天氣型態對雲林地區細懸浮微粒濃度與組成之影響

本研究分析雲林縣麥寮與斗六地區 PM2.5之時空分佈及天氣型態對PM2.5濃度及組成之影響，於2013-2015共計執行11次人工採樣並分析其化學組成(陰陽離子、EC、OC)，另進行11次陰陽離子之逐時現址監測。 利用風速風向之小時變化判別傳輸與滯留型態，並利用天氣圖來判定14種天氣型態。結果發現滯留型態較傳輸型態更易發生PM2.5事件日(≧35μg/m3) ，而在14種天氣型態中又以高壓迴流其事件日發生比率為最高，在麥寮與斗六兩地區分別為42%及67%。PM2.5組成分中之SNA(硫酸鹽、硝酸鹽、銨鹽)佔約29~43%，滯留型態高於傳輸型態。硝酸鹽與銨鹽濃度在14種天氣型態中以高壓迴流為最高，而硫酸鹽濃度則於西南氣流時最高。傳輸型態其PM2.5濃度較對照組(<20μg/m3且該日均溫低於20℃)高出2.3倍左右，滯留型態較對照組高出約3倍，而高壓迴流則較對照組高出近4倍。在組成分之比較上，硝酸鹽及銨鹽於高壓迴流時其相較於對照組之倍率為最高，而硫酸鹽則於西南氣流時為最高。由逐時監測之數據，發現硝酸鹽在滯留型天氣型態下，其每日最大升幅(每日最高濃度與最低濃度差異之幅度)為SNA三種鹽類中最高。計算銨過量之結果，發現滯留型態較傳輸型態有更多之過量銨，而在14種天氣型態中又以高壓迴流最高，而以西南氣流為最低。此外，發現當氣膠酸度較高其NR值低於0.7時，扣除硝酸離子與銨離子結合為硝酸銨(NH4NO3)，剩餘之其他硝酸離子則主要與鈉結合，其次則與鈣結合。

This study examined the temporal and spatial variations of PM2.5 concentrations in Mailiao and Douliou, Yunlin, as well as the effects of synoptic weather types on the concentrations and compositions of PM2.5. Aerosols were collected in 11 sampling periods during 2013-2015. The compositions of aerosols, including water-soluble ionic components, EC, OC, and metals were then analyzed. In addition, hourly water-soluble ionic components were measured by an in situ IC system. The transport/stagnant weather types are determined by hourly variations of the wind speed and direction, while 14 synoptic weather patterns were categorized by a weather chart. The stagnant weather conditions showed a higher probability of PM2.5 episode days (≥35μg/m3) occurring. The episode occurring percentage (episode days/total days, in each weather pattern) was the highest on type P3 (cold high-pressure system moving eastward to the Pacific Ocean with a center beyond 125°E longitude) among the 14 synoptic weather patterns. It was about 42% and 67% in Mailiao and Douliou, respectively. The percentages of SNA (Sulfate, Nitrate, and Ammonium) in PM2.5 ranged from 29% to 43%, while the mean percentage of SNA in the stagnant weather type was higher than that in the transport weather type. Nitrate and ammonium concentrations were the highest for type P3, while sulfate concentration was the highest for P10 (prevailing southwesterly wind flows associated with the existence of a typhoon around South Korean Peninsula or Japan). The mean concentrations of PM2.5 for transport, stagnant, and P3 weather types were respectively 2.3, 3.0, and 4.0 times higher than those of the control group (PM2.5 < 20μg/m3 and temperature < 20°C). Compared to the control group, the increased levels of nitrate and ammonium were the highest on P3, while those of sulfate were highest on P10. Variations of hourly water-soluble ionic components show that the daily maximum increase in levels of nitrate for the stagnant weather type was the highest among SNA. Results of excess ammonium (NH4+excess) indicated that higher values in the stagnant weather type were obtained than those for the transport weather type. Among the 14 synoptic weather patterns, the highest excess ammonium was found in type P3. In addition, when NR values of aerosol are lower than 0.7 (acid aerosol), the remaining nitrate ions (subtracting those combined with ammonium ions) combined mainly (65%) with sodium, while about 22% combined with calcium.