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 deliquesc ent, depending on relative humidity. According to their surface proper ties, aerosol particles are suspected, and in a number of cases have b een 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 prob abilities which were determined under typical laboratory conditions ma y 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 chem icals and/or modify their atmospheric residence times, will be reviewe d: hydrolysis of N2O5 On atmospheric aerosols; reactions of soot and o ther oxidising compounds on soot particles which exhibit pronounced su rface ageing effects; reactions of NO, and water vapour on soot and ot her particulate matter which generate HONO as a photochemical OH sourc e; reactions of OH radicals with surface-adsorbed non-volatile environ mental chemicals on aerosol particles, as well as their impact on atmo spheric residence times.