First long-term and near real-time measurement of atmospheric trace elements in Shanghai, China
Authors: Chang Yunhua , Huang Kan , Deng Congrui , Zou Zhong , Liu Shoudong , Zhang Yanlin 
Published: August 2017

Abstract. Atmospheric trace elements, especially metal species, are an emerging environmental and health concern with poorly constrained on its abundances and sources in Shanghai, the most important industrial megacity in China. Here we continuously performed a one-year (from March 2016 to February 2017) and hourly-resolved measurement of eighteen elements in fine particles (PM2.5) at Shanghai urban center with a Xact multi-metals monitor and several collocated instruments. Independent ICP-MS offline analysis of filter samples was used to validate the performance of Xact that was based on energy-dispersive X-ray fluorescence analysis of aerosol deposits on reactive filter tapes. Mass concentrations (mean ± 1σ; ng m-3) determined by Xact ranged from detection limits (nominally 0.1 to 20 ng m-3) to 14.7 µg m-3, with Si as the most abundant element (638.7 ± 1004.5), followed by Fe (406.2 ± 385.2), K (388.6 ± 326.4), Ca (191.5 ± 383.2), Zn (120.3 ± 131.4), Mn (31.7 ± 38.7), Pb (27.2 ± 26.1), Ba (24.2 ± 25.4), V (13.4 ± 14.5), Cu (12.0 ± 11.4), Cd (9.6 ± 3.9), As (6.6 ± 6.6), Ni (6.0 ± 5.4), Cr (4.5 ± 6.1), Ag (3.9 ± 2.6), Se (2.6 ± 2.9), Hg (2.2 ± 1.7), and Au (2.2 ± 3.4). Metal related oxidized species comprised an appreciable fraction of PM2.5 during all seasons, accounting for 8.3 % on average. As a comparison, atmospheric metal pollution level in Shanghai was comparable with other industrialized cities in East Asia but one or two orders magnitude higher than the sites in North America and Europe. Here our high time-resolution observations over long-term period also offer a unique opportunity to provide robust diurnal profiles for each species, which are useful in determining the sources and processes contributing to the fluctuation of atmospheric trace elements. Besides, various mathematical methods and physical evidences were served as criteria to constrain various solutions of source identification. Results showed that atmospheric trace elements pollution in Shanghai was the interplay of local emissions and regional transport, and different sources of metal species generally have different variation patterns associated with different source regions. Specifically, V and Ni were confirmed as the prominent and exclusive tracer of heavy oil combustion from shipping traffic. Fe and Ba were strongly related to brake wear, and exhibited significant correlation with Si and Ca, suggesting that Si and Ca in Shanghai were primarily sourced from road fugitive dust rather than long-distance dust transport and local building construction sites. Stationary combustion of coal was found to be the major source of As, Se, Pb, Cu and K, and the ratio of As / Se was used to infer that coal consumed in Shanghai likely originated from Henan coal fields in Northern China. Cr, Mn and Zn were the mixed result of emissions from stationary combustion coal, ferrous metals production, and nonferrous metals processing. Ag and Cd in Shanghai urban atmosphere were also the mixture of miscellaneous sources. Collectively, our findings in this study provide baseline data with high detail, which are needed for developing effective control strategies to reduce the high risk of acute exposure to atmospheric trace elements in China's megacities.