Abstract:

Water-soluble organic carbon (WSOC) in atmospheric particulate matter (PM) is an important component of carbonaceous aerosols that has a significant impact on regional climate change and human health owing to its light absorption, hygroscopic properties, and toxic components. In Zhengzhou, a megacity with heavy PM pollution, there is a lack of short-and long-term studies on WSOC. To investigate the pollution characteristics, seasonal variation, sources, and light absorption of water-soluble organic carbon (WSOC) in PM_2.5, seasonal PM_2.5 samples were collected from December 2020 to October 2021. The concentration (using a total organic carbon analyzer) and light absorption parameters (UV-visible spectrophotometer) of WSOC were analyzed, and water-soluble inorganic ions (ion chromatography), organic carbon (OC), and elemental carbon (EC) (thermo-reflective carbon analyzer) were combined to identify the sources of WSOC. The results showed that the WSOC concentration averaged (13.56±7.48) μg∙m⁻³ during the sampling periods and exhibited significant seasonal variations, with the maximum value in winter and the minimum value in summer. Compared to domestic and foreign studies, WSOC pollution in this study was more serious, and its impact on human health and uncertainty in assessing and predicting climate impacts cannot be ignored. The contribution of WSOC to OC was significantly higher in summer than in winter, indicating the significant influence of secondary generations in summer. The major WSOC sources identified by the positive matrix factorization (PMF) model and correlation analysis were biomass burning, secondary generation, and vehicle exhaust emissions, followed by coal burning and soil/construction dust sources. The annual average light absorption index (AAE) was 6.88±1.31, with no significant seasonal variations. The annual average light absorption intensity (A_bs365) was (9.71±5.77) Mm⁻¹. Correlation analysis showed that water-soluble brown carbon (BrC) and WSOC had similar sources during the sampling period, with biomass burning in winter and secondary-generation burning in summer being the main sources. The annual average mass absorption efficiency (MAE₃₆₅) was (0.710±0.206) m²∙g⁻¹, which is a moderate level compared to domestic and foreign studies, and the influence of the WSOC mass unit on radiative forcing in Zhengzhou cannot be ignored. Both A_bs365 and MAE₃₆₅ had the same seasonal variation trend as WSOC, which was related to the composition and emission sources of WSOC in different seasons.

Key words: WSOC, pollution characteristics, seasonal variation, source, light absorption properties

摘要：

大气颗粒物中水溶性有机碳（WSOC），碳质气溶胶的重要组成部分，因其具有吸光性和吸湿性，且含有有毒的组分，对区域气候变化和人体健康具有重要的影响。郑州是颗粒物污染严重的大都市，对WSOC的短期或长期研究均很匮乏。为探究郑州大气PM_2.5中WSOC的污染特征、季节变化、来源和吸光特性，于2020年12月－2021年10月4个不同季节连续采集PM_2.5样品，对WSOC的浓度（总有机碳分析仪）和吸光特性（紫外－可见分光光度计）进行分析，并结合水溶性无机离子（离子色谱），有机碳（OC）和元素碳（EC）（热光反射碳分析仪）数据对WSOC进行来源解析。结果表明，采样期间WSOC的质量浓度年平均值为(13.6±7.48) μg∙m⁻³，且浓度具有明显的冬季高、夏季低的季节特征。与国内外研究对比发现，该研究的WSOC污染较严重，其对人体健康，对气候影响评估和预测的不确定性不容忽视。夏季WSOC对OC的贡献明显高于冬季，表明夏季二次生成的重要影响。正定矩阵因子分解法（PMF）和相关性分析结果显示WSOC主要来源包括生物质燃烧，二次生成和机动车尾气排放，其次是煤燃烧和土壤/建筑尘源。WSOC的光吸收指数（AAE）年平均值为6.88±1.31，没有明显的季节变化。光吸收强度（A_bs365）年平均值为 (9.71±5.77) Mm⁻¹，通过相关性分析发现水溶性棕色碳（BrC）与WSOC具有相似的来源，冬季生物质燃烧，夏季二次生成均为其主要来源。质量吸收效率（MAE₃₆₅）年平均值为 (0.710±0.206) m²∙g⁻¹，与国内外研究相比，其大小处于中等水平，单位质量WSOC对郑州辐射强迫的影响不能忽略。A_bs365和MAE₃₆₅均具有与WSOC相同的季节变化特征，与不同季节WSOC的组成和排放源密切相关。

关键词: 水溶性有机碳, 污染特征, 季节变化, 来源, 吸光特性