| 摘要: | 本文於2015年春季在鹿林山大氣背景觀測站(以下簡稱鹿林山，海拔高度2,862 m)以即時氣膠水溶性離子監測系統(Particle-Into-Liquid-Sampler coupled to an Ion Chromatograph, PILS-IC)監測PM2.5水溶性離子，並結合測站內即時監測儀器監測的PM2.5、PM10大氣質量濃度、PM1、PM10光學吸光及散光係數、氣體污染物濃度、氣膠數目濃度與粒徑分布動態變化等資料進行討論。
在不受生質燃燒、谷風、雲霧事件影響時段，PM2.5大氣質量濃度平均為3.2±0.3 μg m-3，PM2.5水溶性無機離子以陰離子為主，其中SO42-濃度最高，平均為0.7±0.1 μg m-3；陽離子濃度較低，且環境中常呈現NH4+不足以完全中和SO42-和NO3-現象。鹿林山午後易受谷風影響，谷風影響期間CO、O3、RH、PM10、PM2.5數值會上升。三次雲霧事件都發生在午後，CO、O3、PM2.5濃度分別為0.13±0.04 ppm、48.3±9.4 ppbv、16.5±4.1 μg m-3，SO42-、NH4+、NO3-平均濃度分別為3.6±0.8、2.2±1.1、1.5±0.8 μg m-3，顯示受到谷風影響的污染物濃度。計算雲霧期間與大氣SO2平衡而溶解於霧珠的SO42-和PILS-IC量測的SO42-比值(Dissolved Gas over Measured Ions, DIGMI)，發現在“雲霧發生”前段DIGMI略大於1情況較多，“雲霧發生”期間和以後則DIGMI數值小於1，代表雲霧事件大多受谷風傳輸帶來SO42-，變低DIGMI數值。
鹿林山四次生質燃燒事件(含谷風及雲霧事件)中， CO、O3、PM2.5和K+平均濃度分別為0.26±0.3 ppm、74.2±7.9 ppbv、28.8±6.7 μg m-3、0.6±0.1 μg m-3，SO42-、NH4+、NO3-濃度分別為4.1±0.8、3.0±1.0、1.9±0.4 μg m-3；生質燃燒期間，大氣環境長時間出現過剩NH4+ (ExNH4+)，代表足以中和SO42-，推測環境中SO42-結合型態為(NH4)2SO4和(NH4)2SO4。受生質燃燒影響期間出現雲霧時，觀測較多情況DIGMI數值小於1，平均數值為0.71±0.16，代表環境中傳輸氣膠SO42-濃度大於SO2轉化成SO42-濃度。
以不受生質燃燒、谷風、雲霧影響時段的NH4+、K+、NO3-、SO42-濃度為基本案例，比較他時段前述成分濃度差異百分比，當不受生質燃燒影響但受谷風影響時段分別增加98.7%、57.4%、88.8%、40.8%，不受生質燃燒影響但受雲霧影響時段分別增加100.0%、83.6%、98.6%、68.8%。單純受生質燃燒影響時段NH4+、K+、NO3-、SO42-濃度增加100.0%、96.6%、98.8%、69.2%，受生質燃燒影響且發生谷風前述離子濃度增加100.0%、96.6%、98.8%、77.0%，最後，受生質燃燒影響且發生雲霧濃度前述離子濃度各增加100.0%、96.1%、99.1%、74.6%。
;In this study, PM2.5 water-soluble inorganic ions (WSIIs) were monitored using an in-situ Particle-Into-Liquid-Sampler coupled to an Ion Chromatograph (PILS-IC) system at Lulin Atmospheric Background Station (LABS, 2,862 m a.s.l.) in spring 2015. Meanwhile, PM2.5 and PM10 mass concentrations, PM1 and PM10 light-scattering and -absorption coefficients, trace gas concentrations, and dynamic variations of aerosol number concentrations and size spectra monitored at LABS were also adopted for discussion.
PM2.5 mass concentraions were averaged at 3.2±0.3 μg m-3 during the period without been affected by the transported biosmass burning (BB) smoke, upslope wind, and fog event. Among PM2.5 chemical components, anion dominated WSIIs with SO42- averaged at 0.7±0.1 μg m-3 as the predominant component in contrast to relative low concentration of cation with NH4+ incapable of complete neutralizing SO42- and NO3-. Meanwhile, LABS was frequently affected by the upslope wind accompanying with the rises of CO, O3, RH, PM10, and PM2.5. Three cloud events happened in the afternoon to result in the rises of pollutant levels by having the mean values of CO, O3, and PM2.5 at 0.13±0.04 ppm, 48.3±9.4 ppbv, and 16.5±4.1 μg m-3, respectively, and that of SO42-, NH4+, and NO3- at 3.6±0.8, 2.2±1.1, and 1.5±0.8 μg m-3, respectively. The values of Dissolved Gas over Measured Ions (DIGMI) were calculated by dividing the dissolved SO42- concentrations in fog droplets in equilibrium with atmospheric SO2 over SO42- measured by PILS-IC. The DIGMI values were frequently greater than 1 before the occurrence of a cloud event in contrast to less than 1 during and after a cloud event. It indicated that SO42- was transported by the upslope wind from the hill to reduce the DIGMI values in the cloud events.
Durning the four BB events (including upslope and cloud events), mean levels of CO, O3, PM2.5, K+, SO42-, NH4+, and NO3- were 0.26±0.3 ppm, 74.2±7.9 ppbv, 28.8±6.7 μg m-3, 0.6±0.1 μg m-3, 4.1±0.8 μg m-3、3.0±1.0 μg m-3、1.9±0.4 μg m-3, respectively. In most occasions, excess NH4+ (ExNH4+) was found enough to complete neutralizing SO42- to form (NH4)2SO4 and (NH4)2SO4. The DIGMI values were often less than 1 with a mean value of 0.71±0.16 during the fog peroid when influenced by the transported BB smoke. This implied that SO42- in the transported smoke was more than that of the dissolved SO2 in the fog droplets.
Take mean values of NH4+, K+, NO3-, and SO42- during the time period not affected by the transported BB smoke, upslope wind, and fog events as the base case for comparing with that of the other time periods in terms of percentage differences are shown as follows. For the period not affected by the transported BB smoke but under the influence of the upslope wind, the differences for NH4+, K+, NO3-, and SO42- were 98.7%, 57.4%, 88.8%, and 40.8%, respectively. Similarly, the differences for the period not affected by the transported BB smoke but under the influence of fog events were 100.0%, 83.6%, 98.6%, and 68.8%, respectively. Moreover, the differences of NH4+, K+, NO3-, and SO42- for the period affected purely by the transported BB smoke were 100.0%, 96.6%, 98.8%, and 69.2%, respectively. In the case for the period affected by the transported BB smoke and upslope wind, the differences of the aforementioned WSIIs were 100.0%, 96.6%, 98.8%, and 77.0%, respectively. Finally, the differences of the precedent WSIIs were 100.0%, 96.1%, 99.1%, and 74.6%, respectively, for the period affected by the transported BB smoke and fog events. |
