Regensburg 2007 – wissenschaftliches Programm
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UP: Fachverband Umweltphysik
UP 6: Heterogene Prozesse in der Atmosphäre - gemeinsam mit dem Arbeitskreis Athmosphärenchemie (AKAC) der GDCh
UP 6.6: Hauptvortrag
Montag, 26. März 2007, 16:00–16:30, H48
Heterogeneous conversion of nitrogen oxides: Sources of nitrous acid (HONO) — •Jörg Kleffmann — Bergische Universität Wuppertal, D-42097 Wuppertal
Heterogeneous reactions of nitrogen oxides play an important role in atmospheric chemistry. For example, the heterogeneous hydrolysis of N2O5 is a significant sink of NOx in both, the stratosphere and troposphere, strongly affecting ozone concentration and acid rain formation, respectively. Another example is the heterogeneous formation of nitrous acid (HONO) by different reactions of nitrogen oxides. Nitrous acid is of considerable atmospheric interest since the photolysis leads to the formation of the OH radical, the key atmospheric oxidant in the degradation of most air pollutants and a crucial intermediate in the formation of photochemical smog in the troposphere. Recent field studies have demonstrated that the contribution of HONO to the oxidation capacity of the atmosphere has been underestimated and demonstrated that HONO may be the most important OH radical source in the lower atmosphere. Several different sources of nitrous acid have been postulated during the last decades, which are still under controversial discussion. In addition to direct emission, heterogeneous pathways are most probably responsible for the observed HONO formation in the atmosphere. Based on field and laboratory studies, strong photochemical sources involving nitrogen oxides have been postulated to explain the high daytime concentrations of HONO in the atmosphere. The different sources of HONO by heterogeneous conversion of nitrogen oxides, including photochemical reactions, will be discussed in the present study.