Production of N2O5 and ClNO2 through Nocturnal Processing of Biomass-Burning Aerosol

Biomass burning is a source of both particulate chloride and nitrogen oxides, two important precursors for the formation of nitryl chloride (ClNO 2 ), a source of atmospheric oxidants that is poorly prescribed in atmospheric models. We investigated the ability of biomass burning to produce N 2 O 5 (g) and ClNO 2 (g) through nocturnal chemistry using authentic biomass-burning emissions in a smog chamber. There was a positive relationship between the amount of ClNO 2 formed and the total amount of particulate chloride emitted and with the chloride fraction of nonrefractory particle mass. In every fuel tested, dinitrogen pentoxide (N 2 O 5 ) formed quickly, following the addition of ozone to the smoke aerosol, and ClNO 2 (g) production promptly followed. At atmospherically relevant relative humidities, the particulate chloride in the biomass-burning aerosol was rapidly but incompletely displaced, likely by the nitric acid produced largely by the heterogeneous uptake of N 2 O 5 (g). Despite this chloride acid displacement, the biomass-burning aerosol still converted on the order of 10% of reacted N 2 O 5 (g) into ClNO 2 (g). These experiments directly confirm that biomass burning is a potentially significant source of atmospheric N 2 O 5 and ClNO 2 to the atmosphere.