The loss of NO2, HNO3, NO3/N2O5, and HO2/HOONO2 on soot aerosol: A chamber and modeling study

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.): γ(NO2) ≤ 4 × 10-8; γ(HNO3→NO2) ≤ 3 × 10-7; γ(NO3) ≤ 3 × 10-4 (≤10-3); γ(N2O5, hydrolysis) = (4±2)×10-5 ((2±1)×10-4); γ(N2O5, reduction) = (4±2)x10-6; γ(HO2) ≤ 10-2; γ(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 2nd 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.