微粒採樣過程中反應及揮發性物種之研究

Abstract

本研究使用高流量 PM10 採樣器 (Hi-vol PM10 sampler)、 分道採樣 器 (PM10 Dichotomous sampler, Dichot) 及氣固分離器 (Annular Denuder System, ADS) 於新竹空氣品質監測站平行採樣大氣污染物，藉以 了解於採樣過程中微粒物種濃度與實際濃度之差異， 並探討導致此種誤差 之揮發及反應的情形。 濾紙於調理過程中所造成之誤差及大氣污染物之組 成亦列入討論。 採樣時間從八十三年十月至八十四年四月止。 以氣固分離器為標準， 使用石英濾紙之高流量 PM10 採樣器於採樣的 過程中會因二氧化硫吸附及氧化於微粒或被濾紙吸收造成硫酸鹽高估 10 % ， 而硝酸鹽、氯鹽及銨鹽濃度則分別低於真實值之 15 %、2 5 % 及 18 % 。 石英濾紙所收集之 PM10 樣本則於二十四小時調理之過程中因揮發作用 其硝酸鹽、氯鹽及銨鹽分別損失 5 %、6 % 及 8 %； 硫酸鹽則無明顯得差 異。而使用鐵氟龍濾紙之分道採樣器於採樣的過程中其粒徑小於 10 um 之 硝酸鹽、氯鹽及銨鹽分別損失 21 %、32 % 及 21 %，硫酸鹽則高估 8 %； 粒徑小於 2.5 um 硝酸鹽、氯鹽及銨鹽分別損失 21 %、54 % 及 18 %，硫 酸鹽因二氧化硫吸附及氧化於微粒則高估 15 %。比較使用石英濾紙之高流 量 PM10 採樣器及使用鐵氟龍濾紙之分道採樣器， 發現石英濾紙易吸收二 氧化硫、硝酸、氯化氫及氨氣等氣體， 造成硫酸鹽、硝酸鹽、氯鹽及銨鹽 之質量濃濃度略高真實濃度分別為 1 %、8 %、3 % 及 8 %。 由實驗結果與揮發理論相互比較， 發現流經濾紙之氣體與濾紙上已收 集之微粒之間及微粒與微粒堆積之間的反應會導致相當程度之揮發情形。 氣固分離器之濾紙組亦驗證微粒堆積之間的反應會產生額外揮發的現象。 在所有所使用之採樣器之中均發現氯鹽為主要揮發物種。 酸性微粒的分布 以硫酸銨至硫酸氫銨為主，而被鹼性微粒中和的作用亦相當明顯。 The sampling artifacts are formed due to the retention and absorption of gases by sampling media and collected particles, volatilization of collected particles, gas-particle and particle-particle reactions within collected particles. Two Annular Denuder Systems (ADS10 and ADS2.5) were used to quantify sampling artifacts of soluble ionic species determined by the high volume PM10 (Hi-vol PM10) and PM10 dichotomous (Dichot10 and Dichot2.5) samplers. Artifact formation during 24-conditioning of filter samples was important and was also investigated. In addition, characteristics of acidic aerosols in Hsin Chu air monitoring station was also studied. Experimental results show that the PM10 dichotomous sampler with Teflon filters collects 8 % more sulfate, because of adsorption and oxidation of SO2 by the particle deposits, but less nitrate (by 21 %), chloride (by 32 %) and ammonium (by 21 %) than the ADS10 because of volatilization and reactions. While the PM10 dichotomous sampler with Teflon filters collects nearly the same amount of sulfate as the Hi-vol PM10 sampler with quartz filters, it collects much less nitrate (by 8 %), chloride (by 8 %) and ammonium (by 3 %) than the latter because of more volatilization and reactions in its fine fraction.