Ambient Ozone Control in a Photochemically Active Region: Short Term Despiking or Long-Term Attainment?

China has made significant progress decreasing the ambient concentrations of most air pollutants, but ozone (O-3) is an exception. O-3 mixing ratios during pollution episodes are far higher than the national standard in the Pearl River Delta (PRD), thus greater evidence-based control efforts are needed for O-3 attainment. By using a validated O-3 modeling system and the latest regional emission inventory, this study illustrates that control strategies for short-term O-3 despiking and long-term attainment in the PRD may be contradictory. VOC-focused controls are more efficient for O-3 despiking in urban and industrial areas, but significant NO emission reductions and a subsequent transition to a NOx-limited regime are required for O-3 attainment. By tracking O-3 changes along the entire path toward long-term attainment, this study recommends to put a greater focus on NO emission controls region-wide. Parallel VOC reductions around the Nansha port are necessary in summertime and should be extended to the urban and industrial areas in fall with a flexibility to be strengthened on days forecasted to have elevated O-3. Contingent VOC-focused controls on top of regular NOx-focused controls would lay the groundwork for striking a balance between short-term despiking and long-term attainment of O-3 concentrations in the PRD.