Soni, Kirti and Singh, Sachchidanand and Bano, Tarannum and Tanwar, R. S. and Nath, Shambhu (2011) Wavelength Dependence of the Aerosol Angstrom Exponent and Its Implications Over Delhi, India. Aerosol Science and Technology , 45 (12). pp. 1488-1498. ISSN 1521-7388

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Abstract

The aerosol optical depth (AOD), Angstrom coefficients (α and β), and the second-order Angstrom exponent (α ) obtained by Microtops-II sun photometer have been analyzed in the spectral range 0.34–0.87 μm over the urban polluted city of Delhi, In- dia for the period 2007–2008, aiming at investigating the physical and optical properties of aerosols. The average values of AOD at 500 nm, α and β (in the range 340–870 nm) are found to be 0.78 ± 0.32, 0.78 ± 0.28, and 0.45 ± 0.21, respectively, for the entire period of observations. The AOD data show significant curvature in the lnτ versus lnλ relationship suggesting different dominant aerosol types depending on season. In order to analyze further the curvature effect and the relative dominance of aerosol size, α has been calculated in three wavelength bands, i.e., shorter (0.34–0.50 μm), longer (0.675–0.87 μm), and broad (0.34–0.87 μm) during four seasons, summer (April–June), monsoon (July–September), winter (October–January), and spring (February–March) accom-panied with calculations of α , which quantifies the deviation of logarithmic behavior of AOD with lnλ. The α values are found to be positive and higher in the months of October–December and mostly negative in February and March, while close to zero values of α are found in April–August. These results indicate that win-ter season exhibits dominance of fine-mode aerosols while summer relatively higher concentration of coarse-mode particles. On the other hand, monsoon and spring seasons revealed the presence of mixed type, both fine- and coarse-mode aerosols over Delhi.

Item Type:	Article
Additional Information:	Copyright for this article belongs to M/s Taylor & Francis Group.
Uncontrolled Keywords:	Different Spectral Ranges; Optical Depth; Arabian Sea; Atmospheric Turbidity; Maritime Aerosol; Field Campaign; Athens Area; Aeronet; Climatology; Radiation
Subjects:	Engineering Meteorology & Atmospheric Sciences
Divisions:	UNSPECIFIED
Depositing User:	Mr. Abhishek Yadav
Date Deposited:	04 Oct 2012 12:01
Last Modified:	04 Oct 2012 12:01
URI:	http://npl.csircentral.net/id/eprint/649

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