Atmospheric concentrations and air–soil gas exchange of polycyclic aromatic hydrocarbons (PAHs) in remote, rural village and urban areas of Beijing–Tianjin region, North China

Abstract

Forty passive air samplers were deployed to study the occurrence of gas and particulate phase PAHs in remote, rural village and urban areas of Beijing–Tianjin region, North China for four seasons (spring, summer, fall and winter) from 2007 to 2008. The influence of emissions on the spatial distribution pattern of air PAH concentrations was addressed. In addition, the air–soil gas exchange of PAHs was studied using fugacity calculations. The median gaseous and particulate phase PAH concentrations were 222 ng/m3 and 114 ng/m3, respectively, with a median total PAH concentration of 349 ng/m3. Higher PAH concentrations were measured in winter than in other seasons. Air PAH concentrations measured at the rural villages and urban sites in the northern mountain region were significantly lower than those measured at sites in the southern plain during all seasons. However, there was no significant difference in PAH concentrations between the rural villages and urban sites in the northern and southern areas. This urban–rural PAH distribution pattern was related to the location of PAH emission sources and the population distribution. The location of PAH emission sources explained 56%–77% of the spatial variation in ambient air PAH concentrations. The annual median air–soil gas exchange flux of PAHs was 42.2 ng/m2/day from soil to air. Among the 15 PAHs measured, acenaphthylene (ACY) and acenaphthene (ACE) contributed to more than half of the total exchange flux. Furthermore, the air–soil gas exchange fluxes of PAHs at the urban sites were higher than those at the remote and rural sites. In summer, more gaseous PAHs volatilized from soil to air because of higher temperatures and increased rainfall. However, in winter, more gaseous PAHs deposited from air to soil due to higher PAH emissions and lower temperatures. The soil TOC concentration had no significant influence on the air–soil gas exchange of PAHs.

Distribution of atmospheric particulate matter (PM) in rural field, rural village and urban areas of northern China

“…During this period, the observed PM 10 concentrations at all sites were among the lowest of the year. The scavenging effects of precipitation on atmospheric pollutants in northern China has also been demonstrated by other studies (Liu et al, 2008;Wang et al, 2011b). In summary, the seasonal variations of PM 10 concentrations are mainly affected by three factors: coal and biomass fuel combustion for heating in winter, sandstorms during the spring, and summer rain events.…”

“…A similar phenomenon has been reported by Liu et al (2007), who conducted an extensive survey in the Northern China Plain during 2005e2006 and found that the concentrations of PAHs in ambient air in rural villages were similar to, even slightly higher than those in big cities. In a study of atmospheric PAHs in BeijingeTianjin area, no significant difference was found between rural villages and urban sites (Wang et al, 2011b). In fact, primarily due to the previous findings, rural village and rural field sites were designed separately in this study.…”

“…Hence, the major local sources of PM 10 in Beijing are likely to be aerosols associated with over three million motor vehicles on roads, coal-fired power plants, centralized heating boilers, gasoline-stations, and commercial activities (He et al, 2001;Sun et al, 2004;Yang et al, 2011). Immediately next to several other large cities and within an extremely densely populated metropolitan region, emissions from industrial, transportation, as well as household solid fuel combustion in the surrounding area also contribute to a large portion of the air pollution in Beijing Wang et al, 2011aWang et al, , 2011b. PM 10 pollution at a site depends on initial concentrations at the source and removal processes.…”

“…As a result, extra fuel is needed during the heating season, which usually lasts from early November to the middle of March in northern China (Wang et al, 2011b;. It was reported that residential fuel consumption rates in northern China during the winter were generally 1.5e2 times of those in summer (Liu et al, 2008;Qin et al, 2007).…”

Association of soil polycyclic aromatic hydrocarbon levels and anthropogenic impacts in a rapidly urbanizing region: Spatial distribution, soil–air exchange and ecological risk

“…As an important matrix in urban terrestrial environment, soil has been a major sink of contaminates (Jones, 1994;Hippelein and Mclachlan, 1998;Manzetti, 2013) and well interacts with other environmental compartments. On the other hand, contaminated soil may also be a secondary emission source for some contaminates in the atmosphere (Jones, 1994;Hippelein and Mclachlan, 1998;Li et al, 2010;Wang et al, 2011b;Zhang et al, 2011b). Thus, investigations into the occurrence and soilair exchange of contaminates in soil can help to understand the fate of contaminates and impacts of anthropogenic activities on the environment under the backdrop of rapid urbanization.…”