Research Institute for Sustainability Helmholtz Centre Potsdam

Year-round aerosol characteristics and radiative effects in the South Asian pollution outflow over a background site in the Maldives

Aerosol radiative properties using recently available high-quality columnar aerosol data collected at several AERONET sites in South Asia, with a focus on pollution outflow from continental South Asia observed over Hanimaadhoo in Maldives, a small island in northern Indian Ocean are quantified. The seasonal mean aerosol optical depth (AOD) over Hanimaadhoo is ≥ 0.3 (except ca. 0.2 during monsoon season), and single scattering albedo (SSA) is > 0.90 in all seasons. Fine mode aerosols contribute dominantly to AOD. SSA decreases as a function of wavelength due to influence of continental aerosols, except during the monsoon season when its spectral trend reverses due to increase in dust. Carbonaceous aerosols dominate (>90%) contribution to absorption AOD (AAOD). Black carbon (BC) and brown carbon (BrC) contribute >75% and <25%, respectively, to AAOD due to carbonaceous aerosols. The observed seasonal mean aerosol radiative forcing at the surface (ARFSFC), at the top of the atmosphere (ARFTOP) and in the atmosphere (ARFATM) is > −25 Wm-2, >−20 Wm-2 and ~+20 Wm-2, respectively. Aerosol loading and atmospheric heating have increased over this background site over the last decade. A regional-scale analysis of aerosol properties and radiative effects across and surrounding the Indo-Gangetic Plain (IGP) shows that AOD is ≥ 0.3 over entire region, and aerosols reduce seasonally 30–50 Wm-2 of solar radiation reaching the surface, contributing significantly to solar dimming effect. The atmospheric solar heating rate due to aerosols (HR) is ≥ 1 K day−1 across IGP. These high ARFs, ARFESFC and HR, and increasing trends have significant implications to climate and hydrological cycle over South Asia and beyond.

Publication Year

2020

Publication Type

Citation

Ramachandran, S., & Rupakheti, M. (2020). Year-round aerosol characteristics and radiative effects in the South Asian pollution outflow over a background site in the Maldives. Atmospheric Environment, 240: 117813. doi:10.1016/j.atmosenv.2020.117813.

DOI

10.1016/j.atmosenv.2020.117813
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