Nitrous and nitric acid measurements during the INTERCOMP2000 campaign in Melpitz

Measurements were performed at the research site Melpitz (87 m a.s.l., 51 °32′ N and 12°54′E), 41 km north east of the Leipzig conurbation in spring 2000 to measure atmospheric nitrous and nitric acid concentrations, to compare available methods for these acids, and to investigate the distribution of particulate nitrate vs gaseous HNO3. Two different wet denuder methods were run side by side during the experiment: a wet effluent diffusion denuder (WEDD) and a rotating wet annular denuder (RWAN). The concentrations obtained for HONO with both methods agreed very well. At low relative humidity (RH) values, a good agreement was also observed for HNO3 between the two methods. However, significant differences were observed at RH values >80%. Both methods allow the measurement of atmospheric HONO and HNO3 with a fine time resolution even at very low concentration levels. Measurable daytime values for nitrous acid were observed and there were indications for heterogeneous formation. Storage of HONO or nitrite, respectively, on wet surfaces can be a source for observed daytime HONO.