REACTIVE UPTAKE OF HNO3 AND H2SO4 IN SEA-SALT (NACL) PARTICLES

Kinetic information on the substitution of sea-salt chloride by nitrat e was deduced from a smog chamber investigation bn the reaction of air borne NaCl with HNO3. It was found that a measurable reaction only occ urred when the NaCl-particles were present in the form of droplets. Th e substitution of chloride by nitrate was independent of size, which s hows that the generation of the product (HCl gas) was the rare-limitin g reaction step. The rate of this reaction was more than an order of m agnitude slower than the rate at which nitric acid can reach the dropl ets. The substitution of chloride by sulphate, in a reaction between H 2SO4 and NaCl, depended on particle size from which it was concluded t hat the transport of H2SO4 to the aerosol was the rate-limiting proces s. The difference in reaction of the two acids is explained by tie fac t thar sulphuric acid is a condensable species, whereas nitric acid is a gas. From the amount of sulphate as a function of size an uptake co efficient for the condensing sulphuric acid was deduced as 0.1 or high er. (C) 1998 Elsevier Science Ltd. All rights reserved.