Abstract
Abstract. Atmospheric trace elements, especially metal species, are an emerging environmental and health concern with insufficient understanding of their levels and sources in Shanghai, the most important industrial megacity in China. Here we continuously performed a 1 year (from March 2016 to February 2017) and hourly resolved measurement of 18 elements in fine particles (PM2.5) at the Shanghai urban center with an Xact multi-metals monitor and several collocated instruments. Mass concentrations (mean ± 1σ; ng m−3) determined by Xact ranged from detection limits (nominally 0.1 to 20 ng m−3) to 15 µg m−3. Element-related oxidized species comprised an appreciable fraction of PM2.5 during all seasons, accounting for 8.3 % on average. As a comparison, the atmospheric elements concentration level in Shanghai was comparable with that in other industrialized cities in East Asia but 1 or 2 orders of magnitude higher than at sites in North America and Europe. Positive matrix factorization (PMF) was applied to identify and apportion the sources of the elements in the PM2.5 mass. Five different factors were resolved (notable elements and relative contribution in parentheses): traffic-related (Ca, Fe, Ba, Si; 46 %), shipping (V, Ni; 6 %), nonferrous metal smelting (Ag, Cd, Au; 15 %), coal combustion (As, Se, Hg, Pb; 18 %) and ferrous metal smelting (Cr, Mn, Zn; 15 %). The contribution from the exhaust and non-exhaust vehicle emissions, i.e., the traffic-related factor shows a strong bimodal diurnal profile with average concentration over 2 times higher during the rush hour than during nighttime. The shipping factor was firmly identified because V and Ni, two recognized tracers of shipping emissions, are almost exclusively transported from the East China Sea and their ratio (around 3.2) falls within the variation range of V ∕ Ni ratios in particles emitted from heavy oil combustion. Interestingly, nearly half of the K was derived from coal combustion with high mineral affinity (elements associated with aluminosilicates, carbonates and other minerals in coal ash). The contributions of nonferrous metal smelting to the trace elements are consistent with a newly developed emission inventory. Although the precipitation scavenging effect on the mass concentration of the trace elements varied among different species and sources, precipitation could effectively lower the concentration of the traffic- and coal combustion-related trace elements. Therefore, water spray to simulate natural types of precipitation could be one of the abatement strategies to facilitate the reduction of ambient PM2.5 trace elements in the urban atmosphere. Collectively, our findings in this study provide baseline levels and sources of trace elements 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.
Highlights
It is well known that personal exposure to atmospheric aerosols have detrimental consequences and aggravating effects on human health such as respiratory, cardiovascular and allergic disorders (Pope III et al, 2002, 2009; Shah et al, 2013; West et al, 2016; Burnett et al, 2014)
It has been shown that Cu, Cr, Fe and V have several oxidation states that can participate in many atmospheric redox reactions (Litter, 1999; Brandt and van Eldik, 1995; Seigneur and Constantinou, 1995; Rubasinghege et al, 2010a), which can catalyze the generation of reactive oxygenated species (ROSs) that have been associated with direct molecular damage and with the induction of biochemical synthesis pathways (Charrier and Anastasio, 2012; Strak et al, 2012; Rubasinghege et al, 2010b; Saffari et al, 2014; Verma et al, 2010; Jomova and Valko, 2011)
In contrast to traditional trace element measurements, the on-line XRF used in the current study enables measurement of elemental species concentrations with 1 h resolution, which are useful both for source discrimination and in determining the processes contributing to elevated trace element levels through investigation of their seasonal, weekly, weekday-weekend and diurnal cycles
Summary
It is well known that personal exposure to atmospheric aerosols have detrimental consequences and aggravating effects on human health such as respiratory, cardiovascular and allergic disorders (Pope III et al, 2002, 2009; Shah et al, 2013; West et al, 2016; Burnett et al, 2014). It has been shown that Cu, Cr, Fe and V have several oxidation states that can participate in many atmospheric redox reactions (Litter, 1999; Brandt and van Eldik, 1995; Seigneur and Constantinou, 1995; Rubasinghege et al, 2010a), which can catalyze the generation of reactive oxygenated species (ROSs) that have been associated with direct molecular damage and with the induction of biochemical synthesis pathways (Charrier and Anastasio, 2012; Strak et al, 2012; Rubasinghege et al, 2010b; Saffari et al, 2014; Verma et al, 2010; Jomova and Valko, 2011) Lighter elements such as Si, Al and Ca are the most abundant crustal elements next to oxygen, which can typically constitute up to 50 % of the elemental species in remote continental aerosols (Usher et al, 2003; Ridley et al, 2016). These species are usually associated with the impacts of aerosols on respiratory diseases and climate (Usher et al, 2003; Tang et al, 2017)
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