| 摘要: | 本研究於2015年秋季與2016年春季在鹿林山背景觀測站(以下簡稱為鹿林山)以即時氣膠水溶性監測儀(Particle-Into-Liquid-Sampler coupling with Ion Chromatographers, PILS-IC)監測PM2.5(氣動粒徑在2.5 µm以下粒狀污染物)氣膠水溶性無機離子(WSIIs)動態變化，並收集測站監測的PM2.5氣膠質量濃度、PM10與PM1氣膠吸散光係數、氣膠總數目、氣膠粒徑與體積分布、氣體污染物動態變化。
PILS-IC採集的數據會與濾紙樣本做比較，結果顯示兩者在秋天與春天的採樣中，所採集的主要WSIIs (SO42-、NO3-、NH4+、K+)相關性均良好(R2 ≥ 0.75)。在秋季採樣期間，觀察到鹿林山易受谷風影響，對平均PM2.5質量濃度貢獻從6.9 ± 2.1上升至11.5 ± 2.3 µg m-3。
比較兩季數據可以發現，在去除受降雨的影響後，春天的平均PM2.5質量濃度(16.8 μg m-3)為秋天平均(8.0 μg m-3)的兩倍，來自中南半島的生質燃燒煙團造成的高濃度事件，會遮蔽谷風在鹿林山的影響，使谷風的特性不明顯。在春天的採樣中，由逆推軌跡結果發現，三月時氣流主要來自西方的中南半島，而四月開始，轉為來自南方的菲律賓區域。春季[NH4+]/[SO42-]莫耳比以1.5為界，在大於1.5時，[NO3-]/[SO42- ]會隨著[NH4+]/[SO42-]上升而呈現線性的增加，而生質燃燒期間，[NH4+]/(2[SO42-]+[NO3-])莫耳比為0.88 ± 0.25，離子關係呈現接近完全的中和。在討論的三個生質燃燒事件中，平均PM2.5質量濃度為24.9 ± 12.7 μg m-3，平均NH4+、SO42-、NO3-、K+離子濃度分別為1.7 ± 1.0、3.7 ± 1.4、1.4 ± 1.0、0.3 ± 0.2 μg m-3，過剩 NH4+(先與SO42-中和後)與NO3-相關性良好(R2 ≥ 0.70)，顯示氣體同相反應主導硝酸微粒的生成。其中，三個生質燃燒事件共發生四起雲霧事件，可以觀察到氣膠粒徑增長現象，或者因為受到乾淨的氣流影響，使濃度降低，並由粒徑分布觀察到生質燃燒煙團的微粒呈現單峰，但在雲霧事件中，呈現雙峰分布。;Field campaigns were conducted at Lulin Atmospheric Background Station (LABS) from October to November 2015 and March to April 2016. Short-interval variations of water-soluble inorganic ions (WSIIs) of PM2.5 (an aerodynamic diameter equal to or less than 2.5 μm) were monitored using particle-into-liquid sampler coupling with ion chromatographers (PILS-IC). Meanwhile, PM2.5 mass concentration, PM10 and PM1 aerosol absorption and scattering coefficients, aerosol total number concentration, aerosol number and volume size distributions, and gaseous pollutants were also measured at LABS.
The short-interval measurements of WSIIs were compared with collocated filter measurements. Major WSIIs (SO42-, NO3-, NH4+, and K+) were correlated well (R2 ≥ 0.75) between averages of short-interval measurements and filter samples during the study period. In autumn sampling, the effect of upslope wind contribution was obvious to cause PM2.5 increasing from 6.9 ± 2.1 to 11.5 ± 2.3 µg m-3 in average.
Comparing data collected between spring 2016 and autumn 2015, the average PM2.5 mass concentration in spring (16.8 μg m-3) was twice that in autumn (8.0 μg m-3) after excluding rainy periods. Transported biomass burning (BB) smoke form Indochina was verified to cause high PM2.5 mass concentration in spring, which, however, masked upslope wind effects. During spring campaign, five-day backward trajectory analysis showed that the origins were mostly from far west of Indochina in March but changed to from the Philippines in April. Ion equivalent evaluation indicated the molar ratio of [NO3-]/[SO42- ] increased linearly as the molar ratio of [NH4+]/[SO42-] exceeded beyond 1.5. A near complete neutralization among major ions with the ratio of [NH4+]/(2[SO42-]+[NO3-]) at 0.88 ± 0.25 during BB period in spring. In the selected third to fifth BB events, average PM2.5 mass concentration was 24.9 ± 12.7 μg m-3, while average NH4+, SO42-, NO3-, and K+ concentration were 1.7 ± 1.0, 3.7 ± 1.4, 1.4 ± 1.0, and 0.3 ± 0.2 μg m-3, respectively. Excess NH4+ (after neutralizing with SO42-) correlated well with NO3- (R2 ≥ 0.70) indicating NO3- were formed through homogenous gas phase reactions. Four fog events were also observed in the selected BB events. Aerosol either diluted by clean air or possible growth of aerosol in the fog events were observed. As for number size distributions, the particles during BB events presented a unimodal distribution, while bimodal distributions were observed in the fog events in the third to fifth BB events. |
