天津市有机气溶胶的人为和生物源贡献、大气过程及季节性变化研究

Organic aerosols (OA) are directly emitted from primary sources and produced by chemical reactions of their gaseous precursors in the atmosphere. They often account up to 90% of fine aerosol mass and have a great impact on the Earth’s climate system, cause severe human health risks and play an important role in atmospheric chemistry. High aerosol loadings are observed in the East Asian atmosphere that often lead to haze events in East China, particularly over the Jing-Jin-Ji region. In last two decades, much attention has been paid on atmospheric aerosol research in this region, focusing mainly on sulfate and black carbon, and recognized that fossil fuel combustion is the major source of aerosols followed by Asian dust and biomass burning. On the contrary, recent studies showed that the contributions of OA from biological sources are also significant in Northeast Asia, including China. However, the relative importance of such sources to OA loading and their seasonal variations, which are necessary to understand the air quality and climate changes, are not clear in China. Hence, the studies on sources and atmospheric processing of OA are urgently needed over China, particularly Northeast China where the aerosol loading and haze events are higher. Tianjin is a typical metropolis located adjacent to the Bohai Sea covered with rapidly developing economic zone and also dense forest areas. Further the East Asian monsoon, which forms as a result of the thermal difference between the Asian continent and the Pacific Ocean, controls the source regions of the air masses that arrive in Tianjin. Therefore, Tianjin is an ideal location to study the origins and atmospheric processing of aerosols in Northeast China. Here, we propose to investigate the sources such as primary/secondary, natural/anthropogenic and fossil/biogenic origins of OA and their seasonal variations in Northeast China through long-term (over one year period) observations of molecular marker species, stable carbon (13C) and radiocarbon (14C) isotope ratios in the Tianjin urban atmosphere together with the short-period (~2 weeks in each season) observations at background (mountain and onshore) sites in this region. This research could provide comprehensive measurements of OA and their sources, which would be highly helpful to reconcile the atmospheric models to better estimate the OA budget and impacts in North China and its downwind regions.

有机气溶胶（OA）主要来源是直接的一次排放源和由颗粒相前体物在大气中发生光化学转换形成，其占细粒子颗粒物质量的90%，对气候有重要的影响，也危害人类的身体健康。亚洲东部大气中高负荷的气溶胶导致中国东部爆发雾霾，尤其是我国京津冀地区。最近研究表明，生物来源对印度东北部和中国的OA也有很大的贡献。然而，这些来源对OA的影响及其季节变化，对于我们了解空气质量和气候变化也是非常关键的，但在中国研究较缺乏。在这次研究中，我们将通过观察天津市长期（一年以上）稳定碳（13C）同位素以及放射性碳（14C）同位素比值，以及该地区背景区（山地和陆上）的短期（每个季节1〜2周）分子标记物，来研究OA的一次源/二次源，自然/人为和化石/生物来源及其季节变化的机制。本研究可以提供OA特征及其每个季节的来源的综合信息，有助于构建大气模型，以更好地估计大气中OA转换机制及其对区域地区的气候影响。

东亚地区大气中高负荷的气溶胶是导致中国北部（尤其是京津冀地区）雾霾频发的的主要原因。为了更好地评估中国北部地区有机气溶胶（OA）的来源（如一次排放或二次生成、自然源或人为源、化石燃料燃烧或生物排放）及其季节性变化特征，我们分别在天津市的市区（ND）和郊区（HEP）连续采集了一年（2018年7月至2019年6月）的PM2.5样品，并测量了其中的碳质组分（OC、EC和WSOC）、氮质组分（WSTN和WSON）、稳定碳（δ13CTC）、氮（δ15NTN）同位素组成以及放射性碳同位素(14C)、微量元素、有机分子标记物和二元酸及其相关化合物。研究结果显示在中国北方实施严格的管控措施和煤改气、煤改电后，天津市PM2.5的年平均浓度明显下降。碳、氮组分，微量元素，离子，有机分子示踪剂（脱水糖，糖和糖醇类物质）和二元酸及其相关化合物的浓度均表现出明显的季节性特征，即冬季高，夏季低。通过对测量物质之间的质量比、相对丰度的季节变化以及它们与标记物和气象参数的线性关系的研究，并结合PMF模型分析的结果，我们认为水溶性OA主要来源于化石燃料（包括燃煤）和生物质燃烧排放、二次生成、汽车尾气排放、工业排放和沙尘。δ13CTC和δ15NTN的分布进一步证实生物质和煤炭燃烧是天津地区秋季和冬季气溶胶主要来源，而沙尘、生物源和海洋源排放是天津春季和夏季气溶胶的主要来源。此外，二元酸与环境温度、RH、SO42-、气态氧化剂（O3和NO2）和SO2的线性关系表明二元酸及其相关化合物的原位光化学过程在天津地区大气中十分显著，水溶性有机气溶胶（尤其是二元酸）的二次形成和转化在冷期（10月-2月）主要以液相氧化为主导，而在暖期（3月-9月）则是气相氧化更重要。本项目对OA及其来源作了系统性的研究，研究成果将有助于修正大气模型，以更好地评估大气中OA的估算及其对中国北方及其下风向地区的影响。