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.): &ggr;(NO2)≤4¿10-8; &ggr;(HNO3→NO2)≤3¿10-7; &ggr;(NO3)≤3¿10-4(≤10-3); &ggr;(N2O5, hydrolysis)=(4¿2)¿10-5((2¿1)¿10-4); &ggr;(N2O5, reduction)=(4¿2)¿10-6; &ggr;(HO2)≤10-2; &ggr;(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 &mgr;g m-3 soot aerosol, mainly due to the heterogeneous loss of HO2. ¿ 2001 American Geophysical Union