Gest Forum: Study on time variations of elemental composition and source of PM2.5 in Beijing

By: Xiaoyang YANG*, Shijie LIU

February 27, 2019

Figure 4 Factor profiles predicted from PMF model for PM2.5 samples obtained at Beijing

Author(*) Information: Atmospheric Environment Institute, Chinese Research Academy of Environmental Sciences, China

Chemical elements are major components of PM2.5 and crucial tracers to identify the source of aerosol particles using source apportionment models such as Positive Matrix Factorization (PMF) model and Chemical Mass Balance (CMB) model. In this study, PM2.5 samples were collected hourly from November 28, 2016, to May 30, 2017 in a chosen location within Beijing. Mass concentration and elemental composition were detected using an X-ray fluorescence-based online elemental analyzer (PX-375, Horiba, Kyoto, Japan). PM2.5 concentration ranged between 3.4 μg/m3 and 763 μg/m3 and had an average of 91.2 μg/m3 A total of twenty elements were detected and investigated. Among them, Ni had the lowest average concentration at 0.0038 μg/m3, and S had the highest average concentration at 5.82 μg/m3. The levels of Si, Ca, Fe, Mn, Cu, and K were found to be lower than their corresponding values from 2001 and 2006 reported in the literature. PMF model was employed to identify the main source of PM2.5. Based on the PMF source analysis, the primary sources of PM2.5 during the observation period in Beijing, in descending order of contribution to PM2.5, were secondary particles (44.0%), coal burning (28.3%), vehicle emission (17.2%), dust (7.9%), and fireworks (2.5%). The hourly variation trends of the three main sources are similar in winter due to atmospheric diffusion. PM2.5 concentration seemed positively corre-lated to each of the sources. In particular, vehicle emission and secondary particles appeared highly correlated during the winter. The model results also revealed that during different pollution episodes, excluding fireworks during festivals and dust storms, the contribution of secondary particles rose especially quickly, suggesting that the formation of the secondary particles was the crucial instigator in the explosive increase of PM2.5 concentration in Beijing during winter.

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