PM2.5 aerosols from Jinan (36°256'N, 117°106'E) in the North China Plain region were investigated for water-soluble organic acids (WSOAs, i.e., oxalic acid, formic acid, acetic acid, methanesulfonic acid (MSA), and lactic acid) during 30 December 2016 to 21 February 2017. The average PM2.5 concentration was 168.77 μg/m3 with about 90.74% samples beyond the National Ambient Air Quality (NAAQ) standards (Grade II). The total concentration of the measured WSOAs averaged at 1.34 μg/m3, contributing to 0.80% of PM2.5 mass. In the observation, acetic acid was the most abundant WSOA, followed by oxalic acid, lactic acid, formic acid, and MSA. During the period, serious haze events frequently happened. The average concentrations of PM2.5 and every WSOA species were higher in haze than those in non-haze. The correlations among species suggested that WSOAs in haze had complicated sources and secondary pathways, especially aqueous-phase reactions which played an important role on WSOAs. The concentrations of WSOAs declined in the Spring Festival compared with those in the non-Spring Festival due to holiday effect. Fireworks burning during the Spring Festival had different influences on WSOAs with slight increases for acetic acid and lactic acid. Five source factors were identified by positive matrix factorization (PMF) model for five WSOAs, respectively, and the results revealed that secondary reactions were the main sources of WSOAs in haze.

中文翻译：

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济南冬季烟霾和春节期间PM2.5中水溶性有机酸的特征：浓度，形成和来源分配。

研究了华北平原地区济南（36°256'N，117°106'E）的PM2.5气溶胶中的水溶性有机酸（WSOAs，即草酸，甲酸，乙酸，甲磺酸（ （MSA）和乳酸）。平均PM2.5浓度为168.77μg/ m3，其中约90.74％的样品超出了国家环境空气质量（NAAQ）标准（二级）。测得的WSOAs的总浓度平均为1.34μg/ m3，占PM2.5质量的0.80％。在观察中，乙酸是最丰富的WSOA，其次是草酸，乳酸，甲酸和MSA。在此期间，经常发生严重的霾事件。雾霾中PM2.5和每种WSOA物种的平均浓度均高于非雾霾中。物种之间的相关性表明，雾霾中的WSOA具有复杂的来源和次要途径，尤其是水相反应在WSOA中起重要作用。由于节假日的影响，与非春节相比，春节期间WSOA的浓度有所下降。春节期间燃放的烟花对WSOA的影响不同，乙酸和乳酸略有增加。通过正矩阵分解（PMF）模型分别确定了5个WSOA的5个来源因子，结果表明，二级反应是WSOA在雾霾中的主要来源。由于节假日的影响，与非春节相比，春节期间WSOA的浓度有所下降。春节期间燃放的烟花对WSOA的影响不同，乙酸和乳酸略有增加。通过正矩阵分解（PMF）模型分别确定了5个WSOA的5个来源因子，结果表明，二级反应是WSOA在雾霾中的主要来源。由于节假日的影响，与非春节相比，春节期间WSOA的浓度有所下降。春节期间燃放的烟花对WSOA的影响不同，乙酸和乳酸略有增加。通过正矩阵分解（PMF）模型分别确定了5个WSOA的5个来源因子，结果表明，二级反应是WSOA在雾霾中的主要来源。