Chemical Characteristics of Water-Soluble Ions in Particulate Matter in Three Metropolitan Areas in the North China Plain

December Chemical Characteristics of Water-Soluble Ions in Particulate Matter in Three Metropolitan Areas in the North China Xu Dao 0 1 2 3 6 Zhen Wang 0 1 2 4 5 6 Yibing Lv 0 1 2 3 6 Enjiang Teng 0 1 2 3 6 Linlin Zhang 0 1 2 3 6 Chao Wang 0 1 2 3 6 0 Funding: This work was supported by National Natural Science Foundation of China (Grant No. 41101567) to ZW. The authors also thank the financial award from State Scholarship Fund of China Scholarship Council (File No. 201308420277) to support the research at UCSB (to ZW). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript 1 Data Availability: The authors confirm that, for approved reasons, some access restrictions apply to the data underlying the findings. Data used in this paper are only available upon request as they are owned by the National Environmental Monitoring Center (CNEMC). CNEMC has the authority to publish the data. Researchers can send their request and intention of using data to Dr. Guanhua Xing (Program director of atmosphere laboratory of 2 Editor: Qinghua Sun, The Ohio State University , United States of America 3 China National Environmental Monitoring Centre , Beijing , China, 4 School of Resource and Environmental Sciences, Wuhan University , Wuhan, Hubei , China, 5 Department of Geography, University of California Santa Barbara , Santa Barbara, California , United States of America 6 Competing Interests: The authors have declared that no competing interests exist PM2.5 and PM10 samples were collected simultaneously in each season in Beijing, Tianjin and Shijiazhuang to identify the characteristics of water-soluble ion compositions in the North China Plain. The water-soluble ions displayed significant seasonal variation. The dominant ions were NO32, SO422, NH4+ and Cl2, accounting for more than 90% and 86% to the mass of total water-soluble ions in PM2.5 and PM10, respectively. The anion/cation ratio indicated that the ion acidity of each city varied both between sites and seasonally. Over 50% of the ion species were enriched in small particles #1 mm in diameter. The [NO32]/[SO422] ratio indicated that vehicles accounted for the majority of the particulate pollution in Beijing. Shijiazhuang, a city highly reliant on coal combustion, had a higher SO422 concentration. - Particulate matter (PM) in the atmosphere originates from either direct emission or physical and chemical transformation of gaseous pollutants [13]. Atmospheric aerosols have potential effects on human health, radiation balance, climate, and visibility [4, 5]. Air quality has become an increasing public health concern since a series of heavy pollutions of fine particulate matter (PM2.5, particles #2.5 mm in diameter) occurred in Beijing in 2011 winter. According to the WHO air quality guidelines and interim targets for particulate matter in developing countries, the 24hour concentration of PM10 and PM2.5 should be controlled below 150 and 75 mg/m3, respectively [6]. US EPA set the safe PM10 and PM2.5 concentration at 50 and 35 mg/m3, respectively [7]. With the increase in public awareness of the degradation of visibility or hazy weather, China released the Chinese National Ambient Air Quality Standards (NAAQS) in 2012, taking 150 and 75 mg/m3 as the 24-hour PM10 and PM2.5 limits in urban area, respectively, and 70 and 35 mg/m3 as the annual PM10 and PM2.5 limits, respectively. Previous epidemiological research has shown that high levels of particulate pollution lead to increased morbidity and mortality, as well as respiratory symptoms [811]. Smaller particles are deposited more easily in the lungs [9], and are thus more harmful to health than larger particles [12]. The chemical composition of the particles is important for understanding atmospheric visibility [13], as well as the locations of deposition in the lung [14]. Water-soluble ions are a key area of atmospheric environmental research [15]. Water-soluble ions, such as NH4+, Na+, K+, Ca2+, Mg2+, SO422, NO32, F2 and Cl2, are significant components of atmospheric particles [16, 17], which varies depending upon the particle source [18, 19]. North China is one of the regions in China with the highest frequency of haze events [20, 21]. According to the PM monitoring in Beijing during 2001 and 2003,the average 12-hour PM10 mass concentration reached as high as 263.2 mg/ m3 and PM2.5 ranged from 107 to 181 mg/m3 [22]. Another research showed the average PM10 annual mass concentration were 124 mg/m3 in Beijing and 141 mg/ m3 in Tianjin between 2009 to 2010 [23]. Both 24-hour and annual PM concentrations reported are far higher than the limits of NAAQS. Air pollution has increased as a function of population and the diversification of socioeconomic activities. However, there have been few studies on PM2.5 and PM10 with respect to their chemical composition and seasonal variation [24]. The majority of research on this region has focused on the composition [25], seasonal variation [26] and source of the particulate matter [27]. Generally, carbonaceous aerosol is the most abundant component of PM2.5 mass, and the main ions were NH4+, SO422 and NO32 [13, 26, 28]. Different dominant mechanisms for the formation of SO422, NO32 and Cl2 are found in the summer and the spring [29]. Various aerosol speciations associated with PM pollution display a distinct seasonality [30]. Remote sources, which were primarily soil derived Ca2+, Mg2+ and Al, contribute a major part of the PM pollution in spring [13, 30]. Seasonal peaks of organic carbon were commonly found in winter due to the high usage of coal for heating in the region [13, 31]. Simulation showed that the PM2.5 concentration was sensitive to NH3 emission [32]. In general, water-soluble ion species, including Na+, NH4+, K+, Mg2+, Ca2+, Cl2, NO32, and SO242, comprise 25%-50% of the aerosol mass predominantly in the form of sulfates, ammoniums and nitrates [33]. Water-soluble ions can scatter or absorb both incoming solar radiation and thermal radiation emitted from the Earths surface, thus directly change the radiation balance [34]. Previous studies mostly focused on a single size particle either in Beijing or in Tianjin [24, 35]. Only a few studies addressed PM concentrations across the major cities in North China Plain [36]. In addition, these studies seldom referred to the national atmospheric background status at the same period. This study, derived from a national atmospheric monitoring program in 2013, focuses on the water-soluble ion compositions and their variation in particulate matter in 3 metropolises in North China area. Also data from national atmospheric background sites are referred at the same sampling periods. Experiment 1. Sampling To compare the levels of the particulates and water-soluble ions in three cities (Beijing, Tianjin, Shijiazhuang) and four national atmospheric background sites, PM2.5 and PM10 samples were collected simultaneously at the (...truncated)