Aerosol properties over an urban site, Johannesburg measured from sunphotometer

Abstract

In this paper, we present results using ground based Sunphotometer (a passive remote sensing instrument designed to study aerosol properties) as a part of NASA’s AERONET data. The analysis was based on the winter and spring (June – November, 2009) seasonal variations of aerosol optical and microphysical properties. Aerosol optical depth (AOD440) varied from 0.12±0.06 to 0.18±0.08 in winter and between 0.19±0.07 to 0.26±0.06 in spring and the seasonal increment which may be attributed to the effect of biomass burning and long range transport of smoke particles from forest fires. While the Angstrom exponent (α440-870) varied from 1.23±0.33 to 1.46±0.33 and 1.40±0.19 to 1.60±0.21 during winter and spring seasons, respectively. The volume size distribution which is of bimodal log-normal structure has its fine mode dominance at about 0.15μm and the coarse mode at about 4μm. The single scattering albedo (SSA) generally decreased with wavelength for both seasons depicting the presence of absorbing aerosol. The asymmetry parameter (ASY) and the refractive index (both real and imaginary) were also wavelength dependent