都市與農業地區大氣污染物特徵比較

本研究於2023年11月臺灣臺中地區（都市空氣污染研究站, Urban Air Pollution Research Station, UAPRS）及2024年3月臺灣嘉義地區（嘉義氣象站）探討都市地區及農業地區大氣污染物特徵及差異比較，使用現址式空氣組成量測設備（Air Composition Measuring Equipment In-situ 2100, ACME In-situ-2100）以收集氣體與氣膠中水溶性無機離子成分，同時採用環境部空氣品質監測網的逐時大氣污染物濃度及氣象數據，並藉由ISORROPIA II模型推估氣膠含水量。研究結果顯示都市地區在東北季風傳輸時期，因大氣擴散條件佳，使得大氣污染物濃度較低，此時期PM2.5水溶性無機離子以SO42-為主，而在滯留時期PM2.5濃度增加，並以NO3-為主要水溶性無機離子。農業地區PM2.5濃度變化與都市地區相同，但除了區域海洋傳輸時期是以NO3-為主，東北風及西南風傳輸時期和滯留時期則是以NH4+為主。氣態污染物方面，農業地區因大量農業活動，NH3濃度在所有時期平均濃度均高於都市地區，此現象也使農業地區大氣氨氣充足，造成農業地區氣膠中NH4+與水溶性無機陰離子結合後仍有大量NH4+（Remained-NH4+）存在於PM2.5中。在氨氣充足情況下，NH3可與大氣中的酸性氣體經由均相反應結合，減少氣膠中Remained-NH4+的含量，而NH3亦可透過潮解氣膠的含水量以異相反應溶於氣膠中，導致氣膠中Remained-NH4+增加。在農業地區污染事件下平均PM2.5質量散光效率較都市地區高，其中相對濕度<80%情況下，隨著Remained-NH4+在PM2.5中的占比增加，PM2.5質量散光效率也隨之增加，顯示Remained-NH4+與大氣能見度不佳有關。

In this study, to explore and compare the characteristics and variations of atmospheric pollutants between urban and agricultural regions, observations were conducted in Taichung （UAPRS） in November 2023 and Chiayi （Chiayi Meteorological Station） in March 2024. Using Air Composition Measuring Equipment In-situ-2100 （ACME In-situ-2100） to collect water-soluble inorganic ion components of aerosols, and using hourly air pollutant concentration and meteorological data from the Environmental Protection Department's air quality monitoring network, the aerosol water content is estimated using the ISORROPIA II model.The results of the study show that in urban areas, under the influence of the northeast monsoon transport events, favorable atmospheric diffusion conditions lead to lower concentrations of atmospheric pollutants, and the main water-soluble inorganic ion in PM2.5 is SO42-. During the stagnation period, the concentration of PM2.5 increases, with NO3- being the main water-soluble inorganic ion. In agricultural areas, the variation in the concentration of PM2.5 is similar to that in urban areas, but NO3- is the main component during regional marine transport periods, and NH4+ dominates during northeastern and southwestern wind transport periods and the stagnation period. In terms of gaseous pollutants, the concentration of NH3 in agricultural areas is higher than in urban areas during all periods due to extensive agricultural activities. This results in sufficient ammonia in agricultural areas and causes a large amount of NH4+ （Remained-NH4+） to persist in PM2.5 after combining with water-soluble inorganic ions. Under conditions of sufficient ammonia, NH3 can react with acidic gases in the atmosphere through homogeneous reactions, thereby reducing the content of Remained-NH4+ in aerosols. Furthermore, NH3 can dissolve in aerosols through heterogeneous reactions by absorbing water content from deliquescent aerosols, leading to an increase in Remained-NH4+ within the aerosols. During pollution events in agricultural regions, the average mass scattering efficiency of PM2.5 is higher compared to urban areas. When the relative humidity is below 80%, the mass scattering efficiency of PM2.5 increases with the proportion of Remained-NH4+ in PM2.5, indicating that Remained-NH4+ is related to poor atmospheric visibility.