In situ continuous observation of hourly elements in PM_2.5 in urban beijing, China: Occurrence levels, temporal variation, potential source regions and health risks

Elements in fine particles (PM_2.5) have adverse impacts on ecosystems and human health. Using an online multi-heavy metal analyzer, one-year continuous hourly measurements were performed for thirteen elements, namely, K, Ca, Cr, Mn, Fe, Ni, Cu, Zn, As, Se, Ba, Hg and Pb, from June 1, 2016, to May 31, 2017, in urban Beijing. The total concentrations of 13 elements were in the range of 114–136,574 ng/m³, with a mean concentration of 2534 ± 5563 ng/m³. The four dominated elements were K (900 ± 3554 ng/m³), Fe (738 ± 1485 ng/m³), Ca (493 ± 1473 ng/m³) and Zn (174 ± 189 ng/m³). The annual mean concentrations of Cr and As exceeded the guideline values of the World Health Organization and the Chinese National Ambient Air Quality Standard. In the absence of firework-burning episodes and heavy dust storms, K, Cr, Mn, Cu, Zn, As, Se, Hg and Pb showed higher concentrations in autumn and winter, whereas lower concentrations were observed in spring and summer. The higher concentrations of Ca, Fe, and Ba observed in spring were associated with the frequent occurrence of dust. All elements showed higher concentrations on weekends than on weekdays. The diel patterns of Fe, Ba, Ca, Cu, Zn, Ni and Mn showed higher concentrations during peak traffic periods, whereas those of As, Cr, Hg, K, Pb and Se showed lower concentrations in the daytime but higher ones in the nighttime. The potential source function (PSCF) identified that neighboring provinces were the major source regions for most elements, whereas Ni mainly came from Shandong and the eastern ocean in spring and summer. Health risks of PM_2.5 elements (Cr, Mn, Ni, As, Ba and Pb) via the inhalation pathway were estimated. Mn (As) and As posed the highest noncarcinogenic and carcinogenic risks to human health, respectively. Overall, this work can provide more detailed information on the characteristics of elements for the science community and be used in other receptor modelling and health risk assessment studies.