Relationship between peroxyacetyl nitrate and nitrogen oxides in the clean troposphere

Abstract

Nitrogen oxides have a key role in the chemistry of the polluted and the unpolluted atmosphere1–4. It has been proposed that important quantities of nitrogen oxides may be contained in the form of peroxyacetyl nitrate (PAN) especially in the colder regions of the middle and upper troposphere5,6. Surface and aircraft observations of PAN have confirmed its ubiquity in the remote troposphere where it has been measured at mixing ratios of 10–500 p.p.t.v. (parts per 1012 v/v) (refs 7,8). To date, no study that is representative of the remote atmosphere has been made to assess directly the concentrations of PAN compared with that of the inorganic nitrogen oxides (NO and NO2). Here we present the first study in which the mixing ratios of PAN, and nitrogen oxides—as wellas those of peroxypropionyl nitrate (PPN) and O3 and relevant meteorological parameters—were measured concurrently at a location that receives clean, continental air. The results show that in clean conditions nitrogen oxides present in the form of PAN can be as much or more abundant than the inorganic form.