[1] Fifteen years of ''equivalent'' black carbon (EBC) measurements (derived from aethalometer measurements of light absorption) made at Alert in Nunavut, Canada, and Point Barrow in Alaska, United States, were compared for the long-term trends and seasonal cycle. Over the 15-year period from 1989 to 2003, the results revealed a downward trend in EBC concentrations by as much as 54% at Alert and 27% at Barrow for the all-year data, by 49% at Alert and 33% at Barrow for the winter data, and by 53% at Alert for the summer. It was difficult to quantify if there was a decline during the summer for Barrow since there was no clear trend. The difference in trends might be related to changes in circulation in the Arctic, variable source contribution, and/or scavenging of particles. The results revealed that EBC concentrations were 40% higher during the positive phase of the North Atlantic Oscillation than during the negative phase. The source contributions at the two sites were determined by using trajectory analysis techniques, which revealed that Alert came under the influence of Siberia/Europe transport while Barrow showed influence from Siberian and Pacific/Asian transport.

[1] The recent decline in sea ice cover in the Arctic Ocean could affect the regional radiative forcing via changes in sea ice-atmosphere exchange of dimethyl sulfide (DMS) and biogenic aerosols formed from its atmospheric oxidation, such as methanesulfonic acid (MSA). This study examines relationships between changes in total sea ice extent north of 70 N and atmospheric MSA measurement at Alert, Nunavut, during 1980Nunavut, during -2009 at Barrow, Alaska, during 1997 and at Ny-Ålesund, Svalbard, for 1991. During the 1980-1989 and 1990 periods, summer (July-August) and June MSA concentrations at Alert decreased. In general, MSA concentrations increased at all locations since 2000 with respect to 1990 values, specifically during June and summer at Alert and in summer at Barrow and Ny-Ålesund. Our results show variability in MSA at all sites is related to changes in the source strengths of DMS, possibly linked to changes in sea ice extent as well as to changes in atmospheric transport patterns. Since 2000, a late spring increase in atmospheric MSA at the three sites coincides with the northward migration of the marginal ice edge zone where high DMS emissions from ocean to atmosphere have previously been reported. Significant negative correlations are found between sea ice extent and MSA concentrations at the three sites during the spring and June. These results suggest that a decrease in seasonal ice cover influencing other mechanisms of DMS production could lead to higher atmospheric MSA concentrations.

[1] Using both satellite observations of tropospheric NO 2 columns and a number of economic metrics, we investigate the impact of the economic crisis (from 2008 onward) on air quality over Greece, and Athens in particular. The multiannual analysis shows that NO 2 columns over Athens have been significantly reduced in the range 30-40%. This decline is further supported by surface measurements of atmospheric NO 2 mixing ratios. Additionally, the declining local concentrations of NO, CO, and SO 2 are associated with an increase in ozone due to reduced titration by NO. In particular, regression analysis revealed that the reduction of NO 2 (0.3 AE 0.2 ppbv y , respectively. The strong correlations between pollutant concentrations and economic indicators show that the economic recession has resulted in proportionally lower levels of pollutants in large parts of Greece. Citation: Vrekoussis, M

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