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The present study analyzes data from total suspended particulate (TSP) samples collected during 3 years (2005–2008) at Nainital, central Himalayas, India and analyzed for carbonaceous aerosols (organic carbon (OC) and elemental carbon (EC)) and inorganic species, focusing on the assessment of primary and secondary organic carbon contributions (POC, SOC, respectively) and on source apportionment by positive matrix factorization (PMF). An average TSP concentration of 69.6 ± 51.8 µg m−3 was found, exhibiting a pre-monsoon (March–May) maximum (92.9 ± 48.5 µg m−3) due to dust transport and forest fires and a monsoon (June–August) minimum due to atmospheric washout, while carbonaceous aerosols and inorganic species expressed a similar seasonality. The mean OC/EC ratio (8.0 ± 3.3) and the good correlations between OC, EC, and nss-K+ suggested that biomass burning (BB) was one of the major contributing factors to aerosols in Nainital. Using the EC tracer method, along with several approaches for the determination of the (OC/EC)pri ratio, the estimated SOC component accounted for ~25% (19.3–29.7%). Furthermore, TSP source apportionment via PMF allowed for a better understanding of the aerosol sources in the Central Himalayan region. The key aerosol sources over Nainital were BB (27%), secondary sulfate (20%), secondary nitrate (9%), mineral dust (34%), and long-range transported mixed marine aerosol (10%). The potential source contribution function (PSCF) and concentration weighted trajectory (CWT) analyses were also used to identify the probable regional source areas of resolved aerosol sources. The main source regions for aerosols in Nainital were the plains in northwest India and Pakistan, polluted cities like Delhi, the Thar Desert, and the Arabian Sea area. The outcomes of the present study are expected to elucidate the atmospheric chemistry, emission source origins, and transport pathways of aerosols over the central Himalayan region.

During the summer of 2012 a coordinated field campaign was conducted in multiple locations in Greece in order to characterize the ambient particulate matter (PM) levels, its chemical composition and the contribution of the regional and local sources. PM1, PM2.5 and PM10 samples were collected simultaneously at seven different sites in Greece: an urban and a suburban station in Patras, a suburban station in Thessaloniki, a suburban and an urban background station in Athens, a rural background station at the Navarino Environmental Observatory (NEO) in southwestern Peloponnese and a remote background site at Finokalia in the northeastern part of Crete. The sites were selected to facilitate the estimation of the contribution of the local emission sources and long range transport. Sulfate and organics were the major PM1 components in all sites suggesting that high sulfate levels still remain in parts of Europe. The photochemistry of the Eastern Mediterranean can convert rapidly the emitted sulphur dioxide to sulfate. Our analysis indicated significant sulfate production over the area, with high sulfate levels, especially in the remote site of Finokalia, associated with air masses that had passed over Turkey. There was high regional secondary organic aerosol production dominating organic aerosol levels even in a major city like Athens. High organic aerosol levels were associated with air masses that had crossed the Balkans with a significant biogenic component. The average PM2.5 concentration ranged from 13 to 18 μg m−3 in the different sites. There were unexpected significant gradients in the concentrations of secondary aerosol components in length scales of a few hundred kilometers. The low concentrations of measured PM2.5 nitrate are mostly organic nitrates and supermicrometer nitrate associated with sea-salt and dust. Dust was a significant PM10 constituent in all areas and was quite variable in space showing the importance of the local sources.

To better assess the role of atmospheric deposition on seawater productivity in the Eastern Mediterranean 200 sinking particulate matter samples were collected at two different depths in the water column (500 and 1715 m from the surface) during a seven-year period (1999–2005). The samples were analysed for various nutrients and elements of both natural and anthropogenic origin such as nitrogen (N), phosphorus (P), organic matter, CaCO3, Si, Al, Ca, V, Cr, Mn, Fe, Ti, Ni, Cu, Zn, Cd and Pb. Moreover, sediment traps data were compared with atmospheric deposition to assess possible transfer mechanisms of material from the atmosphere to the water column. The amount of dissolved inorganic nitrogen (DIN) deposited via the atmosphere was higher up to a factor of 6 compared to the dissolved organic nitrogen (DON) collected with the sediment traps, indicating significant external N deposition. On the other hand, atmospheric dissolved inorganic phosphorus (DIP) deposition accounted for only 60% of the P measured at upper sediment traps indicating that the atmosphere plays a less significant role of the atmosphere for P compared to N. Atmospheric dust was found to be transferred almost quantitatively from the atmosphere to the deeper water layers, indicating significant impact of vertical mass transfer. The rapid vertical mass transfer during spring can be attributed to the formation of big aggregates around atmospheric dust particles, which settle quite fast. During summer and autumn mass transfer is hindered due to the stratification of the water column and low primary productivity.

Year-round carbon dioxide (CO2) and methane (CH4) concentration measurements, performed for the first time in the city of Athens, Greece from December 21, 2018 to December 31, 2019, are presented in this study and analyzed in relation to atmospheric circulation patterns at a local, regional and long-range transport scale. Clear diurnal and seasonal variations of both greenhouse gases were detected. The observed increased levels during night and early morning hours are attributed to traffic/heating emissions and leakages of residential natural gas for CO2 and CH4, respectively. Using CO2 and CH4 levels simultaneously measured at the regional background site at Finokalia (Greece), increments in their levels due to local and regional anthropogenic sources within the city were assessed. For CO2, maximum and minimum increments were clearly observed during winter and summer respectively, suggesting a greater impact of combustion of fossil fuel and especially of biomass on CO2 levels during winter. On the other hand, CH4 increments were similar in all seasons, suggesting that local sources of CH4 remain quite constant year-round. Through the implementation of the Conditional Probability Function (CPF), the emission sources of theses greenhouse gases have been localized to the northern and the eastern domains of the Athens basin. Stagnant atmospheric conditions were also associated with an increased likelihood of CO2 and CH4 episodes. Backward modeling simulations with FLEXPART and HYSPLIT models indicate an industrial zone and a petrochemical zone, situated to the north and to the west of Athens respectively, as possible CH4 regional sources as well as possible CO2 contributions from southern directions attributed to shipping emissions from the port of Piraeus. The present study provides knowledge needed for the determination of greenhouse gas emission mitigation strategies in Athens.

We present a novel automated system for real-time measurements of water-soluble reactive phosphate (SRP) ions in atmospheric particles. Detection of SRP is based on molybdenum blue chemistry with Sn(II) chloride dihydrate reduction. The instrumentation consists of one particle-into-liquid sampler (PILS) coupled with a 250 cm path length liquid waveguide capillary cell (LWCC) and miniature fiber optic spectrometer, with detection wavelength set at 690 nm. The detection limit was 0.4 nM P, equivalent to 0.03 nmol P m-3 in atmospheric particles. Comparison of SRP in collocate PM2.5 aerosol filter sampling with the PILS-LWCC on line system were in good agreement (n = 49, slope = 0.84, R2 = 0.78). This novel technique offers at least an order of magnitude enhancement in sensitivity over existing approaches allowing for SRP measurements of unprecedented frequency (8 min), which will lead to greater understanding of the sources and impacts of SRP in atmospheric chemistry. © 2016 American Chemical Society.

Slant column (SC) densities of nitrogen dioxide (NO2), formaldehyde (HCHO), glyoxal (CHOCHO) and oxygen dimer (O4) were successfully retrieved for the first time in Athens, by using spectral measurements from a ground-based multi-azimuth Multi-AXis Differential Optical Absorption Spectroscopy (MAX-DOAS) system. The data span the period from October 2012 to March 2014 and measurements were conducted at NOA's (National Observatory of Athens) station in Penteli (38.0°N, 23.9°E, 527 m a.s.l.) at eight azimuth angles and eight off-axis elevation angles. The SCNO2, SCHCHO and SCCHOCHO measurements at +1ο elevation angle, pointing towards the urban area, range from 0.6 to 24·1016, 0.8–9.6·1016 and 0.3–5.2·1015 molec cm−2 (mean daily values throughout the whole period), respectively. Seasonal modulation characterised by summertime maximum and wintertime minimum was observed for HCHO and CHOCHO, while for NO2 the maximum values were recorded during winter. Changes in the diurnal variability of all trace gases with season and day of the week are investigated suggesting a strong link to primary anthropogenic sources for NO2 and a weaker one, compared to photochemistry, for HCHO and CHOCHO. In addition, the impact of the reduced anthropogenic emissions during weekends on the measured SC values was quantified and 30%–50% lower SCNO2 values were found during weekends. The contribution of local urban emissions to the overall recorded amounts of the selected species was assessed. Using meteorological data from NOA's station in Penteli, the impact of the local circulation patterns on the SC levels was estimated, and a strong relation between western wind direction, which is related to the industrial area, and enhanced SC measurements was found.

Two-sized aerosol samples were obtained from a rural site located close to Sinop on the south coastline of the Black Sea. In addition, bulk deposition samples were collected at Varna, located on the west coastline of the Black Sea. Both aerosol and deposition samples were analyzed for the main macronutrients, NO3−, NH4+, and PO43−. The mean aerosol nitrate and ammonium concentrations were 7.1 ± 5.5 and 22.8 ± 17.8 nmol m−3, respectively. The mean aerosol phosphate concentration was 0.69 ± 0.31 nmol m−3, ranging from 0.21 to 2.36 nmol m−3. Interestingly, phosphate concentration over Sinop was substantially higher than those of most Mediterranean sites. Comparison of the atmospheric and riverine inputs for the Black Sea revealed that atmospheric dissolved inorganic nitrogen (DIN) only ranged between 4% and 13%, while the atmospheric dissolved inorganic phosphorus (DIP) fluxes had significantly higher contributions with values ranging from 12% to 37%. The molar N:P ratios in atmospheric deposition for Sinop and Varna were 13 and 14, respectively, both of which were lower than the Redfield ratio (16). The atmospheric molar N:P ratios over the Black Sea were considerably lower than those reported for riverine fluxes (41) and the Mediterranean region (more than 200). The atmospheric P flux can sustain 0.5%–5.2% of the primary production, whereas the N flux can sustain 0.4%–4.8% of the primary production. The contribution of the atmospheric flux may enhance by 2.6 when the new production is considered.

The historical and future impacts of atmospheric deposition of inorganic nitrogen (N) and phosphorus (P) on the marine ecosystem in the east Mediterranean Sea are investigated by using a 1D coupled physical– biogeochemical model, set up for the Cretan Sea as a representative area of the basin. For the present-day simulation (2010), the model is forced by observations of atmospheric deposition fluxes at Crete, while for the hindcast (1860) and forecast (2030) simulations, the changes in atmospheric deposition calculated by global chemistry–transport models are applied to the present-day observed fluxes. The impact of the atmospheric deposition on the fluxes of carbon in the food chain is calculated together with the contribution of human activities to these impacts. The results show that total phytoplanktonic biomass increased by 16% over the past 1.5 centuries. Small fractional changes in carbon fluxes and planktonic biomasses are predicted for the near future. Simulations show that atmospheric deposition of N and P may be the main mechanism responsible for the anomalous N:P ratio observed in the Mediterranean Sea.

International audience; To obtain a comprehensive picture of the spatial distribution of atmospheric phosphorus (P) speciation in the Mediterranean Sea, deposition samples were collected from the eastern (E) and northwestern (NW) Mediterranean and analyzed for both organic and inorganic P forms. Dissolved P, especially in organic form, is dominant during the wet season, while higher insoluble P fluxes are recorded during the dry period, mainly due to dust outbreaks. Wet deposition has a significant contribution to the atmospheric phosphorus flux; over the NW Mediterranean accounting for 80% of the total dissolved phosphorus (TDP). The seven-year average TDP flux during the wet season in the NW basin, of 1.78 mmol m −2 y −1 , is almost double that of the two-year average in the eastern Mediterranean. The difference is attributed mainly to the precipitation height being 2-3 times higher in the NW Mediterranean compared to the East. Dissolved organic phosphorus (DOP) is the dominant P fraction in both wet and dry deposition samples, presenting similar fluxes (1.16 and 0.94 mmol m −2 y −1 , in the eastern and northwestern basins respectively). Finally, assuming that all TDP is bioavailable, atmospheric deposition of TDP could account for up to 38% of new production in the eastern Mediterranean, while during oligotrophic periods of the NW Mediterranean it could increase the new production by 14%.

While cloud condensation nuclei (CCN) production associated with atmospheric new particle formation (NPF) is thought to be frequent throughout the continental boundary layers, few studies on this phenomenon in marine air exist. Here, based on simultaneous measurement of particle number size distributions, CCN properties and aerosol chemical composition, we present the first direct evidence on CCN production resulting from NPF in the eastern Mediterranean atmosphere. We show that condensation of both gaseous sulfuric acid and organic compounds from multiple sources leads to the rapid growth of nucleated particles to CCN sizes in this environment during the summertime. Sub-100 nm particles were found to be substantially less hygroscopic than larger particles during the period with active NPF and growth (the value of κ was lower by 0.2–0.4 for 60 nm particles compared with 120 nm particles), probably due to enrichment of organic material in the sub-100 nm size range. The aerosol hygroscopicity tended to be at minimum just before the noon and at maximum in the afternoon, which was very likely due to the higher sulfate-to-organic ratios and higher degree of oxidation of the organic material during the afternoon. Simultaneous with the formation of new particles during daytime, particles formed during the previous day or even earlier were growing into the size range relevant to cloud droplet activation, and the particles formed in the atmosphere were possibly mixed with long-range-transported particles.

Summarization: Ozone measurements have been performed in the period 2003–2009 at Akrotiri (suburban) and Finokalia (coastal) monitoring stations on the island of Crete, Greece. The main objectives were to investigate the concentration levels of ozone in the region of Crete, its spatial and temporal variability, the effect of air mass origin and local sources on ozone levels, and the frequency of exceedances of the EU limits for ozone concentrations in the area. The observed mean values for Akrotiri and Finokalia stations were 44.5 ± 8.5 and 49.1 ± 10.6 ppbv, respectively. Ozone concentrations were higher during the 8-month period between March and October (52.3 ± 6.8 and 53.0 ± 7.4 ppbv for Akrotiri and Finokalia station, respectively) whereas, in the period November–February, the concentrations were lower (37.7 ± 4.7 and 39.1 ± 6.9 ppbv, respectively). The above values indicate that there is not a west-east gradient of ozone concentration in the studied area. At both stations, AOT40 limit values were higher than the limit set by the European Union (Directive 2008/50/EC). Exceedances of the EU target value were encountered during 88 and 67 % of the time in Akrotiri and Finokalia stations, respectively. Differences on the diurnal patterns and daily ozone maxima between the two stations were attributed to the different characteristics of the two stations and to the effect of local pollution sources to Akrotiri station. The average value of the amplitude of the daily cycle (calculated as the difference between maximum and minimum values) in the case of Akrotiri was 8.3 ppbv, and it was about two times the corresponding value in Finokalia (4.7 ppbv), which is an indication of the effect of the anthropogenic emission produced in the city of Chania to the Aktotiri station environment. At Finokalia, the maximum values were observed 2–4 h later than those at Akrotiri. During springtime, the difference in the maximum values appearance was close to 4 h, with the maximum at Akrotiri at 16:00 (LT) and at Finokalia at about 20:00 (LT). This time difference supports the transfer of gaseous precursors and already formed ozone molecules toward Finokalia. Presented on

The distribution of total and dissolved forms of DMSP and total DMSO was surveyed during two sampling cruises conducted in September 2003 and July 2004 in the North Aegean Sea. During the first cruise the surface concentrations of DMSPt, DMSPd and DMSOt in the coastal group of stations ranged from 20.92 to 23.71 nM, 15.46 to 15.53 nM and 14.90 to 18.73 nM respectively, while in the offshore group the mean concentrations were 27.41 nM (DMSPt) and 14.66 nM ( DMSOt). Concerning the phytoplankton assemblage it was dominated by dinoflagellates. During the second cruise, the surface DMSPt, DMSPd and DMSOt concentrations in the coastal group were not significantly changed compared to the first cruise, while the offshore group presented more elevated values (DMSPt: 33.52 nM; DMSPd: 18.78 nM; DMSOt: 36.49 nM). Interestingly the vertical distribution and the phytoplankton abundance in this cruise were changed, with diatoms being the dominant group in the study area. On both cruises statistically significant correlations between small-sized dinoflagellates ( ≤ 20 μm) as well as coccolithophores and the concentrations of DMSx compounds obtained, suggesting the importance of the above phytoplankton groups in the production and distribution of the these sulphonic forms. At the same time, no significant correlations were observed between DMSx and diatom species. The strong correlation of DMSx species with the group of dinoflagellates coupled with their decorrelation with Chl- a may serve as indirect evidence of heterotrophic forms dominating dinoflagellate taxa thriving in the area during the stratified period. Normal 0 false false false EL X-NONE X-NONE

Particle acidity affects aerosol concentrations, chemical composition, toxicity and nutrient bioavailability. We present a summary of thermodynamic analysis of comprehensive observations of ambient aerosol collected over the US and E.Mediterranean to understand the levels and drivers of aerosol pH. We find that acidic aerosol in the fine mode is ubiquitous, with levels that range between 0 and 2 throughout most of the data examined. The strong acidity is largely from the large difference in volatility between sulfate (the main acidic compound, which resides completely in the aerosol phase) and ammonia (the main neutralizing agent, which partitions between aerosol and gas-phase). This counterintuitive, but thermodynamically consistent finding explains why aerosol acidity in the southeastern United States has not decreased over the last decades, despite a 70% reduction in sulfates and a constant ammonia background. We then demonstrate that evaluation of model-predicted pH is critical for model predictions of semi-volatile species, e.g., nitrate.

During an intensive field campaign on aerosol, clouds, and ice nucleation in the Eastern Mediterranean in April 2016, we measured the abundance of ice nucleating particles (INPs) in the lower troposphere from unmanned aircraft systems (UASs). Aerosol samples were collected by miniaturized electrostatic precipitators onboard the UASs at altitudes up to 2.5 km. The number of INPs in these samples, which are active in the deposition and condensation modes at temperatures from −20 to −30 °C, were analyzed immediately after collection on site using the ice nucleus counter FRIDGE (FRankfurt Ice nucleation Deposition freezinG Experiment). During the 1-month campaign, we encountered a series of Saharan dust plumes that traveled at several kilometers' altitude. Here we present INP data from 42 individual flights, together with aerosol number concentrations, observations of lidar backscattering, dust concentrations derived by the dust transport model DREAM (Dust Regional Atmospheric Model), and results from scanning electron microscopy. The effect of the dust plumes is reflected by the coincidence of INPs with the particulate matter (PM), the lidar signal, and the predicted dust mass of the model. This suggests that mineral dust or a constituent related to dust was a major contributor to the ice nucleating properties of the aerosol. Peak concentrations of above 100 INPs std L−1 were measured at −30 °C. The INP concentration in elevated plumes was on average a factor of 10 higher than at ground level. Since desert dust is transported for long distances over wide areas of the globe predominantly at several kilometers' altitude, we conclude that INP measurements at ground level may be of limited significance for the situation at the level of cloud formation.

During the last years the atmosphere of the Great Athens Area (GAA) and other Greek cities is burdened from extended residential biomass burning for heating purposes. In this work, a series of near real-time and off-line biomass burning tracers are analyzed during intense wood burning events in Athens. The measurements were conducted at an urban background site located in the center of Athens, and in the heart of wood burning activities (winter 2013–2014). The measured tracers include high resolution measurements of non-sea salt potassium (nss-K+), wood burning black carbon (BCwb), the m/z 60 fragment associated with levoglucosan and monosaccharide anhydrides (levoglucosan, mannosan and galactosan) determined on selected filter samples. The suitability of these tracers was evaluated when the prevailing meteorological conditions with low dispersion and deposition mechanisms (low wind speed, absence of precipitation) were associated with high biomass burning emissions at nighttime. During the severe smog periods, the levels of K+, BCwb, m/z 60 and levoglucosan were up to 2.2 μg m−3, 12.5 μg m−3, 3.4 μg m−3 and 8.6 μg m−3, respectively, higher by a factor of at least two, relatively to the non smog periods due to biomass burning. Correlations between biomass burning tracers as well as between monosaccharide anhydrides provided information about the type of material and wood being burned.

Organic carbon (OC), elemental carbon (EC), water-soluble organic carbon (WSOC) and main ions were measured in a total of 1510 PM2.5 daily aerosol samples collected from May 2008 to April 2013 in Athens, Greece. OC and EC concentrations were 2.1 ± 1.3 μg m−3 and 0.54 ± 0.39 μg m−3, accounting for 11 ± 3% and 3 ± 1% of PM2.5 mass, respectively, with an average OC/EC ratio of 4.7 ± 3.1. Significant correlation was found between OC and EC during the whole period, indicating emissions by common primary sources on a regional scale. WSOC concentration ranged from 0.03 to 10.6 μg m−3, with an average of 1.5 ± 0.9 μg m−3. By considering the Finokalia (Crete) station as a reference, it was estimated that, during the warm season in Athens, 67 ± 7% of emitted OC and 53 ± 12% of emitted EC is regional, while, during cold months, the regional contribution of OC is only 33 ± 7% and of EC 29 ± 8%. Furthermore, secondary organic carbon (SOC) was calculated for the warm period of the year (April to October). The estimated SOC constituted about 75 ± 6% of PM2.5 organic carbon in Athens, highlighting significant aging processes on a regional scale. In the period 2011–2013 and during wintertime, an increase in OC and EC levels was observed, attributed to an increase in wood burning for domestic heating due to the economic crisis.

A systematic monitoring of PM2.5 was carried out during a period of three years (from February 2010 to April 2013) at an urban site, at the National Technical University of Athens campus. Two types of 24-h PM2.5 samples have been collected: 271 samples on PTFE and 116 samples on quartz filters. Daily PM2.5 concentrations were determined for both types of samples. Total sulfur, crustal origin elements and elements of a major crustal component (Al, Si, Fe, Ca, K, Mg, Ti) trace elements (Zn, Pb, Cu, Ni, P, V, Cr, Mn) and water soluble ions (Cl−, NO3−, SO42−, Na+, K+, NH4+, Ca2+, Mg2+) were determined on the PTFE samples. Organic carbon (OC), elemental carbon (EC) and water soluble ions were determined on the quartz samples. For the mass closure six components were considered: Secondary Inorganic Aerosol (SIA), Organic Matter (OM), Elemental Carbon (EC), Dust, Mineral anthropogenic component (MIN) and Sea Salt (SS). SIA and OM contributed in the mass of PM2.5 almost equally: 30–36% and 30% respectively. EC, SS and MIN accounted for 5, 4 and 3% respectively of the total PM2.5 mass. Dust accounted for about 3–5% in absence of dust transport event and reached a much higher percentage in case of dust transport event. These contributions justify at least 80% of the PM2.5 mass. Source apportionment analysis has been performed by Positive Matrix Factorization. The combination of the PMF results obtained by both data sets lead to the definition of six factors: 1. SO42−, NH4+, OC (industrial/regional sources, secondary aerosol) 2. EC, OC, K and trace metals (traffic and heating by biomass burning, locally emitted aerosol). 3. Ca, EC, OC and trace metals (urban-resuspended road dust reflecting exhaust emissions), 4. Secondary nitrates 5. Na, Cl (marine source) 6. Si, Al, Ti, Ca, Fe (Dust transported from Sahara). These factors reflect not only main sources contributions but also underline the key role of atmospheric dynamics and aerosol ageing processes in this Mediterranean environment.

Observations show that the Mediterranean troposphere is characterized by a marked enhancement in summertime ozone, with a maximum over the eastern Mediterranean. This has been linked to enhanced photochemical ozone production and subsidence under cloud-free anticyclonic conditions. The eastern Mediterranean is among the regions with the highest levels of background tropospheric ozone worldwide. A 12 yr climatological analysis (1998–2009) of free-tropospheric ozone was carried out over the region based on the ECMWF (European Centre for Medium-Range Weather Forecasts) ERA-Interim reanalysis data and simulations with the EMAC (ECHAM5–MESSy) atmospheric chemistry–climate model. EMAC is nudged towards the ECMWF analysis data and includes a stratospheric ozone tracer. A characteristic summertime pool with high ozone concentrations is found in the middle troposphere over the eastern Mediterranean–Middle East (EMME) in the ERA-Interim ozone data, Tropospheric Emission Spectrometer (TES) satellite ozone data and simulations with EMAC. The enhanced ozone over the EMME during summer is a robust feature, extending down to lower free-tropospheric levels. The investigation of ozone in relation to potential vorticity and water vapour and the stratospheric ozone tracer indicates that the dominant mechanism causing the free-tropospheric ozone pool is the downward transport from the upper troposphere and lower stratosphere, in association with the enhanced subsidence and the limited horizontal divergence observed over the region. The implications of these high free-tropospheric ozone levels on the seasonal cycle of near-surface ozone over the Mediterranean are discussed.

Atmospheric deposition provides significant amounts of nutrients to the continental and marine ecosystems. Using the mesoscale WRF/CMAQ modeling system, the nitrogen (N) and sulfur (S) atmospheric deposition fluxes over the Mediterranean and the Black seas and continental Europe are evaluated for the year 2008. The annual N and S deposition fluxes are calculated to be 4.89 Tg(N) yr −1 and 2.07 Tg(S) yr −1 over continental Europe, 0.92 Tg(N) yr −1 and 0.52 Tg(S) yr −1 over West Mediterranean, 1.10 Tg(N) yr −1 and 0.84 Tg(S) yr −1 over East Mediterranean and 0.36 Tg(N) yr −1 and 0.17 Tg(S) yr −1 over the Black Sea. Inorganic N deposition fluxes are calculated to be about 3 times higher than gaseous organic N deposition fluxes. Comparison to available observations associates the annual mean model estimates with about 40 ± 30% of uncertainty depending on location. Dry deposition dominates over wet deposition for both N and S in agreement with the observations. Results suggest that an important fraction of the N deposited over the Mediterranean basin can be attributed to transported N species while S deposition is dependent more on the local emissions. In Black Sea and West Mediterranean Sea waters the calculated atmospheric N inputs are comparable to the N export measured by sediment traps whereas in the East Mediterranean N input exceeds by a factor of about 5 the N export. Our simulations show that the critical N load of 1 g(N) m −2 yr −1 is exceeded over 84% of the European forested areas.

The surface ozone photolysis rate (J(O1D)) was computed on a daily basis and on a 50 km × 50 km resolution for the 11-year period 2000–2010 at Finokalia meteorological station in Crete, Greece. A radiative transfer model was used, with climatological data from the Moderate Resolution Imaging Spectroradiometer (MODIS) on board NASA's Terra satellite. The area is representative of the Eastern Mediterranean, a region with high variability in aerosol loads and total column ozone. Instantaneous values of J(O1D) computed from the model were validated against corresponding station measurements available during the 5-year period 2002–2006. Monthly mean values of J(O1D) during the 11-year period examined, reveal a statistically significant decreasing trend, based on Terra MODIS data, which shows an overall 13% decrease. The aerosol effect on J(O1D) varies on a daily basis, depending on the aerosol load, and can exceed −10% during dust events, with a median value of −2.3% over the whole period examined. On a seasonal basis, the aerosol effect on J(O1D) follows the seasonal pattern of the aerosol load, with higher values in spring and autumn, due to the increased Saharan dust episodes during these seasons. Linear regression analysis on monthly mean values of total column ozone revealed a statistically significant increasing trend in both Finokalia and Thessaloniki stations. Total column ozone MODIS data were validated against spectroradiometric (columnar) measurements at Thessaloniki station. Sensitivity analysis on the effect of total column ozone on J(O1D) showed that a 10% variation in total ozone causes a corresponding 15–17% change in J(O1D). These results suggest that the decreasing trend in J(O1D) found in the case of Terra MODIS should be attributed mainly to the corresponding increasing trend in total column ozone.

This study investigates the impact of atmospheric deposition on the marine ecosystem of the East Mediterranean Sea. Atmospheric deposition has been suggested to be more important than land inputs of nutrients to the East Mediterranean Sea. For the first time, atmospheric deposition measurements of dissolved inorganic phosphorous and nitrogen over Crete are used together with marine ecosystem observations in the Cretan Sea and a one-dimension physical/biogeochemical marine model. The adopted model configuration successfully reproduces observations of production rates and biomasses of phytoplankton and bacteria in the region. The atmospheric deposition of N and P to the East Mediterranean is shown to increase the primary production by 1–35% depending on season with the maximum impact calculated for summer and fall. Biomasses subsequently increase by 2–26% for phytoplankton and up to 7% for bacteria. The total organic carbon integrated year-around in the first 200 m of the water column increases by about 30%. The results also show the importance of the rate of P preferential to N remineralization in the upper sea water layer for the marine productivity. Simulations indicate that continuous atmospheric inputs of nutrients over several decades can maintain the anomalously high N-to-P ratio observed in the East Mediterranean seawater.

Daily PM2.5 concentrations and composition were monitored at an urban site at 14 m above ground level, at the National Technical University of Athens campus from February to December 2010. Total sulfur, crustal origin elements and elements of a major crustal component (Al, Si, Fe, Ca, K, Mg, Ti) trace elements (Mn, V, Pb, Cu, Zn, Ni) and water soluble ions (Cl – , NO3 – , SO4 2– , Na + , K + , NH4 + , Ca 2+ , Mg 2+ ) were determined. Carbonaceous compounds were determined for a period of one month. Sulfur (sulfates) and carbonaceous material were the most abundant constituents (35% and 30% respectively). Ionic balance calculations revealed a cation deficit in PM2.5 attributed to H + associated with sulfates. The concentrations of the elements of crustal origin presented abrupt increases during Saharan dust transport events. Mass closure was attempted considering Secondary Inorganic Aerosol (SIA), Particulate Organic Matter (POM), Elemental Carbon (EC), Dust, Mineral Anthropogenic Component (MIN) and Sea Salt (SS). The sum of these components accounted for about 75% of the measured PM2.5 concentrations. SIA and carbonaceous material (OM + EC) contributed almost equally for about 30% in the PM2.5 mass, and while the dust contribution was significant during dust transport events, it was only about 5% in absence of such events. The contribution of sea salt was calculated to be about 4%.

To estimate the role of atmospheric deposition on Black Sea biogeochemistry, the chemical composition (particulate matter, carbon, major and trace metals) of both atmospheric deposition and sediment traps material was studied. Lithogenic material was found to be the most abundant constituent in sediment traps (31–34%) followed by carbonates (CC; 21%) and particulate organic carbon (POC; 10%). Particulate matter fluxes in sediment traps were low from January to March with maxima from November to December for both depths (930 m and 1930 m). Particulate organic carbon and lithogenic material present common peaks with particulate matter, indicating that during blooms, phytoplankton produces aggregates and sweep from the surface both lithogenic and anthropogenic elements which are transported rapidly to the deep. Atmospheric deposition was found to supply quantitatively a considerable amount of major and trace metals to the seawater of the Black Sea. More precisely, on average from the surface towards the deeper water layers of the Black Sea 26% and 83% of Al, V, Cr, Mn, Fe, Ni, Cu, Zn, Cd and Pb fluxes were provided by atmospheric deposition, demonstrating its significant role as an external source of major and trace metals in the area.

To assess the origin and transformation of carbonaceous material in the marine boundary layer of the Eastern Mediterranean, a total of 111 size segregated aerosol samples have been collected using a 12-stage Small-Deposit-area low-volume-Impactor (SDI) covering an almost 3 year period. The samples have been analyzed for organic (OC), elemental (EC), water-soluble organic carbon (WSOC) and ionic components. Maxima of OC, EC and WSOC mass size distributions were found in the accumulation mode (0.449 μm) with occasionally a minor, secondary peak in the coarse mode (2.68 μm). OC and WSOC concentrations peak during summertime due to photochemistry, while EC during autumn, and spring. In general, almost 2/3 of OC and EC concentrations are found in the PM 1 fraction of the aerosol with OC being mostly secondary and therefore highly oxidized and water-soluble to a great extent (∼70%). Using the EC-tracer method, it was found that 83 ± 11% of the PM 10 organic carbon is secondary, with the percentage reaching ∼70% for the PM 1 fraction, a value in very good accordance to WSOC/OC ratio. Ammonium sulfate accounts for 75.5 ± 21.7% and 9.3 ± 1.9% of the aerosol mass in the fine and coarse fraction respectively, exhibiting maximum concentrations also in the accumulation mode. It was estimated that, on average, sea salt and mineral dust account for 33% and 45% of the coarse inorganic mass fraction, respectively.

Recent estimates of nutrient budgets for the Eastern Mediterranean Sea (EMS) indicate that atmospheric aerosols play a significant role as suppliers of macro- and micro- nutrients to its Low Nutrient Low Chlorophyll water. Here we present the first mesocosm experimental study that examines the overall response of the oligotrophic EMS surface mixed layer (Cretan Sea, May 2012) to two different types of natural aerosol additions, “pure” Saharan dust (SD, 1.6 mg l-1) and mixed aerosols (A - polluted and desert origin, 1 mg l-1). We describe the rationale, the experimental set-up, the chemical characteristics of the ambient water and aerosols and the relative maximal biological impacts that resulted from the added aerosols. The two treatments, run in triplicates (3 m3 each), were compared to control-unamended runs. Leaching of approximately 2.1-2.8 and 2.2-3.7 nmol PO4 and 20-26 and 53-55 nmol NOx was measured per each milligram of SD and A, respectively, representing an addition of approximately 30% of the ambient phosphate concentrations. The nitrate/phosphate ratios added in the A treatment were twice than those added in the SD treatment. Both types of dry aerosols triggered a positive change (25-600% normalized per 1 mg l-1 addition) in most of the rate and state variables that were measured: bacterial abundance (BA), bacterial production (BP), Synechococcus (Syn) abundance, chlorophyll-a (chl-a), primary production (PP) and dinitrogen fixation (N2-fix), with relative changes among them following the sequence BP>PP≈N2-fix>chl-a≈BA≈Syn. Our results show that the ‘polluted’ aerosols triggered a relatively larger biological change compared to the SD amendments (per a similar amount of mass addition), especially regarding BP and PP. We speculate that despite the co-limitation of P and N in the EMS, the additional N released by the A treatment may have triggered the relatively larger response in most of the rate and state variables as compared to SD. An implication of our study is that a warmer atmosphere in the future may increase dust emissions and influence the intensity and length of the already well stratified water column in the EMS and hence the impact of the aerosols as a significant external source of new nutrients.

This study examines the chemical composition of aerosols over Athens. To achieve this, particulate matter sampling has been conducted on a 6–24 h basis from January 2013 until now. More than 700 aerosol samples were collected at downtown Athens, in Thissio and after mass quantification, were analyzed for major ions (Cl−, Br−, \( {\text{NO}}_{3}^{ - } \), \( {\text{SO}}_{4}^{2 - } \), \( {\text{PO}}_{4}^{ - 3 } \), \( {\text{C}}_{2} {\text{O}}_{4}^{ - 2 } \), \( {\text{NH}}_{4}^{ + } \), K+, Na+, Mg2+, Ca2+), trace elements (Al, As, Ca, Cd, Co, Cr, Cu, Fe, V, Zn, Mn, Ni, Pb, P, S, Sb), organic carbon (OC) and elemental carbon (EC). Aerosol chemical mass closure calculations indicated that carbonaceous aerosol constitutes a major component, along with nitrate and sulfate anions, dust, cations and EC. Principal component analysis (PCA) was also applied to better constrain the aerosol sources over Athens with specific emphasis during the winter time, period characterized by intense biomass burning.

Mineral dust is a complex entity containing a range of iron minerals including poorly crystalline to crystalline iron oxides to clay minerals. Important progress has been made to characterize iron mineralogical compositions in the dust recently. These include the quantification of the content of crystalline hematite and goethite, which appear to show a regional variation in North Africa as a result of the differences in the degree of chemical weathering. Fractional Fe solubility (dissolved to total iron, FFS) in the atmospheric aerosols has been reported to range from 0.1% to 80%. However, FFS is usually less than 0.5% in the non-atmospherically-processed dust, suggesting that FFS can be enhanced by atmospheric processes. One of the atmospheric processes, gravitational settling of dust, which has been previously hypothesized to cause the abovementioned enhancement of FFS during dust transport has been shown to be insignificant. Cycling of dust particles in the clouds, in which pH is usually higher than 4, and in the aerosol phase, in which pH is usually substantially lower, can significantly affect iron speciation and FFS. Laboratory experiments showed that a significant amount of iron (>0.5%) can only be solubilized in the dust when pH is lower than 4. These laboratory data suggest that acid processing rather than cloud processing might be a prime mechanism to cause an increase in FFS in the dust during transport. Further laboratory studies, field measurements, and modelling are needed to increase the ability of models to quantify the atmospheric processing of iron in the dust. (c) 2012 Elsevier B.V. All rights reserved.

Atmospheric particles were measured in the late winter (25 February–26 March 2009) at a remote coastal site on the island of Crete, Greece during the Finokalia Aerosol Measurement Experiment-2009. A quadrupole aerosol mass spectrometer (Q-AMS) was employed to quantify the size-resolved chemical composition of non-refractory submicron aerosol, and a thermodenuder was used to analyze the organic aerosol (OA) volatility. Complementary measurements included particle size distributions from a scanning mobility particle sizer, inorganic and organic particle composition from filter analysis, air ion concentrations, O3, NOx and NOy concentrations, and meteorological measurements. Factor analysis was performed on the OA mass spectra, and the variability in OA composition could best be explained with three OA components. The oxygenated organic aerosol (OOA) was similar in composition and volatility to the summertime OA previously measured at this site and may represent an effective endpoint in particle-phase oxidation of organics. The two other OA components, one associated with amines (Amine-OA) and the other probably associated with the burning of olive branches (OB-OA), had very low volatility but were less oxygenated. Hydrocarbon-like organic aerosol (HOA) was not detected. The absence of OB-OA and Amine-OA in the summer data may be due to lower emissions and/or photochemical conversion of these components to OOA.

To identify the relative contribution of local versus regional sources of particulate matter (PM) in the Greater Athens Area (GAA), simultaneous mass and chemical composition measurements of size segregated particulate matter (PM: PM1, PM2.5 and PM10) were carried out from September 2005 to August 2006 at three locations: one urban (Goudi, Central Athens) and one suburban (Lykovrissi, Athens) in GAA and the third in a regional background site (Finokalia, Crete). The two stations in GAA exceeded the EU-legislated PM10 limit values, both in terms of annual average (59.0 and 53.6 μg m−3 for Lykovrissi and Goudi, respectively) and of 24-h value, while the concentration levels at the remote site of Finokalia indicated an elevated background. High levels of PM2.5 and PM1 were also found at all locations (23.5 and 18.6 for Lykovrissi, while 29.4 and 20.2 μg m−3 for Goudi, respectively). Significant correlations were observed between same PM fractions at both GAA sites indicating important spatial homogeneity within GAA. During the warm season, the PM1 ratio between the GAA and the background site ranged from 1.1 to 1.3. On the other hand this ratio was significantly higher (1.6–1.7) during the cold season highlighting the role of long-range transport and local sources during the warm and cold seasons respectively. Similar seasonal and geographical patterns were observed for nss-SO42−, a secondary compound characteristic of regional sources, confirming the above hypothesis. Regarding the coarse fraction no such seasonal trend was observed for both GAA sites with their ratio (GAA site/Finokalia) being higher than 2 indicating significant contribution from local sources such as road dust and/or constructions as confirmed by Ca2+ measurements. Chemical speciation data showed that on a yearly basis, ionic and crustal mass represent up to 78% of the gravimetrically determined mass for PM10 samples in GAA. The unidentified mass might be attributed to organic carbon (OC) and elemental carbon (EC), in agreement with the results reported by earlier studies in central Athens. The contribution of local sources at both GAA sites was also estimated by considering mass and chemical composition measurements at Finokalia as representative of the regional background. Carbonaceous material, Particulate Organic Matter (POM) and EC, seemed to be the main contributor of the local PM mass within GAA (up to 62% in PM1). Dust from local sources (mainly resuspension) contributed also significantly to the local PM10 mass (up to 33%).

Optical properties of atmospheric aerosol particles have been recorded at a remote location of the Eastern Mediterranean on a continuous basis since 2000. Measurements of aerosol scattering coefficient (bsp) and absorption coefficient (bap) have been conducted, providing the longest data series of such ground based measurements in the Eastern Mediterranean basin. bsp shows an annual cycle with maximum values observed during summer and minimum during winter. In addition, in periods when mineral dust is transported into the area, high values are observed. It has been shown that both the level and the annual variation of bsp can be well represented if ammonium sulfate (AS) and particulate organic matter (POM) are assumed as the only scattering species in the aerosol phase. bap was measured at three wavelengths using two different instruments and a single wavelength data series was extracted. Maximum values of bap were observed during summer and during periods with extended dust transport to the area. If mineral dust particles are present in the atmosphere they can contribute up to 80% of bap levels at the visible wavelengths.

The role of atmospheric urea on the biogeochemical cycle of Water Soluble Organic Nitrogen (WSON) in the Eastern Mediterranean was assessed by collecting and analyzing wet and dry deposition samples and size segregated aerosols during a one year period (2006). In rain water volume weighted mean (VWM) concentration of urea was found equal to 5.5 μM. In atmospheric particles the average concentration of urea in coarse and fine mode was 0.9 ± 1.9 nmol N m− 3 (median 0.0 nmol N m− 3) and 2.2 ± 3.0 nmol N m− 3 (median 1.1 nmol N m− 3), respectively. The percentage contribution of urea to WSON fraction was 0% and 20% in coarse and fine particles respectively. On an annual basis 0.81 mmol m− 2 and 1.78 mmol m− 2 of urea were deposited via wet and dry deposition, contributing to WSON by 10% and 11% respectively. Regression analysis of urea with the main ions and trace metals measured in parallel suggest that soil and anthropogenic activities significantly contribute to atmospheric urea. Comparison of dry deposition of urea using size segregated deposition velocities with urea collected on a glass bead collector suggested the existence of significant fraction of urea in the gas phase.

Primary productivity of continental and marine ecosystems is often limited or co-limited by phosphorus. Deposition of atmospheric aerosols provides the major external source of phosphorus to marine surface waters. However, only a fraction of deposited aerosol phosphorus is water soluble and available for uptake by phytoplankton. We propose that atmospheric acidification of aerosols is a prime mechanism producing soluble phosphorus from soil-derived minerals. Acid mobilization is expected to be pronounced where polluted and dust-laden air masses mix. Our hypothesis is supported by the soluble compositions and reconstructed pH values for atmospheric particulate matter samples collected over a 5-yr period at Finokalia, Crete. In addition, at least tenfold increase in soluble phosphorus was observed when Saharan soil and dust were acidified in laboratory experiments which simulate atmospheric conditions. Aerosol acidification links bioavailable phosphorus supply to anthropogenic and natural acidic gas emissions, and may be a key regulator of ocean biogeochemistry.

Aerosol and rainwater samples have been collected at a rural site located on the coastline of the Eastern Mediterranean, Erdemli, Turkey between January 1999 and December 2007. Riverine sampling was carried out at five Rivers (Ceyhan, Seyhan, Göksu, Berdan and Lamas) draining into the Northeastern Levantine Basin (NLB) between March 2002 and July 2007. Samples have been analyzed for macronutrients of phosphate, silicate, nitrate and ammonium (PO43−, Sidiss, NO3− and NH4+). Phosphate and silicate in aerosol and rainwater showed higher and larger variations during the transitional period when air flows predominantly originate from North Africa and Middle East/Arabian Peninsula. Deficiency of alkaline material have been found to be the main reason of the acidic rain events whilst high pH values (>7) have been associated with high Sidiss concentrations due to sporadic dust events. In general, lowest nitrate and ammonium concentrations in aerosol and rainwater have been associated with air flow from the Mediterranean Sea. Comparison of atmospheric with riverine fluxes demonstrated that DIN and PO43− fluxes to NLB have been dominated by atmosphere (~90% and ~60% respectively) whereas the input of Si was mainly derived from riverine runoff (~90%). N/P ratios in the atmospheric deposition (233); riverine discharge (28) revealed that NLB receives excessive amounts of DIN and this unbalanced P and N inputs may provoke even more phosphorus deficiency. Observed molar Si/N ratio suggested Si limitation relative to nitrogen might cause a switch from diatom dominated communities to non-siliceous populations particularly at coastal NLB.

A variable residence time thermodenuder (TD) was combined with an Aerodyne Aerosol Mass Spectrometer (AMS) and a Scanning Mobility Particle Sizer (SMPS) to measure the volatility distribution of aged organic aerosol in the Eastern Mediterranean during the Finokalia Aerosol Measurement Experiment in May of 2008 (FAME-2008). A new method for the quantification of the organic aerosol volatility distribution was developed combining measurements of all three instruments together with an aerosol dynamics model. Challenges in the interpretation of ambient thermodenuder-AMS measurements include the potential resistances to mass transfer during particle evaporation, the effects of particle size on the evaporated mass fraction, the changes in the AMS collection efficiency and particle density as the particles evaporate partially in the TD, and finally potential losses inside the TD. Our proposed measurement and data analysis method accounts for all of these problems combining the AMS and SMPS measurements. The AMS collection efficiency of the aerosol that passed through the TD was found to be approximately 10% lower than the collection efficiency of the aerosol that passed through the bypass. The organic aerosol measured at Finokalia is approximately 2 or more orders of magnitude less volatile than fresh laboratory-generated monoterpene (α-pinene, β-pinene and limonene under low NOx conditions) secondary organic aerosol. This low volatility is consistent with its highly oxygenated AMS mass spectrum. The results are found to be highly sensitive to the mass accommodation coefficient of the evaporating species. This analysis is based on the assumption that there were no significant reactions taking place inside the thermodenuder.

Atmospheric water-soluble organic nitrogen (WSON) was determined on size-segregated aerosol particles collected during a two years period (2005–2006) in a remote marine location in the Eastern Mediterranean (Finokalia, Crete island). Average concentration of WSON was 5.5 ± 3.9 nmol m −3 and 11.6 ± 14.0 nmol m −3 for coarse (PM 1.3-10 ) and fine (PM 1.3 ) mode respectively, corresponding to 13% of Total Dissolved Nitrogen (TDN) in both modes. Air masses origin and correlation with tracers of natural and anthropogenic sources indicate that combustion process (biomass burning and fossil fuel) and African dust play an important role in regulating levels of WSON in both coarse and fine aerosol fractions. Chemical speciation of organic nitrogen pool was attempted by analyzing 47 fine aerosol samples (PM 1 ) for 17 free amino acids (N-FAA), dimethylamine (DMA) and trimethylamine (TMA). The average concentration of N-FAA was 0.5 ± 0.5 nmol m −3 , while the average concentration of DMA was 0.2 ± 0.8 nmol m −3 , TMA was below detection limit. The percentage contribution of N-FAA and DMA to WSON was 2.1 ± 2.3% and 0.9 ± 3.4%, respectively.

Atmospheric deposition (wet and dry) of major and trace metals (V, Cr, Mn, Fe, Ni, Cu, Zn, Cd and Pb) was monitored at a remote location in the eastern Mediterranean Sea from January 2005 through December 2006. A comparison of atmospheric deposition fluxes with sediment traps data (simultaneously collected) highlighted the significance of atmospheric inputs to the biogeochemical cycling of trace elements. V, Cr, Fe and Pb were mainly associated with the particulate form (64–98%), whilst for Mn, Zn, Cu and Cd the soluble fraction represents 60–70% of the total input. The solubility of all studied metals in both wet and dry deposition was found to decrease with increasing pH values and increasing dust mass. Cr, Mn and Cu fluxes were higher during the dry season compared to those measured during the wet season. For the remaining metals the opposite trend is valid, whilst Fe and Zn are removed from the atmosphere almost equally by wet and dry deposition. Atmospheric deposition of major and trace metals in the eastern Mediterranean Sea was sufficient to balance metals in the water column, indicating the predominant role of atmospheric deposition as an external source of trace elements in the area.

Atmospheric deposition of Total Dissolved Nitrogen (TDN) and Phosphorus (TDP) was studied in bulk deposition samples simultaneously collected at several locations around the Mediterranean, during one year period (June 2001–May 2002). Dissolved Inorganic Phosphorus (DIP) and Nitrogen (DIN) atmospheric deposition fluxes ranged from 243 to 608 μmol m − 2 y − 1 and from 18.1 to 47.7 mmol m − 2 y − 1 respectively, presenting an important spatial variability within the basin. Wet deposition was found to be the main factor controlling DIN deposition in the Mediterranean. The amount of DIN deposited during the wet period was 2–8 times higher than that deposited during the dry season. It was estimated that about 65% of the total DIP was deposited during the wet period. Dust events as well as regional biomass burning were also found to contribute significantly to the DIP deposition. A significant percentage of the TDN and TDP of the samples were in organic form with Dissolved Organic Phosphorus (DOP) and Nitrogen (DON) accounting for 38% and 32% of TDP and TDN respectively. DIN/DIP molar ratio of the bulk deposition varied depending on the location of the sampling site in the Mediterranean basin, presenting an increasing trend from the Western (60) to the Eastern Mediterranean basin (105). This variation is similar to that observed in the seawater column, indicating an important link between atmospheric deposition and seawater productivity of the area.

Aged organic aerosol (OA) was measured at a remote coastal site on the island of Crete, Greece during the Finokalia Aerosol Measurement Experiment-2008 (FAME-2008), which was part of the EUCAARI intensive campaign of May 2008. The site at Finokalia is influenced by air masses from different source regions, including long-range transport of pollution from continental Europe. A quadrupole aerosol mass spectrometer (Q-AMS) was employed to measure the size-resolved chemical composition of non-refractory submicron aerosol (NR-PM1), and to estimate the extent of oxidation of the organic aerosol. Factor analysis was used to gain insights into the processes and sources affecting the OA composition. The particles were internally mixed and liquid. The largest fraction of the dry NR-PM1 sampled was ammonium sulfate and ammonium bisulfate, followed by organics and a small amount of nitrate. The variability in OA composition could be explained with two factors of oxygenated organic aerosol (OOA) with differing extents of oxidation but similar volatility. Hydrocarbon-like organic aerosol (HOA) was not detected. There was no statistically significant diurnal variation in the bulk composition of NR-PM1 such as total sulfate or total organic aerosol concentrations. However, the OA composition exhibited statistically significant diurnal variation with more oxidized OA in the afternoon. The organic aerosol was highly oxidized, regardless of the source region. Total OA concentrations also varied little with source region, suggesting that local sources had only a small effect on OA concentrations measured at Finokalia. The aerosol was transported for about one day before arriving at the site, corresponding to an OH exposure of approximately 4×1011 molecules cm−3 s. The constant extent of oxidation suggests that atmospheric aging results in a highly oxidized OA at these OH exposures, regardless of the aerosol source.

More than 2500 measurements of C 2 –C 8 non-methane hydrocarbons (NMHCs) have been conducted at Finokalia sampling station on the island of Crete over a thirty-month period (September 2003–February 2006), to investigate the factors controlling NMHC levels and estimate their role in the oxidizing capacity of the Eastern Mediterranean atmosphere. Atmospheric concentrations of NMHCs range from below the detection limit (5 pptv) to a few ppbv and present a hydroxyl radical (OH) driven seasonal pattern with lower values during summer. The diel variability was also influenced by the reaction of the NMHC with the OH radical, exhibiting a nighttime maximum and a midday or early afternoon minimum. Long-lived compounds demonstrate higher concentrations under the influence of the northern sector (European continent), indicating that besides chemistry, transport significantly contributes to NMHCs levels in the area. Based on the observed NMHCs diurnal cycles, mean OH radical levels of 3.5 × 10 6 molecules cm −3 have been derived for May–October period.

Measurements of cloud condensation nuclei (CCN) concentrations (cm−3) between 0.2 and 1.0% supersaturation, aerosol size distribution and chemical composition were performed at a remote marine site in the eastern Mediterranean, from September to October 2007 during the FAME07 campaign. Most of the particles activate at ~0.6% supersaturation, characteristic of the aged nature of the aerosol sampled. Application of Köhler theory, using measurements of bulk composition, size distribution, and assuming that organics are insoluble resulted in agreement between predicted and measured CCN concentrations within 7±11% for all supersaturations, with a tendency for CCN underprediction (16±6%; r2=0.88) at the lowest supersaturations (0.21%). Including the effects of the water-soluble organic fraction (which represent around 70% of the total organic content) reduces the average underprediction bias at the low supersaturations, resulting in a total closure error of 0.6±6%. Using threshold droplet growth analysis, the growth kinetics of ambient CCN is consistent with NaCl calibration experiments; hence the presence of aged organics does not suppress the rate of water uptake in this environment. The knowledge of the soluble salt fraction is sufficient for the description of the CCN activity in this area.

Mass and ionic composition of PM2.5 were determined for 1-year period (11/2004–10/2005) in a rural coastal Mediterranean site. The annual mean PM2.5 concentration measured was found to be 13.9 μg m−3. Smaller values were observed during the cold and rainy period compared to the warm and dry one. This may be ascribed to the scavenging of PM2.5 by rainfall during the cold period, in conjunction with the enhanced resuspension of soil dust and increased secondary aerosol formation during the warm period. Weekday/weekend variations and segregation of PM values according to wind direction, showed that local sources are not significant factors controlling the particle levels. Long-range transport is the dominant factor. Short distance to sampling site air paths traveling near ground resulted to larger PM values. Sulfate was found to be the main ionic species with annual mean concentration of 3.2 μg m−3, contributing 23.3% to the measured PM2.5 mass. It exhibited a seasonal variation with higher values in the summer months. The contributions of nitrate and chloride to the PM2.5 mass were 3.3% and 1.2%, respectively. Ammonium had an annual mean concentration of 1.6 μg m−3 and Ca2+ 0.33 μg m−3. They were the dominant cations contributing 11.2% and 2.7%, respectively, to the measured PM mass. In total the ionic species accounted for 45% of the PM2.5 mass. The calcium ions indicate that crustal materials are also important contributors to PM2.5 in this region, even though their major occurrence would be in the coarse mode. Finally Na+, K+ and Mg2+ had annual mean concentrations 0.24, 0.19 and 0.02 μg m−3, respectively. They contributed 3.1%, 0.34% and 0.18%, respectively, to the measured particulate mass. Anthropogenic contribution was calculated to account for 40% of the PM2.5 mass, crustal material (dust) for 25% and marine aerosol 4.3%.

This study investigates the effects of the total solar eclipse of 29 March 2006 on surface air-quality levels over Greece based on observations at a number of sites in conjunction with chemical box modelling and 3-D air-quality modelling. Emphasis is given on surface ozone and other photooxidants at four Greek sites Kastelorizo, Finokalia (Crete), Pallini (Athens) and Thessaloniki, which are located at gradually increasing distances from the path of the eclipse totality and are characterized by different air pollution levels. The eclipse offered the opportunity to test our understanding of air pollution build-up and the response of the gas-phase chemistry of photo-oxidants during a photolytical perturbation using both a photochemical box model and a regional air-quality offline model based on the modeling system WRF/CAMx. At the relatively unpolluted sites of Kastelorizo and Finokalia no clear signal of the solar eclipse on surface O 3 , NO 2 and NO concentrations can be deduced from the observations while there is no correlation of observed O 3 , NO 2 and NO with observed global radiation. The box and regional model simulations for the two relatively unpolluted sites indicate that the calculated changes in net ozone production rates between eclipse and non eclipse conditions are rather small compared to the observed short-term ozone variability. Furthermore the simulated ozone lifetime is in the range of a few days at these sites and hence the solar eclipse effects on ozone can be easily masked by local and regional transport. At the polluted sites of Thessaloniki and Pallini, the solar eclipse effects on O 3 , NO 2 and NO concentrations are revealed from both the measurements and modeling with the net effect being a decrease in O 3 and NO and an increase in NO 2 as NO 2 formed from the reaction of O 3 with NO while at the same time NO 2 is not efficiently photolysed. This result is also supported by a positive correlation of observed global radiation with O 3 and NO and a negative correlation with NO 2 . It is evident from the 3-D air quality modeling over Greece that the maximum effects of the eclipse on O 3 , NO 2 and NO are reflected on the large urban agglomerations of Athens, and Thessaloniki where the maximum of the emissions occur.

Two-stage aerosol samples (PM10–2.5 and PM2.5) were collected at a coastal rural site located in the northeastern Mediterranean, between April 2001 and 2002. A total of 562 aerosol samples were analyzed for trace elements (Fe, Ti, Mn, Ca, V, Ni, Zn, Cr) and water-soluble ions (Na+, NH4+, K+, Mg2+, Ca2+, Cl−, Br−, NO3−, SO42−, C2O42− and MS−:methane sulfonate). PM10, crustal elements, sea salt aerosols and NO3− were mainly associated with the coarse mode whereas non-sea salt (nss)SO42−, C2O42−; MS−, NH4+, Cr and Ni were found predominantly in the fine fraction. Concentrations of aerosol species exhibited orders of magnitude change from day to day and the aerosol chemical composition is heavily affected by dust events under the influence of airflow from North Africa. During the sampling period, 11 specific mineral dust events of duration varying from 1 day to a week have been identified and their influence on the chemical composition of aerosols has been studied in detail. Ionic balance analysis performed in the coarse and fine aerosol fractions indicated anion and cation deficiency due to CO32− and H+, respectively. A relationship between nssSO42− and NH4+ denoted that sulfate particles were partially neutralized (70%) by ammonium. Excess-K/BC presented two distinct ratios for winter and summer, indicating two different sources: fossil fuel burning in winter and biomass burning in summer.

This is the first study that investigates the seasonal variability of nitrate (NO3) radicals in the marine boundary layer over the East Mediterranean Sea. An extensive data set of NO3 radical observations on the north coast of Crete for more than two years (June 2001–September 2003) is presented here. NO3 radicals follow a distinct seasonal dependency with the highest seasonally average mixing ratios in summer (5.6±1.2 pptv) and the lowest in winter (1.2±1.2 pptv). Episodes with high NO3 mixing ratios have been encountered mainly in polluted air masses originating from mainland Greece, Central and East Europe, and Turkey. Ancillary measurements of ozone, nitrogen dioxide (NO2) and meteorological parameters have been conducted and used to reveal possible relationship with the observed NO3 variability. The acquired NO2 nighttime observations provide the up-to-date most complete overview of NO2 temporal variability in the area. The data show correlations of the NO3 nighttime mixing ratios with temperature (positive), relative humidity (negative) and to a lesser extend with O3 (positive). As inferred from these observations, on average the major sink of NO3 radicals in the area is the heterogeneous reaction of dinitrogen pentoxide (N2O5) on aqueous particles whereas the homogeneous gas phase reactions of NO3 are most important during spring and summer. These observations support a significant contribution of NO3 nighttime chemistry to the oxidizing capacity of the troposphere.

The global atmospheric iron (Fe) cycle is parameterized in the global 3-D chemical transport model TM4-ECPL to simulate the proton- and the organic ligand-promoted mineral-Fe dissolution as well as the aqueous-phase photochemical reactions between the oxidative states of Fe (III/II). Primary emissions of total (TFe) and dissolved (DFe) Fe associated with dust and combustion processes are also taken into account, with TFe mineral emissions calculated to amount to ~ 35 Tg-Fe yr−1 and TFe emissions from combustion sources of ~ 2 Tg-Fe yr−1. The model reasonably simulates the available Fe observations, supporting the reliability of the results of this study. Proton- and organic ligand-promoted Fe dissolution in present-day TM4-ECPL simulations is calculated to be ~ 0.175 Tg-Fe yr−1, approximately half of the calculated total primary DFe emissions from mineral and combustion sources in the model (~ 0.322 Tg-Fe yr−1). The atmospheric burden of DFe is calculated to be ~ 0.024 Tg-Fe. DFe deposition presents strong spatial and temporal variability with an annual flux of ~ 0.496 Tg-Fe yr−1, from which about 40 % (~ 0.191 Tg-Fe yr−1) is deposited over the ocean. The impact of air quality on Fe deposition is studied by performing sensitivity simulations using preindustrial (year 1850), present (year 2008) and future (year 2100) emission scenarios. These simulations indicate that about a 3 times increase in Fe dissolution may have occurred in the past 150 years due to increasing anthropogenic emissions and thus atmospheric acidity. Air-quality regulations of anthropogenic emissions are projected to decrease atmospheric acidity in the near future, reducing to about half the dust-Fe dissolution relative to the present day. The organic ligand contribution to Fe dissolution shows an inverse relationship to the atmospheric acidity, thus its importance has decreased since the preindustrial period but is projected to increase in the future. The calculated changes also show that the atmospheric DFe supply to the globe has more than doubled since the preindustrial period due to 8-fold increases in the primary non-dust emissions and about a 3-fold increase in the dust-Fe dissolution flux. However, in the future the DFe deposition flux is expected to decrease (by about 25 %) due to reductions in the primary non-dust emissions (about 15 %) and in the dust-Fe dissolution flux (about 55 %). The present level of atmospheric deposition of DFe over the global ocean is calculated to be about 3 times higher than for 1850 emissions, and about a 30 % decrease is projected for 2100 emissions. These changes are expected to impact most on the high-nutrient–low-chlorophyll oceanic regions.

To identify the sources of aerosols in Greater Athens Area (GAA), a total of 1510 daily samples of fine (PM 2.5) and coarse (PM 10-2,5) aerosols were collected at a suburban site (Penteli), during a five year period (May 2008-April 2013) corresponding to the period before and during the financial crisis. In addition, aerosol sampling was also conducted in parallel at an urban site (Thissio), during specific, short-term campaigns during all seasons. In all these samples mass and chemical composition measurements were performed, the latest only at the fine fraction. Particulate organic matter (POM) and ionic masses (IM) are the main contributors of aerosol mass, equally contributing by accounting for about 24% of the fine aerosol mass. In the IM, nss-SO4(-2) is the prevailing specie followed by NO3(-) and NH4(+) and shows a decreasing trend during the 2008-2013 period similar to that observed for PM masses. The contribution of water in fine aerosol is equally significant (21 ± 2%), while during dust transport, the contribution of dust increases from 7 ± 2% to 31 ± 9%. Source apportionment (PCA and PMF) and mass closure exercises identified the presence of six sources of fine aerosols: secondary photochemistry, primary combustion, soil, biomass burning, sea salt and traffic. Finally, from winter 2012 to winter 2013 the contribution of POM to the urban aerosol mass is increased by almost 30%, reflecting the impact of wood combustion (dominant fuel for domestic heating) to air quality in Athens, which massively started in winter 2013.

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 PM10 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.

To obtain a comprehensive picture on the spatial distribution of water soluble organic nitrogen (WSON) in marine aerosols, samples were collected during research cruises in the tropical and south Atlantic Ocean and during a one year period (2005) over the southern Indian Ocean (Amsterdam island). Samples have been analyzed for both organic and inorganic forms of nitrogen and the factors controlling their levels have been examined. Fine mode WSON was found to play a significant role in the remote marine atmosphere with enhanced biogenic activity, with concentrations of WSON (11.3 ± 3.3 nmol N m–3) accounting for about 84% of the total dissolved nitrogen (TDN). Such levels are similar to those observed in the polluted marine atmosphere of the eastern Mediterranean (11.6 ± 14.0 nmol N m–3). Anthropogenic activities were found to be an important source of atmospheric WSON as evidenced by the ten times higher levels in the Northern Hemisphere (NH) than in the remote Southern Hemisphere (SH). Furthermore, the higher contribution of WSON to TDN (40%) in the SH, compared to the NH (20%), underlines the important role of organic nitrogen in remote marine areas. Finally, Sahara dust was also identified as a significant source of WSON in the coarse mode aerosols of the NH.

Methanesulfonate (MS−) and non-sea-salt sulfate (nss-SO42−), two of the major oxidation products of atmospheric dimethylsulfide (DMS), have been continuously measured in rainwater at three remote islands in the Southern Indian Ocean: Amsterdam since 1991, Crozet since 1992, and Kerguelen since 1993. The annual volume weighted mean (VWM) concentrations of nss-SO42− in rainwater were 3.19, 3.04 and 4.57 μ eq l−1 at Amsterdam, Crozet, and Kerguelen, respectively while the VWM of MS− were 0.24, 0.15 and 0.30 μ eq l−1, respectively. At all three islands, MS− presented a well-distinguished seasonal variation with a maximum during summer whereas the seasonal variation of nss-SO42− was less pronounced, possibly due to the increased anthropogenic influence during the winter period. Furthermore, MS− presented significant interannual variations, in particular at Amsterdam and Crozet, which is closely related to the sea-surface temperature (SST) anomalies). Finally, the nss-SO42− deposition at Crozet Island presented a decreasing interannual trend, reflecting probably reductions in sulfur emissions from Southern Africa. On the contrary no interannual tendency was observed in the nss-SO42− concentrations at Amsterdam Island, indicating that the biogeochemical sulfur cycle at this area is mainly influenced by biogenic emissions.