Implications of Mitigating Ozone and Fine Particulate Matter Pollution in the Guangdong-Hong Kong-Macau Greater Bay Area of China Using a Regional-To-Local Coupling Model

Ultrahigh-resolution air quality models that resolve sharp gradients of pollutant concentrations benefit the assessment of human health impacts. Mitigating fine particulate matter (PM_2.5) concentrations over the past decade has triggered ozone (O₃) deterioration in China. Effective control of both pollutants remains poorly understood from an ultrahigh-resolution perspective. We propose a regional-to-local model suitable for quantitatively mitigating pollution pathways at various resolutions. Sensitivity scenarios for controlling nitrogen oxide (NO_x) and volatile organic compound (VOC) emissions are explored, focusing on traffic and industrial sectors. The results show that concurrent controls on both sectors lead to reductions of 17%, 5%, and 47% in NO_x, PM_2.5, and VOC emissions, respectively. The reduced traffic scenario leads to reduced NO₂ and PM_2.5 but increased O₃ concentrations in urban areas. Guangzhou is located in a VOC-limited O₃ formation regime, and traffic is a key factor in controlling NO_x and O₃. The reduced industrial VOC scenario leads to reduced O₃ concentrations throughout the mitigation domain. The maximum decrease in median hourly NO₂ is >11 μg/m³, and the maximum increase in the median daily maximum 8-hr rolling O₃ is >10 μg/m³ for the reduced traffic scenario. When controls on both sectors are applied, the O₃ increase reduces to <7 μg/m³. The daily averaged PM_2.5 decreases by <2 μg/m³ for the reduced traffic scenario and varies little for the reduced industrial VOC scenario. An O₃ episode analysis of the dual-control scenario leads to O₃ decreases of up to 15 μg/m³ (8-hr metric) and 25 μg/m³ (1-hr metric) in rural areas.