Two-years of NO3 radical observations in the boundary layer over the Eastern Mediterranean M. Vrekoussis1,*, N. Mihalopoulos1, E. Gerasopoulos1,**, M. Kanakidou1, P. J. Crutzen2, and J. Lelieveld2 1Environmental Chemical Processes Laboratory, Department of Chemistry, University of Crete, P.O. Box 2208, 71003 Voutes, Heraklion, Greece 2Max-Planck-Institut für Chemie, Abt. Luftchemie, Mainz, Germany *now at: Institute of Environmental Physics and Remote Sensing IUP/IFE, University of Bremen, Bremen, Germany **now at: Institute of Environmental Research and Sustainable Development, National Observatory of Athens, Athens, Greece
Abstract. This is the first study that investigates the seasonal variability of
nitrate (NO3) radicals in the marine boundary layer over the East
Mediterranean Sea. An extensive data set of NO3 radical observations on
the north coast of Crete for more than two years (June 2001–September 2003) is
presented here. NO3 radicals follow a distinct seasonal dependency with
the highest seasonally average mixing ratios in summer (5.6±1.2 pptv)
and the lowest in winter (1.2±1.2 pptv). Episodes with high NO3
mixing ratios have been encountered mainly in polluted air masses
originating from mainland Greece, Central and East Europe, and Turkey.
Ancillary measurements of ozone, nitrogen dioxide (NO2) and
meteorological parameters have been conducted and used to reveal possible
relationship with the observed NO3 variability. The acquired NO2
nighttime observations provide the up-to-date most complete overview of
NO2 temporal variability in the area. The data show correlations of the
NO3 nighttime mixing ratios with temperature (positive), relative
humidity (negative) and to a lesser extend with O3 (positive). As
inferred from these observations, on average the major sink of NO3
radicals in the area is the heterogeneous reaction of dinitrogen pentoxide
(N2O5) on aqueous particles whereas the homogeneous gas phase
reactions of NO3 are most important during spring and summer. These
observations support a significant contribution of NO3 nighttime
chemistry to the oxidizing capacity of the troposphere.
Citation: Vrekoussis, M., Mihalopoulos, N., Gerasopoulos, E., Kanakidou, M., Crutzen, P. J., and Lelieveld, J.: Two-years of NO3 radical observations in the boundary layer over the Eastern Mediterranean, Atmos. Chem. Phys., 7, 315-327, doi:10.5194/acp-7-315-2007, 2007.