以環形擴散採樣器採集大氣中酸、鹼性氣體輿微粒 - 美國環保署新舊標準方法應用於台灣地區採樣之比較

Abstract

本研究以環形擴散採樣器(ADS)之新、舊標準方法與Bai and Wen(2000)所建議採樣組裝方式，同時對標準方法中幾種可採集之目標物染物及HF氣體做差異性分析及適用性的探討。 由研究結果顯示，不同酸性污染物塗覆溶劑於採樣管內之串聯順序，對後端採集NH3氣體與濾紙夾微粒之結果影響不大。應用differential method之修正方法，對不同酸性氣體污染物採樣時，有其最可信賴之組裝方式，並以此作為該氣體之參考標準方法，將另外兩種方式之採樣結果對該標準方法進行偏差百分率計算。 由實驗計算可知，簡化之US.EPA新標準方法對採集台灣地區低濃度HNO3氣體，將會產生高達300％左右之偏差，但對其較他高濃度物種如HNO2、HCl(>0.8μg/m3)、NH3所造成之偏差則可落在10%接受範圍內。而HF氣體之濃度最可信賴組裝方式則是以兩管塗覆Na2CO3來採集，故以單管Na2CO3之簡化方式在台灣新竹地區低濃度之情況下，亦可能會造成可觀之採樣偏差。最後，依據實驗之結果，在不影響採集結果並能簡化採樣組裝之原則下，對不同採樣氣體做適合之組裝方式建議，希望能對往後以ADS系統在大氣採集上有所幫助。

This study is an evaluation between the methods of previous US.EPA and up-to-date annular denuder system (ADS) to measure acidic and basic gases and particles in the atmosphere. Otherwise, it also applied arrangement recommended by Bai and Wen (2000) to compare with the old and new US.EPA referential method. Experiments of different ADS arrangements for sampling HF gas are also conducted in this study to confirm their sampling suitability for HF gas. Experimental results indicated that different acidic gases coating material almost has no influence on the followed basic gas denuder as well as particles in filter pack. By the differential method, there was a reliable method for specific species. Therefore, sampling deviation could be calculated for the other two devices as compared to the preferential referential method. As the result of experiments, the simple US.EPA method may yield over 300 % relative deviation for sampling HNO3 gas. For typically high HNO2, HCl (>0.8 mg/m3) and NH3 gas concentration in Taiwan as compared to other countries’ measurement data, use one denuder coating with Na2CO3 should yield less than 10% deviation. The reliable assembly for HF gas is two Na2CO3 coated denuders in sequence, using one Na2CO3 denuder may obtain higher relative error at low HF gas concentration condition. In conclusion, this study also provides several simple assemblies to trap gases within acceptable sampling deviation and suggestions in atmosphere sampling.