Seasonal variation of dimethylsulfide in the gas phase and of methanesulfonate and non-sea-salt sulfate in the aerosols phase in the Eastern Mediterranean atmosphere

The seasonal variation of gaseous dimethylsulfide (DMS) and its oxidation products (non-sea-salt sulfate (nss-SO42-) 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 3 2.35 +/- 1.38 nmol m(3), 1sigma 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 O-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 NO3 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), 1sigma uncertainty). Similarly aerosol nss-SO42- varied from 0.6 to 123.9 (average of 41.0 +/- 17.4 nmol m(-3), 1sigma uncertainty). Based on the measured MSA, nss-SO42- and their ratio, the biogenic contribution to nss-SO42- was found to exhibit a well-established seasonal pattern ranging from 1 % during winter to 17% during summer. (C) 2002 Elsevier Science Ltd. All rights reserved.