Kumar Dhananjay, Hegde Prashant, Arun B S, Gogoi Mukunda M, Babu S Suresh
Space Physics Laboratory, Vikram Sarabhai Space Centre, Thiruvananthapuram 695022, India.
Space Physics Laboratory, Vikram Sarabhai Space Centre, Thiruvananthapuram 695022, India.
Sci Total Environ. 2024 Nov 1;949:175072. doi: 10.1016/j.scitotenv.2024.175072. Epub 2024 Jul 29.
Atmospheric aerosols have a serious impact on altering the radiation balance of the vulnerable Himalayan atmosphere. Organic aerosol (OA), one of the least resolved aerosol fractions in the Himalayas, constrain our competence to assess their climate impacts on the region. Here we investigate water-soluble OA molecules in PM samples collected from March to May 2019 at Lachung (27.4°N and 88.4°E), a high-altitude location (2700 m a.s.l.) in the eastern Himalaya, to elucidate their origin and formation process. The dominance of oxalic acid (C) reveals that water-soluble OA in the eastern Himalaya are atmospherically processed. Backward air mass trajectories and mass concentration ratios of organic tracers as well as relationships with inorganic species (K, SO, NH) suggest an anthropogenic origin of water-soluble OA with significant atmospheric processing during long-range transport to the eastern Himalayan region. We used the thermodynamic prediction of aerosol liquid water (ALW) to examine the formation mechanism of secondary OA (SOA) such as oxalic acid. Correlations of ALW with SO and water-soluble organic matter show that ALW is sensitive to both anthropogenic sulfate and water-soluble organic compounds in Himalayan aerosols. A strong positive relationship of C acid with predicted ALW provides evidence of extensive SOA formation from precursors via aqueous phase photochemical processes. This inference is supported by positive correlations of C acid relative abundance with diagnostic mass concentration ratios of C acid to precursor molecules. Our findings underscore the importance of anthropogenic sources and ALW in SOA formation through aqueous phase processes in the eastern Himalaya.
大气气溶胶对脆弱的喜马拉雅大气辐射平衡的改变有着严重影响。有机气溶胶（OA）是喜马拉雅地区解析程度最低的气溶胶组分之一，限制了我们评估其对该地区气候影响的能力。在此，我们研究了2019年3月至5月在喜马拉雅东部高海拔地区（海拔2700米，北纬27.4°，东经88.4°）的拉琼采集的PM样本中的水溶性OA分子，以阐明其来源和形成过程。草酸（C）的主导地位表明喜马拉雅东部的水溶性OA是经过大气加工的。反向气团轨迹、有机示踪剂的质量浓度比以及与无机物种（K、SO、NH）的关系表明，水溶性OA的人为来源在向喜马拉雅东部地区的长距离传输过程中经过了显著的大气加工。我们使用气溶胶水态水（ALW）的热力学预测来研究草酸等二次有机气溶胶（SOA）的形成机制。ALW与SO和水溶性有机物的相关性表明，ALW对喜马拉雅气溶胶中的人为硫酸盐和水溶性有机化合物都很敏感。草酸与预测的ALW之间的强正相关为通过水相光化学过程从前体广泛形成SOA提供了证据。草酸相对丰度与草酸与前体分子诊断质量浓度比的正相关支持了这一推断。我们的研究结果强调了人为源和ALW在喜马拉雅东部通过水相过程形成SOA中的重要性。
