Influence of peroxyacetyl nitrate (PAN) on odd nitrogen in the troposphere and lower stratosphere

Abstract

Nonmethane hydrocarbon breakdown in the atmosphere produces aldehydes of which a fraction are transferred into peroxyacetyl nitrates (PAN) in the presence of NO and NO 2. Since ethane is destroyed photochemically primarily above 1 km, PAN can be introduced into the upper troposphere and lower stratosphere without the need to be transported from the boundary layer where most hydrocarbons are destroyed and where PAN may be lost due to thermal decomposition and heterogeneous loss. Mixing ratios of ethane in the lower troposphere increase by a factor of 4–8 from equatorial to northern mid-latitudes. This difference is directly translatable into a PAN latitude gradient. At mid-latitudes the concentration of PAN below 20 km is 0.1 ppb comparable to and in some instances larger than predicted HO 2NO 2 mixing ratios. Like HO 2NO 2 and HNO 3, PAN serves as a reservoir for odd nitrogen.