First Long-Term and Near Real-Time Measurement of Trace Elements in China’S Urban Atmosphere: Temporal Variability, Source Apportionment and Precipitation Effect
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Atmos. Chem. Phys., 18, 11793–11812, 2018 https://doi.org/10.5194/acp-18-11793-2018 © Author(s) 2018. This work is distributed under the Creative Commons Attribution 4.0 License. First long-term and near real-time measurement of trace elements in China’s urban atmosphere: temporal variability, source apportionment and precipitation effect Yunhua Chang1,2,3, Kan Huang4, Mingjie Xie5, Congrui Deng4, Zhong Zou4,6, Shoudong Liu1,2,3, and Yanlin Zhang1,2,3 1Yale-NUIST Center on Atmospheric Environment, International Joint Laboratory on Climate and Environment Change (ILCEC), Nanjing University of Information Science & Technology, Nanjing 210044, China 2Key Laboratory of Meteorological Disaster, Ministry of Education (KLME)/ Collaborative Innovation Center on Forecast and Evaluation of Meteorological Disasters (CIC-FEMD), Nanjing University of Information Science & Technology, Nanjing 210044, China 3Jiangsu Provincial Key Laboratory of Agricultural Meteorology, College of Applied Meteorology, Nanjing University of Information Science & Technology, Nanjing 210044, China 4Center for Atmospheric Chemistry Study, Shanghai Key Laboratory of Atmospheric Particle Pollution and Prevention (LAP3), Department of Environmental Science and Engineering, Fudan University, Shanghai 200433, China 5School of Environmental Science and Engineering, Nanjing University of Information Science & Technology, Nanjing 210044, China 6Pudong New Area Environmental Monitoring Station, Shanghai 200135, China Correspondence: Yanlin Zhang ([email protected], [email protected]) Received: 30 June 2017 – Discussion started: 1 August 2017 Revised: 29 July 2018 – Accepted: 6 August 2018 – Published: 20 August 2018 Abstract. Atmospheric trace elements, especially metal bution in parentheses): traffic-related (Ca, Fe, Ba, Si; 46 %), species, are an emerging environmental and health concern shipping (V, Ni; 6 %), nonferrous metal smelting (Ag, Cd, with insufficient understanding of their levels and sources in Au; 15 %), coal combustion (As, Se, Hg, Pb; 18 %) and fer- Shanghai, the most important industrial megacity in China. rous metal smelting (Cr, Mn, Zn; 15 %). The contribution Here we continuously performed a 1 year (from March 2016 from the exhaust and non-exhaust vehicle emissions, i.e., the to February 2017) and hourly resolved measurement of 18 traffic-related factor shows a strong bimodal diurnal profile elements in fine particles (PM2:5) at the Shanghai urban cen- with average concentration over 2 times higher during the ter with an Xact multi-metals monitor and several collocated rush hour than during nighttime. The shipping factor was instruments. Mass concentrations (mean ± 1σ; ng m−3) de- firmly identified because V and Ni, two recognized tracers of termined by Xact ranged from detection limits (nominally shipping emissions, are almost exclusively transported from 0.1 to 20 ng m−3) to 15 µg m−3. Element-related oxidized the East China Sea and their ratio (around 3.2) falls within species comprised an appreciable fraction of PM2:5 during the variation range of V = Ni ratios in particles emitted from all seasons, accounting for 8.3 % on average. As a compari- heavy oil combustion. Interestingly, nearly half of the K was son, the atmospheric elements concentration level in Shang- derived from coal combustion with high mineral affinity (ele- hai was comparable with that in other industrialized cities ments associated with aluminosilicates, carbonates and other in East Asia but 1 or 2 orders of magnitude higher than minerals in coal ash). The contributions of nonferrous metal at sites in North America and Europe. Positive matrix fac- smelting to the trace elements are consistent with a newly de- torization (PMF) was applied to identify and apportion the veloped emission inventory. Although the precipitation scav- sources of the elements in the PM2:5 mass. Five different enging effect on the mass concentration of the trace ele- factors were resolved (notable elements and relative contri- ments varied among different species and sources, precipi- Published by Copernicus Publications on behalf of the European Geosciences Union. 11794 Y. Chang et al.: First long-term and near real-time measurement of trace elements tation could effectively lower the concentration of the traffic- of biochemical synthesis pathways (Charrier and Anastasio, and coal combustion-related trace elements. Therefore, wa- 2012; Strak et al., 2012; Rubasinghege et al., 2010b; Saffari ter spray to simulate natural types of precipitation could be et al., 2014; Verma et al., 2010; Jomova and Valko, 2011). one of the abatement strategies to facilitate the reduction of Additionally, lighter elements such as Si, Al and Ca are the ambient PM2:5 trace elements in the urban atmosphere. Col- most abundant crustal elements next to oxygen, which can lectively, our findings in this study provide baseline levels typically constitute up to 50 % of the elemental species in re- and sources of trace elements with high detail, which are mote continental aerosols (Usher et al., 2003; Ridley et al., needed for developing effective control strategies to reduce 2016). These species are usually associated with the impacts the high risk of acute exposure to atmospheric trace elements of aerosols on respiratory diseases and climate (Usher et al., in China’s megacities. 2003; Tang et al., 2017). Health effects of airborne elemental species are not only seen from chronic exposure, but also from short-term acute concentration spikes in the ambient air (Kloog et al., 2013; 1 Introduction Strickland et al., 2016; Huang et al., 2012). In addition, at- mospheric emissions, transport and exposure of trace ele- It is well known that personal exposure to atmospheric ments to human receptors may depend upon rapidly evolving aerosols have detrimental consequences and aggravating ef- meteorological conditions and facility operations (Tchoun- fects on human health such as respiratory, cardiovascular and wou et al., 2012; Holden et al., 2016). Typical ambient trace allergic disorders (Pope III et al., 2002, 2009; Shah et al., element sampling devices collect 12 to 24 h integrated av- 2013; West et al., 2016; Burnett et al., 2014). Among the erage samples, which are then sent off to be lab analyzed chemical components relevant for aerosol health effects, air- in a time-consuming and labor-intensive way. As a conse- borne heavy metals (a very imprecise term without author- quence, daily integrated samples inevitably ignore environ- itative definition; John, 2002, loosely referring to elements mental shifts with rapid temporality and thereby hinder the with atomic density greater than 4.5 g cm−3; Streit, 1991) are efforts to obtain accurate source apportionment results such of particular concern as they typically feature unique prop- as short-term elements pollution spikes related to local emis- erties of bioavailability and bioaccumulation (Morman and sion sources. In fact, during a short-term trace elements ex- Plumlee, 2013; Tchounwou et al., 2012; Fergusson, 1990; posure event, 12 or 24 h averaged sample concentrations for Kastury et al., 2017), representing 7 of the 30 hazardous elemental species like Pb and As may be one order of magni- air pollutants identified by the United States Environmen- tude lower than the 4 h or 15 min average concentration from tal Protection Agency (EPA) in terms of posing the greatest the same day (Cooper et al., 2010). Current source apportion- potential health threat in urban areas (see https://www.epa. ment studies are mainly performed by statistical multivari- gov/urban-air-toxics/urban-air-toxic-pollutants; last access: ate analysis such as receptor models (e.g., Positive Matrix 1 August 2018). Depending on the aerosol composition, ex- Factorization, PMF), which could greatly benefit from high tent and time of exposure, previous studies have confirmed inter-sample variability in the source contributions through that most elemental components of fine particles (PM2:5; par- increasing the sampling time resolution. In this regard, con- ticulate matter with aerodynamic diameter equal to or less tinuous monitoring of ambient elemental species on a real- than 2.5 µm) exert a multitude of significant diseases from time scale is essential for studies on trace element sources pulmonary inflammation, to increased heart rate variability, and their health impacts. to decreased immune response (Fergusson, 1990; Morman Currently, there are only a few devices available for and Plumlee, 2013; Leung et al., 2008; Hu et al., 2012; Pardo the field sampling of ambient aerosols with sub-hourly or et al., 2015; Kim et al., 2016). hourly resolution, i.e., the streaker sampler, the DRUM Guidelines for atmospheric concentration limits of many (Davis Rotating-Drum Unit for Monitoring) sampler and trace elements are provided by the World Health Organiza- the SEAS (Semi-continuous Elements in Aerosol Sam- tion (WHO) (WHO, 2005). In urban atmospheres, ambient pler) (Visser et al., 2015a, b; Bukowiecki et al., 2005; trace elements typically represent a small fraction of PM2:5 Chen et al., 2016). Mass loadings of trace elements col- on a mass basis, while elemental species like Cd, As, Co, lected by these samplers can be analyzed with highly sen- Cr, Ni, Pb and Se are considered as human carcinogens even sitive accelerator-based analytical techniques, in particular in trace amounts (Iyengar and Woittiez, 1988; Wang et al., particle-induced X-ray emission (PIXE) or synchrotron ra- 2006; Olujimi et al., 2015). It has been shown