses domina es
pe iods wi h high alpha concen a ions agains he a i al o as no he n (7%, clus e 6) and di e en
A lan ic ad ec ions om he no hwes (24%, clus e s 2 and 3) and om he wes (14%, clus e s 5 and
7) (Figu e 8a).
In . J. En i on. Res. Public Heal h 2020, 17, 7967 8 o 13
These esul s, wi h none o hem signi ican a 0.05, indica e he weakness o he ela ionship be ween
alpha peak concen a ions and each indi idual me eo ological a iable a his weekly empo al scale
le el. The e o e, o he a mosphe ic p ocesses should be included in he p esen analysis aiming a
unde s anding he me eo ological easons o hese high alpha su ace concen a ions in Bilbao.
Figu e 7. A e aged concen a ion in each season conside ing only hose sampling pe iods egis e ing
alpha concen a ions abo e P90 du ing 2014−2018 (in b acke s below he season).
Due o he impac ha ai low pa e ns ha e o e he su ace wea he condi ions and ae osols
empo al dis ibu ion in a gi en a ea and o e a pe iod o ime [23], backwa d ajec o ies in Bilbao
a e calcula ed and a e used o de e mine he in luence o egional me eo ological pa e ns on alpha
peak concen a ions. Figu e 8a shows he mean ajec o ies (clus e ) o Bilbao a 100 m calcula ed
conside ing all he 26 sampling pe iods abo e P90. Se en ai low pa e ns a e iden i ied by applying
he clus e me hodology explained in S unde [15]. Taking in o accoun he pa hways ollowed by
each ai low pa e n as well as he equency (numbe in b acke s) o each one, he a i al o slow
con inen al sou he n (27%, clus e 4) and ma i ime no he n (28%, clus e 1) ai masses domina es
pe iods wi h high alpha concen a ions agains he a i al o as no he n (7%, clus e 6) and
di e en A lan ic ad ec ions om he no hwes (24%, clus e s 2 and 3) and om he wes (14%,
clus e s 5 and 7) (Figu e 8a).
Figu e 8. Back- ajec o y clus e cen e s (cen oids) ob ained a 100 m agl o pe iods wi h alpha
ac i i y concen a ions (a) abo e he 90 h pe cen ile and (b) below he 10 h pe cen ile du ing he
2014−2018 pe iod a Bilbao. The le numbe s in he cen oids a e an iden i ica ion numbe o he
0
20
40
60
80
100
120
140
160
180
200
Win e Sp ing Summe Au umn
Ac i i y concen a ion (µBq/m3)
(5) (4) (3) (14)
Figu e 8.
Back- ajec o y clus e cen e s (cen oids) ob ained a 100 m agl o pe iods wi h alpha ac i i y
concen a ions (
a
) abo e he 90 h pe cen ile and (
b
) below he 10 h pe cen ile du ing he 2014–2018
pe iod a Bilbao. The le numbe s in he cen oids a e an iden i ica ion numbe o he cen oid and he
igh numbe s (in b acke s) a e he pe cen age o comple e ajec o ies occu ing in ha clus e .
To es ablish he link o hese ai low pa e ns wi h alpha peak concen a ions, we ha e also
calcula ed he ai low pa e ns associa ed wi h he lowes alpha concen a ions egis e ed in Bilbao
(26 pe iods in which alpha concen a ions we e below he 10 h pe cen ile) (Figu e 8b). The compa ison
o bo h (Figu e 8) poin s ou simila i ies be ween ai low pa e ns, bu wi h no able di e ences in
equencies (numbe in b acke s) in hose simila . The lowes alpha concen a ions highligh s he highe
occu ence o wes e n ai lows, and ai masses om he sou h and no h, wi h slow displacemen
(Clus e 1 and Clus e 4 in Figu e 8a), a e no iden i ied. The e o e, bo h Figu es mainly sugges ha he
a i al o con inen al sou he n and ma i ime no he n ai lows is mainly associa ed wi h measu emen s
o high alpha concen a ions in his a ea.
To s udy he ela ionships be ween ai low pa e ns (Figu e 8a) and alpha peak concen a ions,
and wi h he pu pose o no conside he same sampling pe iod wi hin wo di e en ai low pa e ns,
which would c ea e misunde s anding in he esul s, we ha e iden i ied pe sis en sampling pe iods,
i.e., pe iods in which mos o he ajec o ies (abo e 75% o he calcula ed ajec o ies in each pe iod)
a e g ouped in o he same clus e . Ten ou o 26 sampling pe iods a e iden i ied as pe sis en ones:
six wi hin clus e 1, one wi hin clus e 2, and h ee wi hin clus e 4. Figu e 9shows he summa y o
alpha peak concen a ion measu ed and he seasonal dis ibu ion o hese pe sis en sampling pe iods.
They occu ed in au umn/win e seasons in clus e 1 and clus e 4, while he only pe sis en pe iod
co esponding o clus e 2 ook place in sp ing. This esul , hence, epo s ha sampling pe iods
cha ac e ized by p e ailing sou he n and no he n ai lows seems o d i e he occu ence o alpha peak
ac i i y concen a ions in his a ea. The ac o mainly being loca ed in au umn/win e , which is he
we es pe iod in Bilbao (see Sec ion 2.1), would no be in line wi h p e ious s udies [
6
], whe e alpha
ac i i y concen a ions dec ease wi h p ecipi a ion. Howe e , and due o he geog aphic loca ion o he
egion, winds coming om he sou h descending om he Can ab ian Moun ains became wa m and
d y because he Foehn e ec [
24
], and e en wi hin he we es pe iod, unde he a i al o sou he ly
winds, he chances o ain a e nea ly ze o in he egion e en.
In . J. En i on. Res. Public Heal h 2020,17, 7967 9 o 12
In . J. En i on. Res. Public Heal h 2020, 17, 7967 9 o 13
cen oid and he igh numbe s (in b acke s) a e he pe cen age o comple e ajec o ies occu ing in
ha clus e .
To es ablish he link o hese ai low pa e ns wi h alpha peak concen a ions, we ha e also
calcula ed he ai low pa e ns associa ed wi h he lowes alpha concen a ions egis e ed in Bilbao
(26 pe iods in which alpha concen a ions we e below he 10 h pe cen ile) (Figu e 8b). The
compa ison o bo h (Figu e 8) poin s ou simila i ies be ween ai low pa e ns, bu wi h no able
di e ences in equencies (numbe in b acke s) in hose simila . The lowes alpha concen a ions
highligh s he highe occu ence o wes e n ai lows, and ai masses om he sou h and no h, wi h
slow displacemen (Clus e 1 and Clus e 4 in Figu e 8a), a e no iden i ied. The e o e, bo h Figu es
mainly sugges ha he a i al o con inen al sou he n and ma i ime no he n ai lows is mainly
associa ed wi h measu emen s o high alpha concen a ions in his a ea.
To s udy he ela ionships be ween ai low pa e ns (Figu e 8a) and alpha peak concen a ions,
and wi h he pu pose o no conside he same sampling pe iod wi hin wo di e en ai low pa e ns,
which would c ea e misunde s anding in he esul s, we ha e iden i ied pe sis en sampling pe iods,
i.e., pe iods in which mos o he ajec o ies (abo e 75% o he calcula ed ajec o ies in each pe iod)
a e g ouped in o he same clus e . Ten ou o 26 sampling pe iods a e iden i ied as pe sis en ones:
six wi hin clus e 1, one wi hin clus e 2, and h ee wi hin clus e 4. Figu e 9 shows he summa y o
alpha peak concen a ion measu ed and he seasonal dis ibu ion o hese pe sis en sampling
pe iods. They occu ed in au umn/win e seasons in clus e 1 and clus e 4, while he only pe sis en
pe iod co esponding o clus e 2 ook place in sp ing. This esul , hence, epo s ha sampling
pe iods cha ac e ized by p e ailing sou he n and no he n ai lows seems o d i e he occu ence o
alpha peak ac i i y concen a ions in his a ea. The ac o mainly being loca ed in au umn/win e ,
which is he we es pe iod in Bilbao (see Sec ion 2.1), would no be in line wi h p e ious s udies [6],
whe e alpha ac i i y concen a ions dec ease wi h p ecipi a ion. Howe e , and due o he geog aphic
loca ion o he egion, winds coming om he sou h descending om he Can ab ian Moun ains
became wa m and d y because he Foehn e ec [24], and e en wi hin he we es pe iod, unde he
a i al o sou he ly winds, he chances o ain a e nea ly ze o in he egion e en.
Figu e 9. S a is ical alues in ai o alpha peak concen a ions du ing he pe sis en sampling pe iods
a Bilbao and he co esponding seasonal dis ibu ion o he pe iods. The unce ain ies o he means
a e indica ed as he s anda d de ia ion o he a e age Sx/N1/2, whe e N is he numbe o pe sis en
pe iods and he s anda d de ia ion. Clus e s e e o Figu e 8a.
0.0
1.0
2.0
3.0
Win e Sp ing Summe Au umn
Numbe o pe iods
Clus e 1 Clus e 2 Clus e 4
Numbe o
pe sis en pe iods
Mean
(µBq/m3)SD
Max
(µBq/m3)
Min
(µBq/m3)
Clus e 1 6 159 19 247 122
Clus e 2 1 127
Clus e 4 3 152 2 157 149
Figu e 9.
S a is ical alues in ai o alpha peak concen a ions du ing he pe sis en sampling pe iods
a Bilbao and he co esponding seasonal dis ibu ion o he pe iods. The unce ain ies o he means
a e indica ed as he s anda d de ia ion o he a e age Sx/N1/2, whe e N is he numbe o pe sis en
pe iods and he s anda d de ia ion. Clus e s e e o Figu e 8a.
3.3. Case S udies
Case s udies a e needed o e alua e on a eal basis he po en ial in luence o each ai low pa e n
and he associa ed me eo ological condi ions on he alpha peak concen a ions in Bilbao. So, we ha e
analyzed ep esen a i e pe iods o he wo main me eo ological scena ios d i ing hese concen a ions,
i.e., he a i al o con inen al sou he n and ma i ime no he n ai masses. To analyze he in luence o
each ai low pa e n on alpha ac i i y concen a ions, Figu e 10 displays su ace winds (blowing om)
du ing one pe sis en sampling pe iod (02
−
08/10/2018) unde no he ly lows, and om 9 Decembe
2015 o 14 Decembe 2015 unde sou he ly lows. Hou ly e olu ion o
222
Rn is also shown in bo h
pe iods o ep esen he impac o su ace winds on ac i i y concen a ions.
In . J. En i on. Res. Public Heal h 2020, 17, 7967 10 o 13
3.3. Case S udies
Case s udies a e needed o e alua e on a eal basis he po en ial in luence o each ai low pa e n
and he associa ed me eo ological condi ions on he alpha peak concen a ions in Bilbao. So, we ha e
analyzed ep esen a i e pe iods o he wo main me eo ological scena ios d i ing hese
concen a ions, i.e., he a i al o con inen al sou he n and ma i ime no he n ai masses. To analyze
he in luence o each ai low pa e n on alpha ac i i y concen a ions, Figu e 10 displays su ace
winds (blowing om) du ing one pe sis en sampling pe iod (02−08/10/2018) unde no he ly lows,
and om 9 Decembe 2015 o 14 Decembe 2015 unde sou he ly lows. Hou ly e olu ion o 222Rn is
also shown in bo h pe iods o ep esen he impac o su ace winds on ac i i y concen a ions.
The alpha ac i i y concen a ion eco ded in he i s sampling pe iod is 122.5 µBq/m3.
Acco ding o he wind di ec ion a iabili y, wo di e en pe iods can be iden i ied in hese se en
days o sampling (Figu e 10a). This ac allows conside ing his sampling pe iod as sui able o analyze
di e ences in su ace winds unde he same synop ic me eo ological scena io, and i s ela ionship
wi h su ace ac i i y concen a ions. In addi ion, a he end o his sampling pe iod was cons an ly
aining.
The i s ou days, he synop ic condi ions a o ed he p og essi e de elopmen o a daily
e olu ion cycle o su ace winds, blowing om he sou h du ing he nigh , ollowed by he clockwise
swing o no hwes e ly winds du ing he day. Wind speed was less han 2 m/s. This daily e olu ion
o winds a su ace le el ag ees wi h he de elopmen o sea/land b eezes in his a ea [25], which a e
mo e common du ing sp ing and summe . Unde his su ace condi ion, and conside ing he ma ked
daily cycle o 222Rn [26], i is sugges ed an accumula ion p ocess, which p og essi ely aises he
concen a ion o pa icles close o he su ace in his a ea, i.e., i aps he pa icles nea he su ace
and limi s a su icien mixing wi h he ai abo e [27]. The limi a ion o he dispe sion p ocesses would
hus a o he inc ease in he alpha ac i i y concen a ion in his a ea. This daily cycle is b oken a
he end o he sampling pe iod, wi h a sudden change in su ace winds, which s a ed blowing
cons an ly om he no hwes -no h ange and wi h wind speeds highe han in he p e ious days.
Unde hese new condi ions, he dispe sion p ocesses a e a o ed, and oge he wi h he spo adic
ain all du ing hese wo days, cause a dec ease in ac i i y concen a ions in he a ea, as i well
obse ed in he daily e olu ion o 222Rn concen a ions.
Figu e 10. Daily a ia ion o 222Rn ac i i y concen a ion, wind speed and di ec ion, and o al amoun
o p ecipi a ion a Bilbao be ween (a) 2 Oc obe 2018 and 8 Oc obe 2018 (no he ly lows-clus e 1)
0
0.5
1
1.5
2
2.5
3
3.5
0
90
180
270
360
P ecipi a ion Wind di ec ion Rn Wind speed
0,0
10,0
20,0
30,0
40,0
50,0
60,0
70,0
80,0
90,0
100,0
0
90
180
270
360
0:00 0:00 0:00 0:00 0:00 0:00
Rn (Bq/m
3
)
Wind di ec ion (
0
)
Wind di ec ion Rn Wind speed
a) Clus e 1: 02-08/10/2018
02/10/2018 03/10/2018 04/10/2018 05/10/2018 06/10/2018 07/10/2018 08/10/2018
09/12/2015 10/12/2015 11/12/2015 12/12/2015 13/12/2015 14/12/2015
b) Clus e 4: 09-14/12/2015
P ecipi a ion (mm)
Wind speed (m/s)
2
Wind di ec ion (
0
)
Radon (mBq/m3)
X 10
Wind speed (m/s)
(E)
(S)
(W)
(N)
(N)
(E)
(S)
(W)
(N)
(N)
Figu e 10.
Daily a ia ion o 222Rn ac i i y concen a ion, wind speed and di ec ion, and o al amoun
o p ecipi a ion a Bilbao be ween (
a
) 2 Oc obe 2018 and 8 Oc obe 2018 (no he ly lows-clus e 1)
and (
b
) 9 Decembe 2015 and 14 Decembe 2015 (sou he ly lows-clus e 4). No e he di e ences
in scales.
The alpha ac i i y concen a ion eco ded in he i s sampling pe iod is 122.5
µ
Bq/m
3
. Acco ding
o he wind di ec ion a iabili y, wo di e en pe iods can be iden i ied in hese se en days o sampling
(Figu e 10a). This ac allows conside ing his sampling pe iod as sui able o analyze di e ences in
