Modelling the formation of H2SO4-H2O particles

Abstract

This chapter focuses on the factors that affect the formation of new sulfuric acid particles in different atmospheric conditions. It uses atmospheric chemistry gas phase box model coupled with a three mode integral aerosol dynamics model. The simulations show the dependence of the concentration of nuclear mode particles on initial preexisting particles, the intensity of UV radiation, the emissions of dimethylsulphide (DMS), and the ratio of emissions of hydrocarbons and NOx present in air. Atmospheric aerosols have important effects on radiative transfer directly by absorbing and scattering incoming radiation or indirectly by acting as cloud condensation nuclei (CCN). The formation rate of new particles depends on preexisting particles, such as their number concentration, size distribution, and composition, and the amount of condensable vapors, in this case H2SO4 vapor. The concentration of sulfuric acid depends on the concentrations of OH-radicals, SO2, and in marine conditions, also SO3. The first depends on both the ratio of nonmethane hydrocarbons (HC) and nitrogen oxides (NOx) present in air and the intensity and wavelength of UV radiation. The anthropogenic sulfuric emissions and DMS emissions from the ocean determine the concentration of sulfuric oxides. Based on modeling, this chapter discusses how the concentration of H2SO4- H20 nucleation particles depends on the UV radiation, the ratio of HC and NOx, emissions, the DMS emissions, and the concentration of preexisting particles in different conditions (urban, marine, and rural).