Nitrous oxide in coastal waters

We determined atmospheric and dissolved nitrous oxide (N2O) in the surface waters of the central North Sea, the German Bight, and the Gironde estuary. The mean saturations were 104 ± 1% (central North Sea, September 1991), 101 ± 2% (German Bight, September 1991), 99 ± 1% (German Bight September 1992), and 132% (Gironde estuary, November 1991). To evaluate the contribution of coastal areas and estuaries to the oceanic emissions we assembled a compilation of literature data. We conclude that the mean saturations in coastal regions (with the exception of estuaries and regions with upwelling phenomena) are only slightly higher than in the open ocean. However, when estuarine and coastal upwelling regions are included, a computation of the global oceanic N2O flux indicates that a considerable portion (approximately 60%) of this flux is from coastal regions, mainly due to high emissions from estuaries. We estimate, using two different parameterizations of the air-sea exchange process, an annual global sea-to-air flux of 11–17 Tg N2O. Our results suggest a serious underestimation of the flux from coastal regions in widely used previous estimates

Chemical characterization of the inorganic fraction of aerosols and mechanisms of the neutralization of atmospheric acidity in Athens, Greece

The PM<sub>10</sub> mass concentration levels and inorganic chemical composition were determined on 12-h resolution sampling during August 2003 and March 2004, in the centre of Athens, Greece. The August 2003 campaign mean PM<sub>10</sub> mass concentration, obtained by Beta Attenuation at 5 m above ground in Athinas Street, was 56 μg m<sup>−3</sup> while the corresponding value for March 2004 was 92 μg m<sup>−3</sup>. In both campaigns the E.U. imposed daily limit of 50 μg m<sup>−3</sup> was exceeded on several days. During the March campaign, in Athinas Street, additionally obtained DSFU-PM<sub>10</sub> (PM<sub>10-2.5</sub>+PM<sub>2.5</sub>) gravimetric mass concentrations (mean: 121 μg m<sup>−3</sup>) in the "breathing zone", at 1.5 m above ground were significantly higher compared to the respective mean PM<sub>10</sub> mass concentrations obtained by the same method at 25 m above ground, in a second site (AEDA; mean: 86 μg m<sup>−3</sup>) also in the centre of the city. The above findings suggest that, for a realistic estimation of the exposure of citizens to particulate matter, PM<sub>10</sub> sampling in the "breathing zone" (1.5–3 m above ground) is necessary. Such data are presented for the first time for the centre of Athens. In both campaigns, calcium was found to be the predominant component of the coarse fraction while crust-related aluminosilicates and iron were the other major components. The above elements constitute the most important components of the fine fraction, together with the predominant sulphur. All toxic metals were found in concentrations below the established air quality limits, and most of them in lower concentrations compared to older studies. Lead in particular, appeared mostly in the fine fraction and in very low concentrations compared to studies dating more than a decade back. The predominant ions of the coarse fraction have been found to be Ca<sup>2+</sup>, NO<sub>3</sub><sup>−</sup>, Na<sup>+</sup> and Cl<sup>−</sup>, while SO<sub>4</sub><sup>2−</sup>, Ca<sup>2+</sup> and NH<sub>4</sub><sup>+</sup> were the major ionic components of the fine fraction. In the fine particles, a low molar ratio of NH<sub>4</sub><sup>+</sup>/SO<sub>4</sub><sup>2−</sup> indicated an ammonium-poor ambient air, and together with inter-ionic correlations suggested that atmospheric ammonia is the major neutralizing agent of sulfate, while being insufficient to neutralize it to full extend. The formation of NH<sub>4</sub>NO<sub>3</sub> is therefore not favored and additional contribution to the neutralization of acidity has been shown to be provided by Ca<sup>2+</sup> and Mg<sup>2+</sup>. In the coarse particle fraction, the predominantly abundant Ca<sup>2+</sup> has been found to correlate well with NO<sub>3</sub><sup>−</sup> and SO<sub>4</sub><sup>2−</sup>, indicating its role as important neutralizing agent in this particle size range. The proximity of the location under study to the sea explains the important concentrations of salts with marine origin like NaCl and MgCl<sub>2</sub> that were found in the coarse fraction, while chloride depletion in the gaseous phase was found to be limited to the fine particulate fraction. Total analyzed inorganic mass (elemental+ionic) was found to be ranging between approximately 25–33% of the total coarse particle mass and 35–42% of the total fine particle mass

Effects of methane outgassing on the Black Sea atmosphere

International audienceMethane in air and seawater was measured in the Eastern Black Sea during the 10?18 December 1999 BIGBLACK project cruise. The measurements allowed for the calculation of supersaturation ratios and methane fluxes across the air-sea interface. CH4 mixing ratios in air were generally in the 1.8?2.0 ppmv range, while surface (4 m depth) seawater concentrations varied from 5 to 100 ppmv. Above active seep areas, the water was supersaturated at around 500% with respect to the overlying atmosphere. Accordingly, flux densities varied greatly and were up to 4000 umol m-2 day-1. In the Sevastopol harbour, supersaturations up to around 3000%, similar to those at the Danube Delta, were observed, while in the Istanbul harbour supersaturations could not be determined because the very high values of water concentrations have led to detector saturation. Simple modelling shows that the observed fluxes do not have any substantial impact in the methane content of the Black Sea atmosphere, as they could only raise its concentrations by less than 1 ppb. On the other hand, calculations performed as part of the CRIMEA project, show that mud volcano eruptions could episodically raise the methane concentrations well above their regional background for several tens of kilometres downwind

Chemical characterization of the inorganic fraction of aerosols and mechanisms of the neutralization of atmospheric acidity in Athens, Greece

International audienceMass concentration levels and the inorganic chemical composition of PM10 (two fractions; PM10?2.5 and PM2.5) were determined during August 2003 and March 2004, in the centre of Athens, Greece. August 2003 monthly mean PM10 mass concentration, at 5 m above ground, was 56 ?g/m3 and the EU imposed daily limit of 50 ?g/m3 was exceeded on 16 occasions. The corresponding monthly mean for March 2004 was 92 ?g/m3 and the aforementioned daily limit was exceeded on 23 occasions. The PM10 (PM10?2.5+PM2.5) mass concentrations at 1.5 m above ground were found to be approximately 20% higher compared to the respective PM10 measured at 5 m. Consequently, for a realistic estimation of the exposure of citizens to particulate matter, PM10 sampling at a height of 1.5?3 m above ground, in the "breathing zone" is necessary. Such data are presented for the first time for the centre of Athens. In both campaigns, calcium was found to be the predominant component of the coarse fraction while crust-related aluminosilicates and iron were found to be the other major components of the same fraction. The above elements constitute the most important components of the fine fraction, together with the predominant sulphur. Toxic metals were found to be below the air quality limits and in lower concentrations compared to older studies, with the exception of Cu and V for which some increase was observed. Pb, in particular, appeared mostly in the fine fraction and in very low concentrations compared to studies dating more than a decade back. The major ions of the coarse fraction have been found to be Ca2+, NO3? and Cl?, while SO4?2, Ca2+ and NH4+ were the major ionic components of the fine fraction. The low molar ratio of NH4+/SO4?2 indicated an ammonium-poor ambient air, where atmospheric ammonia is not sufficient to neutralize all acidity and the formation of NH4NO3 does not occur to a significant extend. Calcium predominated the coarse fraction and its good correlations with NO3? and SO4?2 indicated its role as an important neutralizing agent of atmospheric acidity in this particle size range. In the fine fraction, both Ca2+ and NH4+ participate in the neutralizing processes with NH4+ being the major neutralizing agent of SO4?2. Chloride depletion from NaCl or MgCl2 was not found to occur to a significant extend. Total analyzed inorganic mass (elemental+ionic) was found to be ranging between approximately 25?33% of the total coarse particle mass and 35?42% of the total fine particle mass

Nitrous oxide emissions from the Arabian Sea

Dissolved and atmospheric nitrous oxide (N2O) were measured on the legs 3 and 5 of the R/V Meteor cruise 32 in the Arabian Sea. A cruise track along 65°E was followed during both the intermonsoon (May 1995) and the southwest (SW) monsoon (July/August 1995) periods. During the second leg the coastal and open ocean upwelling regions off the Arabian Peninsula were also investigated. Mean N2O saturations for the oceanic regions of the Arabian Sea were in the range of 99–103% during the intermonsoon and 103–230% during the SW monsoon. Computed annual emissions of 0.8–1.5 Tg N2O for the Arabian Sea are considerably higher than previous estimates, indicating that the role of upwelling regions, such as the Arabian Sea, may be more important than previously assumed in global budgets of oceanic N2O emissions

The Aegean Sea as a source of atmospheric nitrous oxide and methane

During the EGAMES (Evasion of GAses from the MEditerranean Sea) expedition in July 1993 we determined the concentrations of nitrous oxide and methane in the atmosphere and in the surface waters of the Aegean Sea, the northwestern Levantine Basin, the eastern Ionian Sea and the Amvrakikos Bay. Both gases were found to be supersaturated in all sampled areas. Nitrous oxide was homogeneously distributed with a mean saturation of 105 ± 2%, showing no differences between shelf and open ocean areas, whereas methane saturation values ranged from about 1.2 times (northwestern Levantine Basin) to more than 5 times solubility equilibrium (Amvrakikos Bay estuary). Therefore the Aegean Sea and the adjacent areas were sources of atmospheric nitrous oxide and methane during the study period

Distribution of dissolved inorganic carbon and related parameters in the Thermaikos Gulf (Eastern Mediterranean)

Data on the distribution of dissolved inorganic carbon (measured as TCO2) and related parameters in the Thermaikos Gulf were obtained during May 1997. High TCO2 concentrations were recorded close to the bottom, especially in the northern part of the gulf, as a result of organic matter remineralisation. The positive relatively good correlation between TCO2 and both apparent oxygen utilisation (AOU) and phosphate at the last sampling depth confi rmed the regenerative origin of a large proportion of TCO2. The comparatively conservative behaviour of alkalinity, together with the relatively low value of the homogenous buffer factor β (β = ∂lnfCO2/∂lnTCO2) revealed that calcifi cation or carbonate dissolution takes place on a very small scale, simultaneously with the organic carbon production. The correlations between fCO2 and chlorophyll α, as well as AOU and the surface temperature, revealed that the carbon dioxide fi xation through the biological activity is the principal factor that modulates the variability of fCO2. A rough first estimate of the magnitude of the air-sea CO2 exchange and the potential role of the Thermaikos Gulf in the transfer of atmospheric CO2 was also obtained. The results showed that during May 1997, the Thermaikos Gulf acted as a weak sink for atmospheric CO2 at a rate of -0.60 - -1.43 mmol m-2 d-1, depending on which formula for the gas transfer velocity was used, and in accordance to recent reports regarding other temperate continental shelves. Extensive study of the dissolved inorganic carbon and related parameters, and continuous shipboard measurements of fCO2 a and fCO2 w during all seasons are necessary to safely quantify the role of the Thermaikos Gulf in the context of the coastal margins CO2 dynamics

Greenhouse gases in cold water filaments in the Arabian Sea during the Southwest Monsoon

The distribution of partial pressure of carbon dioxide and the concentrations of nitrous oxide and methane were investigated in a cold water filament near the coastal upwelling region off Oman at the beginning of the southwest monsoon in 1997. The results suggest that such filaments are regions of intense biogeochemical activity which may affect the marine cycling of climatically relevant trace gase

Nine years of UV aerosol optical depth measurements at Thessaloniki, Greece

Spectral measurements of the aerosol optical depth (AOD) and the Ångström coefficient were conducted at Thessaloniki, Greece (40.5° N, 22.9° E) between January 1997 and December 2005 with a Brewer MKIII double-monochromator spectroradiometer. The dataset was compared with collocated measurements of a second spectroradiometer (Brewer MKII) and a CIMEL sun-photometer, showing correlations of 0.93 and 0.98, respectively. A seasonal variation of the AOD was observed at Thessaloniki, with AOD values at 340 nm of 0.52 and 0.28 for August and December respectively. Back trajectories of air masses for up to 4 days were used to assess the influence of long-range transport from various regions to the aerosol load over Thessaloniki. It is shown that part of the observed seasonality can be attributed to air masses with high AOD originating from North-Eastern and Eastern directions during summertime. The analysis of the long-term record (9 years) of AOD showed a downward tendency. A similar decreasing tendency was found in the record of the PM$_{10}$ aerosol measurements, which are conducted near the surface at 4 air-quality monitoring stations in the area of the city of Thessaloniki

Methane in the surface waters of the Arabian Sea

More than 2000 measurements of atmospheric and dissolved methane (CH44) were performed in the central and northwestern Arabian Sea as part of the German JGOFS Arabian Sea Process Study during three cruises in March, May/June, and June/July 1997. Mean CH4 saturations in the surface waters of the central Arabian Sea were in the range of 103–107%. Significantly enhanced saturations were observed in the coastal upwelling area at the coast of Oman (up to 156%) and in an upwelling filament (up to 145%). The CH4 surface concentrations in the upwelling area were negatively correlated to sea surface temperatures. Area‐weighted, seasonally adjusted estimates of the sea‐air fluxes of CH4 gave annual emissions from the Arabian Sea of 11–20 Gg CH4, suggesting that previously reported very high surface CH4 concentrations might be atypical owing to the interannual variability of the Arabian Sea and that the emissions derived from them are probably overestimates