摘 要 中部地區臭氧污染以秋季、春季最嚴重，天氣類型則為高壓迴流與熱帶低壓北移型容易形成事件日。為驗證在不同天氣類型下大氣結構對污染物濃度的垂直擴散限制情況，本文以繫留探空儀針對台中盆地行星邊界層內500公尺的氣象因子及污染物濃度進行四次實驗，採樣地點位於都會區內的中興大學及位於郊區的彰化縣芬園鄉茄老國小各兩次。由垂直虛位溫、風場、O3、NO、NO2、NOX、NMHC濃度剖面圖，藉以討論大氣結構及污染物濃度分佈趨式。 夜間因輻射冷卻呈現從地表開始逆溫的情形，午間間逆溫層高度常超過500公尺。在所觀測到的案例中，容易形成高臭氧事件日的高壓出海天氣型、高壓迴流天氣型及熱帶低壓北移型其清晨逆溫層抬升較晚，對早晨NOx與NMHC排放擴散受限，正午混合層升至500m以上，下午則出現在300m高度左右，可見光化開始時段的逆溫層高度對臭氧累積濃度潛勢有加強之作用。太平洋高壓西伸型單案例觀察到清晨逆溫現象不明顯，曾經研究中部地區在太平洋高壓西伸型時發現，近地面之臭氧濃度無法躍上高值，極可能受混合層較高利污染物擴散有關。 四次實驗實驗顯示夜間因輻射冷卻從地面呈現明顯逆溫，污染物濃度隨高度呈指數遞增或遞減，可以C(H)﹦Ｃ0×exp(-AH)表示，夜間擴散經驗係數（A值）及R2值顯示：夜間O3濃度分佈呈現隨高度增加而濃度遞增的趨勢。NO、NO2、NOx等地面原生性污染物則呈現隨高度遞減的結果。污染物R2值以O3及NO較佳，代表O3及NO濃度分佈隨高度成指數變化，CH4及NMHC濃度並無明顯的隨高度變化。 Ozone concentrations were analyzed from the data collected by the nine air-quality monitoring stations in the central region of Taiwan during 1996-1998. It shows that ozone episodes (O3≧80 ppb) occured most often during Autumn with fewer in Spring. High ozone concentrations happened mostly during easterly winds which mainly happen under two conditions. It occurs when high pressure occupies mainland China and the East China Sea and when the tropical low pressure moves northwind and starts to influence the Taiwan region. To analyse the vertical structure of the boundary layer of various synoptic weather patterns and determine its effect on ozone concentration over Taichung Basin, two field campaigns had been performed at urban station (Chung-Hsing University ) and suburban station (Chieh-Lao elementary school), during Fall 1998 and Spring 1999, respectively. The vertical meteorological factor vitural potential temperature profiles and wind profiles were derived from tethersonde. The O3、NO、NO2、NOX and NMHC concentrations vertical profiles were collected at ground and height of 30、100、300、500 meters by black-covered Teflon sampling bag. These results showed that the atmospheric boundary layer was well mixed during daytime, and not during night time because of radiational inversion. During ozone episodes the mixed layer heights were low ( in the range 300-500 m) at 9 a.m. which favors the percursors of photochemical pollution such as Nitrogen Oxides and NMHC to accumulate and cause high ozone day. Measurements of pollutants showed that they well mixed at the higher portions of the mixed layer during the daytime. During nighttime, ozone concentration decreased near the ground and exponentially increased with altitude to a maximum near 500 m above ground level. The NO、NO2 and NMHC decreased with altitude, and are almost not detectable above 300 m.
