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 PM2.5 and its main water-soluble ions (Cl^-, NO_3^-, SO_4^(2-) and 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_2CO_3 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 SO_4^( 2-) concentrations 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.
Highlights
Fine particulate matter (PM2.5) is the main air pollutant in many cities of China
For NO3– and NH4+, concentrations obtained by honeycomb denuder system (HDS) were lower than those obtained by filtration system (FS) in winter
Different concentrations of coating solutions were coated on denuders ions species were extracted from denuders after sampling determining optimum concentration of coating solutions by IC
Summary
Water-soluble ions are the main components of atmospheric PM2.5 (He et al, 2001; Gao et al, 2011). They can affect human heath, reduce visibility, acidify rain water, and alter the radiation balance of the atmosphere (Ding et al, 2008; Ostro et al, 2009; Polichetti et al, 2009; Cao et al, 2012; Robichaud and Ménard, 2014). Accurate measurements of atmospheric PM2.5 and its compositions are essential for understanding aerosol properties and effects. The conventional measurement of PM2.5 and its compositions is filtration system (FS), which includes a 2.5 μm cut inlet. PM2.5 concentrations are determined by weighing before and after sampling, and main water-
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