Variation between near-surface and columnar aerosol characteristics during the winter and summer at Delhi in the Indo-Gangetic Basin

Abstract Aerosol characteristics were studied over Delhi, a typical urban station in the Ganga basin in Northern India, during two contrasting weather conditions: winter and summer, to explain the changes in columnar and surface aerosol characteristics with the help of ground based measurements and CALIPSO satellite data. The near-surface mean aerosol mass concentrations of PM 10 and PM 2.5 (±standard deviation) were observed to be ∼200 (±24) and 118 (±33) μg m −3 , respectively, during the winter and ∼168 (±31) and 55 (±12) μg m −3 , respectively, during the summer. PM 2.5 was found to be about two times higher than the PM 10 concentration during the winter period. Aerosol mass size distribution showed bi-modal nature during both the periods, with relative dominance of fine-particle mass concentrations during the winter, having low R eff value (0.63±0.05 μm) and coarse-particle mass concentrations during the summer, having large R eff value (1.52±0.60 μm). The concurrent measurement of columnar aerosol optical depth (AOD) showed high values (>0.60 at 500 nm) during both the periods. The Angstrom exponent ( α ) over the station, however, also suggests relatively large contribution of fine-mode particles during the winter ( α ∼1.02) and coarse-mode dust particles during the summer ( α ∼0.51). The observed features in the surface and columnar measured aerosol characteristics during two different seasons are explained using the vertical winds coupled with the vertical profile of aerosols.

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