Atmospheric Environment 37 (2003) 195–208 Chemical composition of size-resolved atmospheric aerosols in the eastern Mediterranean during summer and winter H. Bardouki a , H. Liakakou a , C. Economou a , J. Sciare b , J. Smol ! ık c , V. $ Zd ! ımal c , K. Eleftheriadis d , M. Lazaridis e , C. Dye f , N. Mihalopoulos a, * a Environmental Chemical Processes Laboratory, Department of Chemistry, University of Crete, P.O. Box 1470, 71409 Heraklion, Greece b LSCE, Orme des Merisiers, Bat 709, CE Saclay, 91191 Gif-sur-Yvette Cedex, France c Institute of Chemical Process Fundamentals AS CR, Prague, Czech Republic d Institute of Nuclear Technology—Radiation Protection, N.C.S.R. ‘‘Demokritos’’, Athens, Greece e Technical University of Crete, Chania, Greece f NILU, PO Box 100, N 2007 Kjeller, Norway Received 29 May 2002; received in revised form 2 October 2002; accepted 9 October 2002 Abstract The chemical composition of aerosols has been determined in 30 size-resolved samples collected using a Berner low- pressure impactor during two campaigns conducted at a coastal site in the Eastern Mediterranean in July 2000 and in January 2001. Sulfate ðSO 2 4 Þ and ammonium ðNH þ 4 Þ have been identified as the main ionic components of the sub- micronic aerosol fraction, with SO 2 4 accounting for up to 38% of the total fine mass and up to 65% of the total ionic mass during both seasons. On the other hand, nitrate ðNO  3 Þ; chloride ðCl  Þ; sodium ðNa þ Þ and calcium ðCa 2þ Þ were identified as the main components of the super-micron mode. The ionic organic compounds (including carboxylic, dicarboxylic and ketoacids) were distributed both between sub-micron and super-micron mode, indicating origin from both gas-to-particle conversion and heterogeneous reactions on pre-existing particles. The total water-soluble ionic organic fraction although accounting for only up to 1–2% of both coarse ð> 1 mmÞ and fine ðo1 mmÞ mass fractions, accounts for up to 15% of the organic carbon (OC) mass. NH þ 4 was found to be significantly correlated to non-sea-salt sulfate (nss-SO 2 4 ), with NH þ 4 =nss-SO 2 4 molar ratio ranging from 1.3 to 2, the lower ratio associated with transport from the W sector. Chloride depletion was observed mainly during summer and was significantly correlated with NO  3 concentrations, with a molar ratio of 0.80, indicating the reaction of nitric acid with NaCl as the main source of NO  3 in the area. Total ionic mass both in the fine and coarse fraction accounted for up to 58% of the total aerosol mass during both seasons. An attempt to perform a mass closure analysis indicates that nss-SO 2 4 and organic carbon are the main components of the fine fraction with relative contributions of 38% and 16%, respectively. In the coarse fraction, the ionic part accounts for 58%, mineral dust for 32% and the remaining non-identified part of 12–30% could be partly attributed to water. r 2002 Elsevier Science Ltd. All rights reserved. Keywords: Size resolved aerosol composition; Regional pollution; Eastern Mediterranean 1. Introduction Atmospheric aerosols affect the Earth’s climate both directly through scattering and absorption of solar radiation and indirectly acting as cloud condensation AE International – Europe *Corresponding author. Tel.: +30-810-393-662; fax: +30- 810-393-601. E-mail address: mihalo@chemistry.uoc.gr (N. Mihalopoulos). 1352-2310/02/$-see front matter r 2002 Elsevier Science Ltd. All rights reserved. PII:S1352-2310(02)00859-2