Source Apportionment of Regional Ozone Pollution Observed at Mount Tai, North China: Application of Lagrangian Photochemical Trajectory Model and Implications for Control Policy

To better understand the characteristics and trace the sources of regional ozone (O-3) in the North China Plain (NCP), we analyzed 1-year continuous observations obtained at Mount Tai in 2018 and compared with previous data from 2006-2009. In the warm seasons (April-September), O-3 pollution (defined as a maximum daily 8-h average O-3 mixing ratio that exceeds 75 ppbv) occurred frequently (59%-92% of days) and O-3 concentrations significantly increased (especially in July-September) from 2006-2009 to 2018. We applied the Lagrangian photochemical trajectory model, built on the coupling of the Lagrangian backward trajectory model and Master Chemical Mechanism box model, to identify the source regions, key precursors, and emission sectors. The NCP was identified as the major source region with an average contribution of 74% +/- 27% to the regional O-3 concentrations during the O-3 episodes in April-September. Regional O-3 formation was highly NOx-sensitive in air masses traveling from the southern part of the NCP but limited by anthropogenic hydrocarbons (especially alkenes) in air masses from the northern part of the NCP. The reduction of emissions from transportation and industry sectors would significantly reduce the regional O-3 concentrations. Biomass burning also exerts a significant influence on regional O-3 concentrations under certain circumstances. This study demonstrates that the regional background O-3 at mountaintop levels is a good indicator of surface O-3 pollution over a wide spatial coverage, and provides guidance for regional collaboration on emission control to mitigate photochemical air pollution over the NCP.

Automated summary

The study found that the North China Plain is the major source region of regional O3, with reductions in emissions from transportation and industry significantly decreasing O3 concentrations. O3 formation in the southern region is highly NOx-sensitive, while in the northern region it is limited by anthropogenic hydrocarbons like alkenes. Biomass burning also influences regional O3 concentrations under certain circumstances.