The Effect of Relative Humidity on Continental Average Aerosols

In this paper, the authors extracted and investigated the effect of relative humidity (RH) on some microphysical and optical properties of continental polluted aerosols from OPAC (Optical Properties of Aerosols and Clouds) at the spectral range of 0.25 μm to 2.5 μm and eight relative humidities (0%, 50%, 70%, 80%, 90%, 95%, 98%, and 99%). The microphysical properties extracted were radii, volume, number and mass mix ratios as functions of RH while the optical properties were optical depth, extinction, scattering and absorption coefficients single scattering albedo, refractive indices and asymmetric parameters also at eight RHs. Using the microphysical properties, effective hygroscopic growth factors and effective radii of the mixtures were determined while using optical properties we determined the enhancement parameters, effective refractive indices and angstrom coefficients. Using the effective hygroscopic growth, we determined the dependence of the effective hygroscopicity parameter as a function of RH, while using enhancement parameters; we determined the effect of humidification factor on RH and wavelengths. The effective hygroscopic growth and enhancement parameters were then parameterized using some models to determine the effective hygroscopicity parameter, bulk hygroscopicity and humidification factors. We observed that the data fitted the models very well. The effective radii decrease with the increase in RH while the effective hygroscopic growth increases with the increase in RH, and this is in line with the increase in angstrom parameters, and this shows increase in mode size with the increase in RH. The angstrom coefficients show that the mixture has a bimodal type of distribution with the dominance of fine mode particles.