Roles of So2 and secondary organics in the growth of nanometer particles in the lower atmosphere

A theoretical investigation on the influence of SO2 and secondary organics on the growth of nanometer particles was carried out. Depending on the ambient SO2 concentration, its reactive uptake coefficient with nuclei needs to reach values between about 0.0001 and 0.01 to make the nuclei grow into a CCN size within their atmospheric lifetime. The well-known liquid-phase reactions were shown to lead much lower uptake coefficients, being too slow to significantly assist nuclei growth under conditions typical of the lower troposphere. Potential existence of other reactions involving SO2, confined possibly on the nuclei surface layers, would be worth searching for experimentally in the laboratory. The influences of secondary organics on nuclei growth were shown to depend crucially on their thermodynamic properties. Only organics with sufficiently low volatility and high gas-phase production rate can contribute significantly to the growth. Because of the Kelvin effect, the nuclei initial growth is dictated by the condensation of the least volatile organics, or alternately of inorganic compounds, from the gas phase. Of organics found ubiquitously from the particulate phase in the lower troposphere, most can be considered rather unimportant for nanometer particle growth. (C) 1999 Elsevier Science Ltd. All rights reserved.