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Multi-Year Analysis of Aerosol Properties Retrieved from the Ångström Parameters for Different Spectral Ranges over Pune

Category: Optical/Radiative Properties and Remote Sensing

Volume: 16 | Issue: 12 | Pages: 3266-3280
DOI: 10.4209/aaqr.2016.06.0268
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Amol R. Kolhe1,2, Ganesh V. Pawar1, Sandeep R. Varpe3, Pallath Pradeep Kumar2, Panuganti C. S. Devara4, Gajanan R. Aher 1

  • 1 Department of Physics, Nowrosjee Wadia College, Pune 411001, India
  • 2 Department of Physics, Savitribai Phule Pune University, Pune 411007, India
  • 3 International Institute of Information Technology, Pune 411057, India
  • 4 Amity Centre for Ocean-Atmospheric Science and Technology, Amity University Haryana, Manesar, Gurgaon 122 413, India

Highlights

Aerosol properties reveal seasonal cycle with strong departures from long-term mean.

Box-Whisker plots depict strong spectral dependence of Ångström exponent.

Aerosol ensemble at Pune consists of four aerosol types viz., UI, CM, DD and MT.

Winter shows dominance of UI and relatively less occurrence of MT type aerosols.

Pre-monsoon aerosol scenario is driven by mixture of MT, UI and DD type aerosols.


Abstract

The present study evaluates the temporal variation of aerosol optical depth (AOD500 nm) and the Ångström parameters [viz., Ångström exponent (AE, α), Ångström turbidity coefficient (β) and second order Ångström exponent (α′)] at a tropical observing site, Pune (18°32′N; 73°49′E, 559 m AMSL) during 2008–15. Six-year means for winter and pre-monsoon seasons together are found to be 0.534 ± 0.13, 1.054 ± 0.27, 0.254 ± 0.08 and 0.167 ± 1.33 for AOD500 nm, AE, β and α′ respectively. Average month-to-month variability of AOD500 nm, AE, β and α′ during 2008–15 depicts seasonal cycle with strong departures with respect to long-term means. Frequency distributions for AOD, AE and β are positively skewed (skewness = 0.77, 0.32 and 1.14 respectively) while it is negatively skewed for α′ (skewness = –0.18). Analysis of AE difference, curvature parameter difference (α2–α1) and AOD500 nm–AE440-870 nm contour density map reveals that the aerosol ensemble at Pune consists of four aerosol types viz., UI (urban/industrial), CM (clear maritime), DD (desert dust) and MT (mixed type). Their relative magnitudes, however, differ during winter and pre-monsoon seasons. Thus, the contour density map shows dominance of UI and relatively less occurrence of MT type aerosols during winter. In pre-monsoon, however, the aerosol scenario is driven by MT type aerosol although UI and DD type aerosols show their remarkable existence.

Keywords

Aerosol optical depth Ångström exponent Ångström turbidity coefficient Aerosol loading Aerosol sources


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