The effect of sampling artifacts on the mass concentrations obtained by manual PM2.5 samplers
|Keywords:||多濾紙PM10-PM2.5採樣器;半揮發性物質;濾紙面速度;固氣分離器;濾紙動態量測系統;MFPPS;evaporated loss;face velocity;PMD;FDMS-TEOM|
|Abstract:||本研究使用多濾紙PM10-PM2.5採樣器(Multi-Filter PM10-PM2.5 Sampler, MFPPS)與一部雙通道採樣器(Dichotomous Sampler, Dichot)、一部符合美國聯邦參考方法(Federal Reference Method, FRM)的WINS PM2.5採樣器及一部搭載濾紙動態量測系統的震盪錐形微量天平(tapered element oscillating microbalance with the filter dynamic measurement system, FDMS-TEOM)於交通大學的校園進行並列採樣，其中MFPPS的頻道2加裝了多孔金屬片固氣分離器(porous metal denuder, PMD)，以收集採樣過程中微粒揮發掉的質量濃度。
研究結果顯示，因揮發造成的質量濃度損失占修正揮發後之日平均PM2.5質量濃度(PM2.5,Mcorr)約 5.8至36%，且此比例隨著濾紙上微粒負荷量的降低及濾紙面速度的上升有增加的趨勢。分析PMD採集到的微粒揮發成分發現，採樣過程揮發掉的NH4+、NO3- 及Cl-濃度占PM2.5,Mcorr的平均百分比分別為9.5 ± 6.2、5.4 ± 3.7、及 2.0 ± 1.3 %，而在各物種中平均所占的比例則分別為46.4 ± 19.2、66.9 ± 18.5及74.4 ± 14.0 %。濾紙調理的部分，在連續調理秤重24、48、72、96及120小時後，PM2.5,Mcorr濃度分別降低了3.5 ± 1.8、5.1 ± 1.7、6.2 ± 2.5、7.4 ± 3.3及8.5 ± 3.2 %。FDMS-TEOM和手動濾紙採樣器比對的結果顯示，由於受採樣過程及濾紙後續調理過程微粒揮發損失的影響，WINS、Dichot及MFPPS所測得之日平均PM2.5質量濃度分別較FDMS-TEOM的量測結果低了16.6 ± 9.0、15.2 ± 10.6及12.5 ± 8.8 %。而以PMD測得之微粒揮發量修正後的PM2.5,Mcorr，其測值與FDMS-TEOM的量測結果相當接近，顯示FDMS-TEOM能修正採樣干擾的影響，是一部準確的PM2.5即時監測器。|
In this study, the multi-filter PM10-PM2.5 sampler (MFPPS) was collocated with a dichotomous sampler (Dichot, Andersen, Model SA-241), a WINS PM2.5 sampler (Thermo, Model 2000-FRM), and a tapered element oscillating microbalance with the filter dynamic measurement system (FDMS-TEOM, Thermo, Model 1405-DF) were conducted at Taiwan Nation Chiao-Tung University (NCTU) campus. In order to evaluate the evaporation loss of fine particles (PM2.5), porous metal denuders (PMDs) were installed in sampling channels of the MFPPS to measure the concentration of evaporated ion species during sampling. Results showed that the evaporation loss in PM2.5 was severe during sampling, accounting for 5.8 to 36.0 % of the corrected daily average PM2.5 concentration (PM2.5,Mcorr) and the percentage increased with decreasing loaded particle mass and increasing filtration velocity. During 24-h sampling, the evaporated NH4+, NO3- and Cl- concentrations accounted for 9.5 ± 6.2, 5.4 ± 3.7, and 2.0 ± 1.3 % in PM2.5,Mcorr, respectively, or 46.4 ± 19.2, 66.9 ± 18.5, and 74.4 ± 14.0 %, in the concentration of each species, respectively. The PM2.5,Mcorr concentration was decreased by 3.5 ± 1.8 % after 24-h conditioning, and was further decreased by 5.1 ± 1.7, 6.2 ± 2.5, 7.4 ± 3.3 and 8.5 ± 3.2 % after 48, 72, 96, and 120-h conditioning, respectively. Due to the evaporation loss, daily average PM2.5 concentrations measured by the WINS, Dichot, and MFPPS were lower than those the FDMS-TEOM by 16.6 ± 9.0, 15.2 ± 10.6 and 12.5 ± 8.8 %, respectively. When the MFPPS PM2.5 concentrations were corrected for the evaporated loss determined by the PMD, good agreement with those by the FDMS-TEOM was achieved. This indicates the FDMS-TEOM with the capability to adjust for sampling artifacts is an accurate real-time PM2.5 monitor.
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