ION CHEMISTRY RELEVANT FOR CHEMICAL-IONIZATION DETECTION OF SO3

Rate constants and products were measured for over 50 ion-molecule rea ctions involving SO3 or ions formed from SO3. All negative ions studie d reacted with SO3 at or near the collisional rate by a variety of pro cesses including charge transfer, O- transfer, ligand exchange, and cl ustering. Ambient negative ions tended to form SO4- or SO4- core ions. A chemical ionization detection scheme for monitoring SO3 in the atmo sphere is presented based on CO3-(H2O)(n=0-1) or NO3-(H2O)(n=0-1) as t he primary ions. The proposed scheme can be used in conjunction with p revious schemes for monitoring SO2 and H2SO4 concentrations to measure all three gases simultaneously. The measurements also confirm that th e ion chemistry used in separate studies to monitor the reaction of SO 3 with H2O is correct and rapid and that the reaction of SO3 with posi tive ion water clusters does not contribute to H2SO4 production in the atmosphere.