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Pao Yue-kong Library, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong http://www.lib.polyu.edu.hk The Hong Kong Polyl technic Universitty Department of Civil and Environmental Engineering INTEGRATED DATA ANALYSIS AND CHARACTERIZATION OF PHOTOCHEMICAL OZONE IN SUBTROPICAL HONG KONG By LING ZHENHAO A Thesis Submitted in Partial Fulfilment of the RRequirements for the degree of Doctor of Philosophy Octobere 2013 CERTIFICATE OF ORGINALITY I hereby declare that this thesis is my own work and that, to the best of my knowledge and belief, it reproduces no material previously published or writtten, nor material that has been accepted for the award of any other degree or diploma, except where due acknowledgement has been madde in the text. _________________________________ (Signed) LING ZHENHAO (Name of student) I Abstract To understand the photochemical O3 pollution at different elevations in mountainous areas, and to provide a conceptual description of O3 pollution in Hong Kong, a number of field campaigns were undertaken in different locations in Hong Kong and the inland PRD region, which were followed by in-depth data analysis and model simulation. Intensive field measurements were concurrently conducted for the first time at a mountain site (TMS) and an urban site at the foot of the mountain (TW) from September to November 2010. The mixing ratios of air pollutants were greater at TW than those at TMS, except for O3. The relatively higher levels of O3 at TMS were attributed to the combined influence of NO titration, vertical meteorological conditions, regional transport and mesoscale circulations. The photochemical O3 formation at TMS was mostly influenced by VOCs, with measurable influence of NOx, while O3 production at TW was generally limited by the concentrations of VOCs. By using a photochemical box model coupled with master chemical mechanism (PBM-MCM), the photochemical reactivity at the above two sites were investigated. It was found that slightly higher HO2 concentrations were found at TMS, while much higher OH concentrations were estimated at TW, suggesting that the HOx cycling processes were different at the two sites due to the differences of O3 and its precursors. The O3 formation was dominated by the reaction of HO2 + NO at the two sites, while O3 was mainly destroyed by the reactions of OH + NO2 at TW, and by the O3 photolysis and the reaction of O3 + HO2 at TMS. Furthermore, more O3 could be produced for each radical generated at TMS. Since VOCs are the most important chemicals contributing to high O3 production in Hong Kong and the inland PRD region, identification of VOC sources and II quantification of source contributions could provide valuable information for the formulation and implementation of O3 pollution control measures. A new reactivity-based approach, combining the Positive Matrix Factorization (PMF) model with an observation-based model (OBM), was developed in this study. A new parameter, i.e., Relative Incremental Reactivity (RIR) – weighted value, considering both the emissions and reactivity of VOCs, was used to evaluate the contributions of VOC sources and the major species to O3 formation. In the inland PRD region, ten VOC sources were identified, while seven sources were identified in Hong Kong. Among all the sources, vehicular- and solvent-related emissions contributed significantly to ambient VOCs. In addition, the RIR-weighted values indicated that the O3 formation in inland PRD and Hong Kong was controlled by a small number of VOC species in specific sources. Sensitivity analysis on the basis of relative O3 reduction efficiency (RORE) indicated that the O3 reduction was the most effective when the identified VOC sources and the major species from these sources were cut by certain percentages. Finally, to formulate and implement effective control strategies for O3 pollution, a conceptual model was developed for the first time in Hong Kong based on the integrated data analysis at Tung Chung (TC) in Hong Kong between 2005 and 2010. By comparing meteorological parameters between O3 and non-O3 episode days, it was found that high temperatures, strong solar radiation, low wind speeds and relative humidity, northeasterly and/or northwesterly prevailing winds were favorable for the O3 formation, while tropical cyclones were most conducive to the occurrence of O3 episodes. Backward trajectories simulation and graphical illustration of O3 pollution suggested that super-regional and regional transport were other factors that contributed to high O3 levels in Hong Kong. The photochemical O3 formation, III generally VOC-limited in Hong Kong, was controlled by a small number of VOCs, which were mainly from solvent usage and vehicular emissions. Overall, the results of this study suggested that mesoscale circulations had a significant influence on the distributions of air pollutants in mountainous areas in Hong Kong, and the cycling processes among radicals, the production and destruction of O3 were different at the mountain and urban sites due to the different levels of O3 and its precursors. It is recommended that before the formulation and implementation of VOC control strategies, the abundance and reactivity of each VOC in each source should be considered. This study has provided an alternative way to more efficiently alleviate O3 pollution by controlling specific VOCs in certain VOC sources and highlighted the importance of monitoring these VOCs. IV The novelty of this study In this study, to investigate the characteristics of photochemical air pollutants and the impact factors for the O3 variations at different elevations in mountainous areas in Hong Kong, concurrent field measurements were firstly conducted at the mountain site (Mt. Tai Mo Shan, TMS) and the low-elevation urban site (Tsuen Wan, TW) in Hong Kong from September to November 2010. A newly developed photochemical box model coupled with master chemical mechanism (PBM-MCM) was applied to and constrained by the above full suite of air pollutants at TMS and TW to understand chemical mechanisms of photochemical reactivity under the influence of different levels of O3 and precursors, including the HOx budget, the OH chain length, and calculated O3 production for the first time in Hong Kong. Previous studies demonstrated that the O3 formation was generally VOC-limited in Hong Kong, where most of the VOC control measures were mass-based. As such, a new reactivity-based method, combining the PMF and an observation-based model (OBM), was firstly developed based on the data collected in the inland PRD. This reactivity-based method was further used to investigate the roles of VOC sources in the O3 formation in the urban area of Hong Kong, and the implications for VOC control policy were emphasized by considering both reactivity and abundance of VOC sources. Finally, to obtain a full picture of O3 pollution in Hong Kong, a conceptual model based on the 6-year monitoring data at Tung Chung (TC) was firstly developed by investigating the influence of meteorological conditions, O3-precursors relationship and sources of O3 precursors in 2005-2010. The significance of the conceptual modeling results to the future O3 control policy formulation and implementation was highlighted. V PUBLICATIONS 1. Ling, Z.H., Guo, H*., Cheng, H.R., Yu, Y.F., 2011. Sources of ambient volatile organic compounds and their contributions to photochemical ozone formation at a site in the Pearl River Delta, southern China. Environmental Pollution, 159, 2310-2319. 2. Ling, Z.H., Guo, H*., Zheng, J.Y., Louie, P.K.K., Cheng, H.R., Jiang, F., Cheung, K., Wong, L.C., Feng, X.Q., 2013. Establishing a conceptual model for photochemical ozone pollution in subtropical Hong Kong. Atmospheric Environment, 76, 208-220. 3. Guo, H*., Ling, Z.H., Cheung, K., Jiang, F., Wang, D.W., Simpson, I.J., Barletta, B., Meinardi, S., Wang, T.J., Wang, X.M., Saunders, S.M., Blake, D.R., 2013. Characterization of photochemical pollution at different elevations in mountainous areas in Hong Kong. Atmospheric Chemistry and Physics 13, 3881-3898. 4. Ling, Z.H. and Guo, H*., 2013. Contribution of VOC sources to photochemical ozone formation and its control policy implication in Hong Kong. Environmental Science and Policy, 10.1016/j.envsci.2013.12.004. 5. Ling, Z.H., Guo, H*., Lam, S.H.M, Saunders, S.M., 2013. Atmospheric photochemical reactivity and ozone production at two sites in Hong Kong: Application of a photochemical box model with master chemical mechanism (PBM-MCM). In preparation. 6. Guo, H*., Ling, Z.H., Cheung, K., Wang, D.W., Simpson, I.J., Blake, D.R., 2012. Observations of isoprene, methacrolein (MAC) and methyl vinyl ketone (MVK) at a mountain site in Hong Kong. Journal of Geophysical Research-Atmosphere 117, D19303, doi: 10.1029/2012JD017750, 2012. 7. Guo, H*., Ling, Z.H., Simpson, I.J., Blake, D.R., Wang, D.W., 2012. Acetone in the atmosphere of Hong Kong: Abundance, sources and photochemical precursors, Atmospheric Environment 65, 80-88, 10.1016/j.atmosenv.2012.10.027.

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