Sun-sky radiometer-derived column-integrated aerosol optical and physical properties over a tropical urban station during 2004-2009

This paper reports the first observational results of aerosol characteristics over Pune, India (an AERONET site), using CIMEL Sun-sky radiometer. Here 5 years of observational data have been analyzed. The aerosol loading, in terms of the aerosol type and optical depth, undergoes strong seasonal variation over Pune with coarse-mode aerosols dominating during premonsoon season while fine-mode anthropogenic pollution particles result in boundary layer haze during postmonsoon and winter months. The daily mean AOD(440) at this location ranged between 0.10 and 1.12, with the most frequently occurring value in the range 0.45-0.55. The overall mean for the 5 year period is 0.49, with a day-to-day variability of about 36.7%. The annual average of CWV over the region shows a fluctuating trend with a marginal increase in the last 2 years. CWV shows strong annual cycle with two maxima, one in the postmonsoon and the other in the premonsoon season. Angstrom exponent (alpha) varies in the range 0.3-1.7, with large seasonal variability. The spectral variation of SSA has been found to be large during the postmonsoon season as compared to that in the other seasons. Real n(lambda) and imaginary k(lambda) parts of complex refractive index show contrasting spectral behavior during the observational period. The average asymmetry factor (g) representative of the total aerosol layer exhibits a distinct wavelength dependence with g = 0.70 (0.02) at 440 nm and decreasing to 0.64 (0.04) at 1020 nm.