Spatial and Seasonal Variations of Polycyclic Aromatic Hydrocarbons (PAHs) in Ambient Particulate Matter (PM10, PM2.5) in Three Mega-Cities in China and Identification of Major Contributing Source Types

Beijing, is the political, economic and cultural center of China. Tianjin and Shijiazhuang, located close to Beijing are also two mega-cities with huge population. The rapid economic development in the three cities in the last decades has caused severe air pollution problems, especially airborne PAHs pollution, in both gaseous and particulate phases, which has resulted in considerable harm to the health of local residents. In this study, a total of 671 air samples were collected in the three cities and reference site, and four national air quality background sites. Concentrations and seasonal variations were discussed to describe the pollution status and identify possible sources. The results showed that concentrations of BaP, a PAH that serves as an indicator of PAH pollution, exceeded the Chinese national standard by 4–12 times. PAH concentrations varied significantly in different seasons, with similar trends in the three cities. The toxic equivalents quantity (i.e., quantity of total PAHs with an equivalent toxicity to BaP) ranged from 13.35 to 22.54 ng/m3 during the central heating period of winter and spring. These concentrations greatly exceeded the Chinese national standards for 24-h average (2.5 ng/m3) and annual average (1.0 ng/m3) concentrations of BaP. Two ratios that are indicative of PAH source, Pyr/BaP and BaP/BghiP, revealed that high percentages of the PAH pollution were contributed by coal combustion.