Abstract
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.
Highlights
Aerosol particles in the atmosphere which comprised both soluble and insoluble aerosols, affect the earth’s radiation balance in both direct and indirect ways [1]
The direct effect is influenced by the hygroscopicity of the aerosol particles, while the indirect is the tendency for cloud formation and resulting cloud properties all due to changes in Relative humidity
Key factors in determining whether a particular aerosol has a net positive or negative direct radiative forcing influence on the Earth’s radiation budget include the spatial distribution of the aerosol, its physical state and associated optical properties Haywood and Boucher [7], which depend on the hygroscopicity of the aerosol [8]
Summary
Aerosol particles in the atmosphere which comprised both soluble and insoluble aerosols, affect the earth’s radiation balance in both direct and indirect ways [1]. The direct effect is influenced by the hygroscopicity of the aerosol particles, while the indirect is the tendency for cloud formation and resulting cloud properties all due to changes in Relative humidity. The direct effect causes the scattering and absorption of short-wave solar and long-wave thermal radiation by the aerosol particulates These changes in relative humidity modify the micro-physical (e.g., shape and size modification), chemical compositions (e.g. heterogeneous chemical reactions) and optical properties of the hygroscopic aerosol mixtures and mixtures containing some contribution of non-hygroscopic aerosols like for example organic carbon or black carbon [2] [3]. Atmospheric aerosols undergo heterogeneous chemistry as they are transported through the atmosphere These reactions cause Chemical Modification of the Atmosphere as well as Chemical Modification of the Airborne Mineral Dust Particles. Hygroscopic properties of aerosol particles can be determined by their physical and chemical characteristics [9] [10]
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