Characteristics of atmospheric aerosol particles and their role in aerosol radiative forcing over the northwestern Indian Himalaya in particular and over India in general

Abstract

Recent investigations suggest that the accumulation of polluted aerosols at mountain sites of the Indian Himalaya potentially may accelerate the seasonal warming. In view of the importance of aerosols, the present study was carried out over Mohal (1154 m) during April 2006 to March 2010. The investigation of the optical properties of aerosols such as single-scattering albedo (SSA), asymmetry parameter (AP), and their effect on aerosol radiative forcing (ARF) from this part of India are also reported in earlier studies. However, those studies did not fully focus on the radiative effect of aerosols. In this study, we focus on this important aspect; the ARF was computed using the atmospheric radiation transfer model (RTM). The radiative properties of aerosols used in RTM are retrieved from Optical Properties of Aerosol and Cloud (OPAC) model. The seasonal highest SSA at 0.5 μm was obtained in premonsoon season (0.875 ± 0.03) and lowest in winter (0.754 ± 0.07). The seasonal highest AP at 0.5 μm was obtained in premonsoon (0.678 ± 0.01) and lowest in winter (0.654 ± 0.01). The mean (period April 2006 to March 2010) values of ARF at the surface, top of the atmosphere, and the atmosphere are estimated to be −19.1 ± 1.9, +0.5 ± 3.3, and +19.6 ± 3.7 W m−2, respectively. During the dust-laden period, this study reports strong response to atmospheric forcing; this increases the atmospheric heating rate by a factor 2.4 when compared to low aerosol-laden period. Based on review of the literature, it is found that in the northern and eastern subcontinent of India, the large decrease in surface reaching solar radiation is due to the abundance of desert dust aerosols. In the western and southern subcontinent of India, the large decrease in surface reaching solar radiation is mainly due to the abundance of anthropogenic aerosols.