未來氣候變遷對地表臭氧之影響─傳送機制與化學機制之探討

Abstract

藉由14年Yonagunijima(YON)地表臭氧觀測資料分析與討論，使我進一步想要了解─未來氣候變遷的傳送機制和化學機制之改變對臭氧的影響。YON地表臭氧與其他氣象參數的觀測資料分析結果顯示，其臭氧濃度變化主要是受水平傳送機制調控。為驗證分析解結果，本研究使用HYSPLIT模式模擬不同臭氧濃度變異的氣流軌跡，並使用群集分析探討不同源區與行經路徑對YON臭氧變化之影響。若氣流源於東亞大陸，則有較大的機率造成YON臭氧濃度增加，若氣流源於太平洋或南海，則有較大機率造成YON臭氧濃度下降。 YON的資料分析顯示水平傳輸在季風地區的重要性。未來氣候變遷其環流結構隨之改變，勢必會影響這些區域的臭氧濃度。為了探討未來全球暖化氣候變遷對臭氧濃度的影響，本研究使用CESM模擬未來情境，並設計五組實驗(固定為相同的排放)探討化學機制與傳送機制對臭氧濃度的影響。化學機制分為溫度與水氣對反應速率的影響：溫度升高對臭氧的影響有明顯的海陸差異，陸地為增加海洋為減少。由於陸地的淨化學反應是增加臭氧，而海洋則是減少臭氧，當溫度升高化學反應式增快，因此呈現陸地增加而洋面減少之現象；整體來說平均地表臭氧濃度下降0.34 ppb。水氣增加對化學反應的影響使臭氧濃度下降，全球平均約降2.18 ppb。在溫度與濕度的共同影響下，平均地表臭氧濃度下降2.53 ppb。傳送機制的改變則造成地表臭氧濃度增加1.32 ppb，其重要性(相對於化學機制)隨高度增加。綜合以上各項因素，未來氣候變遷的情境下，地表臭氧濃度下降1.21 ppb。

The result of 14-year Yonagunijima(YON) O3 observation data showed the importance of meteorological transport, and thus inspired me to study the role of the transport and chemistry play in O3 concentration under a future climate scenario. The aim of this study is to separate the contribution of transport and chemistry on O3 concentration change under the RCP4.5 future climate scenario. Observational data analysis showed that atmospheric circulation should be more important than chemistry in influencing regional O3. Backward trajectory cluster analysis was applied to support this conclusion. O3 over YON tends to be higher if the airflow originates from the continent or passing through East China Sea, but lower if the airflow originates from the Pacific oceans or South China Sea. Such influences have strong signatures of seasonal and inter-annual variations. Under future climate change scenario, atmospheric circulation and monsoon will change which, in turn, influences O3 concentration. CESM global model was used to study the O3 change in future climate scenario and sort out the contributions from meteorological transport and chemistry. Five experiments with fixed emission were conducted by controlling temperature or moisture in chemistry calculation. Warming climate leads to an increase in surface O3 over polluted areas, but a decrease in remote areas. The overall chemistry over land is to produce O3 whereas that over remote areas is to destruct O3. The net effect of rising temperature is to decrease global surface O3 by 0.34 ppb. Wetter climate leads to a decrease in global surface O3 by 2.18 ppb. The net effect of chemistry, including temperature effect and moisture effect, is to decrease global average O3 by 2.53 ppb, and it implies the domination of moisture effect. The net effect of meteorologic transport is to increase global surface O3 by 1.32 ppb, and the effect becomes more significant with increasing height. All mechanisms conbined, surface O3 decreases by 1.21 ppb under the RC future climate scenario.