Increasing impacts of the relative contributions of regional transport on air pollution in Beijing: Observational evidence.

Benefiting from the pollution controls implemented by the Chinese government, the concentrations of PM, SO, NO and CO showed a significant decrease in Beijing during 2013-2017. In this study, an observation-based method was employed to estimate the relative contributions of regional transport (MaxRTC) and local emissions (MinLEC) to air pollutant levels during 2013-2017 in Beijing. The results showed that the MaxRTC to SO and PM increased significantly over the five years, while those to CO and NO changed little. Furthermore, the difference in the emissions control efficiency (ΔECE) between Beijing (receptor region) and Shijiazhuang (source region), which refers to the concentration changes corresponding to unit emission changes of a certain air pollutant between the two regions, was introduced to verify the estimated variation in MaxRTC and MinLEC over 2013-2017. The negative value of ΔECE found for PM and SO supports the conclusion of an increasing effect of regional transport. This implies that local emissions control alone is not adequate for mitigating Beijing's air pollution, especially with the demand for continuously improving air quality. Joint prevention and control with regard to air quality on a regional scale is more important and urgent in the next Five-Year Plan.