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Diurnal and Seasonal Variation of Spectral Properties of Aerosols over Dehradun, India

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Volume: 9 | Issue: 1 | Pages: 32-49
DOI: 10.4209/aaqr.2008.06.0019
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Sapna Rana, Yogesh Kant , V.K Dadhwal

  • Indian Institute of Remote Sensing (NRSA), Dept. of Space, Govt. of India, 4 Kalidas Road, Dehradun, India

Abstract

The diurnal variation of Aerosol Optical Depth (AOD) and its spectral properties over non-cloudy days in summer and winter seasons of two years are studied. Spectral dependence of AOD shows higher values at shorter wavelengths which decreases gradually towards longer wavelengths for the summer as well as the winter period. Results suggest that during high relative humidity and stable conditions, the AOD is found to be relatively low (clear day) as compared to unstable meteorological conditions (turbid). Air mass back trajectory for 5 days of high and low AOD in March indicate that the sources of loading come from far to the west in central Asia, whereas during winter, the sources are from east and south-east direction in the Indo-Gangetic plain. The diurnal variation of Ǻngström exponent () has lowest values in the morning hours with a variation of around 5-17% for clear day and around 11-20% for turbid day, signifying the presence of larger particles. Due to inversion more fine particles lead to an increase in the  value. The intraseasonal variability in March (summer) is high and interseasonal variation in January (winter) is not observed and is also confirmed by ‘’ values. Size distribution of aerosols showed peak loading ranging around a 0.07 m radius. Aerosol loading on turbid days was due to fine mode particles and the simultaneous presence of fine- and coarse-mode particles on clear days.

Keywords

Aerosol optical depth Multi wavelength solar radiometer Ǻngström turbidity parameters Size distribution Effective radius


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