A simple analytical model of aerosol properties with account for hygroscopic growth 2. Scattering and absorption coefficients

A new microphysical model of aerosol size spectra accounting for hygroscopi c growth is used to calculate the aerosol scattering and absorption coeffic ients of solar and longwave radiation. Dependence of the extinction coeffic ient is explored theoretically, starting from the Junge [1963] power spectr a of the dry aerosol anti the Kohler equation [Khvorostyanov and Curry, thi s issue]. It is shown that the general dependence of the aerosol scattering and absorption coefficients on lambda and H can be presented in the form s igma similar to lambda(-gamma)(1-H)(R). This model explains both the empiri cal angstrom wavelength law and Kasten [1969] Hanel [1976] humidity law and identifies a functional relationship between them. The empirical coefficie nts of these laws are related to the aerosol microstructure and to each oth er by a very simple relationship. An explanation is offered for the spectra l behavior of the scattering coefficient and its variation with relative hu midity for various types of atmospheric hazes. It is shown that at very hig h humidities a dense haze with visibility less than kin may form under subs aturated conditions and without activated droplets. Application of this mod el to the longwave spectrum allows us to explain quantitatively the negativ e temperature dependence of atmospheric absorption in the atmospheric windo w without depending on the presence of water vapor dimers. Recommendations for aerosol optical and microphysical measurements are given. This simple m odel can be used as a tool in remote sensing for evaluation of aerosol scat tering and absorption optical thicknesses and for parameterization of aeros ol optical properties in general circulation and cloud models.