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

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 tin parentheses: at 50% r.h.): (NO2) less than or equal to 4x10(-8); gamma (HNO3--> NO2)less than or equal to 3x10(-7); gamma (NO3)less than or equal to 3x 10(-4) (less than or equal to 10(-3)); gamma (N2O5, hydrolysis) = (4 +/-2)x10(-6); ((2 +/-1)x10(-4)); gamma (N2O5, reduction) = (4 +/-2)x10(-6); gamma (HO2) less than or equal to 10(-2); gamma (HO2NO2) less than or equal to 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 mug m(-3) soot aerosol, mainly due to the heterogeneous loss of HO2.