AIDA

Abstract. The heterogeneous loss of NO₂, HNO₃, NO₃ / N₂O₅, and HO₂ / HO₂NO₂ on soot aerosol was investigated in a large aerosol chamber for interaction times of up to several days. By fitting a detailed model to the measured time pro­files of the trace gas concentrations in the presence / absence of soot aerosol, the fol­lowing reaction probabilities have been deduced at 294 K and <10 ppm H₂O (in parentheses: at 50% r.h.): gamma(NO₂) = 4×10^-8; gamma(HNO₃->NO₂) = 3×10^-7; gamma(NO₃) = 3× 10^-4 (=10^-3); gamma(N₂O₅, hydrolysis) = (4±2)×10^-5 ((2±1)×10^-4); gamma(N₂O₅, reduction) = (4±2)×10^­6; gamma(HO₂) = 10^-2; gamma(HO₂NO₂) = 10^-5. These results were adopted in a series of box model calculations for four-day sum­mer smog episodes, probing a wide range of NO emission rates. The 2^nd day ozone maxima were reduced up to 10 % in the presence of 20 µg m^-3 soot aerosol, mainly due to the heterogeneous loss of HO₂.