Abstract
The present work focused on the effect of relative humidity (RH) on some microphysical and optical properties of maritime tropical aerosols from the software package OPAC (Optical Properties of Aerosols and Clouds) data 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 mix ratio, number mix ratio and mass mix ratio as a function of RH while the optical properties were optical depth, extinction, scattering and absorption coefficients single scattering albedo, refractive indices and asymmetric parameters. The hygroscopic growth and enhancement parameters were then parameterized by using some models to determine the hygroscopicity, bulk hygroscopicity, humidification factors and some other parameters that depend on RH and/or wavelengths. The results showed that the data fitted our models very well and can be used to extrapolate the hygroscopic growth at any RH and enhancement parameters at any RH and wavelengths. The importance of determining gfmix(RH) as a function of RH and volume fractions, mass fractions and number fractions, and enhancement parameters as a function of RH. The effective radii increases with the increase in RH, while Angstrom coefficients decrease with the increase in RH and this signifies the dominance of coarse mode particles. The angstrom coefficients show that the mixture has bimodal type of distribution and the mode size increases with the increase in RH.
Highlights
Atmospheric aerosol particles reveal changes in their microphysical and optical characteristics with their ambient relative humidity (RH) due to the water uptake [1]-[3]
Since atmospheric aerosols are far from being a single component, the question is how relative humidity influences the optical properties of natural aerosol mixtures, which can contain both soluble and insoluble components
Its value is specific to the chemical composition of the aerosol particle [4] [5]
Summary
Atmospheric aerosol particles reveal changes in their microphysical and optical characteristics with their ambient relative humidity (RH) due to the water uptake [1]-[3]. Since atmospheric aerosols are far from being a single component, the question is how relative humidity influences the optical properties of natural aerosol mixtures, which can contain both soluble and insoluble components. These hygroscopic atmospheric aerosols undergo droplet growth, evaporation and phase transformation from a solid particle to a saline droplet which usually occurs spontaneously when the RH reaches a level called the deliquescence humidity. Ambient aerosols generally composed of external and internal mixtures of particles with different chemical compounds, chemical compositions and physical properties such as soot, sulphate, nitrate, organic carbon and mineral dust. The state of mixing of these components is crucial for understanding the role of aerosol particles in the atmosphere
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