Investigation of physical and optical properties of aerosol over high altitude stations along the sub-Himalayan region of North-Eastern India

Abstract

The present study focuses on exploring the spectral dependency of atmospheric extinction, the size distribution of aerosols, black carbon concentration and absorption and compensation parameter along the sub-Himalayan region of northeastern India, a field campaign was conducted from 1st February to 20th February 2018. Measurements were taken at three different stations in Arunachal Pradesh i.e., Tawang (2990 m a.s.l), New Palin (1300 m a.s.l.), and Geku (200 m a.s.l.). Techniques of Ångström exponent's curvature effect has been used to determine the aerosol size distribution over the stations. The mean black carbon concentration was 3.98 ± 1.03 μg m−3, 4.27 ± 1.22 μg m−3 and 2.38 ± 1.05 μg m−3 at Tawang, New Palin, and Geku respectively. The daily mean absorption coefficient at 370 nm (σ370) was (1.46 ± 0.56) × 10−4, (1.84 ± 0.42) × 10−4, and (1.85 ± 1.8) × 10−4 at Tawang, New Palin, and Geku. Whereas daily mean absorption coefficient at 880 nm (σ880) was (0.33 ± 0.08) × 10−4, (0.42 ± 0.05) × 10−4, and (0.2 ± 0.17) × 10−4. The σ370 was 126%, 125%, and 164% higher than the absorption at the longer wavelength (880 nm) which indicates a higher biomass burning BC. The average Absorption Ångström Exponent (AAE) at 370–880 nm were 1.59 ± 0.23, 1.63 ± 0.23 and 2.28 ± 0.57 at Tawang, New Palin, and Geku. In addition, at Tawang, New Palin, and Geku, the average AAE in the shorter spectral range (370–520 nm) were 2.43 ± 0.97, 2.41 ± 1.22 and 3.09 ± 1.54, whereas in longer spectral range (520–880 nm) were 1.05 ± 0.05, 1.13 ± 0.18 and 1.44 ± 0.33, respectively.