ATMOSPHERIC NITROGEN-COMPOUNDS - OCCURRENCE, COMPOSITION AND DEPOSITION

Traffic in cities and on highways is an important contributor to NOy a tmospheric pollution in open areas. In this situation both the concent ration and composition of NOy compounds show a wide variation and are dependent on meteorological and atmospheric chemical conditions. The p roportion of NOz compounds (HNO3+nitrate+PAN+ PPN+N2O5+organic nitrate s) increases while that of NOx decreases with increasing ozone concent rations. The dry deposition velocity of NO2 was determined to be 0.2 c m s(-1) above vegetation. The dry deposition contribution of the diffe rent NOy compounds was evaluated. The possibility that a significant c ontribution is caused by a group of unidentified NOy compounds cannot be excluded. Therefore, future investigations of atmospheric pollution of sensitive ecosystems, at conditions with a relatively high atmosph eric content of NOy compared to that of NH3, ought to take into consid eration the possible contribution from unidentified NOy compounds. Thi s also implies that atmospheric research into the identity, occurrence , sources and sinks of these compounds-as well as further developments of sampling and analytical methods-should be given a high priority.