资源环境科技发展态势分析平台

The rapid changes in the pattern of atmospheric warming as well as the degradation of glaciers in the Himalayas point to the inevitability of accurate source characterization and quantification of the impact of aerosols. In this regard, optical and chemical properties of aerosols, and their role in radiative effects are examined over a remote high-altitude site Lachung (27.4°N, 88.4°E, 2700 m a.s.l.) in the eastern Himalayas during August-2018 to February-2020. It is found that the sulphate (SO₄²⁻) and carbonaceous aerosols (both organic carbon - OC and elemental carbon - EC) significantly contribute to the total aerosol mass loading in winter (DJF) and spring (MAM), resulting in high values of scattering and absorption coefficients. In both cases, aerosol single scattering albedo (SSA) is relatively higher in winter (> 0.85) due to a significantly higher amount of OC (OC/EC > 8). However, SSA ~ 0.8 in spring despite having higher SO₄²⁻ concentrations (SO₄²⁻/EC > 4.0 and SO₄²⁻/OC ~ 1.0) than winter. A reverse pattern is seen in summer-monsoon (JJAS) having lower SO₄²⁻/EC < 2 and SO₄²⁻/OC < 0.5, resulting in SSA as low as ~0.65. The seasonal values of aerosol direct radiative forcing in the top of the atmosphere (DRF_TOA) are as high as −2.9 ± 1.2 Wm⁻² during winter due to abundant OC and DRF_TOA is −2.8 ± 0.5 Wm⁻² during spring due to abundant SO₄²⁻ concentrations. The most abundant SO₄²⁻ concentrations in spring also leads to the highest surface cooling of −16.7 ± 4.9 Wm⁻². Along with SO₄²⁻, EC mass concentration is also higher in spring. This translates to an atmospheric heating rate of ~0.39 K day⁻¹ corresponding to the atmospheric DRF of 10.6 ± 4.4 Wm⁻², which is 34% higher than the atmospheric absorption in winter. The seasonal pattern of forcing influenced by the heterogeneous sources and chemical composition of aerosols over the eastern Himalayan site is significantly influenced by the transport of aerosols from the Indo-Gangetic Plains of India.