Heterogeneous processes involving atmospheric particulate matter

Atmospheric aerosol particles differ widely by size, surface area, and chemical composition. The particles are either dry solid or deliquescent, depending on relative humidity. According to their surface properties, aerosol particles are suspected, and in a number of cases have been shown, to interact with gaseous environmental chemicals, radicals, and other reactive intermediates. However, for many potential surface reactions the reaction probabilities are still unknown. Reaction probabilities which were determined under typical laboratory conditions may differ from reaction probabilities under real atmospheric conditions. The following classes of heterogeneous reactions, which directly or indirectly affect the degradation rates of airborne environmental chemicals and/or modify their atmospheric residence times, will be reviewed: hydrolysis of N2O5 On atmospheric aerosols; reactions of soot and other oxidising compounds on soot particles which exhibit pronounced surface ageing effects; reactions of NO, and water vapour on soot and other particulate matter which generate HONO as a photochemical OH source; reactions of OH radicals with surface-adsorbed non-volatile environmental chemicals on aerosol particles, as well as their impact on atmospheric residence times.