Tropospheric O
3 is a noxious ambient pollutant that severely damages human health. In this study, a considerable number of model simulations with comprehensive designs have been conducted to investigate the formation and depletion of tropospheric O
3 over the Guangdong-Hong Kong-Macau Greater Bay Area (GBA) and the Asia-Pacific Region. Station-based observational results indicate that, over the last two decades (2000–2019), O
3 concentration significantly increases over the GBA, with a rate of 0.5–1.0 ppbv yr
-1. A matrix of emission reduction experiments is then designed and executed to figure out the formation of O
3 pollution over the GBA. According to the simulation results, to reduce ~10 ppbv O
3 formations, dramatic elimination (>25%) in NO
x or anthropogenic Volatile Organic Compounds (AVOCs) emission is required. O
3 formation is more sensitive to NO
x reduction compared to AVOCs reduction in most cases, while during some episodes reducing AVOCs is a more effective way to impede O
3 formation. Meanwhile, the lack of halogen chemical processes over the coastal region limits our ability to accurately simulate O
3 concentration. Implementing the CMAQ model with novel bromine and iodine mechanisms, we show distinct halogen-mediated O
3 depletion features over the land and ocean in the Asia-Pacific region. Across a coastline-centric 400-km-wide belt from onshore to offshore, averaged maximum gradient of O
3 loss reaches 1.1 ppbv/100 km at surface level. To further analyze the relationship between the coastal O
3 depletion and oceanic airflow, a novel Lagrangian-based concept of Ocean Air Occupation Ratio (OAOR), defined as the total period that an oceanic air parcel resides within a specific area, has been proposed and investigated. We show that the OAOR increases at the largest rate of 10–15%/100 km across a coastline-centric 400-km-wide belt, resembling the O
3 depletion – shoreline distance relationship. Further analysis shows that for regions where OAOR is lower than 30%, the surface O
3 depletion near-linearly increases as a function of OAOR at the rate of 1ppbv/10%. Additionally, an extension of the concept, the Air Parcel Resident Time, is studied and shows its ability to reveal tracer sources' key areas in various dispersion conditions. As part of efforts to improve our understanding of tropospheric O
3 formation and depletion regarding the effect of bromine and iodine chemistry, we call for more monitoring and modeling studies on O
3 formation and depletion, which could further benefit the design of O
3 pollution prevention and control policies.
| Date of Award | 2021 |
|---|
| Original language | English |
|---|
| Awarding Institution | - The Hong Kong University of Science and Technology
|
|---|
| Supervisor | Jimmy Chi Hung FUNG (Supervisor) & Alexis Kai Hon LAU (Supervisor) |
|---|