Spatial distribution and seasonal variation of atmospheric bulk deposition of polycyclic aromatic hydrocarbons in Beijing–Tianjin region, North China
Introduction
Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous environmental contaminants that are formed during the incomplete combustion of fossil and biofuels, and are serious health concern in the world (Zhang et al., 2009). Once enter into the atmosphere, PAHs are distributed between gas and particle phases and subject to removal mechanisms, such as oxidative and photolytic reactions, wet and dry deposition. It has been demonstrated that wet and dry deposition events are the major processes that remove PAHs from the atmosphere (Bidleman, 1988, Cousins et al., 1999). Researches on atmospheric PAHs deposition have been carried out widely in different parts of world (Halsall et al., 1997, Franz et al., 1998, Golomb et al., 2001, Park et al., 2001, Bae et al., 2002, Garban et al., 2002, Gigliotti et al., 2005, Terzi and Samara, 2005, Gocht et al., 2007, Tasdemir and Esen, 2007). In China, however, limited studies have been systematically performed on atmospheric PAHs deposition (Wu et al., 2005, Zhang et al., 2008).
There are two widely used methods to estimate PAH deposition. The first one uses gas and particulate phase PAHs concentration, and the deposition flux is calculated by multiplying the concentration and deposition velocity (Fang et al., 2004, Gigliotti et al., 2005). However, there are many uncertainties for determining the deposition velocity, which is influenced by particle size, meteorological conditions, properties of the receptor surface, and physical and chemical properties of the particle (Cousins et al., 1999). In the second method gaseous and particulate phase PAHs are collected directly on an artificial surface, such as metal pans, coated or uncoated glass fiber filter (GFF), plates filled fluid, greased surfaces, and water surface (Odabasi et al., 1999; Garban et al., 2002, Ollivon et al., 2002, Wu et al., 2005, Gocht et al., 2007, Pekey et al., 2007, Su et al., 2007, Tasdemir and Esen, 2007, Zhang et al., 2008), and the deposition flux can be calculated by PAHs concentration and sampling period. But the second method also has some drawbacks, which are PAHs re-volatilization from the collection surface and photo-degradation during sampling. Compared with the first method, the second one is more accurate and widely used in other studies.
Beijing and Tianjin are two of the largest cities in northern China. The high population growth and rapid industrialization and urbanization during the last decades have resulted in significant environmental problems, including severe PAH contamination (Tao et al., 2004). In addition, the PAH emission density in the North China Plain is among the highest in China and domestic coal combustion, biomass burning, and coking industry are the major contributors to PAH emissions in this area (Zhang et al., 2007).
The objectives of this study were to (1) measure bulk deposition concentration and fluxes (dry + wet deposition) of PAHs in remote, rural village and urban areas in Beijing–Tianjin region; (2) investigate the spatial and seasonal variations of the bulk deposition fluxes of PAHs in this region; (3) assess the influence of PAH emission sources, local population distribution, and atmospheric PAH concentration on the deposition fluxes of PAHs.
Section snippets
Sampling
There were 40 background, rural village and urban sampling locations in Beijing–Tianjin region (Fig. 1). All sampling sites were selected far from industrial areas and roadsides, and located in open areas without trees, buildings or any other sheltering objects near them. Detailed sampling information about sampling height, longitude, latitude and sampling periods were presented in Table S1 in Supplementary material.
Stainless steel buckets (i.d. 32 ± 0.5 cm, height 50 cm, flat-bottom) were used
PAHs concentration in the deposition
All of 15 PAHs were detected in the deposition samples, and the concentrations of individual PAHs in the deposition samples in different seasons are presented in Table 1. The annually averaged concentrations of 15 PAHs (∑PAH15) varied from 4.22 to 24.81 μg/g, with an arithmetic mean of 11.81 μg/g for the whole study region. Higher proportions of individual PAHs with three rings (50.4%) and four rings (36.5%) were observed in the deposition samples, followed by five and six ring (10.8%), and two
Conclusions
The concentrations of PAHs in bulk deposition samples (dry and wet deposition) were measured to examine the seasonal variation, spatial distribution, emission sources and deposition fluxes in remote, rural and urban areas of Beijing–Tianjin region, North China during spring, summer, fall and winter in 2007–2008. The annually averaged PAHs concentrations and deposition flux were 11.81 ± 4.61 μg/g and 5.22 ± 3.89 μg/m2/day respectively, and PHE, FLA, PYR, BbF and CHR had the highest deposition
Acknowledgement
This study is supported by National Basic Research Program (2007CB407301), National Science Foundation of China (Grant 140710019001 and 40730737), and China Scholarship Council (to Wentao Wang). The project described was also supported by Award Number P42 ES016465 and P30ES00210 from the National Institute of Environmental Health Sciences. The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institute of Environmental
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