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

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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) × 10−6; 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.