Role of the NO 3 radicals in oxidation processes in the eastern Mediterranean troposphere during the MINOS campaign

During the MINOS campaign (28 July-18 Au- gust 2001) the nitrate (NO3) radical was measured at Fi- nokalia station, on the north coast of Crete in South-East Europe using a long path (10.4 km) Differential Optical Ab- sorption Spectroscopy instrument (DOAS). Hydroxyl (OH) radical was also measured by a Chemical Ionization Mass- Spectrometer (Berresheim et al., 2003). These datasets rep- resent the first simultaneous measurements of OH and NO 3 radicals in the area. NO3 radical concentrations ranged from less than 3◊10 7 up to 9◊10 8 radicals . cm 3 with an average nighttime value of 1.1◊10 8 radicals . cm 3 . The observed NO3 mixing ratios are analyzed on the ba- sis of the corresponding meteorological data and the volatile organic compound (VOC) observations which were mea- sured 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.