In recent years, the Indian capital city of Delhi has been impacted by very high levels of air pollution, especially during winter. Comprehensive knowledge of the composition and sources of the organic aerosol (OA), which constitutes a substantial fraction of total particulate mass (PM) in Delhi, is central to formulating effective public health policies. Previous source apportionment studies in Delhi identified key sources of primary OA (POA) and showed that secondary OA (SOA) played a major role but were unable to resolve specific SOA sources. We address the latter through the first field deployment of an extractive electrospray ionization time-of-flight mass spectrometer (EESI-TOF) in Delhi, together with a high-resolution aerosol mass spectrometer (AMS). Measurements were conducted during the winter of 2018/19, and positive matrix factorization (PMF) was used separately on AMS and EESI-TOF datasets to apportion the sources of OA. AMS PMF analysis yielded three primary and two secondary factors which were attributed to hydrocarbon-like OA (HOA), biomass burning OA (BBOA-1 and BBOA-2), more oxidized oxygenated OA (MO-OOA), and less oxidized oxygenated OA (LO-OOA). On average, 40 % of the total OA mass was apportioned to the secondary factors. The SOA contribution to total OA mass varied greatly between the daytime (76.8 %, 10:00–16:00 local time (LT)) and nighttime (31.0 %, 21:00–04:00 LT). The higher chemical resolution of EESI-TOF data allowed identification of individual SOA sources. The EESI-TOF PMF analysis in total yielded six factors, two of which were primary factors (primary biomass burning and cooking-related OA). The remaining four factors were predominantly of secondary origin: aromatic SOA, biogenic SOA, aged biomass burning SOA, and mixed urban SOA. Due to the uncertainties in the EESI-TOF ion sensitivities, mass concentrations of EESI-TOF SOA-dominated factors were related to the total AMS SOA (i.e. MO-OOA + LO-OOA) by multiple linear regression (MLR). Aromatic SOA was the major SOA component during the daytime, with a 55.2 % contribution to total SOA mass (42.4 % contribution to total OA). Its contribution to total SOA, however, decreased to 25.4 % (7.9 % of total OA) during the nighttime. This factor was attributed to the oxidation of light aromatic compounds emitted mostly from traffic. Biogenic SOA accounted for 18.4 % of total SOA mass (14.2 % of total OA) during the daytime and 36.1 % of total SOA mass (11.2 % of total OA) during the nighttime. Aged biomass burning and mixed urban SOA accounted for 15.2 % and 11.0 % of total SOA mass (11.7 % and 8.5 % of total OA mass), respectively, during the daytime and 15.4 % and 22.9 % of total SOA mass (4.8 % and 7.1 % of total OA mass), respectively, during the nighttime. A simple dilution–partitioning model was applied on all EESI-TOF factors to estimate the fraction of observed daytime concentrations resulting from local photochemical production (SOA) or emissions (POA). Aromatic SOA, aged biomass burning, and mixed urban SOA were all found to be dominated by local photochemical production, likely from the oxidation of locally emitted volatile organic compounds (VOCs). In contrast, biogenic SOA was related to the oxidation of diffuse regional emissions of isoprene and monoterpenes. The findings of this study show that in Delhi, the nighttime high concentrations are caused by POA emissions led by traffic and biomass burning and the daytime OA is dominated by SOA, with aromatic SOA accounting for the largest fraction. Because aromatic SOA is possibly more toxic than biogenic SOA and primary OA, its dominance during the daytime suggests an increased OA toxicity and health-related consequences for the general public.

中文翻译：

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使用萃取电喷雾电离质谱法对印度德里的有机气溶胶成分进行高度时间分辨的化学形态分析和来源分配

近年来，印度首都德里受到高度空气污染的影响，尤其是在冬季。全面了解有机气溶胶 (OA) 的组成和来源，有机气溶胶 (OA) 占德里总颗粒物质量 (PM) 的很大一部分，对于制定有效的公共卫生政策至关重要。以前在德里进行的资源分配研究确定了主要 OA (POA) 的关键来源，并表明次要 OA (SOA) 发挥了重要作用，但无法解决特定的 SOA 来源。我们通过在德里首次现场部署提取电喷雾电离飞行时间质谱仪 (EESI-TOF) 和高分辨率气溶胶质谱仪 (AMS) 来解决后者。测量是在 2018/19 年冬季进行的，在 AMS 和 EESI-TOF 数据集上分别使用正矩阵分解 (PMF) 来分配 OA 的来源。AMS PMF 分析产生了三个主要因素和两个次要因素，这些因素归因于类烃 OA (HOA)、生物质燃烧 OA (BBOA-1 和 BBOA-2)、更多氧化的氧化 OA (MO-OOA) 和较少氧化的氧化 OA (LO-OOA)。平均而言，总 OA 质量的 40% 分配给次要因素。SOA 对总 OA 质量的贡献在白天（76.8%，当地时间 10:00–16:00 (LT)）和夜间（31.0%，21:00–04:00 LT）之间变化很大。EESI-TOF 数据的更高化学分辨率允许识别单个 SOA 源。EESI-TOF PMF 分析总共产生了六个因素，其中两个是主要因素（主要生物质燃烧和烹饪相关的 OA）。其余四个因素主要是次生来源：芳香 SOA、生物 SOA、老化生物质燃烧 SOA 和混合城市 SOA。由于 EESI-TOF 离子灵敏度的不确定性，EESI-TOF SOA 主导因子的质量浓度与总 AMS SOA（即 MO-OOA + LO-OOA) 通过多元线性回归 (MLR)。芳香族 SOA 是白天的主要 SOA 成分，占 SOA 总质量的 55.2%（占总 OA 的 42.4%）。然而，它对总 SOA 的贡献在夜间下降到 25.4%（占总 OA 的 7.9%）。这一因素归因于主要由交通排放​​的轻芳烃化合物的氧化。白天生物源 SOA 占 SOA 总质量的 18.4%（占总 OA 的 14.2%），夜间占 SOA 总质量的 36.1%（占总 OA 的 11.2%）。日间老化生物质燃烧和混合城市 SOA 分别占 SOA 总质量的 15.2% 和 11.0%（占总 OA 质量的 11.7% 和 8.5%），占 SOA 总质量的 15.4% 和 22.9%（4.8% 和 7.1%） % 总 OA 质量），分别在夜间。对所有 EESI-TOF 因子应用了一个简单的稀释分配模型，以估计由局部光化学产生 (SOA) 或排放 (POA) 引起的观察到的白天浓度的比例。发现芳香族 SOA、老化的生物质燃烧和混合城市 SOA 都以当地的光化学生产为主，可能来自当地排放的挥发性有机化合物 (VOC) 的氧化。相比之下，生物源 SOA 与异戊二烯和单萜的扩散区域排放的氧化有关。这项研究的结果表明，在德里，夜间高浓度是由交通和生物质燃烧导致的 POA 排放造成的，而白天的 OA 以 SOA 为主，芳香族 SOA 占最大比例。因为芳香族 SOA 可能比生物源性 SOA 和原发性 OA 毒性更大，