Abstract
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 Angstrom parameters α and β were used.
Highlights
Aerosols play an important role in earth’s radiation budget, air quality and environmental health (Prospero et al, 1983; Satheesh and Ramanathan, 2000; Pinker et al, 2001)
The natural sources of aerosols are more important than the anthropogenic aerosols, but regionally anthropogenic aerosols are more important (Kaufman and Fraser, 1983; Ramanathan et al, 2001)
Added to the natural sources are the anthropogenic sources of aerosols, such as combustion, industrial activity, transport and mining that contribute to regional-scale differences in aerosol properties
Summary
Aerosols play an important role in earth’s radiation budget, air quality and environmental health (Prospero et al, 1983; Satheesh and Ramanathan, 2000; Pinker et al, 2001). The natural sources of aerosols are more important than the anthropogenic aerosols, but regionally anthropogenic aerosols are more important (Kaufman and Fraser, 1983; Ramanathan et al, 2001). The sources and sinks of aerosols are so varied and distributed over the globe, that their physical properties and optical effects show distinct variation with geographic locations. Natural sources, such as volcanic activity, produce synoptic scale effects; while other sources, such as wind blown dust, sea-spray, convective and general circulations produce regional-scale effects in modulating background aerosols. The global studies of the aerosols properties are of great importance
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