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 (O3) is an exception. O3mixing 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 O3attainment. By using a validated O3modeling system and the latest regional emission inventory, this study illustrates that control strategies for short-term O3despiking and long-term attainment in the PRD may be contradictory. VOC-focused controls are more efficient for O3despiking in urban and industrial areas, but significant NOxemission reductions and a subsequent transition to a NOx-limited regime are required for O3attainment. By tracking O3changes along the entire path toward long-term attainment, this study recommends to put a greater focus on NOxemission 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 O3. 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 O3concentrations in the PRD.