有机物（OM）是特大城市细颗粒物（PM2.5）的主要组成部分，活性气相前体物在大气环境下氧化形成的二次气溶胶（SOA）占比贡献大。中等及半挥发性有机物（I/SVOCs）是重要的SOA前体物，在分子水平上识别I/SVOCs化学组分及浓度特征，对于识别大气有机物的来源及化学转化具有重要意义。本研究在北京市海淀区清华大学观测站开展了大气气相及颗粒相I/SVOCs化学组分及浓度的离线观测，采集了2022年1月至3月、7月和10月不同季节的昼夜大气有机物样本。采用全二维色谱-飞行时间质谱（GC×GC-ToF-MS），通过非靶标识别结合层级聚类（HCA）及正交偏最小二乘判别分析（OPLS-DA），识别了不同污染程度下气态有机物和颗粒态有机物中的特征物种。利用正交因子矩阵分解（PMF），解析了大气I/SVOCs的来源。研究结果表明，不同季节气态有机物质量浓度排序为2021年冬季（20.00 ?g/m3）>2022年秋季（6.44 ?g/m3）>2022年春季（5.36 ?g/m3）>2022年夏季（4.05 ?g/m3），气态有机物中I/SVOCs的占比约为30%，其主要的化学组分包括羧酸、酮、酯和醛类有机物。不同季节颗粒态有机物中质量浓度排序为2021年冬季（719 ng/m3）> 2022年春季（612 ng/m3）> 2022年秋季（88 ng/m3）> 2022年夏季（52 ng/m3），颗粒态有机物中中等及半挥发性组分占比约为40%，其主要化学组分为含氧组分，如羧酸、酮、醇、酯类有机物。采暖季气态有机物在高湿污染时段下的特征有机物是醛、酮、醇及有机酸，低湿污染时段下的特征有机物是多环芳烃和含氯有机物。颗粒态有机物在相对湿度较高的大气条件下细颗粒物浓度相应更高，特征有机物是有机酸、醛和含氧芳烃。采暖季颗粒态I/SVOCs的主要来源包括烹饪、燃煤、生物质燃烧、机动车、溶剂使用和二次生成因子，气态I/SVOCs主要来自生物质燃烧、燃煤、自然及烹饪源、汽油车、溶剂和柴油车。冬季污染时段颗粒态和气态I/SVOCs的主要来源分别是烹饪和汽油车，春季污染时段颗粒态和气态I/SVOCs的主要来源分别是生物质燃烧和柴油车。

Organic matter (OM) is a major component of fine particulate matter (PM2.5) in megacities, with a large contribution from secondary aerosols (SOA) formed by the oxidation of reactive gas-phase precursors in the atmospheric environment. Intermediate and semi-volatile organic compounds (I/SVOCs) are important SOA precursors, and the identification of chemical components and concentration characteristics of I/SVOCs at the molecular level is important for identifying the sources and chemical transformations of atmospheric organic compounds.In this study, off-line observations of the chemical fractions and concentrations of atmospheric gas-phase and particle-phase I/SVOCs were carried out at Tsinghua University observatory in Haidian District, Beijing, China, and diurnal atmospheric organic matter samples were collected in different seasons from January to March, July and October 2022. Laboratory identification and semi-quantitative methods for atmospheric I/SVOCs were established based on full two-dimensional chromatography-time-of-flight mass spectrometry (GC×GC-ToF-MS). Target and non-target identification combined with hierarchical clustering (HCA) qualitatively identified the characteristic species in gaseous particulate organic matter at different pollution levels. The source contribution of atmospheric I/SVOCs was quantitatively resolved using orthogonal factor matrix decomposition (PMF).The results of the study showed that the mass concentrations of gaseous organics in different seasons were ranked as autumn 2022 (22.1 μg/m3) > summer 2022 (14.4 μg/m3) > spring 2022 (12.9 μg/m3) > winter 2021 (12.4 μg/m3), and the percentage of I/SVOCs in gaseous organics was 30-40%, and their main chemical components include ketones and esters, aldehydes and aromatic hydrocarbon organics. The mass concentrations in particulate organic matter in different seasons are ranked as spring 2022 (4.4 μg/m3) > winter 2021 (2.7 μg/m3) > autumn 2022 (0.8 μg/m3) > summer 2022 (0.4 μg/m3), and the proportion of medium and semi-volatile components in particulate organic matter is 40-60%, and the main chemical components are carboxylic acids, polycyclic aromatic hydrocarbons and aromatic hydrocarbons.The characteristic organics of gaseous organic matter in winter and spring under high PM2.5 hours are nitrile and ether organics. Specific species include furan p-ketones (anhydrides), ester organics such as ethylene glycol diacetate and dimethyl succinate, and ketones such as acetonyl acetate and methyl ethyl ketone, mainly associated with biomass combustion and secondary generation. The gaseous characteristic substances corresponding to the time periods with higher pollution levels of PM2.5 and NO2 concentrations in summer and autumn have a wide range of chemical categories, including esters, ketones, anhydrides, alicyclic hydrocarbons and polycyclic aromatic hydrocarbons. Particulate state characteristic substances include highly volatile alicyclic hydrocarbons, and low volatile alcohols and esters organic substances.The major sources of gaseous I/SVOCs in winter and spring included solvent use (29%), gasoline vehicles (22%), coal combustion (19%), and biomass burning (15%). Major sources of particulate I/SVOCs include cooking (23%), solvent use (19%) and high oxidation state factors (17%).