Spectral Variation of Total Column Aerosol Optical Depth over Rajkot: A Tropical Semi-arid Indian Station

Ritweej Rajeev Ranjan；H. P. Joshi；K. N. Iyer

Atmospheric aerosol ； Aerosol optical depth ； Ångström parameters ； Sun photometer

Aerosol and Air Quality Research

7卷1期（2007 / 03 / 01）

33 - 45

英文

Spectral aerosol optical depth (AOD) measurements, estimated from two hand-held, microprocessor-based sun photometers [MICROTOPS-Ⅱ (version 2.43 & 5.5)] over Rajkot, India were analyzed from March 2005 to March 2006 (a total of 167 days of clear-sky observations). The results showed seasonal variation with high values in summer and low values in winter. The summer increase is found to be due to the high wind speed producing larger amounts of wind-driven dust particles. The winter AOD values decrease more at higher wavelengths, indicating a general reduction in the number of bigger particles. Also during the winter months the wind direction changed to southerly and southeasterly bringing air from more rural areas to the measurement site. The amplitude of the observed high AOD values in summer is higher (low during winter) for longer wavelengths, which shows that coarse particles contribute more to the observed variation as compared to sub-micron particles. To characterize the aerosol optical depths, the Ångström parameters α and β were used.