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Home  >  Volume 22 (2012)

Radiative Forcing of Urban Aerosols in the Near Infrared Region by B. I. Tijjani. Volume 22 (November, 2012), pp 85 – 94
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We study the radiative forcing of Urban aerosols at the near infrared region

(1.0 μm to 4.0μm) using data from the Optical Properties of Aerosol and Clouds software. Radiative forcing at different wavelengths and Relative humidities (RHs) are calculated and analysed. The other parameters that were analysed in order to be able to understand the nature of the particles and their distributions are the effective refractive indicies, optical depths, single scattering albedo, extinction, scattering and absorption coefficients. From the analysis, it was discovered that radiative forcing (in a form of cooling) increases with relative humidities (RH) and is dependent on wavelengths. The nature of the increments of the radiative forcing with RH reflects the dominance of fine particles. This is because as a result of the increase in RH from 0 to 50%, large particles started sedimenting which caused the increase in fine particles. As the RH increases the concentrations of larger particles continue to decrease so the concentration of fine particles continue to increase which result in decrease in effective radii and increase in Angstrom coefficients. The analysis of the Angstrom coefficients showed the dominance of fine particles. The analysis of optical depth with wavelengths and RHs together with the comparison with scattering and absorption coefficients, hygsroscopicity factor and humidification factor, show that the particles are very hygroscopic and have bimodal type of size distributions with majority satisfying Junge type of distribution with a small component of lognormal.