| 摘要: | 由於大氣氣膠在時間尺度有快速變化特性，因此唯有進行氣膠連續監測，才得以解析氣膠的時間變化和污染來源。本文利用環保署北部氣膠超級測站2002年3月至2008年12月連續觀測數據，探討氣膠特性受環境因子及污染產生源的影響，研究議題包括探討近七年來氣膠特性變化、大陸冷高壓影響、二次有機碳生成量、車輛排放與光化學反應比較、特殊事件日(黃沙事件、節慶日及高濃度事件)氣膠特性、以及大氣能見度與氣膠消光等。 研究結果顯示，大多數氣膠成分都有逐年下降的趨勢，但硫酸鹽的變化趨勢是逐年上升，且在冬季會有最高值，夏季有最低值，但有機碳(OC)、元素碳(EC)與黑碳(BC)最低值發生在秋季。在秋季與冬季常有冷高壓事件、黃沙事件及高濃度事件的發生，冷高壓事件與黃沙事件若氣流傳輸過程中經過大陸沿岸，則PM2.5硫酸鹽濃度會大量增加。高濃度事件是以PM2.5日平均值大於50 μg m-3篩選，主要受到高壓迴流及高壓推擠天氣型態影響，前者會導致本地污染物累積後者則傳輸跨境污染物。另外，節慶日(春節、清明節、中元節及中秋節)如果沒有受到天氣影響，則民俗活動就會凸顯其影響。 每日各小時PM2.5二次有機碳是以每日早上6點至9點的(OC/EC)平均值進行估算，結果指出四季都會有二次有機碳的生成，大約占有機碳的10%至15%左右。比較機動車輛排放與光化學反應時段PM2.5成分發現，當每日臭氧最大濃度小於80 ppb時，機動車輛排放程度會比較嚴重；當每日臭氧最大濃度大於80 ppb時，光化學反應產生的污染程度則會比較嚴重。 以迴歸模式探討氣膠光學特性可以發現，氣膠消光係數主要是受到未量測的PM2.5成分、PM2.5硝酸鹽、PM2.5硫酸鹽、PM2.5 EC及相對溼度的影響；大氣能見度則是受到PM2.5硝酸鹽、PM2.5硫酸鹽及相對溼度影響。 Owing to fast variations of atmospheric aerosol in temporal scale, aerosol time variations and source contributions can only be resolved by way of continuous monitoring. This study adopts continuous monitoring data ranged from March 2003 to December 2008 at the North Aerosol Supersite of the Taiwan Environmental Protection Administration to investigate the effects of environment factors and pollution sources on aerosol properties. The study subjects include aerosol property variations in recent seven years, the influence of continental high, formation of secondary organic carbons, comparisons of mobile vehicle emissions and photochemical reactions, aerosol properties in the selected events (Yellow Dust, Festivals, and high concentration), and atmospheric visibility affected by aerosol extinction. The results show that the level of most aerosol components except for sulfate has a decreasing trend in years. In addition, most aerosol components apparently have the highest level in winter and with the lowest level in summer in a year. Nonetheless, organic carbon (OC), elemental carbon (EC), and black carbon (BC) exhibit their lowest concentrations in autumn. During years, continental cold-high event, Yellow Dust event, and high concentration event frequently occurred in autumn and winter. For continental cold-high event and Yellow Dust event, high PM2.5 sulfate level was observed when the air masses transport along the coastline of Mainland China. High concentration event is selected by having daily PM2.5 level above 50 μg m-3. This event is caused by weather type such as anticyclonic outflow or high-pressure pushing, the former renders local pollution accumulation and the latter transports trans-boundary pollutants to Taiwan. For days with festival activities (e.g., the Spring Festival, the Tomb-Sweeping Festival, the Mid-Summer Festival, and the Moon Festival), pollution is affected by festival activities if the weather does not interfere with pollutant behaviors. Hourly PM2.5 secondary organic carbon was estimated by using (OC/EC) averages taken from 6:00 to 9:00 every morning. The estimated PM2.5 secondary organic carbon appeared in every season and accounted for 10 to 15% of OC. PM2.5 components between the time periods for mobile vehicle emissions and photochemical reactions are compared. Mobile vehicle emissions are found related to higher PM2.5 component concentrations when the daily ozone maximum level is below 80 ppb. In contrast, photochemical reactions are responsible for higher PM2.5 component concentrations when the daily ozone maximum level is above 80 ppb. Regression analysis on aerosol optical property reveals that aerosol light-extinction is mainly affected by components not detected in PM2.5, PM2.5 nitrate, PM2.5 sulfate, PM2.5 EC, and relative humidity. For atmospheric visibility, it is influenced by PM2.5 nitrate, PM2.5 sulfate, and relative humidity. |
