BACKGROUNDPolycyclic aromatic hydrocarbons (PAHs), as a typical persistent organic pollutant, widely exist in the environment and have high stability. Studying of the content distribution and source analysis of PAHs in soil will provide a technical basis for PAHs pollution prevention and control, ecological environment improvement and environmental protection policy-making.

OBJECTIVESIn order to investigate the content, composition and source of PAHs in the soil environment of different functional areas in Beijing City.

METHODSA large-scale sampling was carried out in the core area of Beijing City. At the same time, regional sampling was carried out for different functional areas such as industrial areas, agricultural planting areas, water source protection areas and residential areas. A total of 459 topsoil samples were collected, and the monomer contents of 16 PAHs were analyzed by gas chromatography-mass spectrometry (GC-MS).

RESULTSThe average values of the total contents of 16 PAHs (∑₁₆PAHs) in topsoil of the three subregions in the core area (southeast, center and northwest) were 153.7, 333.2 and 142.9μg/kg, respectively. The average values of ∑₁₆PAHs in topsoil of the industrial zone, including Southeast Factory, Shougang Industry and Datai Coal Mine, were 1006.9, 1379.4 and 146.8μg/kg, respectively. The average values of ∑₁₆PAHs in topsoil of the water-conserving areas, Huairou and Miyun, were 86.4μg/kg and 154.5μg/kg, respectively. The average values of ∑₁₆PAHs in topsoil of four agricultural planting regions (Changping, Pinggu, Fangshan and Tongzhou) were 109.0, 118.3, 106.8 and 94.2μg/kg, respectively. The average value of ∑₁₆PAHs in topsoil of residential areas was 131.1μg/kg. Compared with previous research results on the content and distribution characteristics of PAHs, the content of PAHs in the topsoil in Beijing City showed a decreased trend, which was related to the decrease in the use of coal and the increase in the use of natural gas in Beijing City in recent years. The composition of PAHs in different functional areas was different. The proportion of heavy and medium rings PAHs were higher in industrial areas. The proportion of light rings PAHs in water-conserving areas, agricultural planting regions and residential areas was higher than that in industrial areas, which might be due to the different sources of PAHs in different functional areas. The results of principal component analysis-multiple linear regression method showed that the main sources of PAHs in the core area were tail gas emissions and leakage during oil storage and transportation, which contributed 81.46% and 18.54%, respectively. The main sources of PAHs in the topsoil of the industrial area were coal combustion and tail gas emissions, which contributed 62.65% and 37.35%, respectively. The main sources of PAHs in residential areas were tail gas emissions and natural gas combustion sources, with contribution rates of 53.30% and 46.70%, respectively.

CONCLUSIONSFurther strengthening traffic control, continuing to reduce the proportion of coal in energy structure, and increasing the proportion of clean energy are effective ways to reduce PAHs emissions and pollution in Beijing City.