The Ångström Exponent and Turbidity of Soot Component in the Radiative Forcing of Urban Aerosols

Abstract

In this work, we extracted data from Optical Properties of Aerosols and Clouds (OPAC) using FORTRAN program to model the effect of soot on optical depth, scattering coefficient, absorption coefficient, single scattering albedo, extinction coefficient and asymmetry parameter at spectral range of 0.25 to 1.00 ƒÝm for eight different relative humidities (RHs) (0, 50, 70, 80, 90, 95, 98 and 99%). The concentration of sootwas varied as 1.10 ¡Ñ 10.., 1.20 ¡Ñ 10..and 1.30 ¡Ñ 10.......... while the insoluble and water soluble were kept constant at 1.50 and 15,000 cm-3 respectively. The optical parameters were used to determine the Radiative forcing (RF).
Origin 50 software was used to plot the graphs. SPSS 16.0 Software was used to determine the Angstrom exponent, Ą and Curvature, Ą2. The Ą reflects the dominance of fine-mode particles while Ą2 at 0% RH reflects
the dominance of coarse-mode particles and at 50-99%RHs reflects the dominance of fine-mode particles, the turbidity, ƒÒ indicates a relatively hazy atmosphere, the Aerosol Optical Depth (AOD) show a relatively higher
value indicating a polluted urban air, the asymmetry parameter, g falls between 0.64 and 0.77. However, from our graphs of Radiative forcing against wavelength, we report that addition of soot concentration reflects
warming effect; therefore soot has a relatively high absorption coefficient.
Keywords: Soot, Angstrom exponent, Turbidity, Radiative forcing, Aerosols