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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.

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.

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.

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

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 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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

During the MINOS campaign (28 July-18 August 2001) the nitrate (NO3) radical was measured at Finokalia station, on the north coast of Crete in South-East Europe using a long path (10.4 km) Differential Optical Absorption Spectroscopy instrument (DOAS). Hydroxyl (OH) radical was also measured by a Chemical Ionization Mass-Spectrometer (Berresheim et al., 2003). These datasets represent the first simultaneous measurements of OH and NO3 radicals in the area. NO3 radical concentrations ranged from less than 3x107 up to 9x108 radicals· cm-3 with an average nighttime value of 1.1x108 radicals· cm-3. The observed NO3 mixing ratios are analyzed on the basis of the corresponding meteorological data and the volatile organic compound (VOC) observations which were measured simultaneously at Finokalia station. The importance of the NO3 radical chemistry relatively to that of OH in the dimethylsulfide (DMS) and nitrate cycles is also investigated. The observed NO3 levels regulate the nighttime variation of DMS. The loss of DMS by NO3 during night is about 75% of that by OH radical during day. NO3 and nitrogen pentoxide (N2O5) reactions account for about 21% of the total nitrate (HNO3(g)+NO-3(g)) production.

The cycling of inorganic bromine in the marine boundary layer (mbl) has received increased attention in recent years. Bromide, a constituent of sea water, is injected into the atmosphere in association with sea-salt aerosol by breaking waves on the ocean surface. Measurements reveal that supermicrometer sea-salt aerosol is substantially depleted in bromine (often exceeding 50%) relative to conservative tracers, whereas marine submicrometer aerosol is often enriched in bromine. Model calculations, laboratory studies, and field observations strongly suggest that the supermicrometer depletions reflect the chemical transformation of particulate bromide to reactive inorganic gases that influence the processing of ozone and other important constituents of marine air. Mechanisms for the submicrometer enrichments are not well understood. Currently available techniques cannot reliably quantify many Br containing compounds at ambient concentrations and, consequently, our understanding of inorganic Br cycling over the oceans and its global significance are uncertain. To provide a more coherent framework for future research, we have reviewed measurements in marine aerosol, the gas phase, and in rain. We also summarize sources and sinks, as well as model and laboratory studies of chemical transformations. The focus is on inorganic bromine over the open oceans outside the polar regions. The generation of sea-salt aerosol at the ocean surface is the major tropospheric source producing about 6.2 Tg/a of bromide. The transport of Br from continents (as mineral aerosol, and as products from biomass-burning and fossil-fuel combustion) can be of local importance. Transport of degradation products of long-lived Br containing compounds from the stratosphere and other sources contribute lesser amounts. Available evidence suggests that, following aerosol acidification, sea-salt bromide reacts to form Br2 and BrCl that volatilize to the gas phase and photolyze in daylight to produce atomic Br and Cl. Subsequent transformations can destroy tropospheric ozone, oxidize dimethylsulfide (DMS) and hydrocarbons in the gas phase and S(IV) in aerosol solutions, and thereby potentially influence climate. The diurnal cycle of gas-phase Br and the corresponding particulate Br deficits are correlated. Higher values of Br in the gas phase during daytime are consistent with expectations based on photochemistry. We expect that the importance of inorganic Br cycling will vary in the future as a function of both increasing acidification of the atmosphere (through anthropogenic emissions) and climate changes. The latter affects bromine cycling via meteorological factors including global wind fields (and the associated production of sea-salt aerosol), temperature, and relative humidity.

Hydroxyl radical (OH) concentrations were measured in August 2001 at Finokalia Station on the northeastern coast of Crete during the Mediterranean Intensive Oxidant Study (MINOS). OH was measured based on selected ion chemical ionization mass spectrometry (SI/CIMS) with a time resolution of 30 sec and signal integration of 5 min. The corresponding accuracy, precision, and detection limit were 20% (1s), 11\% (1s), and 2.4 x 105 molecules cm-3 (2s), respectively. OH levels showed a strong diurnal variability with high maxima (approximately 2 x 107 molecules cm-3) occurring around 13:30 LT (10:30 UTC) and nighttime values below the detection limit. Daily 24-hour average concentrations varied between 3.6-6.7 x 106 cm-3. For the total measurement period (6-21 August) the mean and standard deviation were 4.5 ± 1.1 x 106 cm-3. The OH data set is analyzed based on a classification into three periods: I: Aug 6-8, II: Aug 9-11, III: Aug 13-18. For each of the three periods the measured OH concentrations are described by the empirical function [OH] = a J(O1D)b, with J(O1D) being the ozone photolysis frequency and a = 1.4 x 1010 s cm-3, 1.7 x 1010 s cm-3, 2.2 x 1010 s cm-3, and b = 0.68, respectively. Taking into account the estimated precision of the OH measurements this empirical function using three values for a and one value for b explains 99% of the observed variance of OH. A detailed sensitivity analysis using a CH4-CO box model was performed to interpret this relationship, in particular the meanings of the pre-exponential factor a and the exponent b. It was found that the value of b which represents the total logarithmic dependence of [OH] on J(O1D) includes the individual contributions from the photolysis of O3, NO2, HCHO, HONO, and H2O2 which could be determined using the box model. For the conditions prevailing during the MINOS campaign the exponent b was found to be dominated by the contributions from O3- and NO2-photolysis. For the individual functional dependences between [OH] and J(O1D), [OH] and J(NO2), and J(NO2) and J(O1D) the partial logarithmic derivatives were determined to be 0.5, 0.6, and 0.3, respectively. Overall, the box model yields a value of 0.70 for the exponent b in very good agreement with the corresponding value derived from the empirical analysis of the measurements. This empirical approach in which the chemical air mass characteristics influencing the OH radical balance and thereby, the self-cleansing efficiency of the atmosphere, are represented by only two parameters which are constant over quite substantial time periods may be used in future experiments to test and compare OH measurements made in different atmospheric environments.

Methanesulfonate (MS − ), an exclusive oxidation product of dimethylsulfide (DMS), has been analyzed in rainwater at Amsterdam Island (37°50′S 77°32′E) in the Southern Indian Ocean from 1991 to 1999. Rainwater MS − concentrations range from 0.004 to 4.59 μmol l −1 with a volume weighted mean value of 0.24 μmol l −1 and present a well distinguished seasonal variation with higher values in summer, in line with the seasonal variation of its gaseous precursor (DMS), which was measured on a daily basis since 1990. The interannual variability of MS − in rainwater follows closely that of DMS, indicating that MS − in rainwater can be used as a surrogate to study long-term variations of atmospheric DMS, and further confirms the findings of Sciare et al. (J. Geophys. Res. 105 (2000a) 26 369), that large-scale anomalies occurred in the biogenic sulfur cycle in the Southern Indian Ocean during the studied period. Furthermore, on a monthly basis, the MS − anomalies in the rainwater were found to be closely related to sea-surface temperature (SST) anomalies. The correlation between MS − and SST is consistent with that observed between gaseous DMS and SST in the area and indicates an important coupling between the oceanic and the atmospheric compartments of the biogeochemical sulfur cycle.

Formaldehyde (HCHO) concentrations have been measured in 66 rain samples during the rainy season (September 1999–May 2000) at Heraklion (25°07′E, 35°20′N; Crete) a coastal urban location in the eastern Mediterranean. HCHO concentrations vary between 0.42 and 11.14 μM, in the range of HCHO levels reported at other locations worldwide. The annual volume-weighted mean (VWM) rainwater HCHO concentration is 3.05 μM and comprised ∼3% of the dissolved organic carbon. Formaldehyde levels in rainwater depend on the air mass origin. The per event deposition of HCHO when air masses originate from NW Europe, Balkans or Turkey is 2–4 times higher than that from Africa or from marine sectors indicating strong influence from anthropogenic sources. The significant correlation of formaldehyde with non-sea-salt sulfate, nitrate and ammonium also indicates a significant anthropogenic component in HCHO levels. Formaldehyde is found to correlate significantly with formate and acetate with a ratio of formate to formaldehyde close to 1. According to our measurements rainwater HCHO and TOC could significantly contribute to the productivity of the eastern Mediterranean seawater. In particular, the rainwater can be an important supplier of the HCHO reservoir in the seawater. In addition the rainwater TOC levels can provide to phytoplankton species up to 32% of the organic carbon needed for new production.

The seasonal variation of gaseous dimethylsulfide (DMS) and its oxidation products (non-sea-salt sulfate (nss-SO 4 2− ) and methanesulfonic acid (MSA) have been investigated at a remote coastal location in the Eastern Mediterranean. Daytime atmospheric DMS concentrations were measured in the range 0.3–8.9 nmol m −3 (with an average of 2.35±1.38 nmol m −3 , 1 σ uncertainty) and present a well distinguished seasonal cycle with higher values in summer. The seasonal variation of atmospheric DMS is in line with that of seawater DMS concurrently measured in the Cretan Sea. Monthly atmospheric DMS concentrations are significantly correlated with sea-surface temperature. By the mean of a 0-D model based on atmospheric DMS observations, the DMS flux calculated for spring and summer is in reasonable agreement with the fluxes deduced from the seawater DMS data and the wind speed. The diurnal variation of atmospheric DMS was investigated during a 4-day intensive campaign in September 1997 and shows a nighttime minimum, which could be explained by the presence of NO 3 radicals, which are highly reactive towards DMS. Aerosol MSA concentrations varied seasonally from below detection limit (0.04) to 0.99 (average of 0.27±0.15 nmol m −3 , 1 σ uncertainty). Similarly aerosol nss-SO 4 2− varied from 0.6 to 123.9 (average of 41.0±17.4 nmol m −3 , 1 σ uncertainty). Based on the measured MSA, nss-SO 4 2− and their ratio, the biogenic contribution to nss-SO 4 2− was found to exhibit a well-established seasonal pattern ranging from 1% during winter to 17% during summer.

The spatial and temporal distribution of Dimethylsulfide (DMS),Dimethylsulfoniopropionate (DMSP) – its precursor –,Dimethylsulfoxyde (DMSO) – one of its oxidation products –Carbonyl sulfide (COS) and Carbonyl disulfide (CS2) wereinvestigated during nine oceanographic cruises carried out in six majortidal European estuaries between July 1996 and May 1998. Low levels ofDMS were recorded (mean of 0.6 nM, standard deviation (σ) 0.3 nM)during these 9 cruises. Positive correlations between DMS and salinitywere frequently observed, with the highest DMS concentrations in theplume of estuaries, which could be explained by change in phytoplanktonspeciation from estuarine to shelf waters. Strong correlation betweenDMSP and DMS was reported for most of the estuaries denoting a simpleconservative mixing of riverine and marine waters controlled by tide. Incontrast to DMS, significant levels of COS and CS2 with meanconcentrations of 220 ± 150 (pM; pM =10−12 M) and 25 ± 6 pM respectively wererecorded in four estuaries, indicating that estuaries could be asignificant source of these compounds.

High-resolution measurements of gas and aerosols’ chemical composition along with meteorological and turbulence parameters were performed over the Aegean Sea (AS) during an Etesian outbreak in the framework of the Aegean-GAME airborne campaign. This study focuses on two distinct Etesian patterns, with similarities inside the Marine Atmospheric Boundary Layer (MABL) and differences at higher levels. Under long-range transport and subsidence the pollution load is enhanced (by 17% for CO, 11% for O 3 , 28% for sulfate, 62% for organic mass, 47% for elemental carbon), compared to the pattern with a weaker synoptic system. Sea surface temperature (SST) was a critical parameter for the MABL structure, turbulent fluxes and pollutants’ distribution at lower levels. The MABL height was below 500 m asl over the eastern AS (favoring higher accumulation), and deeper over the western AS. The most abundant components of total PM 1 were sulfate (40-50%) and organics (30-45%). Higher average concentrations measured over the eastern AS (131 ± 76 ppbv for CO, 62.5 ± 4.1 ppbv for O 3 , 5.0 ± 1.1 μg m - 3 for sulfate, 4.7 ± 0.9 μg m - 3 for organic mass and 0.5 ± 0.2 μg m - 3 for elemental carbon). Under the weaker synoptic system, cleaner but more acidic air masses prevailed over the eastern part, while distinct aerosol layers of different signature were observed over the western part. The Aitken and accumulation modes contributed equally during the long-range transport, while the Aitken modes dominated during local or medium range transport.

High winter-time PM10, sulfate, nitrate and ammonium levels in Istanbul were investigated using a high resolution WRF/CMAQ mesoscale model system. The results suggested that the system was capable of producing the magnitudes. PM10 levels calculated by the model underestimated the observations with an average of 10 % at Bogazici University sampling station, whereas an overestimation of 12 % is calculated for all stations. Base case results together with the sensitivity studies pointed significant contribution of local sources.

A one-month experiment was performed at Amsterdam Island in January 1998, to investigate the factors controlling the short-term variations of atmospheric dimethylsulfide (DMS) and its oxidation products in the mid-latitudes remote marine atmosphere. High mixing ratios of DMS, sulfur dioxide (SO2) and dimethylsulfoxide (DMSO) have been observed during this experiment, with mean concentrations of 395 parts per trillion by volume (pptv) (standard deviation, σ = 285, n = 500), 114 pptv (σ = 125, n = 12) and 3 pptv (σ = 1.2, n = 167), respectively. Wind speed and direction were identified as the major factors controlling atmospheric DMS levels. Changes in air temperature/air masses origin were found to strongly influence the dimethylsulfoxide (DMSO)/DMS and SO2/DMS molar ratios, in line with recent laboratory data. Methanesulfonic acid (MSA) and non-sea-salt sulfate (nss-SO4 2−) mean concentrations in aerosols during this experiment were 12.2± 6.5 pptv (1σ, n=47) and 59 ± 33 pptv (1σ, n=47), respectively. Evidence of vertical entrainment was reported following frontal passages, with injection of moisture-poor, ozone-rich air. High MSA/ nss-SO4 2− molar ratios (mean 0.44) were calculated during these events. Finally following frontal passages, few spots in condensation nuclei (CN) concentration were also observed.

A new technique based on the nebulization/reflux principle (Cofer chamber mist) has been used to sample atmospheric dimethylsulfoxide (DMSO). DMSO is reduced to DMS by sodium borohydride (NaBH 4 ) and DMS is subsequently analyzed by gas chromatography. Recovery and reproducibility of the analysis are of the order of 90% and better than 10%, respectively. This analytical method has been also successfully applied to DMSO determinations in rainwater and aerosols.

Dimethylsulfide (DMS), sulfur dioxide (SO2), dimethylesulfoxide (DMSO), sulfate (SO2-4) and methanesulfonate (MSA) were measured at a coastal site, Pointe de Penmarc’h, over a 25 day period during May and June 1993. Measurements were also performed to estimate the DMS flux from the algal beds around the Penmarc’h lighthouse and from the surrounding sea water. Similar atmospheric measurements were conducted at a second site approximately 2 km inland from Penmarc’h. A comparison between the 2 sites indicates similar patterns of DMS concentration at each site, with values at the inland site being generally 10–15% lower. The concentrations of the aerosol phase products such as methanesulfonic acid and sulfate are examined in the light of air mass origins. The fraction of nss SO2-4 produced from biogenic sources is estimated to be less than 25%. The yield of MSA and DMSO from DMS oxidation are assessed from their relative concentrations and estimates of their atmospheric lifetime.

Dimethylsulfide (DMS) measurements in the seawater of the subtropical and the temperate western Indian Ocean were conducted for the first time from 3 December to 20 December 1997. In total, 443 surface seawater DMS determinations were performed between 24°–49° S and 50° E–77° E with a frequency of 1 sample every 10 km. An important spatial variability was observed in seawater DMS concentrations with values ranging from 0.9 to 35.8 nM. DMS maxima coincided in most cases with thermal fronts and were in reasonable agreement with mean pigment figures obtained from satellite observations. The deduced DMS fluxes are consistent with long-term observations of atmospheric DMS and rainwater concentrations of nss- SO4= and MSA measured at Amsterdam island (37° S, 77° E); then account for the differences observed in atmospheric DMS concentrations between Amsterdam island and Cape Grim, Indian Ocean monitoring stations.

The influence of NOx (NO+NO2) concentrations on the product distribution of the OH-initiated oxidation of DMS has been studied at room temperature using total NOx concentrations varying from 0 to ∼1800 ppbv (30–600 ppbv NO2 and 140–1760 ppbv NO). Clear trends in the formation yields of the products SO2, COS, MSA, MTF (methyl thiolformate), MSPN (methanesulphonyl peroxynitrate), DMSO and DMSO2 have been observed with variation in NOx. The presence of low levels of NO reduces the yields of both MTF and COS to zero. The formation yields of MSA and DMSO2 increase with increasing NOx concentration, whereas the yields of DMSO and SO2 decrease. The following approximate changes in the yield, not corrected for possible loss processes, have been measured for variation of NOx between 0 and ∼1800 ppbv: DMSO decreases from 20 to 3%S; DMSO2 increases from 3 to 15%S, SO2 decreases from 70 to 30%S and MSA increases from 4 to 17%S. Under the experiments conditions NOx levels of several tens of ppbv are required before a perceptible change is observed in the MSA yield. If applicable to the atmosphere such a situation is only likely to be observed near coastal areas affected by pollution. MSPN (CH3SO2O2NO2) is observed as an oxidation product in the presence of NO2 even at low levels (e.g. 60 ppbv). Its possible role as a NOx reservoir in the troposphere is considered.

A continuous record of dimethylsulfoxide (DMSO) in rainwater was performed at Amsterdam island (37°S 77°E) from December 1995 to February 1997. Eighty one rainwater samples were collected. DMSO, methanesulfonic acid (MSA), the major anions, and cations were analyzed. DMSO concentrations ranged from 7.0 to 369 nM, with a distinct seasonal variation. The mean concentrations during the summer and the winter periods were 90 nM and 25.6 nM respectively. The observed DMSO seasonal cycle is in line with the observations of DMS in the atmosphere and MSA in rainwater, measured simultaneously during the reported period. However, the summer to winter ratio of DMSO is significantly lower than that observed for DMS and MSA. The DMSO to MSA ratio and its observed seasonal variability are also presented. The implications on the biogenic sulfur cycle are discussed.

Studies describing the chemical composition of fine aerosol (PM2.5) in urban areas are often conducted during few weeks only, and at one sole site, giving thus a narrow view of their temporal and spatial characteristics. This paper presents a one-year (11 September 2009–10 September 2010) survey of the daily chemical composition of PM2.5 in the region of Paris, which is the second most populated "Larger Urban Zone" in Europe. Five sampling sites representative of suburban (SUB), urban (URB), northeast (NER), northwest (NWR) and south (SOR) rural backgrounds were implemented. The major chemical components of PM2.5 were determined including elemental carbon (EC), organic carbon (OC), and the major ions. OC was converted to organic matter (OM) using the chemical mass closure methodology, which leads to conversion factors of 1.95 for the SUB and URB sites, and 2.05 for the three rural ones. On average, gravimetrically determined PM2.5 annual mass concentrations are 15.2, 14.8, 12.6, 11.7 and 10.8 μg m−3 for SUB, URB, NER, NWR and SOR sites, respectively. The chemical composition of fine aerosol is very homogeneous at the five sites and is composed of OM (38–47%), nitrate (17–22%), non-sea-salt sulfate (13–16%), ammonium (10–12%), EC (4–10%), mineral dust (2–5%) and sea salt (3–4%). This chemical composition is in agreement with those reported in the literature for most European environments. On the annual scale, Paris (URB and SUB sites) exhibits its highest PM2.5 concentrations during late autumn, winter and early spring (higher than 15 μg m−3 on average, from December to April), intermediates during late spring and early autumn (between 10 and 15 μg m−3 during May, June, September, October, and November) and the lowest during summer (below 10 μg m−3 during July and August). PM levels are mostly homogeneous at the regional scale, on the whole duration of the project (e.g. for URB plotted against NER sites: slope = 1.06, r2 = 0.84, n = 330), suggesting the importance of mid- or long-range transport, and regional instead of local scale phenomena. During this one-year project, two third of the days exceeding the PM2.5 2015 EU annual limit value of 25 μg m−3 were due to continental import from countries located northeast, east of France. This result questions the efficiency of local, regional and even national abatement strategies during pollution episodes, pointing the need for a wider collaborative work with the neighbourhood countries on these topics. Nevertheless, emissions of local anthropogenic sources lead to higher levels at the URB and SUB sites compared to the others (e.g. 26% higher on average at the URB than at the NWR site for PM2.5, during the whole campaign), which can even be emphasised by specific meteorological conditions such as low boundary layer heights. OM and secondary inorganic species (nitrate, non-sea-salt sulfate and ammonium, noted SIA) are mainly imported by mid- or long-range transport (e.g. for NWR plotted against URB sites: slope = 0.79, r2 = 0.72, n = 335 for OM, and slope = 0.91, r2 = 0.89, n = 335 for SIA) whereas EC is primarily locally emitted (e.g. for SOR plotted against URB sites: slope = 0.27; r2 = 0.03; n = 335). This database will serve deepest investigations of carbonaceous aerosols, metals as well as the main sources and geographical origins of PM in the region of Paris.

To assess sources and major processes controlling vertical transport of both anthropogenic and natural chemical species in deep basins of the Eastern Mediterranean Sea (SE Ionian Sea, Nestor site), we performed chemical characterization (elemental carbon, major and trace metals and polycyclic aromatic hydrocarbons) of marine sinking particles. Sediment traps were deployed at five successive depths, 700 m, 1200 m, 2000 m, 3200 m and 4300 m from the sea surface, during the period of May 2007 to October 2008. Fluxes of all measured species exhibited minimum values from January to March 2008 and maximum from April to September 2008, with an evident covariance revealing a common and rapid vertical transport mechanism from 700 m down to 4300 m depth. Crustal matter flux from atmospheric deposition plays an important role in the temporal variability of particulate matter with significant contribution from biogenic constituents namely the seasonal succession in the export of planktonic biomass, expressed by particulate organic carbon (POC), carbonates and biogenic Si fluxes (Stavrakakis et al., 2012). Tracers (elemental carbon, retene) of the devastating forest fires occurred in August 2007 in southern Greece, were detected at sediment trap material in all depths with a delay of 15 days at 4300 m, indicating a rapid and well-coupled transport of sinking particulate material between the sea-surface and deep layers of the Eastern Mediterranean Sea. Lateral inputs of pollutants at the deepest trap (4300 m) are probably of importance, due to the influence of deep Adriatic water at the study site.

Time series of photolysis rates of ozone (JO1D) and nitrogen dioxide (JNO2), for the period 2002–2006, at the remote coastal Finokalia station on Crete Island (25°60′E, 35°24′N), were used in order to investigate the factors that control their levels and their temporal characteristics. The study focuses on the main climatological aspects of the photolysis rates and investigation of the factors that control their variability, with emphasis on the quantification of aerosol and total ozone effects. The average Aerosol Optical Depth in the area which equals to 0.27 ± 0.13, leads to percentage reduction of JNO2 in the range 5–14% at 60° solar zenith angle (sza). For typical ozone column content (300–315 DU) the respective range of reduction for JO1D is 8–24%. Overall, at regional AOD background levels (~0.1) the percentage reduction of both JNO2 and JO1D is lower than 6%, in the range of sza 15–75°. Dust is shown to be 1.5 times more efficient absorber than average aerosol types in the area. During high aerosol loads (AOD 0.5–0.7) the percentage reduction of Js can raise to 40% for high sza.

Trace gases concentrations in the boundary layer (BL) and the free troposphere are studied in the Eastern Mediterranean based on an updated nested-grid application of GEOS-CHEM global model and airborne observations that were collected over the Greek territory during the AEGEAN GAME airborne field campaign in September 2011. Modelled concentrations are studied against measurements along the flight tracks. Moreover, the spatial distribution of the pollutants over the study domain is examined in relation to the prevailing wind regime. The role of the long-range transport of pollution is investigated particularly through the northern and eastern boundaries due to the prevailing NE circulation. It is found that the model captures adequately carbon monoxide (CO) and ozone (O3) levels within the troposphere. CO and O3 concentrations over the Aegean Sea can exceed the background levels attributed either to transport downwind the local sources or to long range transport particularly from the northern and eastern part of the domain under the strong NE Etesian winds.

Atmospheric samples collected during rice straw burning at four different locations in Viet-Nam during the dry (March 1992, February 1993) and wet season (August 1992) were analysed for CO2, CO, and CH4. The emission ratios relative to CO2 for CO and CH4 for rice straw burning during the dry season were comparable to those observed on samples collected during burning of savanna in Africa or forest in the USA. During the wet season, however the emission ratios for CO and CH4 relative to CO2 were 3 to 10 times higher. With these emission ratios and estimates of rice production from Southeastern Asia, we estimated that burning of rice straw emits annually about 2.2 Tmol of CO (26 TgC) and 0.2 Tmol of CH4 (2.4 TgC) to the atmosphere. Taking into account these new results, CO and CH4 fluxes from biomass burning could be reevaluated by 5-21% and 5-24%, respectively, in respect with previous estimates of these gas emissions from all biomass burning activities.

The products of the 254 nm photolysis of ppm levels of DMDS have been studied as a function of the O2 partial pressure at 760 Torr (N2 + O2) and 298±2 K. The major sulfur containing compounds detected were SO2 and CH3SO3H (methane sulfonic acid, MSA) and the major carbon containing compounds were CO, HCHO, CH3OH and CH3OOH (methyl hydroperoxide). Within the experimental error limits the observed sulfur and carbon balances were approximately 100%. CH3OOH has been observed for the first time in such a photooxidation system. Its observation provides evidence for the formation of CH3 radicals by the further oxidation of the CH3S radicals formed in the primary photolysis step. From the behavior of the DMDS photolysis products as a function of the O2 partial pressure, O3 concentration and added OH radical source it is postulated that the further reactions of CH3SOH (methyl sulfenic acid), formed in the reaction OH + CH3SCCH3 → CH3SOH + CH3S, are the main source of MSA in the 254 nm photolysis of DMDS. Some of the possible implications of the results of this study for the degradation mechanisms of other atmospherically important organic sulfur compounds, in particular DMS, are briefly considered.

Organic acids attract increasing attention as contributors to atmospheric acidity, secondary organic aerosol mass and aerosol hygroscopicity. Oxalic acid is globally the most abundant dicarboxylic acid, formed via chemical oxidation of gas-phase precursors in the aqueous phase of aerosols and droplets. Its lifecycle and atmospheric global distribution remain highly uncertain and are the focus of this study. The first global spatial and temporal distribution of oxalate, simulated using a state-of-the-art aqueous-phase chemical scheme embedded within the global 3-dimensional chemistry/transport model TM4-ECPL, is here presented. The model accounts for comprehensive gas-phase chemistry and its coupling with major aerosol constituents (including secondary organic aerosol). Model results are consistent with ambient observations of oxalate at rural and remote locations (slope = 1.16 ± 0.14, r2 = 0.36, N = 114) and suggest that aqueous-phase chemistry contributes significantly to the global atmospheric burden of secondary organic aerosol. In TM4-ECPL most oxalate is formed in-cloud and less than 5 % is produced in aerosol water. About 62 % of the oxalate is removed via wet deposition, 30 % by in-cloud reaction with hydroxyl radical, 4 % by in-cloud reaction with nitrate radical and 4 % by dry deposition. The in-cloud global oxalate net chemical production is calculated to be about 21–37 Tg yr−1 with almost 79 % originating from biogenic hydrocarbons, mainly isoprene. This condensed phase net source of oxalate in conjunction with a global mean turnover time against deposition of about 5 days, maintain oxalate's global tropospheric burden of 0.2–0.3 Tg, i.e. 0.05–0.1 Tg-C that is about 5–9 % of model-calculated water soluble organic carbon burden.

Simultaneous measurements of rain acidity and dimethyl sulfide (DMS) at the ocean surface and in the atmosphere were performed at Amsterdam Island over a 4 year period. During the last 2 years, measurements of sulfur dioxide (SO2) in the atmosphere and of methane sulfonic acid (MSA) and non-sea-salt-sulfate (nss-SO4 2-) in rainwater were also performed. Covariations are observed between the oceanic and atmospheric DMS concentrations, atmospheric SO2 concentrations, wet deposition of MSA, nss-SO4 2-, and rain acidity. A comparable summer to winter ratio of DMS and SO2 in the atmosphere and MSA in precipitation were also observed. From the chemical composition of precipitation we estimate that DMS oxidation products contribute approximately 40% of the rain acidity. If we consider the acidity in excess, then DMS oxidation products contribute about 55%.

This study examines the chemical composition of aerosols over the Greater Istanbul Area. To achieve this 325 (PM(10)) aerosol samples were collected over Bosphorus from November 2007 to June 2009 and were analysed for the main ions, trace metals, water-soluble organic carbon (WSOC), organic (OC) and elemental carbon (EC). PM(10) levels were found to be in good agreement with those measured by the Istanbul Municipality air quality network, indicating that the sampling site is representative of the Greater Istanbul Area. The main ions measured in the PM(10) samples were Na(+), Ca(2+) and non-sea-salt sulphates (nss-SO(4)(2-)). On average, 31% of Ca(2+) was found to be associated with carbonates. Trace elements related to human activities (as Pb, V, Cd and Ni) obtained peak values during winter due to domestic heating, whereas natural origin elements like Al, Fe and Mn peaked during the spring period due to dust transport from Northern Africa. Organic carbon was found to be mostly primary and elemental carbon was strongly linked to fuel oil combustion and traffic. Both OC and EC concentrations increased during winter due to domestic heating, while the higher WSOC to OC ratio during summer can be mostly attributed to the presence of secondary, oxidised and more soluble organics. Factor analysis identified six components/sources for aerosol species in PM(10), namely traffic/industrial, crustal, sea-salt, fuel-oil combustion, secondary and ammonium sulfate.