Formation and Transport of Atmospheric Aerosol over Athens, Greece

Advances in Meteorology, 2010

Aerosol optical depth at 550 nm () and fine-mode (FM) fraction data from Terra-MODIS were obtained over the Greater Athens Area covering the period February 2000–December 2005. Based on both and FM values three main aerosol types have been discriminated corresponding to urban/industrial aerosols, clean maritime conditions, and coarse-mode, probably desert dust, particles. Five main sectors were identified for the classification of the air-mass trajectories, which were further used in the analysis of the ( and FM data for the three aerosol types). The HYSPLIT model was used to compute back trajectories at three altitudes to investigate the relation between -FM and wind sector depending on the altitude. The accumulation of local pollution is favored in spring and corresponds to air masses at lower altitudes originating from Eastern Europe and the Balkan. Clean maritime conditions are rare over Athens, limited in the winter season and associated with air masses from the Western or Nort...

Aerosol optical depth at 550 nm (AOD 550 ) and fine-mode (FM) fraction data from Terra-MODIS were obtained over the Greater Athens Area covering the period February 2000-December 2005. Based on both AOD 550 and FM values three main aerosol types have been discriminated corresponding to urban/industrial aerosols, clean maritime conditions, and coarse-mode, probably desert dust, particles. Five main sectors were identified for the classification of the air-mass trajectories, which were further used in the analysis of the (AOD 550 and FM data for the three aerosol types). The HYSPLIT model was used to compute back trajectories at three altitudes to investigate the relation between AOD 550 -FM and wind sector depending on the altitude. The accumulation of local pollution is favored in spring and corresponds to air masses at lower altitudes originating from Eastern Europe and the Balkan. Clean maritime conditions are rare over Athens, limited in the winter season and associated with air masses from the Western or Northwestern sector. The coarse-mode particles origin seems to be more complicated proportionally to the season. Thus, in summer the Northern sector dominates, while in the other seasons, and especially in spring, the air masses belong to the Southern sector enriched with Saharan dust aerosols.

International Journal of Climatology, 2012

This study analyses the weather conditions, the main pathways and transport mechanisms favouring the presence of specific aerosol types over Athens, Greece. On the basis of the aerosol optical depth at 550 nm (AOD 550 ) and fine mode (FM) values from a Terra-MODIS dataset in the period 2000-2005, three main aerosol types are identified (urban/industrial, UI; clean maritime, CM; and desert dust, DD), each one corresponding to different optical characteristics and source regions. The UI aerosols are associated with polluted air masses from Europe, the CM aerosols with clean Atlantic air masses and the DD aerosols with air masses from North African arid regions carrying significant amount of dust in certain cases. The comparison of the three aerosol types with the air masses from their favourable sector constitutes a first 'quick-validation' of the identification scheme. Thus, the incidence of transport from Europe explain 81% of the variability in the observed UI type, while the 73% of the Atlantic air masses correspond to the CM type; the 50% of the African air masses can be considered as DD aerosols over Athens. The mean synoptic meteorological patterns, favouring the presence of each aerosol type, are also investigated. Further analysing the air-mass trajectories at three altitudes, the transport mechanisms of the aerosol types are identified. The results clearly show that the UI aerosols are mainly transported within the boundary layer, while the CM conditions are associated with Atlantic air masses at higher altitudes. Moreover, the DD aerosols are transported either in the upper atmosphere or in the whole atmospheric column. This is among the first studies conducted over Athens aiming at investigating the weather conditions, pathways and transport mechanisms that favour the presence of aerosols of different characteristics.

Atmospheric Chemistry and Physics Discussions, 2015

Detailed aerosol chemical predictions by a comprehensive model system (i.e. PMCAMx, WRF, GEOS-CHEM), along with airborne and ground-based observations, are presented and analysed over a wide domain covering the Aegean Archipelago. The studied period is 10 successive days in 2011, characterized by strong northern winds, which is the most frequently prevailing synoptic pattern during summer. The submicron aerosol load in the lower troposphere above the archipelago is homogenously enriched in sulfate (average modelled and measured submicron sulfate of 5.5 and 5.8 µg m −3 , respectively), followed by organics (2.3 and 4.4 µg m −3) and ammonium (1.5 and 1.7 µg m −3). Aerosol concentrations smoothly decline aloft, reaching lower values (< 1 µg m −3) above 4.2 km altitude. The evaluation criteria rate the model results for sulfate, ammonium, chloride, elemental carbon, organic carbon and total PM 10 mass concentrations as "good", indicating a satisfactory representation of the aerosol chemistry and precursors. Higher model discrepancies are confined to the highest (e.g. peak sulfate values) and lowest ends (e.g. nitrate) of the airborne aerosol mass size distribution, as well as in airborne organic aerosol concentrations (model underestimation ca. 50 %). The latter is most likely related to the intense fire activity at the eastern Balkan area and the Black Sea coastline, which is not represented in the current model application. The investigation of the effect of local variables on model performance revealed that the best agreement between predictions and observations occurs during high winds from the northeast, as well as for the area confined above the archipelago and up to 2.2 km altitude. The atmospheric ageing of biogenic particles is suggested to be activated in the aerosol chemistry module, when treating organics in a sufficient nitrogen and sulfate-rich environment, such as that over the Aegean basin. More than 70 % of the predicted aerosol mass over the Aegean Archipelago during a representative Etesian episode is related to transport of aerosols and their precursors from outside the modelling domain.

Atmospheric Chemistry and Physics, 2007

Mass concentration levels and the inorganic chemical composition of PM 10 (two fractions; PM 10−2.5 and PM 2.5 ) were determined during August 2003 and in the centre of Athens, Greece. August 2003 monthly mean PM 10 mass concentration, at 5 m above ground, was 56 µg/m 3 and the EU imposed daily limit of 50 µg/m 3 5 was exceeded on 16 occasions. The corresponding monthly mean for March 2004 was 92 µg/m 3 and the aforementioned daily limit was exceeded on 23 occasions. The PM 10 (PM 10−2.5 +PM 2.5 ) mass concentrations at 1.5 m above ground were found to be approximately 20% higher compared to the respective PM 10 measured at 5 m. Consequently, for a realistic estimation of the exposure of citizens to particulate matter, PM 10 10 sampling at a height of 1.5-3 m above ground, in the "breathing zone" is necessary. Such data are presented for the first time for the centre of Athens. In both campaigns, calcium was found to be the predominant component of the coarse fraction while crustrelated aluminosilicates and iron were found to be the other major components of the same fraction. The above elements constitute the most important components of the 15 fine fraction, together with the predominant sulphur. Toxic metals were found to be below the air quality limits and in lower concentrations compared to older studies, with the exception of Cu and V for which some increase was observed. Pb, in particular, appeared mostly in the fine fraction and in very low concentrations compared to studies dating more than a decade back. The major ions of the coarse fraction have been found 20 to be Ca 2+ , NO − 3 and Cl − , while SO −2 4 , Ca 2+ and NH + 4 were the major ionic components of the fine fraction. The low molar ratio of NH + 4 /SO −2 4 indicated an ammonium-poor ambient air, where atmospheric ammonia is not sufficient to neutralize all acidity and the formation of NH 4 NO 3 does not occur to a significant extend. Calcium predominated the coarse fraction and its good correlations with NO − 3 and SO −2 4 indicated its role as 25 an important neutralizing agent of atmospheric acidity in this particle size range. In the fine fraction, both Ca 2+ and NH + 4 participate in the neutralizing processes with NH + 4 being the major neutralizing agent of SO −2 4 . Chloride depletion from NaCl or MgCl Abstract Introduction Conclusions References Tables Figures Back Close Full Screen / Esc Printer-friendly Version Interactive Discussion

Atmospheric Environment, 2012

Aerosol particles in coastal areas result from a complex mixing between sea-spray aerosols locally generated at the sea surface by breaking waves and a continental component arising from natural and/or anthropogenic sources. This paper presents physicochemical characterization of aerosols observed during meteorological conditions characteristics of coastal areas. In particular, we study the influence of sea-breezes and land-breezes as well as the fetch variation, which superpose on larger synoptic conditions, on aerosol properties. This was achieved using a physical, chemical and optical analysis of the aerosol data acquired in May 2007 on the French Mediterranean coast. The aerosol distributions were measured using a TSI SMPS 3081 model and the chemical characterization was made using an Ion Chromatography analysis (IC) and a thermo-optical technique. In addition, aerosol optical characteristics were provided by aethalometer (absorption) and nephelometer (scattering) measurements. For low wind speeds, we detect high aerosol number concentrations as well as high NO À 3 and carbonaceous compounds contributions, which are observed even when the aerosol is sampled in pure maritime air masses. These results indicate that air masses are strongly impacted by pollution transported over the Mediterranean. In addition, the combination of low wind speeds and land/sea-breezes lead to the production of new ultrafine particle formation events that seem to take place over the sea before being transported back to the coast. Under higher wind speed conditions, aerosol number and mass concentrations of smaller sizes are significantly lowered due to the dispersion of anthropogenic pollutants. Optical measurements reveal that mean scattering and absorbing coefficients are about 15.2 Mm À1 and 3.6 Mm À1 , respectively. Associated mean aerosol single scattering albedo is found to be about 0.87 and 0.94 (at 520 nm) for continental and maritime influences.

This study assesses the atmospheric aerosol load and behaviour (size and seasonal dependent) of the major inorganic and organic aerosol ionic components (i.e., acetate, (C 2 H 3 O 2-), formate, (HCO 2-), fluoride, (F-), chloride, (Cl-), nitrite, (NO 2-), nitrate, (NO 3-), phosphate, (PO 4 3-), sulfate, (SO 4 2-), oxalate, (C 2 O 4 2-), sodium, (Na +), potassium, (K +), ammonium, (NH 4 +), magnesium, (Mg 2+) and calcium (Ca 2+), in Iasi urban area, northeastern Romania. Continuous measurements were carried out over 2016 by means of a cascade Dekati Low-Pressure Impactor (DLPI) performing aerosol size classification in 13 specific fractions evenly distributed over the 0.0276 up to 9.94 µm size range. Fine particulate Cl-, NO 3-, NH 4 + and K + exhibited clear minima during the warm seasons and clear maxima over the cold seasons, mainly controlled by corroboration between factors such as enhancement in the emission sources, changes in the mixed layer depth and specific meteorological conditions. Fine particulate SO 4 2did not show much variation with respect to seasons. Particulate NH 4 + and NO 3ions were identified as critical parameters controlling aerosols chemistry in the area. The measured concentrations of particulate NH 4 + and NO 3in fine mode (PM 2.5) aerosols were found to be in reasonable good agreement with modelled values for winter but not for summer, an observation reflecting actually the susceptibility of NH 4 NO 3 aerosols to be lost due to volatility over the warm seasons. Clear evidences have been obtained for the fact that in Iasi, northeastern Romania, NH 4 + in PM 2.5 is primarily associated with SO 4 2and NO 3but not with Cl-. However, indirect ISORROPIA-II estimations showed that the atmosphere in the investigated area might be ammonia-rich during both the cold and warm seasons, such as enough NH 3 to be present to neutralize H 2 SO 4 , HNO 3 and HCl acidic components and to generate fine particulate ammonium salts, in the form of (NH 4) 2 SO 4 , NH 4 NO 3 and NH 4 Cl. ISORROPIA-II runs allowed us estimating that over the warm seasons ~ 35 % of the total analyzed samples presented pH values in the very strong acidity fraction (0-3 Atmos. Chem. Phys. Discuss.,

Atmospheric Chemistry and Physics, 2007

The properties of atmospheric aerosol particles in Marseille and Athens were investigated. The studies were performed in Marseille, France, during July 2002 and in Athens, Greece, during June 2003. The aerosol size distribution and the formation and growth rates of newly formed particles were characterized using Differential Mobility Particle Sizers. Hygroscopic properties were observed using a Hygroscopic Tandem Differential Mobility Analyzer setup. During both campaigns, the observations were performed at suburban, almost rural sites, and the sites can be considered to show general regional background behavior depending on the wind direction. At both sites there were clear pattern for both aerosol number concentration and hygroscopic properties. Nucleation mode number concentration increased during the morning hours indicating new particle formation, which was observed during more than 30% of the days. The observed formation rate was typically more than 1 cm −3 s −1 , and the growth rate was between 1.2-9.9 nm h −1 . Based on hygroscopicity measurements in Athens, the nucleation mode size increase was due to condensation of both water insoluble and water soluble material. However, during a period of less anthropogenic influence, the growth was to a larger extent due to water insoluble components. When urban pollution was more pronounced, growth due to condensation of water soluble material dominated.

A long-term (2000)(2001)(2002)(2003)(2004)(2005) monitoring of aerosol data from the moderate resolution imaging spectroradiometer (MODIS) is analyzed focusing on the Greater Athens Area (GAA) in the Eastern Mediterranean region. The MODIS aerosol optical depth standard product (AOD at 550 nm) and its respective ratio attributed to fine-mode (FM) particles are employed to evaluate the seasonal variability of the aerosol properties over Athens. The climatological trend of both parameters in the period 2000-2005 is nearly absent, while remarkable year-to-year variability can be observed. The seasonal analysis reveals a significant AOD variability over Athens, with minimum values in winter ðAOD 550 $0:2Þ, and maximum in summer ðAOD 550 $0:45Þ. Regarding the FM fraction, maximum values are present in spring and minimum in summer, thus revealing the dominance of FM and coarse-mode particles, respectively. For the whole data set, a method is implemented to distinguish the main aerosol types (urban/industrial (hereafter UI), clean maritime (hereafter CM type) and desert dust (hereafter DD) over Athens, based on both AOD and FM values. Because of the mixing processes in the atmosphere the majority of the cases (46.6%) belong to a mixed (hereafter MT) aerosol type. The UI aerosols are more frequent in spring (41.2%) and less in winter (9.1%), while the coarse particles, probably DD, more frequent in summer (35.8%) and less in winter (3.5%). In contrast, the clean atmospheric conditions are more frequent in winter (23.9%), when the mixing processes are also well established (63.5%). For each aerosol type, the mean AOD 550 and FM values are also computed. Their seasonal variability exhibits a clear summer maximum for UI, CM and MT aerosols, while the DD exhibits maximum in spring. As regards the FM values of the different aerosol types they exhibit a rather constant variation with small fluctuations from season to season. r

Atmospheric Chemistry and Physics, 2013

The chemical composition and water uptake characteristics of sub-micrometer atmospheric particles in the region of the Aegean Sea were measured between 25 August and 11 September 2011 in the framework of the Aegean-Game campaign. High timeresolution measurements of the chemical composition of the particles were conducted using an airborne compact Time-Of-Flight Aerosol Mass Spectrometer (cTOF-AMS). These measurements involved two flights from the island of Crete to the island of Lemnos and back. A Hygroscopic Tandem Differential Mobility Analyzer (HTDMA) located on the island of Lemnos was used to measure the ability of the particles to take up water. The HTDMA measurements showed that the particles were internally mixed, having hygroscopic growth factors that ranged from 1.00 to 1.59 when exposed to 85 % relative humidity. When the aircraft flew near the ground station on Lemnos, the cTOF-AMS measurements showed that the organic volume fraction of the particles ranged from 43 to 56 %. These measurements corroborate the range of hygroscopic growth factors measured by the HTDMA during that time. Good closure between HT-DMA and cTOF-AMS measurements was achieved when assuming that the organic species were hydrophobic and had an average density that corresponds to aged organic species. Using the results from the closure study, the cTOF-AMS measurements were employed to determine a representative aerosol hygroscopic parameter κ mix for the whole path of the two flights. Calculated κ mix values ranged from 0.17 to 1.03 during the first flight and from 0.15 to 0.93 during the second flight. Air masses of different origin as determined by back trajectory calculations can explain the spatial variation in the chemical composition and κ mix values of the particles observed in the region. 1 Introduction Atmospheric aerosol particles affect the global radiative balance of the Earth by directly absorbing and scattering solar radiation (i.e. direct effect; Haywood and Boucher,