Monitoring of the Eyjafjallajökull volcanic aerosol plume over the Iberian Peninsula by means of four EARLINET lidar stations

ACPD 11, 29681–29721, 2011 Monitoring of the Eyjafjallaj¨ okull volcanic aerosol plume M. Sicard et al. Title Page Abstract Introduction Conclusions References Tables Figures J I J I Back Close Full Screen / Esc Printer-friendly Version Interactive Discussion Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Atmos. Chem. Phys. Discuss., 11, 29681–29721, 2011 www.atmos-chem-phys-discuss.net/11/29681/2011/ doi:10.5194/acpd-11-29681-2011 © Author(s) 2011. CC Attribution 3.0 License. Atmospheric Chemistry and Physics Discussions This discussion paper is/has been under review for the journal Atmospheric Chemistry and Physics (ACP). Please refer to the corresponding final paper in ACP if available. Monitoring of the Eyjafjallaj¨ okull volcanic aerosol plume over the Iberian Peninsula by means of four EARLINET lidar stations M. Sicard1,2, J. L. Guerrero-Rascado3,4,*, F. Navas-Guzm´ an3,4, J. Preißler5, F. Molero6, S. Tom´ as1,2, J. A. Bravo-Aranda3,4, A. Comer´ on1, F. Rocadenbosch1,2, F. Wagner5, M. Pujadas6, and L. Alados-Arboledas3,4 1Dept. of Signal Theory and Communications, Remote Sensing Lab., Universitat Polit` ecnica de Catalunya, Barcelona, Spain 2Institut d’Estudis Espacials de Catalunya, Universitat Polit` ecnica de Catalunya, Barcelona, Spain 3Andalusian Centre for Environmental Research, Junta de Andaluc´ ıa, University of Granada, Granada, Spain 4Applied Physics Department, University of Granada, Granada, Spain 5Centro de Geof´ ısica de ´ Evora, ´ Evora, Portugal 6Centro de Investigaciones Energ´ eticas Medioambientales y Tecnol´ ogicas, Madrid, Spain 29681 ACPD 11, 29681–29721, 2011 Monitoring of the Eyjafjallaj¨ okull volcanic aerosol plume M. Sicard et al. Title Page Abstract Introduction Conclusions References Tables Figures J I J I Back Close Full Screen / Esc Printer-friendly Version Interactive Discussion Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | ∗now at: Centro de Geof´ ısica de ´ Evora, ´ Evora, Portugal Received: 19 October 2011 – Accepted: 26 October 2011 – Published: 3 November 2011 Correspondence to: M. Sicard ([email protected]) 29682 ACPD 11, 29681–29721, 2011 Monitoring of the Eyjafjallaj¨ okull volcanic aerosol plume M. Sicard et al. Title Page Abstract Introduction Conclusions References Tables Figures J I J I Back Close Full Screen / Esc Printer-friendly Version Interactive Discussion Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Abstract Lidar and sun-photometer measurements were performed intensively over the Iberian Peninsula (IP) during the eruption of Eyjafjallaj¨ okull volcano (Iceland) in April–May 2010. The volcanic plume hit all the IP stations for the first time on 5 May 2010. A thorough study of the event is conducted for the period 5–8 May. Firstly the spatial5 and temporal evolution of the plume is described by means of lidar and sun-photometer measurements supported with backtrajectories. The volcanic aerosol layers observed over the IP were rather thin (<1000 m) with a top height up to 11–12 km. The mean optical thicknesses associated to those layers were rather low (between 0.013 and 0.020 over the whole period). Punctually on 7 May the optical thickness reached peak10 values near 0.10. Secondly the volcanic aerosols are characterized in terms of extinction and backscatter coefficients, lidar ratios, ˚ Angstr¨ om exponents and linear particle depolarization ratio. Lidar ratios at different sites varied between 30 and 50 sr without a marked spectral dependency. Similar extinction-related ˚ Angstr¨ om exponents varying between 0.6 and 0.8 were observed at different sites. The temporal evolution of15 the backscatter-related ˚ Angstr¨ om exponents points out a possible decrease of the volcanic particle size as the plume moves from west to east. Particle depolarization ratios on the order of 0.06–0.08 confirmed the coexistence of both ash and non-ash particles. Additionally profiles of mass concentration were obtained with a method using the opposite depolarizing effects of ash particles (strongly depolarizing) and non-ash20 particles (very weakly depolarizing), and sun-photometer observations. In Granada the ash mass concentration was found approximately 1.5 higher than that of non-ash particles, and probably did not exceed the value of 200 µg m−3during the whole event. 29683 ACPD 11, 29681–29721, 2011 Monitoring of the Eyjafjallaj¨ okull volcanic aerosol plume M. Sicard et al. Title Page Abstract Introduction Conclusions References Tables Figures J I J I Back Close Full Screen / Esc Printer-friendly Version Interactive Discussion Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | 1 Introduction The eruption of the Eyjafjallaj¨ okull volcano, an ice-covered stratovolcano with a summit elevation of 1666 m a.s.l. situated in Southern Iceland, started on 14 April 2010 and stopped on 21 May 2010. This eruption threw volcanic aerosols with variable intensity several kilometers up in the atmosphere (Langmann et al., 2011) which were trans-5 ported mostly towards Europe and led to air travel disruption in Northern and Central Europe from 15 April onwards and in South Europe in May 2010. Many major Northern and Central European countries closed their airspace completely during several days. In total more than 100 000 flights were canceled that affected more than 10 millions passengers. The event might have contributed relatively quickly to a decrease of the10 global surface temperature since ash particles reflect the solar radiation, and the emission of greenhouse gases decreased significantly during the air travel disruptions in April and May. In the long term volcanic aerosols are well-known to have a notable impact on the Earth radiative budget because of their large scale dispersion and their long residence times in the atmosphere.15 The lidar technique is one of the most relevant remote sensing tools to study atmospheric aerosols. In the past volcanic aerosols (VA) have been observed by lidars a long time after they have been ejected in the stratosphere (Langford et al., 1995; Borrmann et al., 1995; Wandinger et al., 1995; Di Girolamo et al., 1996) and less frequently in the troposphere (Pappalardo et al., 2004; Villani et al., 2006; Wang et al.,20 2008). The Eyjafjallaj¨ okull volcanic plume was followed in near-real time by many scientists from different fields of atmospheric sciences all over the world but especially in Europe since the very first day of the eruption. While many results obtained in Northern and Central Europe have already been published (Ansmann et al., 2010, 2011; Flentje et al., 2010; Wiegner et al., 2011; Gasteiger et al., 2011; Schumann et al., 2011; Emeis25 et al., 2011) only very few results about the situation in Southern Europe can be found in peer-reviewed literature (Balis et al., 2010; Mona et al., 2011; Toledano et al., 2011). 29684 ACPD 11, 29681–29721, 2011 Monitoring of the Eyjafjallaj¨ okull volcanic aerosol plume M. Sicard et al. Title Page Abstract Introduction Conclusions References Tables Figures J I J I Back Close Full Screen / Esc Printer-friendly Version Interactive Discussion Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Most of the 29 lidar stations that formed EARLINET (European Aerosol Research Lidar Network) started the monitoring of the Eyjafjallaj¨ okull event on 15 April (Pappalardo et al., 2010). Four of those stations are situated in the Iberian Peninsula (IP) and are members of SPALINET (Spanish and Portuguese Aerosol Lidar Network) (Sicard et al., 2009). While the plume travelled sometimes less than two days before it was observed5 at North and Central European stations and was not detected higher than 8 km, it took at least three to five days to reach the IP where it was detected at altitudes as high as 11–12 km. The VA layers reaching the IP were very faint compared to those observed in Northern and Central Europe. For those reasons it is assumed that the volcanic plumes observed over the IP have different properties in terms of composition and particle size10 compared to those observed over Northern and Central Europe. The peculiar situation of the IP with respect to the transport pattern of the volcanic plumes makes lidar measurements over the IP suitable to evaluate dispersion model boundary conditions. Indeed, Molero et al. (2010) already investigated the accuracy of models such as EURAD (EURopean Air Pollution Dispersion, http://www.eurad.uni-koeln.de/index e.html)15 and FLEXPART (http://transport.nilu.no/flexpart) over the IP by means of lidar measurements. Until 5 May only sporadic, isolated volcanic plumes were observed over the IP, especially on 19 and 20 April. On 4 May a change in the synoptic situation caused the strongest intrusion of VA over the IP from the Atlantic Ocean eastward. This paper20 focuses on the monitoring of the volcanic plume over the IP observed by means of four lidar stations during the period 5–8 May 2010. We only concentrate on lofted VA plumes, i.e. not coupled to the planetary boundary layer (PBL), because in situ measurements in the PBL are not available at all sites to differentiate VA from local aerosols and to study the mixing processes occurring in the PBL, and because the distribution25 of the VA plume in the troposphere is of great interest for air traffic. In this paper we refer to volcanic aerosols and not only volcanic ash. Volcanic aerosols are a mixture of ash particles (volcanic glass, minerals and lithic fragments), volcanic gases such as sulphur dioxide (SO2), carbon dioxide (CO2) and hydrogen (H2), and droplets of 29685 ACPD 11, 29681–29721, 2011 Monitoring of the Eyjafjallaj¨ okull volcanic aerosol plume M. Sicard et al. Title Page Abstract Introduction Conclusions References Tables Figures J I J I Back Close Full Screen / Esc Printer-friendly Version Interactive Discussion Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | water vapor (H2O), hydrochloric acid (HCl) and hydrofluoric acid (HF) among others (http://volcanoes.usgs.gov/hazards/gas/s02aerosols.php). Ash particles fall out quite rapidly due to their large mass so that over the IP, far away from the source, their contribution may be significantly reduced. On the contrary the residence time of sulfate aerosols is much longer for they can reside in the atmosphere for several months.5 This paper is organized as follows: Sect. 2 briefly presents the instrumentation; in Sect. 3 the spatial and temporal evolution of the volcanic plume over the IP is described; and in Sect. 4 the vertical characterization of the VA is presented in terms of their optical properties and an estimate of their mass concentration is shown. Conclusions are made in Sect. 5.10 2 Instruments 2.1 Lidars The four lidar systems involved in this study all belong to EARLINET and SPALINET. A short description of them can be found in Sicard et al. (2009, 2011). The principal characteristics of those systems are presented in Table 1. The institutions involved are:15 –Centro de Geof´ ısica de ´ Evora, ´ Evora (Portugal, 38.57◦N, 7.91◦W, 293 m above sea level, a.s.l.); –Centro de Investigaciones Energ´ eticas Medioambientales y Tecnol´ ogicas, Madrid (Spain, 40.46◦N, 3.72◦W, 665 m a.s.l.); –Universidad de Granada, Granada (Spain, 37.16◦N, 3.58◦W, 680 m a.s.l.);20 –Universidad Polit´ ecnica de Catalu˜ na, Barcelona (Spain, 41.39◦N, 2.11◦E, 115 m a.s.l.). All four systems participated in an intercomparison campaign in Madrid from 18 October to 5 November 2010 in the framework of the EARLINET quality assurance program 29686 ACPD 11, 29681–29721, 2011 Monitoring of the Eyjafjallaj¨ okull volcanic aerosol plume M. Sicard et al. Title Page Abstract Introduction Conclusions References Tables Figures J I J I Back Close Full Screen / Esc Printer-friendly Version Interactive Discussion Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | and were satisfactorily compared to the reference system of Potenza, Italy (for more details see Molero et al., 2011). Coordinated measurements started on 15 April 2010 and intensified on 5 May accordingly with the intrusion. All measurements were inverted using the two-component elastic lidar inversion algorithm (Fernald, 1984; Sasano and Nakane, 1984; Klett, 1985) and a constant lidar ratio of 50 sr. All nighttime measure-5 ments were also inverted using the Raman lidar inversion algorithm (Ansmann et al., 1990; 1992). 2.2 Sun-photometers Some columnar aerosol properties of interest were measured by CIMEL sun-sky photometers in ´ Evora, Granada and Barcelona. For Madrid the sun-photometer in C´ aceres10 (located approximately 250 km southwest of Madrid) was used. All sun-photometers are part of the Aerosol Robotic Network (AERONET, http://aeronet.gsfc.nasa.gov/) (Holben et al., 1998). The instrument provides information about, among other properties, the aerosol optical thickness (AOT) at 340, 380, 440, 500, 675, 870 and 1020 nm in ´ Evora, Madrid and Granada, and at 440, 675, 870 and 1020 nm in Barcelona, as well15 as the single scattering albedo and the ˚ Angstr¨ om exponent between pairs of wavelengths. A common product of AERONET is the fine and coarse mode AOT at 500 nm (O’Neill et al., 2003). Inversion products such as the volume size distribution are also provided. In this paper we calculated the ˚ Angstr¨ om exponent between the wavelengths of 44020 and 675 nm from Level 1.5 (cloud screened data) at ´ Evora, Granada and Barcelona and from Level 2.0 (quality assured data) at Madrid. For ´ Evora, Madrid and Granada we used the AOT at 500 nm and for Barcelona the AOT at 500 nm was calculated with the one at 440 nm and the ˚ Angstr¨ om exponent calculated between the wavelengths of 440 and 675 nm.25 29687 ACPD 11, 29681–29721, 2011 Monitoring of the Eyjafjallaj¨ okull volcanic aerosol plume M. Sicard et al. Title Page Abstract Introduction Conclusions References Tables Figures J I J I Back Close Full Screen / Esc Printer-friendly Version Interactive Discussion Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | 3 Evolution of the Eyjafjallaj¨ okull VA plume over the IP: 5–8 May 2010 3.1 Synoptic situation A complex system developed during the period 5–8 May 2010. Figure 1 shows the synoptic situation over Western Europe in terms of sea level pressure for every day of the period 4–9 May at 12:00 UTC. The start of the period is characterized by a deep5 anticyclone located south of Iceland and west of Ireland, while a low pressure system affected Southern France. On 5 and 6 May a front formed in the Atlantic west of the IP’s coasts as a new low pressure system appeared at the 40◦W longitude. During 6–8 May this new low pressure system swept over the Atlantic Ocean eastwards towards the IP leading to pronounced easterly winds starting on 8 May. From 9 May on, this low10 pressure gradient settled over the north of the IP producing several days of instable conditions with broken clouds and low intensity rains. Backtrajectories have been calculated with the HYSPLIT (Hybrid Single Particle Lagrangian Integrated Trajectory Model) (Draxler and Rolph, 2003; Rolph, 2003) model provided by NOAA–ARL (National Oceanic and Atmospheric Administration–Air Re-15 sources Laboratory) to check the air-masses origin. Figure 2 shows 120-h backtrajectories arriving at the four stations at 6 altitude levels between 500 and 5500 m with a resolution of 1000 m for each day at 12:00 UTC. The length of the trajectories corresponds to 5 days. In ´ Evora and Madrid a transport over Iceland is visible every day at two or more altitude levels. In ´ Evora the backtrajectories are similar on 5 and 6 May:20 all altitude levels show a transport over Iceland 3 to 4 days prior to the plume arrival. On 7 May the same pattern persists except for the 500-m altitude level. On 8 May only the 500and 1500-m altitude levels show transport over Iceland approximately 5 days prior to the plume arrival. In Madrid on 5 May only air masses at altitude levels above 3500 m travelled over Iceland 2 to 3 days prior to arrival. On 6 and 7 May the situation25 is similar to that of ´ Evora. On 8 May only the altitude levels below 2500 m show transport over Iceland approximately 4 days prior to arrival. The situation in Granada and Barcelona is slightly different. On 5 May mesoscale transports dominate. On 6 May 29688 ACPD 11, 29681–29721, 2011 Monitoring of the Eyjafjallaj¨ okull volcanic aerosol plume M. Sicard et al. Title Page Abstract Introduction Conclusions References Tables Figures J I J I Back Close Full Screen / Esc Printer-friendly Version Interactive Discussion Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | the air masses at altitude levels below 3500 m have all been transported over Iceland 5 days (at 500 and 1500 m) and 3–4 days (at 2500 and 3500 m) prior arrival. On 7 May all trajectories travel over Iceland 3 days (Granada) and 4–5 days (Barcelona) prior to arrival. On 8 May only the altitude levels below 2500 m show clearly a transport over Iceland with travelling times of 4 to 5 days.5 In summary, according to the synoptic situation and the backtrajectory analysis, the VA plume entered the IP from west-northwest at all altitude levels and with relatively short transport times from Iceland between 2 and 4 days. Along the intrusion the plume transported from Iceland reaches the IP at lower altitudes and longer transport times. In the southern and eastern IP the plume appears on 6 May at lower altitudes.10 3.2 Spatial and temporal evolution of the VA plume over the IP The spatial and temporal evolution of the VA plume over the IP is analyzed through the time series of vertical profiles of range-square corrected lidar signals (RSCS). Figure 3 shows the RSCS time series of the four Iberian stations over the whole period. All the measurements performed by the four stations are plotted. The height, if15 not otherwise stated, is reported above sea level (a.s.l.). Below the lidar time series the sun-photometer total, coarse and fine mode AOT at 500 nm, as well as the ˚ Angstr¨ om exponent calculated between the wavelengths of 440 and 675 nm are reported for each station. Figure 4 shows the AOT of the lofted layers of VA, hereinafter called AOTVA, at 532 nm measured by the lidar stations as a function of height and time with a time res-20 olution of 1 h. In this section AOTVA was calculated by the integration of the backscatter profiles inverted with the two-component elastic lidar inversion algorithm multiplied by a constant lidar ratio of 50 sr. The layers below 2 km that might have been coupled to the PBL have been discarded in order to minimize the influence of local aerosols in the analysis. The measurements with clouds or optically extremely thin VA layers (leading25 to large errorbars in the retrieval of the optical coefficients) are discarded in Fig. 4. The thickness of lofted VA layers is hereinafter called ∆hVA. Table 2 gives the daily mean AOTVA, AOTVA, and layer thickness, ∆hVA, of the lofted VA layers. The minimum and 29689 ACPD 11, 29681–29721, 2011 Monitoring of the Eyjafjallaj¨ okull volcanic aerosol plume M. Sicard et al. Title Page Abstract Introduction Conclusions References Tables Figures J I J I Back Close Full Screen / Esc Printer-friendly Version Interactive Discussion Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | in Germany (Ansmann et al., 2010) or in Italy (Mona et al., 2011) and suggests the coexistence of both aerosol types. Below 2.5 km (not shown) the particle depolarization ratio is around 0.045 which is a typical value at Granada when only local aerosols are present (Bravo-Aranda and Navas-Guzm´ an, 2011). However the backtrajectories below 2.5 km and the synoptic analysis (Sect. 3) indicated that VA are present and5 mixed with local aerosols in the lowermost layer. The mean value of 0.045 suggests then that the depolarization effect of the VA in the lowermost layer is also on the order of 0.045, which leads to a higher contribution of non-ash particles in the lowermost layer (see Sect. 4.2) than in the 2.6–2.9 km layer. From Fig. 6, the mean AEβ 355−532 and AEβ 532−1064 are 0.73±0.07 and 1.68±0.31, respectively. This indicates again that10 the backscatter coefficient changes more sensitively at longer wavelengths. The similar values of 0.73–0.79 found for the αand the β-related ˚ Angstr¨ om exponents at 355/532 nm clearly reflects the fact that the lidar ratios at both wavelengths are nearly equal. The mean α-related ˚ Angstr¨ om exponent, 0.79±0.54, is similar to that in ´ Evora the day before and is also representative of rather medium-size particles.15 4.1.3 8 May 2010, 16:00 UTC, Granada – Barcelona In the afternoon of 8 May almost all the downward moving VA layers have mixed with the upward developing local PBL. Two lofted layers are still visible in Fig. 7: in Granada an extremely thin VA layer is observed between 3.00 and 3.35 km while in Barcelona a VA layer is visible around 2.2–2.9 km. For the sake of clarity the Granada profiles20 are not represented above 2.9 km and those of Barcelona below 3.0 km. The sunphotometer AOT and the fine mode fraction are, respectively around 0.15 and 80 % in Granada and 0.13 and 70 % in Barcelona. In Granada AOTVA is 0.005 at 355 nm and 0.002 at 532 nm. At 1064 nm AOTVA is less than 0.001. In Barcelona AOTVA is higher: 0.025 at 355 nm and 0.010 at 532 nm. In both cases the AOT of the lofted25 VA represents a small fraction of the columnar AOT (between 1 and 7 %). Because those values are extremely low their interpretation should be done very cautiously. 29696 ACPD 11, 29681–29721, 2011 Monitoring of the Eyjafjallaj¨ okull volcanic aerosol plume M. Sicard et al. Title Page Abstract Introduction Conclusions References Tables Figures J I J I Back Close Full Screen / Esc Printer-friendly Version Interactive Discussion Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | The backscatter coefficients reach very low values which do not exceed 1 Mm−1sr−1. The β-related ˚ Angstr¨ om exponents at 355/532 nm oscillate around similar values at both sites (2.35 ±0.20 and 2.37 ±0.27 in Granada and in Barcelona, respectively). This result indicates that the backscatter coefficient is highly wavelength-dependent at short wavelengths. In Granada the mean AEβ 532−1064 (1.45 ±0.17) and the mean5 particle depolarization ratio (0.075) are similar to their respective values at 04:00 UTC. 4.2 Estimate of the mass concentration Mass concentration is one of the most critical parameters for airspace restrictions related to volcanic aerosol plumes. Shortly after the end of the Eyjafjallaj¨ okull eruption the UK Meteorological Office distinguished between 3 contamination levels: low10 (<200 µg m−3), medium (200 to 4000 µg m−3) and high (>4000 µg m−3) (Schumann at al., 2011). At present 2000 µg m−3is considered as the maximum tolerable concentration for continuous flight operation. Mass concentrations have been calculated from backscatter coefficients for ash and non-ash particles. The method used to distinguish between both types of particles15 is based on the work by Tesche et al. (2009) and refined recently for ash and finemode particles by Tesche et al. (2011) and Ansmann et al. (2011). The method uses the opposite depolarizing effects of ash particles (strongly depolarizing) and non-ash particles (very weakly depolarizing). Only the Granada system had a depolarization channel (at 532 nm) operative during the period 5–8 May 2010, so that profiles of mass20 concentration were only calculated for this station. For the sake of clarity the wavelength dependency of all coefficients has been omitted in this section. We remark that the method is applied under the assumption of external mixing only. As the Eyjafjallaj¨ okull eruption was sub-glacial, it is unlikely that internal mixing such as sulfur coating on ash occurred due to the high concentration of water vapor present in the ash cloud25 (Thomas and Prata, 2011). 29697 ACPD 11, 29681–29721, 2011 Monitoring of the Eyjafjallaj¨ okull volcanic aerosol plume M. Sicard et al. Title Page Abstract Introduction Conclusions References Tables Figures J I J I Back Close Full Screen / Esc Printer-friendly Version Interactive Discussion Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | If we call βthe total aerosol backscatter coefficient, the backscatter coefficients of ash, βa, and non-ash particles, βna, can be calculated, respectively as: βa=β(δ−δna) (δa−δna) (1−δa) (1−δ)(1) and βna =β(δ−δa) (δna −δa) (1−δna) (1−δ)(2)5 where δaand δna represent the ash and non-ash linear particle depolarization ratios, respectively. Pure ash and pure non-ash particle depolarization ratios are reasonably well known as δa=0.36 and δna =0.01 (Ansmann et al., 2010; Groß et al., 2010; Tesche et al., 2011), respectively. The mass concentrations of ash, ma, and non-ash particles, mna, are given in terms of backscatter coefficient, respectively as:10 ma=ρa Cc AOTc βaSa(3) and mna =ρna Cf AOTf βnaSna (4) where ρaand ρna are the ash and non-ash particle mass density, and Saand Sna are the ash and non-ash particle lidar ratio. The two ratios, Cf AOTfand Cc AOTc, also called15 mean extinction-to-mass conversion factors represent the ratio of volume concentration to AOT for the fine (non-ash) and the coarse (ash) mode, respectively. For pure ash and non-ash particles, respectively, ρa=2.6 g cm−3(http://volcanoes. usgs.gov/ash/properties.html#density; Schumann et al., 2011) and ρna =1.6 g cm−3 (Bukowiecki et al., 2011), and Sa=50±10 sr and Sna =60±20 sr (Tesche et al., 2011;20 Ansmann et al., 2011). The ratios of volume concentration to AOT were calculated 29698 ACPD 11, 29681–29721, 2011 Monitoring of the Eyjafjallaj¨ okull volcanic aerosol plume M. Sicard et al. Title Page Abstract Introduction Conclusions References Tables Figures J I J I Back Close Full Screen / Esc Printer-friendly Version Interactive Discussion Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | from AERONET-derived level 1.5 inversion products on 8 May 2010, at 06:35 and 07:00 UTC. The size distributions associated to those inversions are shown in Fig. 8. They are very similar and exhibit an enhanced fine (non-ash) mode. Note en passant that similar size distributions were obtained in Madrid by ground-based in-situ measurements (Revuelta et al., 2011). This result is completely different to similar observa-5 tions made in Germany at the beginning of the eruption (Ansmann et al., 2011) where the fine (non-ash) and coarse (ash) mode predominance were inverted, the enhanced mode being that of coarse (ash) particles, and where the volume concentration was higher by a factor 10. The mean extinction-to-mass conversion factors for the fine (nonash) and the coarse (ash) modes are Cf AOTf =0.255×10−6m and Cc AOTc =0.89×10−6m,10 respectively. In order to justify the use of the columnar values of the mean extinction-to-mass conversion factors in the VA layers, the non-ash and the ash AOT fractions are calculated for the lidar at 04:00 and 16:00 UTC and compared, respectively, to the fine (non-ash) and coarse (ash) mode fractions of the sun-photometer at 06:35 and 07:00 UTC. In this15 section the lidar-derived AOTVA was calculated as: AOTVA =Z VA layer (βnaSna +βaSa).(5) Table 3 summarizes the values found for both instruments. Even though the AERONET AOT uncertainty is known to be ≤ ±0.01 for wavelengths greater than 440 nm (Holben et al., 1998; Dubovik et al., 2000), here the AOT at 500 nm is expressed with three20 digits in order to minimize differences due to truncation in the calculation of the fine and coarse mode fractions. For the same reason the lidar-derived AOTVA is expressed with four digits. The VA layers at 04:00 and 16:00 UTC are found around 2.6–2.9 km and 3.00–3.35 km, respectively. In those layers, the ratio of lidar-derived non-ash AOT to AOTVA is nearly constant between both lidar measurements around 80–82 %. In the25 atmospheric column the sun-photometer fine (non-ash) mode fraction is around 87– 89 %. Given the relatively good agreement between those numbers and besides the 29699 ACPD 11, 29681–29721, 2011 Monitoring of the Eyjafjallaj¨ okull volcanic aerosol plume M. Sicard et al. Title Page Abstract Introduction Conclusions References Tables Figures J I J I Back Close Full Screen / Esc Printer-friendly Version Interactive Discussion Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | lack of size distribution measurements in the VA layers, the above-mentioned method can be further applied to our lidar measurements. The results are shown in Fig. 9 for the VA layers identified at 2.6–2.9 km at 04:00 UTC and at 3.00–3.35 km at 16:00 UTC. As a consequence of the low particle depolarization ratios observed around 0.06–0.075 (see Figs. 6 and 7) compared to Central Europe5 (Ansmann et al., 2010, 2011; Tesche et al., 2011) or Southeastern Europe (Mona et al., 2011) the ash and non-ash particle mass concentrations appear approximately in the same order of magnitude. They roughly fluctuate in the range 60–180 µg m−3at 04:00 UTC and 1.5–3.5 µg m−3at 16:00 UTC. In the afternoon the mass concentration is around 30 to 50 times smaller than what is observed at 04:00 UTC. Those propor-10 tions are also reflected by the difference observed between both AOTVA. It is worth noting that the AOTVA at Granada reaches the highest values of the period in the night between 7 and 8 May (see Fig. 4) without a significant change neither in the thickness of the layers nor in the particle depolarization ratio. Thus it leads to high values of the backscatter coefficient and also of the mass concentration. It is quite probable that15 the mass concentration of neither the ash nor the non-ash particles found in lofted VA layers exceeded the value of 200 µg m−3in Granada in the period 5–8 May 2010. 5 Conclusions During the Eyjafjallaj¨ okull eruption the strongest intrusion of volcanic aerosols in the Iberian Peninsula occurred during 5–8 May 2010. Volcanic aerosols were first observed20 at the westernmost lidar station in ´ Evora. Lofted VA layers showed a downward motion from 6 May onwards. The mean AOT of those layers was rather low (between 0.013 and 0.020 in all stations over the whole period) with a peak on 7 May. Even though the thickness of the VA layers was spatially and temporally quite variable, rather thin layers (<1000 m) with a top height up to 11–12 km were observed. A significant increase25 in the total AOT, as well as in the fine mode AOT, is observed along the intrusion which indicates an increase of the aerosol load of rather small size in the PBL since 29700 ACPD 11, 29681–29721, 2011 Monitoring of the Eyjafjallaj¨ okull volcanic aerosol plume M. Sicard et al. Title Page Abstract Introduction Conclusions References Tables Figures J I J I Back Close Full Screen / Esc Printer-friendly Version Interactive Discussion Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | the lofted VA layers optical thickness did not change significantly during the intrusion. The backtrajectory analysis which shows transport time from Iceland on the order of 3 days at the beginning of the period and on the order of 5 days at the end corroborates this result: the size of the lofted VA decreases with increasing age. Contrarily to lidar stations from Northern and Central Europe that detected optically very thick lofted VA5 layers most of the VA that reached the IP were already coupled to the PBL. Lidar ratios at different sites varied between 30 and 50 sr without a marked spectral dependency between 355 and 532 nm. Values near 50 sr were observed on 7 May over Madrid in high VA layers above 4 km (AOTVA =0.095 at 532 nm) and on 8 May over Granada in VA layers between 2.5 and 3.0 km (AOTVA =0.078 at 532 nm). Smaller val-10 ues between 30 and 40 sr were observed over ´ Evora on 7 May in a VA layer between 2.5 and 4.0 km (AOTVA =0.070 at 532 nm). Similar extinction-related ˚ Angstr¨ om exponents varying between 0.6 and 0.8 were observed in ´ Evora and Granada. In terms of backscatter-related ˚ Angstr¨ om exponents an increase is observed between sites with time: e.g. at 355/532 nm, 0.22 is measured in ´ Evora on 7 May, 0.73 is measured in15 Granada on 8 May (morning), and ∼2.35 is measured in Granada and Barcelona on 8 May (afternoon). This result points out a possible decrease of the volcanic particle size as the plume moves from west to east. The relatively low linear particle depolarization ratio at 532 nm measured in the VA layers in Granada around 0.065–0.075 further indicates the coexistence of ash and non-ash particles.20 An estimate of the mass concentration of ash and non-ash particles has been performed in Granada by using the opposite depolarizing effects of ash particles (strongly depolarizing) and non-ash particles (very weakly depolarizing), and sun-photometer observations. In the morning of 8 May both the ash and non-ash mass concentration varied between 60 and 180 µg m−3in a VA layer with an optical thickness of 0.101.25 Later the mass concentration varied between 1.5 and 3.5 µg m−3in a VA layer with an optical thickness of 0.0025. In both cases the ash mass concentration was approximately 1.5 higher than the non-ash mass concentration. Given that the case selected in the morning of 8 May had one of the highest optical thicknesses it is quite probable 29701 ACPD 11, 29681–29721, 2011 Monitoring of the Eyjafjallaj¨ okull volcanic aerosol plume M. Sicard et al. Title Page Abstract Introduction Conclusions References Tables Figures J I J I Back Close Full Screen / Esc Printer-friendly Version Interactive Discussion Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | that the mass concentration of neither the ash nor the non-ash particles found in lofted VA layers exceeded the value of 200 µg m−3in Granada in the period 5–8 May 2010. Appendix A The uncertainty of AOTVA can be deduced from the uncertainty of the backscatter5 coefficient profiles. There are two terms to consider: –The systematic error (dβsyst): the sum of the error due to a range-dependent lidar ratio and the error due to an erroneous backscatter coefficient at the calibration height; –The statistical error (dβstat) due to the observation noise.10 On the one hand, the systematic errors, d(AOTVA)syst, are correlated with range, so that the variance associated to AOTVA due to systematic errors falls like 1/N2(Barlow, 1989), being Nthe number of samples in the VA layer: V(AOTVA)syst =[d(AOTVA)syst]2 N2(A1) and15 d(AOTVA)syst =N·qV(AOTVA)syst =N·∆z·S·qV(βsyst) (A2) where ∆zrepresents the range resolution and Sthe lidar ratio. If we call dβmax syst the maximum of dβsyst in the VA layer, then a conservative approximation of the uncertainty of AOTVA due to systematic errors can be written as: d(AOTVA)syst ≤N·∆z·S·dβmax syst .(A3)20 29702 ACPD 11, 29681–29721, 2011 Monitoring of the Eyjafjallaj¨ okull volcanic aerosol plume M. Sicard et al. Title Page Abstract Introduction Conclusions References Tables Figures J I J I Back Close Full Screen / Esc Printer-friendly Version Interactive Discussion Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | On the other hand, the statistical error, d(AOTVA)stat, is uncorrelated with range, so that the variance associated to AOTVA due to the statistical error falls now like 1/N (Barlow, 1989): V(AOTVA)stat =[d(AOTVA)stat]2 N(A4) and5 d(AOTVA)stat =pN·qV(AOTVA)stat =pN·∆z·S·qV(βstat).(A5) Again if we call dβmax stat the maximum of dβstat in the VA layer, a conservative approximation of the uncertainty of AOTVA due to the statistical error can be written as: d(AOTVA)stat ≤pN·∆z·S·dβmax stat .(A6) Acknowledgements. This work is supported by the 7th Framework Programme project10 Aerosols, Clouds, and Trace Gases Research Infrastructure Network (ACTRIS) (grant agreement no. 262254); by the MICINN (Spanish Ministry of Science and Innovation) and FEDER funds under the project TEC2009-09106/TEC, and the Complementary Actions CGL200908031-E/CLI and CGL2010-09225-E. It has also been supported by FCT (Fundac˜ ao para a Ciˆ encia e a Tecnologia) through the National Re-equipment Program REDE/1527/RNG/2007.15 Jana Preißler was funded by FCT (grant SFRH/BD/47521/2008). Juan Luis Guerrero-Rascado was partially funded by FCT (grant SFRH/BPD/63090/2009) and by the Spanish Ministry of Education (grant EX2009-0700). The authors gratefully acknowledge the Earth Sciences Division of the Barcelona Supercomputing Center and the Universidad de Extremadura for the use of the Barcelona and C´ aceres AERONET sun-photometer data, respectively, and the NOAA20 Air Resources Laboratory (ARL) for the provision of the HYSPLIT transport and dispersion model and READY website (http://www.arl.noaa.gov/ready.html) used in this publication. The Barcelona team wishes to acknowledge the gracious collaboration of Fernando Comer´ on who helped to set up the lidar on 8 May 2010 after the flight he was supposed to take was cancelled because of the closure of the Barcelona airspace.25 29703 ACPD 11, 29681–29721, 2011 Monitoring of the Eyjafjallaj¨ okull volcanic aerosol plume M. Sicard et al. Title Page Abstract Introduction Conclusions References Tables Figures J I J I Back Close Full Screen / Esc Printer-friendly Version Interactive Discussion Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | References Alados-Arboledas, L., Lyamani, H., and Olmo, F. J.: Aerosol size properties at Armilla, Granada (Spain), Q. J. R. Meteorol. Soc., 129, 1395–1413, 2003. Alados-Arboledas, L., M¨ uller, D., Guerrero-Rascado, J. L., Navas-Guzm´ an, F., P´ erezRam´ ırez, D., and Olmo, F. J.: Optical and microphysical properties of fresh biomass burning5 aerosol retrieved by Raman lidar, and starand sun-photometry, Geophys. Res. Lett., 38, L01807, doi:10.1029/2010GL045999, 2011. Ansmann, A., Riebesell, M., and Weitkamp, C.: Measurement of atmospheric aerosol extinction profiles with a Raman lidar, Opt. Lett., 15, 746– 748, 1990. Ansmann, A., Wandinger, U., Riebesell, M., Weitkamp, C., and Michaelis, W.: Independent10 measurement of extinction and backscatter profiles in cirrus-clouds by using a combined Raman elastic-backscatter lidar, Appl. Opt., 31, 7113–7131, 1992. Ansmann, A., Tesche, M., Groß, S., Freudenthaler, V., Seifert, P., Hiebsch, A., Schmidt, J., Wandinger, U., Mattis, I., M¨ uller, D., and Wiegner, M.: The 16 April 2010 major volcanic ash plume over Central Europe: 27 EARLINET lidar and AERONET photome-15 ter observations at Leipzig and Munich, Germany, Geophys. Res. Lett., 37, L13810, doi:10.1029/2010GL043809, 2010. Ansmann, A., Tesche, M., Seifert, P., Groß, S., Freudenthaler, V., Apituley, A., Wilson, K. M., Serikov, I., Linn´ e, H., Heinold, B., Hiebsch, A., Schnell, F., Schmidt, J., Mattis, I., Wandinger, U., and Wiegner, M.: Ash and fine mode particle mass profiles from EARLINET-20 AERONET observations over Central Europe after the eruptions of the Eyjafjallaj¨ okull volcano in 2010, J. Geophys. Res., 116, D00U02, doi:10.1029/2010JD015567, 2011. Balis, D., Giannakaki, E., Mamouri, R. E., Kokkalis, P., Papayannis, A., and Tsaknakis, G.: EARLINET observations of the Eyjafjallaj¨ okull ash plume over Greece, in: “Lidar Technologies, Techniques, and Measurements for Atmospheric Remote Sensing VI”, Proceedings of SPIE,25 SPIE Remote Sensing 2010, Toulouse, France, 20–23 September 2010, 7832–32, 2010. Barlow, R. J. (Ed.): Statistics. A Guide to the Use of Statistical Methods in Physical Sciences, Wiley, Chichester, 1989. Borrmann, S., Dye, J. E., Baumgardner, D., Proffitt, M. H., Margitan, J. J., Wilson, J. C., Jonsson, H. H., Brock, C. A., Loewenstein, M., Podolske, J. R., and Ferry, G. V.: Aerosols as30 dynamic tracers in the lower stratosphere, J. Geophys. Res., 100, 11147–11156, 1995. Bravo-Aranda, J. A. and Navas-Guzm´ an, F.: Centro Andaluz de Medio Ambiente, Universidad 29704 ACPD 11, 29681–29721, 2011 Monitoring of the Eyjafjallaj¨ okull volcanic aerosol plume M. Sicard et al. Title Page Abstract Introduction Conclusions References Tables Figures J I J I Back Close Full Screen / Esc Printer-friendly Version Interactive Discussion Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | de Granada – Junta de Andaluc´ ıa, Avd. Mediterr´ aneo s/n, 18071, Granada, Spain, private communication, 1 June 2011. Bukowiecki, N., Zieger, P., Weingartner, E., Jur´ anyi, Z., Gysel, M., Neininger, B., Schneider, B., Hueglin, C., Ulrich, A., Wichser, A., Henne, S., Brunner, D., Kaegi, R., Schwikowski, M., Tobler, L., Wienhold, F. G., Engel, I., Buchmann, B., Peter, T., and Baltensperger, U.: Ground-5 based and airborne in-situ measurements of the Eyjafjallaj¨ okull volcanic aerosol plume in Switzerland in spring 2010, Atmos. Chem. Phys., 11, 10011–10030, doi:10.5194/acp-1110011-2011, 2011. Di Girolamo, P., Pappalardo, G., Spinelli, N., Berardi, V., and Velotta, R.: Lidar observations of the stratospheric aerosol layer over Southern Italy in the period 1991–1995, J. Geophys.10 Res., 101, 18765–18774, 1996. Dubovik, O., Smirnov, A., Holben, B. N., King, M. D., Kaufman, Y. J., Eck, T. F., and Slutsker, I.: Accuracy assessments of aerosol optical properties retrieved from Aerosol Robotic Network (AERONET) Sun and sky radiance measurements, J. Geophys. Res., 105(D8), 9791–9806, 2000.15 Draxler, R. R. and Rolph, G. D.: HYSPLIT (HYbrid Single-Particle Lagrangian Integrated Trajectory) Model access via NOAA ARL READY Website: http://ready.arl.noaa.gov/HYSPLIT.php, NOAA Air Resources Laboratory, Silver Spring, MD, USA, 2011. Emeis, S., Forkel, R., Junkermann, W., Sch¨ afer, K., Flentje, H., Gilge, S., Fricke, W., Wiegner, M., Freudenthaler, V., Groß, S., Ries, L., Meinhardt, F., Birmili, W., M¨ unkel, C., Obleit-20 ner, F., and Suppan, P.: Measurement and simulation of the 16/17 April 2010 Eyjafjallaj¨ okull volcanic ash layer dispersion in the northern Alpine region, Atmos. Chem. Phys., 11, 2689– 2701, doi:10.5194/acp-11-2689-2011, 2011. Fernald, F. G.: Analysis of atmospheric lidar observations: some comments, Appl. Opt., 23, 652–653, 1984.25 Flentje, H., Claude, H., Elste, T., Gilge, S., K¨ ohler, U., Plass-D¨ ulmer, C., Steinbrecht, W., Thomas, W., Werner, A., and Fricke, W.: The Eyjafjallaj¨ okull eruption in April 2010 detection of volcanic plume using in-situ measurements, ozone sondes and lidar-ceilometer profiles, Atmos. Chem. Phys., 10, 10085–10092, doi:10.5194/acp-10-10085-2010, 2010. Gasteiger, J., Groß, S., Freudenthaler, V., and Wiegner, M.: Volcanic ash from Iceland over30 Munich: mass concentration retrieved from ground-based remote sensing measurements, Atmos. Chem. Phys., 11, 2209–2223, doi:10.5194/acp-11-2209-2011, 2011. Groß, S., Gasteiger, J., Freudenthaler, V., Schnell, F., and Wiegner, M.: Characterization of the 29705 ACPD 11, 29681–29721, 2011 Monitoring of the Eyjafjallaj¨ okull volcanic aerosol plume M. Sicard et al. Title Page Abstract Introduction Conclusions References Tables Figures J I J I Back Close Full Screen / Esc Printer-friendly Version Interactive Discussion Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Table 3. Sun-photometer total, fine and coarse mode AOT at 500 nm and lidar-derived total, non-ash and ash AOT at 532 nm at Granada on 8 May 2010. The numbers in parenthesis represent the fraction of AOT of the mode considered to the AOT total (AOT for the sun-photometer and AOTVA for the lidar). AOT AOTfAOTcAOTVA RVA layer βnaSna RVA layer βaSa Lidar 04:00 UTC 2.6–2.9 km 0.101 0.083 (82 %) 0.018 (18 %) Sun-phot. 06:35 UTC 0.376 0.334 (89 %) 0.042 (11 %) Sun-phot. 07:00 UTC 0.358 0.313 (87 %) 0.045 (13 %) Lidar 16:00 UTC 3.00–3.35 km 0.0025 0.002 (80 %) 0.0005 (20 %) 29712 ACPD 11, 29681–29721, 2011 Monitoring of the Eyjafjallaj¨ okull volcanic aerosol plume M. Sicard et al. Title Page Abstract Introduction Conclusions References Tables Figures J I J I Back Close Full Screen / Esc Printer-friendly Version Interactive Discussion Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | 30 Figure 1. Synoptic situation at 1200 UTC on (a) 4, (b) 5, (c) 6, (d) 7, (e) 8 and (f) 9 May 2010. Dark and light and colors represent low and high pressures, respectively. 5 Fig. 1. Synoptic situation at 12:00 UTC on (a) 4, (b) 5, (c) 6, (d) 7, (e) 8 and (f) 9 May 2010. Dark and light colors represent low and high pressures, respectively. 29713 ACPD 11, 29681–29721, 2011 Monitoring of the Eyjafjallaj¨ okull volcanic aerosol plume M. Sicard et al. Title Page Abstract Introduction Conclusions References Tables Figures J I J I Back Close Full Screen / Esc Printer-friendly Version Interactive Discussion Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | 31 Figure 2. 120-hour (5 days) backtrajectories arriving in Évora, Madrid, Granada and Barcelona at 1200 UTC on 5, 6, 7 and 8 May 2010 at 500, 1500, 2500, 3500, 4500 and 5500 m above ground level. 5 Fig. 2. 120-h (5 days) backtrajectories arriving in ´ Evora, Madrid, Granada and Barcelona at 12:00 UTC on 5, 6, 7 and 8 May 2010 at 500, 1500, 2500, 3500, 4500 and 5500 m a.g.l. 29714 ACPD 11, 29681–29721, 2011 Monitoring of the Eyjafjallaj¨ okull volcanic aerosol plume M. Sicard et al. Title Page Abstract Introduction Conclusions References Tables Figures J I J I Back Close Full Screen / Esc Printer-friendly Version Interactive Discussion Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | 32 1 2 Figure 3. Evolution of the lidar range-square corrected signal from 5 to 8 May, 2010, at Évora, Madrid, Granada and Barcelona. Below the lidar signal 3 time series the sun-photometer total (black circles), coarse mode (red circles) and fine mode (blue circles) AOT at 500 nm are reported. The mean 4 Ångström exponent is reported as green squares (right axis). The vertical gray bars indicate the time periods discussed in Section 4.5 6 May 7 May 8 May 06 12 18 00 Évora 2.5 5.0 Madrid 06 12 18 00 06 12 18 00 06 12 18 00 5 May 00 2.5 5.0 Barcelona 2.5 5.0 5.0 Granada 0.2 0.4 Ang. exp. 0.5 1.5 2.5 0.2 0.4 Height [km asl] Height [km asl] Height [km asl] Height [km asl] AOT AOT Ang. exp. 0.5 1.5 0.2 0.4 AOT Ang. exp. 0.5 1.5 Ang. exp. 0.5 1.5 0.2 0.4 AOT Fig. 3. Evolution of the lidar range-square corrected signal from 5 to 8 May 2010, at ´ Evora, Madrid, Granada and Barcelona. Below the lidar signal time series the sun-photometer total (black circles), coarse mode (red circles) and fine mode (blue circles) at 500 nm are reported. The mean ˚ Angstr¨ om exponent is reported as green squares (right axis). The vertical gray bars indicate the time periods discussed in Sect. 4. 29715 ACPD 11, 29681–29721, 2011 Monitoring of the Eyjafjallaj¨ okull volcanic aerosol plume M. Sicard et al. Title Page Abstract Introduction Conclusions References Tables Figures J I J I Back Close Full Screen / Esc Printer-friendly Version Interactive Discussion Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | 33 1 Figure 4. AOT of lofted VA layers at 532 nm versus height from 5 to 8 May, 2010. The 2 vertical gray bars indicate the time periods discussed in Section 4. 3 4 ÉVORA MADRID GRANADA BARCELONA AOT Fig. 4. AOT of lofted VA layers at 532 nm versus height from 5 to 8 May 2010. The vertical gray bars indicate the time periods discussed in Sect. 4. 29716 ACPD 11, 29681–29721, 2011 Monitoring of the Eyjafjallaj¨ okull volcanic aerosol plume M. Sicard et al. Title Page Abstract Introduction Conclusions References Tables Figures J I J I Back Close Full Screen / Esc Printer-friendly Version Interactive Discussion Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | 34 1 2 3 4 5 6 7 024 0 100 200 30 60 90 0123 355 nm 532 nm 1064 nm Height [km asl] Bsc. Coeff. [Mm-1·sr-1] 355 nm 532 nm Ext. Coeff. [Mm-1] 355 nm 532 nm Lidar Ratio [sr] 355/532 nm  355/532 nm  532/1064 nm Ang. exp. 1 Figure 5. Volume backscatter and extinction coefficients, lidar ratios, and - (blue and green 2 curves) and -related (black curve) Ångström exponents on 7 May 2010 at 0100 UTC at 3 Évora (solid lines) and Madrid (dash lines). 4 5 32 ± 4 39 ± 10 1.05 ± 0.43 0.68 ± 0.63 0.22 ± 0.40 52 ± 27 Fig. 5. Volume backscatter and extinction coefficients, lidar ratios, and β- (blue and green curves) and α-related (black curve) ˚ Angstr¨ om exponents on 7 May 2010 at 01:00 UTC at ´ Evora (solid lines) and Madrid (dash lines). 29717 ACPD 11, 29681–29721, 2011 Monitoring of the Eyjafjallaj¨ okull volcanic aerosol plume M. Sicard et al. Title Page Abstract Introduction Conclusions References Tables Figures J I J I Back Close Full Screen / Esc Printer-friendly Version Interactive Discussion Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | 35 0 6 12 18 1.5 2.0 2.5 3.0 30 60 900 300 600 900 0123 0.0 0.1 0.2 355 nm 532 nm 1064 nm Height [km asl] Bsc. Coeff. [Mm-1·sr-1] 355 nm 532 nm Lidar ratio [sr] 355 nm 532 nm Ext. Coeff. [Mm-1] () 355/532 nm () 355/532 nm () 532/1064 nm Ang. exp. Part. depol. ratio 1 Figure 6. Volume backscatter and extinction coefficients, lidar ratios, - (blue and green 2 curves) and -related (black curve) Ångström exponents and linear particle depolarization 3 ratio on 8 May 2010 at 0400 UTC at Granada. 4 5 47 ± 7 48 ± 16 1.68 ± 0.31 0.79 ± 0.54 0.73 ± 0.07 0.066 ± 0.005 Fig. 6. Volume backscatter and extinction coefficients, lidar ratios, β- (blue and green curves) and α-related (black curve) ˚ Angstr¨ om exponents and linear particle depolarization ratio on 8 May 2010 at 04:00 UTC at Granada. 29718 ACPD 11, 29681–29721, 2011 Monitoring of the Eyjafjallaj¨ okull volcanic aerosol plume M. Sicard et al. Title Page Abstract Introduction Conclusions References Tables Figures J I J I Back Close Full Screen / Esc Printer-friendly Version Interactive Discussion Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | 36 0,0 0,5 1,0 2,0 2,4 2,8 3,2 0123 0,0 0,1 0,2 355 nm 532 nm 1064 nm Height [km asl] Bsc. Coeff. [Mm-1·sr-1] () 355/532 nm () 532/1064 nm Ang. Exp. Part. depol. ratio 1 Figure 7. Volume backscatter coefficients, -related Ångström exponents and linear particle 2 depolarization ratio on 8 May 2010 at 1600 UTC at Granada (solid lines) and Barcelona (dot 3 lines). 4 5 2.37 ± 0.27 0.075 ± 0.007 1.45 ± 0.17 2.35 ± 0.20 Fig. 7. Volume backscatter coefficients, β-related ˚ Angstr¨ om exponents and linear particle depolarization ratio on 8 May 2010 at 16:00 UTC at Granada (solid lines) and Barcelona (dot lines). 29719 ACPD 11, 29681–29721, 2011 Monitoring of the Eyjafjallaj¨ okull volcanic aerosol plume M. Sicard et al. Title Page Abstract Introduction Conclusions References Tables Figures J I J I Back Close Full Screen / Esc Printer-friendly Version Interactive Discussion Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | 37 0,01 0,1 1 10 0,00 0,02 0,04 0,06 0635 UTC 0700 UTC Particle radius (m) dV(r)/dlnr (m3·m-2) 1 Figure 8. AERONET size distributions at Granada on 8 May 2010, at 0635 and 0700 UTC. 2 The ratio of volume concentration to AOT for the fine (non-ash) and the coarse (ash) mode 3 are indicated in black at 0635 UTC and in gray at 0700 UTC. 4 5 6 Cf/AOTf Cc/AOTc 0.25 0.26 1.00 0.78 Fig. 8. AERONET size distributions at Granada on 8 May 2010, at 06:35 and 07:00 UTC. The ratio of volume concentration to AOT for the fine (non-ash) and the coarse (ash) mode are indicated in black at 06:35 UTC and in gray at 07:00 UTC. 29720 ACPD 11, 29681–29721, 2011 Monitoring of the Eyjafjallaj¨ okull volcanic aerosol plume M. Sicard et al. Title Page Abstract Introduction Conclusions References Tables Figures J I J I Back Close Full Screen / Esc Printer-friendly Version Interactive Discussion Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | 38 0 6 12 18 1,5 2,0 2,5 3,0 0 60 120 180 240 Non-ash Ash Total Bsc. Coeff. [Mm-1·sr-1] Mass conc. [g·m-3] Height [km asl] Non-ash Ash (a) 1 0,0 0,1 0,2 2,0 2,4 2,8 3,2 024 Non-ash Ash Total Height [km asl] Bsc. Coeff. [Mm-1·sr-1] Non-ash Ash Mass conc. [g·m-3](b) 2 Figure 9. Mass concentration profiles of ash and non-ash particles at Granada on 8 May 2010, 3 at (a) 0400 and (b) 1600 UTC. 4 Fig. 9. Mass concentration profiles of ash and non-ash particles at Granada on 8 May 2010, at (a) 04:00 and (b) 16:00 UTC. 29721