A semi-analytical method for calculating rates of new sulfate aerosol formation from the gas phase

Abstract

The formation of new aerosol from the gas phase is commonly represented in atmospheric modeling with parameterizations of the steady state nucleation rate. Present parameterizations are based on classical nucleation theory or on nucleation rates calculated with a numerical aerosol model. These parameterizations reproduce aerosol nucleation rates calculated with a numerical aerosol model only imprecisely. Additional errors can arise when the nucleation rate is used as a surrogate for the production rate of particles of a given size. We discuss these errors and present a method which allows a more precise calculation of steady state sulfate aerosol formation rates. The method is based on the semi-analytical solution of an aerosol system in steady state and on parameterized rate coefficients for H2SO4 uptake and loss by sulfate aerosol particles, calculated from laboratory and theoretical thermodynamic data. et al., 2000; Kulmala et al., 2004a, and references therein). Among these, sulfuric acid stands out due to its very low vapor pressure, its numerous sources, and its ubiquity. In clean areas, such as over oceans, sulfuric acid appears as the driving force of secondary aerosol formation (Clarke, 1992; Brock et al., 1995), while over continents and in particular in the continental boundary layer, recently formed aerosol particles contain in addition to sulfate substantial amounts of ammonia (Smith et al., 2005) or organic matter (Allan et al., 2006; Cavalli et al., 2006), which may be involved in their formation process (Coffman and Hegg, 1995; Kulmala et al., 2004b). Secondary aerosol formation can significantly increase concentrations of aerosol particles and cloud condensation nuclei, and therefore requires dependable representations in atmospheric models (Kulmala et al., 2004a).