NO3 measurements during MINOS campaign and their role in the oxidation capacity of Eastern Mediterranean atmosphere

M. Vrekoussis1, H. Berresheim2, V. Baboukas3, V. Gros3, M. Kanakidou1, J. Lelieveld3, N. Mihalopoulos1

1 University of Crete, Environmental Chemical Processes Laboratory (ECPL), P.O Box 1470, 71409 Heraclion, Greece (mvrek@chemistry.uoc.gr, mihalo@chemistry.uoc.gr)
2 Deutscher Wetterdienst Meteorologisches Observatorium (DWD)
3 Max Planck Institute for Chemistry, Airchemistry Department, Mainz, Germany


Free radicals are known to play an important role in atmospheric chemistry. It has been found, that in most cases, two radicals, the hydroxyl (OH) radical during daytime and the nitrate (NO3) during nighttime, by reacting with an important number of Volatile Organic Compounds regulate the oxidation capacity of the atmosphere. However, measurements of OH, NO3, have been proven difficult due to their high reactivity and the low concentration. Consequently the relative contribution of these two radicals to the oxidation capacity of the atmosphere is still an open question.
Simultaneous measurements of both radicals have been performed, for the first time to our knowledge, in the marine place in the southern Europe during the Minos campaign (25th of July to 18th of August 2001). Nitrate radical was measured using the Differential Optical Absorption Spectroscopy (DOAS) with a path of a total of 10.4 km. Hydroxyl radicals were measured by Chemical Ionization Mass-Spectrometer. OH radicals range from less than 105 molecules/cm3 during night up to 2.9.107 molecules/cm3 with a mean value of 5.6.106 molecules/cm3. On the other hand NO3 radical ranged from less than 3*107 molecules/cm3 up to 90.1*107 molecules/cm3 (on 12th of August) with an average value of 11.3*107 (molecules/cm3). Thus, on average, the NO3 levels exceed those of OH by a factor of 20. In these work the NO3 measurements will be presented in details and their relative contribution to degradation processes of species like dimethylsulfide (DMS), alkenes and alkanes will be examined.