Increasing importance of regional emission controls for further reduction of PM2.5 in Beijing

Over the past decade, Beijing has achieved positive results in controlling fine particulate matter (PM_2.5) pollution. However, it remains a challenge to further reduce PM_2.5 concentrations to a lower level, such as the World Health Organization's air quality guidelines (5 μg/m³). In this study, PM_2.5 concentrations and emission reductions over eight years covering two policy periods of air pollution abatement (2013–2017 and 2018–2020) were compared to investigate the efficiency of emission controls in Beijing and surrounding areas. An approach based on observational data, particularly including data from a regional atmospheric background station, was employed to calculate the relative contributions of the local emissions and regional transport. Results show that local emission reductions play a more important role in decreasing PM_2.5 in Beijing. However, following a substantial decrease in local emissions over the first period, the relative contribution of regionally transported PM_2.5 reached more than 50 % during the second period. The results indicate that joint regional prevention and control of air pollution are needed for Beijing in the future. In addition, the background PM_2.5 concentrations over the North China Plain show an increasing trend in recent years, which may be attributed to the increased atmospheric oxidation capacity, thereby posing a challenge for further regional air quality management.