To evaluate sampling artifacts of PM 2.5 with conventional filtration system (FS), a contrastive study between the FS and a honeycomb denuder system (HDS) in measuring atmospheric concentrations of PM 2.5 and its main water-soluble ions (Cl -, NO 3 -, SO 4 2and NH 4 + ) was conducted at a urban site in Tianjin, China in both summer and winter. In this study, we confirmed the optimum concentration of absorbents of Na 2 CO 3 and citric acid for HDS were 3% and 6% in summer experiments and 4% and

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... riments and 4% and 5% in winter experiments. Daily mean concentrations of Clobtained by HDS were higher than those by FS both in summer and winter. In contrast, the HDS gave lower daily mean SO 4 2concentrations than FS in both summer and winter. For NO 3 and NH 4 + , concentrations obtained by HDS were lower than those obtained by FS in winter. However, the HDS gave larger values of NO 3 and NH 4 + than FS in summer. The different results of different ions were in response to the concentrations of interfering gases in ambient air and chemical characteristics of ionic species. In addition, the concentrations of PM 2.5 obtained by HDS were higher than those obtained by FS in summer, while virtually no significant difference between HDS and FS in winter. Our study points out that investigating optimum concentrations of coating solutions before denuder system sampling is necessary. Moreover, it is essential to make careful evaluation and modification when applying FS in highly polluted Environment, especially for PM 2.5 ions determining.