The loss of NO 2 , HNO 3 , NO 3 /N 2 O 5 , and HO 2 /HOONO 2 on soot aerosol: A chamber and modeling study

The heterogeneous loss of NO 2 , HNO 3 , NO 3 /N 2 O 5 , and HO 2 /HO 2 NO 2 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 H 2 O (in parentheses: at 50% r.h.):γ(NO 2 ) ≤ 4× 10 −8 ; γ(HNO 3 →NO 2 ) ≤ 3× 10 −7 ; γ(NO 3 ) ≤ 3 × 10 −4 (≤10 −3 ); γ(N 2 O 5 , hydrolysis)=(4±2) ×10 −5 ((2±1 ) × 10 −4 ); γ(N 2 O 5 , reduction)=(4±2) × 10 −6 ; γ(HO 2 ≤ 10 −2 ; γ(HO 2 NO 2 ) ≤ 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 HO 2 .