The Effect of Hygroscopic Growth on Urban Aerosols

Abstract

In this paper some microphysical and optical properties of urban aerosols were extracted from OPAC to determine the effect of hygroscopic growth at the spectral range of 0.25?m to 2.5?m and eight relative humidities (RHs) (0, 50, 70, 80, 90, 95, 98, and 99%). The microphysical properties extracted were radii, volume mix ratio, number mix ratio and mass mix ratio as a function of RH while the optical properties are scattering and absorption coefficients and asymmetric parameters. Using the microphysical properties, growth factors of the mixtures were determined while using optical properties we determined the enhancement parameters and were then parameterized using some models. We observed that the data fitted the models very well. The angstrom coefficients which determined the particles’ sizes distribution  increases with the increase in RHs except at the delinquent point where it decreases with the increase in RHs. The mixture was determined to have bimodal type of distribution with the dominance of fine mode particles.

Keywords: microphysical properties, optical properties, hygroscopic growth, parametrazition, enhancement parameters.