Assessing the impacts of atmospheric conditions under climate change on air quality over the Pearl River Delta, China

M.Phil.Literature has reported that climate is projected to be most likely to change. Atmospheric stability, which has strong effects on vertical mixing of air pollutants and thus air quality, may be affected under climate change. This study aims to enhance understanding of the sensitivity of air pollution to vertical atmospheric conditions, and to develop models to assess the impacts of climate change on the future air quality in near future (2030-2039) and far future (2090-2099) under two RCP scenarios (RCP 4.5 and RCP 8.5). The study has developed a Generalized Linear Model (GLM) to determine the correlations of ozone, respirable suspended particulates and sulphur dioxide with atmospheric conditions using 1994–2003 monthly the Weather and Research Forecast Model (WRF) downscaled reanalysis data in the Pearl River Delta (PRD). The study adopts Principal Component Regression (PCR) to address the multi-collinearity issue and thus studied variables’ contributions based on the loading and model coefficient of each component that when combined showed a good explanation to air pollutant concentration, with refined indices of agreement of 0.533 - 0.814.High pollutant concentration generally occurs under relatively low mid-level troposphere temperature gradients, low relative humidity, weak southerly wind (or strong northerly wind) and weak westerly wind (or strong easterly wind). High concentration cases are typically under strong north-easterly wind or calm wind conditions. Yet, under the complicated pollutant transport mechanisms, the correlations vary among pollutant species, seasons, and weather variables at various altitudes. Generally, pollutant sensitivity to meteorological variables is found to be greater in winter than in other seasons, and the ozone sensitivity differs from other two pollutants. Applying our GLMs to the years with anomalous pollutants’ concentration levels, it is found that climate conditions up to mid troposphere (700mb), which is strongly related to the topography and geography of the study sites, play an important role in influencing surface pollutant concentrations.Ensemble of General Circulation Models (GCMs) has revealed that near future and far future surface temperature are projected to increase significantly, especially in the far future or RCP 8.5 scenario. 800mb – 700mb temperature difference is projected to decrease and surface temperature – dew point difference is projected to increase in certain circumstances. The arithmetic mean of projections has revealed a decrease in levels of air pollutants in June-July-August and an increase in other seasons. The shifts are more significant in the far future, and in the scenarios of RCP 8.5. Surface temperature contributes the most to the change of projected air pollutant concentration, explaining from 56.9% to 65.2% of the total variations for the three pollutants in RCP 8.5. Other notable contributions include positive effects of vertical temperature gradient and the temperature - dew point difference on the pollutant concentration. Increase in intensity and frequency of pollution levels are revealed in December-January-February and March-April-March: the occurrence proportion of pollutant concentration greater than the current 95th percentile is 9.5% - 9.6% and 6.4% - 9.2% respectively.The study concludes that air quality is strongly associated with vertical meteorological condition in the PRD. Climate change is projected to have remarkable impacts on future air quality, and future air quality emission control policies should be more stringent to address air pollution problems.空氣污染危害公眾健康及周邊環境，於大城市正受到廣泛關注。同時，過去研究顯示氣候變化具相當機會在未來發生。氣候變化能透過大氣穩定性，改變未來空氣污染物的垂直混合以致地面空氣質量。本研究旨在提升空氣質量對垂直大氣情況敏感度的了解，同時建立數據模型推算受氣候變化影響下的天氣狀況。本研究先使用ＷＲＦ模型，並以動力降尺度法，估算出1994至2003年珠江三角洲垂直氣象狀況。然後研究建立一個廣義線性模型（ＧＬＭ），把得出之氣象變數與實測臭氧，可吸入懸浮粒子及二氧化硫含量進行相關分折。針對多重共線性的問題，研究使用主成分回歸分析（ＰＣＲ），透過主成分的負荷量及主成分對污染物濃度的相關系數，了解每個氣象變數對污染物濃度的相關性。這些氣象變數合共解釋了相當程度污染物濃度的變化，其中IOA指數在0.533及0.814之間。研究結果顯示高污染物濃度出現於相對濕度較低、南風較弱（或北風較強）、西風較弱（或東風較強）、或中部對流層溫度下降坡度較慢的情況。一般而言，高污染物濃度出現於東北風主導環流或者風速微弱的情況。然而，基於空氣污染物複雜的傳送方式，其與氣象相關性因污染物種類、季節及高度而改變。臭氧與氣象相關性相對二氧化硫及可吸入懸浮粒子有顯著不同，同時三種污染物相關性在冬季一般較其他季節為強。把模式應用於異常污染情況，發現與地面至中層對流層（７００ｍｂ高度）的氣象受地面明顯影響，在控制地面高污染物濃度的情況扮演著重要的角色。研究使用大氣環流模式，預測根據ＲＣＰ４.５和ＲＣＰ８.５各氣象變數在近將來（２０３０－２０３９年）和遠將來（２０９０－２０９９年）的變化。這些集合的模式顯示將來的地面溫度將會明顯上升，尤以遠將來或ＲＣＰ８.５為甚。７００ｍｂ與８５０ｍｂ的中層溫差在個別情況將會下降，而地面溫度與露點溫度差在個別情況將會上升。使用ＧＬＭ預測大氣環境對近將來的空氣質量的影響，研究發現六－七－八月污染物濃度的算術平均在將來會下降，而其他季節的空氣污染物濃度的算術平均將會上升。改變於對遠將來及ＲＣＰ８.５更為明顯。表面溫度對預測之空氣污染物帶來最大貢獻，對三種污染物在ＲＣＰ８.５情境下合共變化之５６.９％至６５.２％。其他可觀之貢獻包括垂直溫差與溫度－露點溫度差對空氣污染物濃度的正面影響。另外，將來污染程度的強度與頻率在十二－一－二月及三－四－五月稍為增加：現時95百分位值在將來的出現機會分別在該兩季節增加至９.５％ － ９.６％及６.４％ － ９.２％。本研究總結氣象因素對空氣質量之明顯影響。氣候變化預測對將來的空氣質量帶來一定程度的影響，當局應加強考慮氣候變化之影響，加強將來的空氣污染排放控制政策之監控，以針對將來空氣污染問題。Tong, Cheuk Hei.Thesis M.Phil. Chinese University of Hong Kong 2017.Includes bibliographical references (leaves 101-114).Abstracts also in Chinese.Title from PDF title page (viewed on …)