Microscopic morphology and seasonal variation of health effect arising from heavy metals in PM2.5 and PM10: One-year measurement in a densely populated area of urban Beijing

In order to study the sustained impact of particulate matter on urban residents, 572 PM2.5 and PM10 samples in all were attained simultaneously from a densely populated area of Beijing from September 2015 to August 2016. 11 types of heavy metals were determined as to better ascertain the seasonal variation characteristics of particle composition. In the course of the year, the mean concentrations of PM2.5 and PM10 were detected to be 102.45 mu g m(-3) and 144.75 mu g m(-3), respectively. From general perspective, winter turned out to be the longest in haze day quantity and the highest in particle concentration, followed by spring, autumn and summer, successively. The mass concentrations of numerous PM2.5 elements fluctuated evidently in the decreasing order of Ba, Zn, Mn, Sr, Cu, Pb, Cr, V, Ni, Cd and Sb. In contrast with other seasons, winter displayed the most evident increase of metal content in particulates, especially under the condition of haze. Relationship between different size particles was also reckoned with in this study. High concentration ratio of PM2.5 and PM10 (0.76-0.84) was detected during haze period, and PM2.5 was accounted as a primary pollutant during haze-fog day in Beijing. Moreover, the carcinogenic and non-carcinogenic risk posed by detected heavy metals was investigated. Cr posed the highest carcinogenic risk, and in the meantime, as compared with other non-carcinogenic metals, value of Pb was the highest in Hazard Quotient. Risk arising from Cr and Cd in winter shall be noteworthy, and accordingly it may pose danger or potential risk to adults in haze days. Eventually, a large amount of fly ash and soot particles in winter samples were indicated from SEM-EDX analysis results, whereas those are rarely detected in summer samples.