Evaluation of continuous emission reduction effect on PM2.5 pollution improvement through 2013–2018 in Beijing

Abstract

Beijing has achieved significant air quality improvement over the past decade. In this study, we applied a simulation technique on pollutant monitoring data to investigate the contribution of emission reduction (ERE) and meteorological effects (ME) to the improvement of air quality. We measured the daily PM2.5 concentrations during four months (representing the four seasons) in 2013 and 2018. We found that the concentrations of NH4+, NO3−, and SO42− decreased from 2013 to 2018, but the proportion of NO3− in PM2.5 showed an apparent increase. Multiple scenarios were simulated using the WRF-CAMx model to determine the impact of ERE and ME on air pollution. The results showed that both variables positively contributed to the annual air quality improvement, with ERE contributing more than 70% to the total PM2.5 reduction. However, their seasonal contributions showed notable differences. In winter, ME contributed more than 40 μg/m3 to the PM2.5 decrease, which was much higher than that in other seasons. This suggests that the positive effect of pollutant emission reduction on air quality may have been weakened under extremely adverse meteorological conditions. Hence, the monitoring and modeling results were coupled to evaluate the secondary conversion degree. We found that the emissions of precursors, including SO2 and NOx, notably decreased, but both the local and regional conversion degrees increased from 2013 to 2018. Therefore, for effective air pollution reduction, we suggest that future air pollution mitigation measures should focus on reducing secondary pollution in Beijing.