NOy speciation with a combined wet effluent diffusion denuder-aerosol collector coupled to ion chromatography

A wet effluent denuder-aerosol collector (WEDD/AC) system coupled to ion ch romatography for the measurement of atmospheric HONO, HNO3 and particulate nitrite, nitrate and sulfate is described. Several experiments were perform ed to outline its performance. The main features are low detection limits a nd a fast response to concentration changes which enables measurements with high time resolution. In contrast to highly soluble gases, the collection efficiency of less soluble gases is shown to depend on the Henry's law cons tant rather than on the uptake kinetics. To improve the collection efficien cy for HONO under simultaneous presence of acidifying gases, NaHCO3 was add ed to the effluent solution. The system was tested in a field campaign in t he suburban area of Zurich, Switzerland. Elevated concentrations of nitrous acid up to 3.2 ppb were detected during the measurement campaign. The diur nal variation of the HONO to NO2 ratio clearly points to a fast and persist ent process producing HONO in the atmosphere. The correlation with NOx and black carbon suggests a heterogeneous formation of MONO, and is consistent with a reaction on soot aerosol particle surfaces postulated from previous laboratory results. (C) 1999 Elsevier Science Ltd. All rights reserved.