Be-7是宇宙源放射性同位素，由平流層中的氧和氮受到宇宙射線照射分裂所產生，Be-7富集於平流層及上部對流層中，因此Be-7可做為平流層與對流層間垂直氣團交換的示蹤劑。Pb-210是由Rn-222衰變所產生，Rn-222是惰性氣體，從地表裂隙逸散到大氣中，因此Pb-210富集於低層地表。大氣中Po-210是由Pb-210衰變所產生，而Po-210/Pb-210活度比值增加可表示氣溶膠的停留時間增加。由於Pb-210、Po-210和Be-7皆為親顆粒性核種，會吸附到氣溶膠上，再經由降雨而帶至地表，所以這些核種可以當作大氣與大氣污染物的示蹤劑。偵測雨水中Pb-210、Po-210和Be-7的活度、通量與比值，可用來了解大氣和大氣污染物在大氣中傳輸、交換及循環的情形。本研究於成功大學地科系頂樓，採集2008年6月至2009年12月的雨水樣品，採樣間隔為幾小時至一天。
　　在Pb-210、Po-210和Be-7活度與降雨量的變化關係中，顯示降雨量低於~2 cm時活度高且變化大，當降雨量大於~2 cm時活度較為穩定不隨雨量變化。在降雨量大時活度低且相對穩定顯示氣溶膠主要受到雲內雨除清除，而降雨量小時活度高且變化大主要是因為氣溶膠受到雲下沖刷所清除。單次降雨事件中Pb-210、Po-210和Be-7的通量變化中，濕季時的通量低於乾季時的通量，是由於乾季時主要是沖刷所清除，可更有效清除大氣中的氣溶膠。Po-210/Pb-210活度比值在夏季時也明顯偏低，顯示夏季時氣溶膠因受到頻繁降雨清除，造成停留時間較短。長時間尺度的Pb-210、Po-210和Be-7的年平均通量分別是0.80、0.0052和6.53 dpm/m^-2/y，皆低於前人在台北南港所測得的值，可能是由於北部在冬季及早春時降雨較台南地區頻繁。
　　梅雨事件B與C中，顯示Pb-210、Po-210和Be-7的活度與通量具有相同的趨勢，是由於梅雨B與C主要受到清除效率的機制（沖刷與雨除）所影響。而梅雨A與U中核種活度與通量的變化則是受到鋒面水平移動影響，進而造成來源有所變化。觀察梅雨Po-210/Pb-210和Be-7/Pb-210比值可合理解釋梅雨氣團的水平及垂直移動，還可用來指示梅雨氣團的傳輸以及氣溶膠受到降雨清除的強度與效率。在梅雨A與B事件中，Po-210/Pb-210比值變化程度大是因為梅雨鋒面水平移動帶來新的氣團與汙染物到台南地區；而Be-7/Pb-210比值減少是因為梅雨A雨B的垂直氣團交換減弱，造成比值變化大甚至降到零。在梅雨C和U事件中，Po-210/Pb-210比值逐漸降低是因為降雨而有效清除大氣中的氣溶膠，且梅雨鋒面沒有水平移動，在台南地區滯留，使得側向輸入的Po-210很少，顯示出Po-210/Pb-210隨著時間及降雨而減少；另外從Be-7/Pb-210比值可發現弱的水平移動伴隨著較強的垂直氣團交換，Be-7/Pb-210比值在梅雨降雨階段都維持較高的值。
　　Pb-210、Po-210和Be-7可有效用來示蹤在颱風時大氣及汙染物的傳輸過程。在兩場颱風事件中（2008年的卡玫基颱風與2009年的莫拉克颱風）皆顯示相似的Po-210/Pb-210及Be-7/Pb-210比值變化。Po-210/Pb-210在初始值時高，颱風接近時受降雨清除而降低，當颱風眼登陸台灣時降到低點，當颱風眼離開台灣時盛行西南氣流，引進新的氣團和汙染物，使的雨水中Po-210/Pb-210比值升高，之後便隨著降雨清除而降低。Be-7/Pb-210比值在颱風登陸前的降雨中出現高峰值，是因為颱風眼牆附近的平流層—對流層垂直氣團交換很強。在颱風登陸之後Be-7/Pb-210比值便降低，是由於登陸後颱風的垂直交換減弱。

　　Be-7 is a cosmogenic radionuclide produced primarily in the stratosphere and upper troposphere and is widely used to study the vertical exchange of air mass between the stratosphere and troposphere. In contrast, Pb-210 and Po-210 as the decay products of Rn, are enriched mostly in the air mass of lower atmosphere and the ratio of Po-210/Pb-210 increases with increasing residence time of air-borne aerosols. Being particle-reactive, these radionuclides are chiefly scavenged from the atmosphere via aerosol adsorption and subsequent rainfall precipitation, and hence measurements of these radionuclides provide a useful tracer for understanding the transport of air-mass and air-borne pollutants in the atmosphere. This study, investigated the temporal changes of Pb-210, Po-210 and Be-7 activities in rainwater collected from station NCKU, Taiwan from June, 2008 to December, 2009, with the sampling time interval being about several hours to one day.
　　The relationship between activities of radionuclides and rain fluxes shows that high activities occurs when the rainfall amount of each sample is less than ~2 cm, and the activities remain relatively constant when the rainfall amount is > ~2 cm. The lower and relatively constant activities of radionuclides at high rain flux indicate the in-cloud rainout scavenging mechanism, while the increased activities of radionuclides at low rain flux indicate the below-cloud washout scavenging mechanism. The single-event fluxes of Pb-210, Po-210 and Be-7 for each sample are lower in wet seasons than in dry seasons further confirming that the more efficient scavenging is caused by more pronounced effect of washout in dry seasons. On the other hand, the Po-210/Pb-210 activity ratios are lower in summer indicating more frequent rainfall scavenging in summer causes the shorter residence time of aerosols in the atmosphere. The long-term mean fluxes of Pb-210, Po-210 and Be-7 are 0.80, 0.0052 and 6.53 dpm/m2/y respectively, significantly lower than those reported for a station located at Taipei, ~300 km north of our study site, which may be partly attributed to more frequent rainfalls during winter and early spring in Taipei.
　　The activities and fluxes of Pb-210, Po-210 and Be-7 during plum rain events B and C both show similar temporal variation patterns, suggesting that the scavenging effect (washout vs. rainout) plays an important role for the aerosols/radionuclides scavenging. On the other hand, the activities and fluxes of radionuclides for plum rain events A and U are more likely affected by the movement of plum rain front as well as the sources/origin of air mass. The observed Po-210/Pb-210 and Be-7/Pb-210 ratios in all plum rains can be plausibly explained by the horizontal and vertical movement of the plum rain air mass. These ratios are useful indicators of physical transport of air mass and of the scavenging intensity of aerosols by plum rain precipitation. In plum rain events A and B, in Po-210/Pb-210 the large variation can be attributed to the horizontal movement which brings fresh air-mass and air-borne pollutants into the sampling site and the decreased Be-7/Pb-210 ratios are caused by weakly vertical air-mass exchange. In plum events C and U, the Po-210/Pb-210 ratio decreases efficient scavenging of aerosols by the rainfall and limited lateral input of Po-210 due to the weak horizontal movement of the plum rain front. Interestingly, the weak horizontal exchange is accompanied by the strong vertical exchange of air- mass as seen from the Be-7/Pb-210.
　　This study shows that Pb-210, Po-210 and Be-7 are useful for tracing the transport of air mass and aerosols pollutants during the typhoon events. Two typhoons during 2008-2009, Kalmaegi and Morakot, both show similar temporal variation patterns in Po-210/Pb-210 and Be-7/Pb-210 ratios. Po-210/Pb-210 is high in the initial period, and decreases when typhoon eye wall is approaching and then almost reaches minimum when the typhoon eye lands on Taiwan. When the typhoon eye leaves Taiwan, the prevailing southwesterly flow brings fresh air mass and air-borne pollutants, increasing the Po-210/Pb-210 ratios in the rain and then the ratio decreases again by rainfall scavenging. Meanwhile Be-7/Pb-210 ratio reaches maxima just before typhoon eye lands on Taiwan, suggesting the intensified vertical air-mass exchange between the stratosphere and troposphere in the typhoon eye wall. Then the decreases of Be-7/Pb-210 ratio after typhoon eye lands on Taiwan suggests quickly weakened/diminishing of the vertical exchange of air mass.

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