Spatiotemporal source apportionment of ozone pollution over the Greater Bay Area

Abstract

It has been found that ozone (O3) pollution episodic cases are prone to appear when the Greater Bay Area (GBA) is under the control of typhoons and subtropical high-pressure systems in summer. To prevent this pollution effectively and efficiently, it is essential to understand the contribution of O3 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 of tracking the emission periods of O3 precursors. Subsequently, the updated OSAT module was applied to investigate the spatiotemporal contribution of precursor emissions to the O3 concentration over the GBA in July and August 2016, when several O3 episodic cases appeared in this period. Overall, the emissions within the GBA, from other regions of Guangdong province (GDo), and from the neighboring provinces were the three major contributors, accounting for 23 %, 15 %, and 17 % of the monthly average O3 concentration, respectively. More than 70 % of the O3 on the current day was mainly formed from the pollutants emitted within 3 d, and the same day's emission contributed approximately 30 %. During the O3 episodes, when the typhoon approached, more pollutants emitted 2–3 d before from the GDo and adjacent provinces were transported to the GBA, leading to an increase in O3 concentrations within this region. Under the persistent influence of northerly wind, the pollutants originating from eastern China earlier than 2 d previously can also show a noticeable impact on the O3 over the GBA on the present day, accounting for approximately 12 %. On the other hand, the O3 pollution was primarily attributed to the local emission within 2 d when the GBA was mainly under the influence of the subtropical high-pressure systems. These results indicate the necessity for considering 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 spatiotemporal information about the sources of O3 pollution, which could aid in the development of effective and timely control policies.