Spatiotemporal Source Apportionment of Ozone Pollution over the Greater Bay Area

It has been found that ozone (O ₃) pollution episodic case is prone to appear when the Greater Bay Area (GBA) is under the control of typhoons and sub-tropical high-pressure systems in summer. To prevent these pollutions effectively and efficiently, it’s essential to understand the contribution of O ₃ precursors emitted from different periods and areas under these unfavorable weather conditions. In this study, we further extended the Ozone Source Apportionment Technology (OSAT) from the Comprehensive Air Quality Model with Extensions (CAMx) model to include the function to track the emission periods of O ₃ precursors. Then the updated OSAT module was applied to investigate the spatial-temporal contribution of precursors emissions to the O ₃ concentration over the GBA in July and August 2016, when several O ₃ episodic cases appeared in this period. Overall, the emissions within GBA, from other regions of Guangdong province (GDo), and the neighbouring provinces are the three major contributors, which account for 23 %, 15 %, and 17 % of monthly average O ₃ concentration, respectively. More than 70 % of O ₃ in the current day is mainly formed from the pollutants emitted within 3 days and the same day’s emission contributed approximately 30 %. During the O ₃ episodes, when typhoon approached, more pollutants emitted 2–3 days ago from the GDo and adjacent provinces were transported to the GBA, leading to the increase of O ₃ in this region. Under the persistent influence of northerly wind, the pollutants originating from eastern China earlier than 2 days ago can also show an obvious impact on the O ₃ over the GBA in the present day, accounting for approximately 12 %. On the other hand, the O ₃ pollution is primarily attributed to the local emission within 2 days when the GBA is mainly under the influence of the sub-tropical high-pressure systems. These results indicated the necessity to consider the influence of meteorological conditions in implementing the control measures. Meanwhile, analogous relationships between source area/time and receptor were derived by the zero-out method, supporting the validity of the updated OSAT module. Our approach and findings could offer more spatial-temporal information about the sources of O ₃ pollutions, which could aid in the development of effective and timely control policies.