Full metadata record
| DC Field | Value | Language |
|---|---|---|
| dc.contributor | Department of Civil and Environmental Engineering | en_US |
| dc.contributor.advisor | Guo, Hai (CEE) | en_US |
| dc.creator | Zhou, Beining | - |
| dc.identifier.uri | https://theses.lib.polyu.edu.hk/handle/200/14439 | - |
| dc.language | English | en_US |
| dc.publisher | Hong Kong Polytechnic University | en_US |
| dc.rights | All rights reserved | en_US |
| dc.title | Confronting warm-season ozone pollution in China : integrating global challenges, regional impacts, and local emission constraints | en_US |
| dcterms.abstract | Surface ozone (O₃) pollution is a long-standing and intractable environmental problem that poses risks to human health and ecosystems, participates in atmospheric chemistry, and contributes to global warming. Despite ongoing efforts, widespread O₃ pollution during warm seasons remains a global challenge. In particular, China has experienced the most severe O₃ pollution with high and increasing O₃ levels over the past decade. However, this escalating O₃ pollution has not been fully addressed from a global perspective due to the delay in establishing a nationwide O₃ monitoring network in China. Therefore, the first aim of this thesis is to comprehensively assess the current status of warm-season O₃ pollution in China and worldwide, and to identify the current challenges of O₃ pollution control. Moreover, although China has been regarded as a large source of O₃ and its precursors, regional transport of air pollutants from upwind source regions with emerging emissions, such as Southeast Asia and marine shipping, could further exacerbate O₃ pollution in China. Hence, the second aim of this thesis zooms in on South China, where increasingly severe O₃ pollution has occurred in recent summers, to elucidate the transport impacts from Southeast Asia under the prevailing summer monsoon. In addition, as a secondary pollutant, surface O₃ is formed through complex reactions among its precursors, with volatile organic compounds (VOCs) playing a key role. Accurate quantification of VOC emissions is critical for O₃ pollution research, especially when using air quality models, yet current emission inventories are subject to significant biases. This gap motivates the third aim of this thesis to develop an observational constraint on VOC emissions to better represent local VOC emissions and improve O₃ modeling studies. | en_US |
| dcterms.abstract | To understand the current O₃ pollution in China and worldwide, as well as its emerging challenges, ground-level O₃ measurements at over 4,300 monitoring stations across 48 countries were compiled, showing significantly high O₃ concentrations with the fastest-ever increasing rate in China during warm seasons from 2014 to 2019. This unintentional rise in O₃ levels, primarily caused by emission reductions in nitrogen oxides (NOx) and fine particulate matter (PM2.5), underscores the necessity and urgency of coordinated emission controls for all O₃ precursors (both NOx and VOCs) and PM2.5. Meanwhile, increases in O₃ levels were also observed in developed regions, where emissions of O₃ precursors have already been substantially reduced, particularly in the western United States, southern and central Europe, and eastern Australian cities, indicating new challenges in O₃ air quality management. On the one hand, previously overlooked sources of O₃ precursors have emerged after traditional combustion-related sources were effectively reduced, such as the extensive use of volatile chemical products. On the other hand, the climate penalty on O₃ has intensified under a warming and drying climate, with more frequent and severe climate extremes amplifying high O₃ pollution episodes and O₃ exposures. As such, holistic management of multiple pollutants under a changing climate is urgently needed to confront this global threat. | en_US |
| dcterms.abstract | To further understand the regional impacts on worsening summer O₃ pollution over South China in the recent decade, O₃ and its precursors from 2013 to 2022 were analyzed, revealing more frequent region-wide high O₃ episodes with elevated concentrations. Notably, 39 region-wide high O₃ episodes occurred under strong summer monsoon influences, which challenged the conventional view that clean air brought by the monsoon solely dilutes air pollution. Using a chemical transport model (WRF-CMAQ), the mechanisms building up these O₃ episodes were explored. While local emissions primarily drove daytime O₃ formation in South China, regional emissions from upwind mainland Southeast Asia and shipping activities in the South China Sea substantially contributed to O₃ pollution in South China by 4 ppbv. Unexpectedly, the Beibu Gulf acted as a critical O₃ reservoir, where O₃ and its precursors from upwind regions and ship emissions underwent chemical processing and accumulated, sustaining high O₃ levels and supplying O₃ to South China through prevailing southwesterly winds. These findings redefine the dual role of the summer monsoon, demonstrating that it can both alleviate pollution and facilitate the transboundary transport of air pollutants. Moreover, the growing emissions in Southeast Asia and shipping activities introduce a new challenge to O₃ mitigation in South China, highlighting the need for international cooperation to manage transboundary pollution. | en_US |
| dcterms.abstract | To constrain VOC emissions based on observations, concurrent VOC measurements were carried out across the Pearl River Delta (PRD) region, the most populous and developed city cluster in South China, during the summer of 2018. A mass-balance calculation, accounting for both physical and chemical processes, was developed to quantitatively estimate anthropogenic VOC emissions. After applying this observational constraint, the speciated emissions of VOCs exhibited clear diurnal variations and corrected the spatially concentrated priori emissions, reducing peak emissions in central PRD cities by 15% – 36% and elevating the sparse emissions in other cities. These observation-constrained VOC emissions improved the model simulations, better reproducing the spatiotemporal variations of VOCs and alleviating the biases from -55% – 85% to -13% – 13%. Moreover, simulations of peak O₃ concentrations were also amended to reduce the biases by 5% – 12% during high O₃ episodes. This observational constraint has effectively combined VOC field measurements with air quality modeling to achieve better simulations of VOCs and O₃, providing scientific support for further studies on the impacts of local and short-term emission changes on O₃ pollution, as well as its control strategies. | en_US |
| dcterms.abstract | In summary, this thesis provides a multi-scale perspective for addressing the emerging O₃ pollution in China, encompassing a global overview of the status and current challenges of O₃ pollution control, a regional investigation of transboundary transport to South China, and a local observational emission constraint on key O₃ precursors to advance O₃ pollution research and management. These findings serve as a scientific basis for formulating more effective O₃ air quality control policies in China to confront the persistent challenges of surface O₃ pollution in a changing climate. | en_US |
| dcterms.extent | xv, 175 pages : color illustrations | en_US |
| dcterms.isPartOf | PolyU Electronic Theses | en_US |
| dcterms.issued | 2026 | en_US |
| dcterms.educationalLevel | Ph.D. | en_US |
| dcterms.educationalLevel | All Doctorate | en_US |
| dcterms.accessRights | open access | en_US |
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