Abstract
Ambient air samples were collected simultaneously at three sites in winter and summer to investigate the characteristic variations of PAHs in northern Taiwan. In winter, the highest concentration was observed at urban site (225 ± 25.0 ng m–3), followed by industrial and rural sites (173 ± 28.7 and 148 ± 12.9 ng m–3, respectively). However, in summer, the highest PAHs concentration was measured at rural site (230 ± 8.0 ng m–3), followed by urban and industrial sites (205 ± 29.2 and 200 ± 44.1 ng m–3, respectively). Based on the air mass back trajectory, the air mass passing through more PAH sources before reaching the sampling site is the reason for higher PAH level being measured at rural site in summer. The highest BaP-TEQ concentration measured at rural site in summer suggests that human exposure to PAHs in summer should receive more attention. Based on the diagnostic ratios, samples collected at industrial site in two seasons are closely related to combustions of solid fuel and petroleum. At rural and urban sites, PAHs measured in winter are influenced by mixed sources of solid fuel/petroleum combustions and petroleum evaporation, while the sources of PAHs are more related to petroleum evaporation in summer. The gas/particle partitioning coefficients (Kp) correlated well with the sub-cooled liquid vapor pressures (PoL) of PAHs with the slopes higher than –1 (the r2 ranging from 0.835 to 0.909). The slope values indicate that both adsorption and absorption might govern gas/particle partitioning of PAHs. Comparison between different models reveals that adsorption of soot carbon is the major mechanism governing gas/particle partitioning.
Highlights
Polycyclic aromatic hydrocarbons (PAHs) are a group of organic compounds composed of multiple aromatic rings, which are mainly formed during incomplete combustion and pyrolysis of materials containing carbon and hydrogen, such as coal, oil, wood and petroleum products (Ravindra et al, 2008)
Sampling In order to investigate the characteristics of PAHs in different areas located in Taoyuan City, ambient air samples were simultaneously collected at 3 sites, including a rural site, an urban site and an industrial site
In summer, the PAHs concentration measured at rural site was the highest (219–237 ng m–3), followed by urban site (170–246 ng m–3) and industrial site (140–244 ng m–3)
Summary
Polycyclic aromatic hydrocarbons (PAHs) are a group of organic compounds composed of multiple aromatic rings, which are mainly formed during incomplete combustion and pyrolysis of materials containing carbon and hydrogen, such as coal, oil, wood and petroleum products (Ravindra et al, 2008). After being released from the sources into atmosphere, gas/particle partitioning of PAHs affects their transport, degradation, deposition and subsequent fate in the environment (Lv et al, 2016). Gas/particle partitioning of SVOC or PAHs can be governed by adsorption onto surface, absorption into the organic matter (OM) of aerosol or the combination of adsorption and absorption (Pankow, 1994). Pankow and Bidleman (1992) reported that well correlation between the observed log of gas/particle partitioning coefficient (logKp) and log of the PAH subcooled liquid vapor pressure (logP0L) according to Eq (2), and the slope values are usually close to –1, which corresponds to adsorption mechanism. In order to include the role of soot into the calculation of gas/particle partitioning, Dachs and Eisenreich (2000) established a soot-air partition coefficient (KSA) and proposed a method for the evaluation of both roles played by adsorption onto soot and absorption into organic matter. Pankow and Bidleman (1992) reported that well correlation between the observed log of gas/particle partitioning coefficient (logKp) and log of the PAH subcooled liquid vapor pressure (logP0L) according to Eq (2), and the slope values are usually close to –1, which corresponds to adsorption mechanism. Pankow (1994) indicates that Eq (2) is linearly correlated if absorption is the dominant mechanism, which reveals that regardless of the importance of adsorbent or absorbent in gas/particle partitioning, the plot of logKp vs logP0L should be correlated with the slope close to –1. Goss and Schwarzenbach (1998)
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