Effects of the increased UV radiation and biogenic VOC emissions on ultrafine sulphate aerosol formation

A sectional model (AEROFOR) for the formation of sulphuric acid-water particles has been developed. The model includes gas-phase chemistry and aerosol dynamics. An increased UV-B irradiation penetrating into the troposphere due to stratospheric ozone depletion causes via the SO2 oxidation route an enhanced nucleation potential for new H2SO4-H2O particles as well as the growth of particles to CCN size. Using AEROFOR we show that after a nucleation event the nucleated particle concentration is linearly dependent on increased UV-B irradiation with a positive slope. On the other hand, due to increased CO2 concentration photosynthetic rates of plants will increase, and it is likely that enhanced photosynthesis in forests will increase emissions of biogenic volatile organic compounds (BVOC) such as isoprene and monoterpenes, We show that the nucleated particle concentration decreases with increasing BVOC emission, but this dependence is not linear. We investigate the strength of these opposite effects and fit a straight line for such UV-B and BVOC conditions which yield a certain particle number density. The coupling between O-3, OH and particle concentrations as a function of UV-B and BVOC emission is also demonstrated. (C) 1999 Elsevier Science Ltd. All rights reserved.