On alkyl nitrates, O3, and the "missing NOy"

Abstract

We describe measurements of NO2, total peroxy nitrates (∑PNs), total alkyl nitrates (∑ANs), and HNO3 using thermal dissociation followed by laser-induced fluorescence detection of NO2 at three continental locations. The ∑AN observations are unique and provide novel constraints on atmospheric photochemistry. At a rural site in California, measurements over a full annual cycle show that ∑ANs are routinely 10-20% of NOy. At this rural site, at a suburban site in California and an urban site in Houston, Texas, both the absolute concentration of ∑ANs and the fraction of the higher oxides of nitrogen (NOz) represented by ∑ANs are greater than or equal to values reported in any prior observations. Although the contrast with prior observations is striking, we show that large abundances of ∑ANs are consistent with simple chemical models of tropospheric ozone production and with the few prior comprehensive model studies. We also show that ∑ANs are a large part, if not all, of the "missing NOy" reported in many prior experiments and emphasize that the ratios of ∑ANs/NOz and Of O3/∑ANs are especially useful for evaluating chemical models and comparing observations at different sites. Copyright 2003 by the American Geophysical Union.