桃園地區臭氧污染與氣象條件相關性之探討

Abstract

大氣中的臭氧為二次污染物，是NOX、NMHC等前驅物經光化反應所形成的，近地表處若存在過多臭氧，對人體健康、生態環境有不良影響。本研究透過1995年至2004年的逐時污染物濃度及氣象資料，以事件日討論、統計分析等方式，探討境內污染源眾多的桃園地區臭氧污染與氣象條件之相關性。 季節變化上，夏季雖然光照良好，但大氣對流旺盛、混合層高度提高，臭氧濃度並不高。而以雨季前後、風速較小、大氣相對較穩定的春、秋二季的臭氧濃度較高。日變化則大致以中午前後的臭氧濃度最大，但冬、夏的型態卻不盡相同。夏季因上午風速偏低且太陽輻射強烈，午間濃度快速上升至高值，隨後因大氣擴散良好及強勁的海風而濃度下降，呈現單峰型。冬季的夜晚因近地逆溫而有濃度累積偏高的現象，使其日夜濃度差異不如夏季明顯。 本文篩選出14個事件日來探討嚴重污染個案所伴隨之大氣環境，發現臭氧濃度之變化不外乎同時受前驅物濃度和氣象條件的影響。事件日之綜觀天氣多為高壓迴流、颱風外圍環流影響、偏南氣流等類型。且臭氧濃度大致與NOX濃度、風速、雲量、能見度為負相關，而與氣溫、日照時數為正相關。但由於光化反應相當複雜，參與物種眾多，使臭氧與前驅物及氣象因子間並非呈現簡單的直線關係。若以因子分析、判別分析之方法，對中午12時臭氧濃度進行預測分組，結果以太陽輻射、大氣擴散這兩個因子的判別能力最強，但高濃度組卻有正確率過低之問題。此外，最大混合層高度與臭氧濃度變化之相關性仍值得深入討論。 空間分布可分下列幾點說明：1.受滴定作用影響，排放源多的都市臭氧濃度反而最低。2.海陸風環流在盛行風不明顯的夏季主導污染物空間中的傳送，夏季午後以內陸龍潭的濃度最高，且其最大濃度可能比沿海地區延遲一至二小時出現。3.除夏季外，臭氧濃度以人口較少的沿海一帶最大。4.上午陸風將前驅物傳送至海上累積，經陽光照射後形成大量臭氧，午後再受西北方向的海風將其送回沿海地區，進而造成污染。

The air pollution events due to high industrialization become one of the most important environmental issues in Taiwan. In particular, ozone concentration will not only cause human respiratory disease, but also damage plants and buildings. Ozone is a secondary pollutant that is generated by its precursors such as NOX and NMHC through complex photo-chemical reactions. The surface ozone data and meteorological data collected by EPA and CWB during January 1995– December 2004 are analyzed. The hourly data are executed by BASIC computer program to characterize temporal and spatial variation of ozone concentration in Tao-Yuan. On seasonal change, higher ozone concentration usually appears in spring and autumn, and the lower concentration frequently occurs in summer when atmospheric condition is good for dispersion. As to daily variation, in summer time, the strong solar insolation may cause higher ozone concentration at noon. While in winter time, high ozone concentration may occur after sunset and before sunrise duo to surface inversion. In addition, 14 episodes with higher ozone concentration are selected as cases for detailed discussion. In all, some synoptic patterns was important to the occurrence of ozone episodes. Statistics show that the weather condition of high temperature, low cloudiness, and weak wind are considered favorable for the production and accumulation of ozone. Other factors that may affect the atmospheric dispersion, such as mixing height, ventilation index, and precursors emission are suggested for further exploration. The spatial distribution of ozone in Tao-Yuan is also influenced by local land-sea breeze circulation. It is believed that inland pollutant was carried out seaward by land breeze, and changed into ozone through solar insolation. When the sea breeze on sets, the high concentration of ozone may occurred in coastal areas, such as Guan-yin and Da-yuan.