Variability in Nocturnal Nitrogen Oxide Processing and Its Role in Regional Air Quality

Abstract
Nitrogen oxides in the lower troposphere catalyze the photochemical production of ozone (O 3 ) pollution during the day but react to form nitric acid, oxidize hydrocarbons, and remove O 3 at night. A key nocturnal reaction is the heterogeneous hydrolysis of dinitrogen pentoxide, N 2 O 5 . We report aircraft measurements of NO 3 and N 2 O 5 , which show that the N 2 O 5 uptake coefficient, g(N 2 O 5 ), on aerosol particles is highly variable and depends strongly on aerosol composition, particularly sulfate content. The results have implications for the quantification of regional-scale O 3 production and suggest a stronger interaction between anthropogenic sulfur and nitrogen oxide emissions than previously recognized.