Rapid increase in summer surface ozone over the North China Plain during 2013-2019: a side effect of particulate matter reduction control?

While the elevated ambient levels of particulate matters with aerodynamic diameter of 2.5 mu m or less (PM2.5) are alleviated largely with the implementation of effective emission control measures, an opposite trend with a rapid increase has been seen in surface ozone (O-3) in the North China Plain (NCP) region over the past several years. It is critical to determine the real culprit causing such a large increase in surface O-3. In this study, 7-year surface observations and satellite retrieval data are analyzed to determine the long-term change in surface O-3 as well as driving factors. Results indicate that anthropogenic emission control strategies and changes in aerosol concentrations as well as aerosol optical properties such as single-scattering albedo (SSA) are the most important factors driving such a large increase in surface O-3. Numerical simulations with the National Center for Atmospheric Research (NCAR) Master Mechanism (MM) model suggest that reduction of 03 precursor emissions and aerosol radiative effect accounted for 45 % and 23 % of the total change in surface O-3 in summertime during 2013-2019, respectively. Planetary boundary layer (PBL) height with an increase of 0.21 km and surface air temperature with an increase of 2.1 degrees C contributed 18 % and 12 % to the total change in surface O-3, respectively. The combined effect of these factors was responsible for the rest of the change. Decrease in SSA or strengthened absorption property of aerosols may offset the impact of aerosol optical depth (AOD) reduction on surface O-3 substantially. While the MM model enables quantification of an individual factor's percentage contributions, it requires further refinement with aerosol chemistry included in the future investigation. The study indicates an important role of aerosol radiative effect in development of more effective emission control strategies on reduction of ambient levels of O-3 as well as alleviation of national air quality standard exceedance events.

Automated summary

This study analyzes surface observations and satellite retrieval data to determine the increase in surface ozone in the North China Plain region, finding that anthropogenic emission control strategies and changes in aerosol concentrations are the main driving factors. Numerical simulations indicate that reduction of O3 precursor emissions and aerosol radiative effect contribute significantly to the increase in surface ozone, emphasizing the importance of considering aerosol chemistry in future research for developing more effective emission control strategies.