Aerosol and Air Quality Research, 18: 2600–2611, 2018 Copyright © Taiwan Association for Aerosol Research ISSN: 1680-8584 print / 2071-1409 online doi: 10.4209/aaqr.2018.07.0270 Wet Deposition of PCDD/Fs in Taiwan Yen-Yi Lee1, Wen-Che Hou1*, Jinning Zhu2*, Weiwei Wang2* 1 Department of Environmental Engineering, National Cheng Kung University, Tainan 70101, Taiwan 2 School of Resources and Environmental Engineering, Hefei University of Technology, Hefei 246011, China ABSTRACT In 2017, the seasonal variations in the wet deposition fluxes of total-PCDD/Fs-WHO2005-TEQ in ambient air were evaluated in Taiwan. The results showed the annual wet deposition fluxes of total-PCDD/Fs-WHO2005-TEQ to be –2 –1 –2 42.5 pg WHO2005-TEQ m month , and the seasonal distributions were 53.3, 62.9, 26.7 and 27.1 pg WHO2005-TEQ m –1 month in spring, summer, autumn and winter, respectively. The average Stot of total-PCDD/Fs-WHO2005-TEQ was 12300. There were obvious seasonal variations in Stot, for which the values were 13840, 6540, 8280 and 20540 in spring, summer, autumn, and winter, respectively. The average concentration of total-PCDD/Fs-WHO2005-TEQ in the rain were –1 0.453, 0.176, 0.218 and 0.649 pg WHO2005-TEQ L in spring, summer, autumn and winter, respectively. Atmospheric deposition is the major removal pathway for PCDD/Fs. The results of this study provide an evaluation of the adverse effects of PCDD/Fs exposure on human health, and provide a reason for the government to be concerned and to enact better control on air pollution. Keywords: PM2.5; PCDD/Fs; Wet deposition; Scavenging ratio. INTRODUCTION and windblown particulates. On the other hand, vehicular emissions, industrial exhaust gases, power plants, and open Particulate matter (PM) is a complex mixture of solid burning are major anthropogenic sources (Pipalatkar et al., and liquid particles suspended in the air (Ghosh et al., 2014; Liu et al., 2015; Wang et al., 2015; Tseng et al., 2014). According to previous studies, the concentration of 2016; Hsu et al., 2017). According to Frank et al. (2006), PM is affected by both its physical characteristics, the weather condition, including temperature, humidity, rain including size morphology, composition and porosity, and scavenging, and wind speed, and the local geography, such its chemical characteristics, such as the composition of as topography and surface soil, can be important factors ionic components, trace metals, and organic carbon (Schmid contributiong to ambient PM concentrations. Besides et al., 2007; Hu et al., 2012). Depending on its aerodynamic primary sources, directly emitted pollutants, the secondary diameters, PM is classified into four categories: PM2.5 (less sources, which are usually formed through photochemical than 2.5 µm), PM10 (less than 10 µm), and TSP (total reaction should also be taken into consideration. Therefore, suspended particles, less than 100 µm). In recent decades, environmental conditions and saturation ratios are important several epidemiological studies have interlinked a positive factors related to the ambient concentration of PM from correlation between exposure and health impact. Moreover, both primary sources and secondary sources (Harrison et due to its health impact, especially in the case of fine al., 1997; Marcazzan et al., 2001; Frank et al., 2006). particulates (PM2.5), PM has become one of the most Polychlorinated dibenzo-p-dioxins (PCDDs) and notorious forms of air pollution (Saldarriaga-Norena et al., polychlorinated dibenzofurans (PCDFs) have the similar 2009; Wang et al., 2014; Liao et al., 2015; Lu et al., 2016). structures and are defined as persistent organic pollutants The major sources of PM can be divided into two major (POPs). The emission sources of PCDD/Fs are very categories: naturally formed and anthropogenic. Natural multivariate. Similar to PM, the sources of PCDD/Fs can sources include volcanic eruptions, wood burning, sea salts, be divided into anthropogenic sources and natural sources. According to previous research, anthropogenic activities account for the major emissions, including municipal solid waste incinerators, medical waste incinerators, traffic * Corresponding author. emission (Hashimoto et al., 1990; Ni et al., 1999; Oh et E-mail address: [email protected] (W.C. Hou); al., 1999; Prange et al., 2003; Chen et al., 2017b). POPs [email protected] (J. Zhu); are semi-volatile and hydrophobic compounds. These [email protected] (W. Wang) characteristics increase their resistance to environmental Lee et al., Aerosol and Air Quality Research, 18: 2600–2611, 2018 2601 degradation and their ability to accumulate in soil, water, County, Chiayi in Chiayi City, Puzi and Xingang in Chiayi and food (Hu et al., 2009; Cheruiyot et al., 2015, 2016; County, Erlin, Changhua and Siansi in Changhua County, Chi et al., 2016; Redfern et al., 2017). Moreover, PCDD/Fs Dali, Xitun, Shalu, Zhongming and Fengyuan in Taichung tend to be adsorbed on the surfaces of particulate matter City, Shilin, Tatung, Zhongshan, Guting, Songshan, (Wang et al., 2010; Huang et al., 2011a; Lee et al., 2016). Yangming and Wanhua in Taipei City, Taitung and According to Wang et al. (2010), ambient transport is the Guanshan in Taitung County, Annan, Shanhua, Xinying major PCDD/Fs disperse route. Besides their persistency, and Tainan in Tainan City, Magong in Penghu County. the toxicity of PCDD/Fs is also a major concern to scientists. The health impact of PCDD/Fs has been proven by several Scavenging Ratio previous studies (Liem et al., 2000; Montesano and Hall, Due to the slightly solubility, the flux of PCDD/F wet 2001). Long-term exposure to PCDD/Fs can cause damage deposition in the form of take vapor dissolution into rain to the immune system, retardation in the development of and the removal of suspended particulates by precipitation the endocrine system, and destruction of the reproductive must be taken into consideration. functions (Bock and Köhle, 2006). Since PCDD/Fs are The gas scavenging ratio (Sg) can be estimated by: semi-volatile compounds, gas-particle partitioning plays an important role. The partitions of PCDD/Fs include between Sg = RT/H (1) surface soil and water and between gas and particle phases in the atmosphere, which usually differ due to different Sg: the gas scavenging ratio of PCDD/Fs (dimensionless); concentrations, pollutant properties, vapor pressures, and R: the universal gas constant (82.06 × 10–6 m3 atm mol–1 K–1); the atmospheric temperature (Pankow, 1987; Chang et al., T: ambient temperature (K); 2004; Lee et al., 2016; Zhu et al., 2017a, b). Both dry and wet H: the Henry constant (m3 atm mol–1). deposition are important pathways for removing PCDD/Fs Moreover, meteorological factors and particle from the air to the soil and water system (Welsch-Pausch et characteristics are both important influences of particle al., 1995; Horstmann and McLachlan, 1997; Lohmann and scavenging. The concentrations of the gas phase in the air Jones, 1998; Ren et al., 2007). The dry deposition is an (Sg) should also be taken into consideration. Therefore, the important route for PCDD/Fs to transfer from air to land or gas scavenging ratio can be calculated by: water. While the wet deposition is a combination removal pathway of PCDD/Fs from vapor to rain and precipitation Sg = Crain,dis/Cg (2) (Lohmann and Jones, 1998). Therefore, due to different weather conditions, the concentrations will vary from area to Sg: the gas scavenging ratio of PCDD/Fs (dimensionless); area. This study focuses on seasonal variations in atmospheric Crain,dis: the dissolved-phase concentration of PCDD/Fs in wet deposition fluxes of total-PCDD/Fs-WHO2005-TEQ in the raindrop; different areas in Taiwan. In addition, seasonal variations in Cg: the concentration of PCDD/Fs in the gas phase. the scavenging ratio and the total-PCDD/Fs-WHO2005-TEQ The particle scavenging ratio is defined as the ratio of concentrations in the rain in different areas in Taiwan are the concentration of the particle phase in a raindrop compared and discussed. divided by the concentrations of the particle phase in the air, where Sp, can be calculated by: MATERIALS AND METHOD Sp = Crain,particle/Cp (3) Sample Collection In this study, the meteorological data, including ambient where Sp: the particle scavenging ratio of PCDD/Fs temperature and rainfall, were collected from 48 local air (dimensionless); quality stations in 9 cities and 13 counties in 2017 in Taiwan. Crain,particle: the particle-phase concentration of PCDD/Fs in The PCDD/F concentration and gas-particle partition data the raindrop; were retrieved from our previous study (Lee et al., 2018). Cp: the concentration of PCDD/Fs in the particle phase. The name and the location of the 48 air quality stations are The total precipitation scavenging is the sum of gas and as follows: Dongshan and Yilan in Yilan County, Hualien particle scavenging (Stot) can be calculated by: in Hualien County, Kinmen in Kinmen County, Chushan, Nantou and Puli in Nantou County, Pingtung, Hungchun Stot= Sg (1 – Φ) + Sp × Φ (4) and Chaojhou in Pingtung County, Sani, Miaoli and Toufen in Miaoli County, Dayuan, Zhongli, Pingchen, Stot: the total scavenging ratio of PCDD/Fs (dimensionless); Taoyuan, Longtan and Guanyin in Taoyuan City, Daliao, Φ: the fraction of PCDD/Fs bound to particles. Siaogang, Renwu, Tsoying, Linyuan, Qianqiu, Meinung, Due to a lack of real measured data or the particle Fuxing, Nanzih, Fongshan and Ciaotou in Kaohsiung City, scavenging ratios of PCDD/Fs, the Sp (Sp was 42000) values Keelung in Keelung City, Matsu in Lienchiang County, of OCDD and OCDF measured by Eitzer and Hites (1989) Douliou, Lunbei and Mailiao in Yunlin County, Sanchong, were averaged and used here. Tucheng, Yonho, Xizhi, Banqiao, Linkou, Tamsui, Cailiao, Xindian, Xinzhuang and Wanli in New Taipei City, Wet Deposition Hsinchu in Hsinchu City, Zhudong and Hukou in Hsinchu Wet deposition is the removal of particles in the 2602 Lee et al., Aerosol and Air Quality Research, 18: 2600–2611, 2018 atmosphere by precipitation (rainfall and cloud droplets).