The Indo-Gangetic Plains (IGP) experience high levels of airborne particulate matter (PM), especially during the dry season. Contributing to PM are natural and anthropogenic emissions and the atmospheric transformation of gases to form particles. Regional smog events occur frequently during wintertime and provide an atmospheric medium for aerosol processing. Here, we investigate the chemical composition and sources of PM at a representative site in the northern IGP during the second Nepal Ambient Monitoring and Source Testing Experiment (NAMaSTE 2). In Lumbini, Nepal, the 24 h average PM_2.5 and PM₁₀ concentrations ranged 48–295 and 60–343 μg m^–3, respectively, from December 20, 2017, to January 1, 2018. On average (± standard deviation), PM_2.5 was composed of 39 ± 7% organic carbon (OC), 5 ± 2% elemental carbon (EC), and 20 ± 6% secondary inorganic ions (ammonium, nitrate, and sulfate), 2.0% chloride, and 1.3% potassium. Biomass burning was a major PM source, indicated by a median levoglucosan concentration of 3.5 μg m^–3. Secondary organic aerosol (SOA) derived from biomass burning was indicated by high concentrations of nitromonoaromatic compounds (e.g., 4-nitrocatechol peaking at 435 ng m^–3). During periods of fog, characterized by high relative humidity (RH) and relatively low solar radiation, nitroaromatic concentrations dropped despite levoglucosan remaining high, indicating that their formation was suppressed. Chemical signatures of SOA indicated that volatile organic compound (VOC) precursors were primarily combustion-derived, with small contributions from biogenic VOC. Through molecular markers and chemical mass balance (CMB) modeling, sources of PM_2.5 OC were identified as cow dung burning (24 ± 16%), other biomass burning (20 ± 7%), plastic/garbage burning (4.7 ± 3.2%), vehicle emissions (3.1 ± 1.4%), coal combustion (0.3 ± 0.2%), and SOA from monoaromatic VOC (4.1 ± 0.8%), diaromatic VOC (8.9 ± 4.0%), cresol (0.3 ± 0.4%), isoprene (0.4 ± 0.2%), monoterpenes (1.5 ± 0.6%), and sesquiterpenes (3.2 ± 0.7%). Understanding the levels of PM in Lumbini, along with its chemical composition and sources of OC, contributes to a better understanding of regional air quality episodes in the IGP.

中文翻译：

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尼泊尔蓝毗尼的冬季空气质量：细颗粒有机碳的来源

印度恒河平原（IGP）的空气中颗粒物（PM）含量较高，尤其是在干旱季节。造成PM的因素包括自然和人为排放以及气体在大气中的转化以形成颗粒。区域性烟雾事件在冬季频繁发生，为气溶胶处理提供了一种大气介质。在这里，我们在第二次尼泊尔环境监测和源测试实验（NAMaSTE 2）中调查了IGP北部一个代表性站点的PM的化学成分和来源。从2017年12月20日至2018年1月1日，尼泊尔伦比尼（Lumbini）的24小时平均PM _2.5和PM ₁₀浓度分别为48–295和60–343μgm ^–3。下午_2.5由39±7％的有机碳（OC），5±2％的元素碳（EC）和20±6％的次级无机离子（铵，硝酸盐和硫酸盐），2.0％的氯和1.3％的钾组成。生物质燃烧是主要的PM来源，左旋葡聚糖的中位浓度为3.5μgm ^–3。高浓度的硝基单芳族化合物（例如，4-硝基邻苯二酚在435 ng m ^–3处达到峰值）表明，生物质燃烧产生的次级有机气溶胶（SOA））。在以高相对湿度（RH）和相对较低的太阳辐射为特征的雾气时期，尽管左旋葡聚糖含量很高，但硝基芳香族化合物的浓度却下降了，这表明它们的形成被抑制了。SOA的化学特征表明，挥发性有机化合物（VOC）前体主要来自燃烧，而生物源VOC贡献很小。通过分子标记和化学物质平衡（CMB）建模，PM _2.5的来源OC被确定为牛粪燃烧（24±16％），其他生物质燃烧（20±7％），塑料/垃圾燃烧（4.7±3.2％），车辆排放（3.1±1.4％），煤炭燃烧（0.3±0.2） ％）和单芳香族VOC（4.1±0.8％），二芳香族VOC（8.9±4.0％），甲酚（0.3±0.4％），异戊二烯（0.4±0.2％），单萜（1.5±0.6％）和倍半萜的SOA （3.2±0.7％）。了解蓝毗尼中的PM含量及其化学成分和OC的来源，有助于更好地了解IGP中的区域空气质量事件。