Increasing atmospheric oxidizing capacity weakens emission mitigation effort in Beijing during autumn haze events

Although strict mitigation measures have been implemented since 2013 in Beijing-Tianjin-Hebei (BTH), China, air pollution still frequently occurs. Observations reveal that during pollution episodes in autumn, fine particulate matter (PM2.5) concentrations have not decreased, and particularly, ozone (O-3) concentrations have increased remarkably from 2013 to 2015 in Beijing. Additionally, a concurrence of O-3 and particulate pollution with high secondary aerosol contributions has been observed frequently, indicating high atmospheric oxidizing capacity (AOC) during particulate pollution. The WRF-Chem model simulations show elevated O-3 concentrations and high fractions of oxygenated secondary aerosols (OSA) in PM2.5 (0.53-0.73) during the severe pollution period. During daytime there exhibits an AOC-sufficient regime with the persistently high OSA fraction and an AOC-deficient regime with varied OSA fractions, separated by the O-3 level of 80 mu g m(-3). Our results suggest that increasing AOC can considerably weaken the emission mitigation effort by enhancing the secondary aerosol formation

Automated summary

Despite the strict mitigation measures implemented in the Beijing-Tianjin-Hebei region since 2013, air pollution still occurs frequently, with no decrease seen in PM2.5 and a significant increase in O-3 concentrations in Beijing during autumn pollution episodes. Observations show a high atmospheric oxidizing capacity during particulate pollution, with elevated O-3 concentrations and high levels of oxygenated secondary aerosols present in PM2.5 during severe pollution periods. Results suggest that increasing atmospheric oxidizing capacity can weaken emission mitigation efforts by enhancing secondary aerosol formation.