PAH contamination in Beijing's topsoil: A unique indicator of the megacity's evolving energy consumption and overall environmental quality

To improve its air quality, Beijing, the capital of China, has implemented high-cost pollution control measures mainly focused on shifting its energy mix. However, the effectiveness of these measures has long been questioned, especially given the recent problem of severe haze. The main study objectives are to achieve independent, although indirect, information on Beijing's air pollution by measuring the level of polycyclic aromatic hydrocarbon (PAH) contamination in topsoil and to examine how soil contamination reflects energy consumption. Soil sampling data from two years, 2004 and 2013, were used. The key findings are as follows: 1) although the total PAH content in the topsoil did not significantly decrease from 2004 to 2013, the composition changed considerably; 2) as of 2013, vehicle emissions replaced coal combustion as the leading source of soil PAHs, which validates the existing policy measures regarding vehicle purchasing and traffic volume; 3) the regional transport of atmospheric pollutants, as indicated by the contribution of coking sources in 2013, is not negligible; and 4) appropriate policy measures are needed to control the growing practice of burning biomass. Overall, this study demonstrates that the PAH contamination in topsoil represents an informative indicator of Beijing's energy consumption and overall environmental quality.