Comparison of Filtration System and a Honeycomb Denuder-Based System for Sampling PM2.5 in Tianjin, China

ABSTRACT

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^–, NO₃^–, SO₄^2– and NH₄⁺) 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 Na₂CO₃ and citric acid for HDS were 3% and 6% in summer experiments and 4% and 5% in winter experiments. Daily mean concentrations of Cl^– obtained by HDS were higher than those by FS both in summer and winter. In contrast, the HDS gave lower daily mean SO₄^2– concentrations than FS in both summer and winter. For NO₃^– and NH₄⁺, concentrations obtained by HDS were lower than those obtained by FS in winter. However, the HDS gave larger values of NO₃^– and NH₄⁺ 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.