| 摘要: | 本文於2017年8、10月及2018年3、4月，在台灣鹿林山空氣品質測站(海拔2,862公尺)進行大氣氣膠觀測，目的是解析東亞大氣背景及受中南半島生質燃燒煙團傳輸影響的氣膠化學特性。
觀測期間分為前期(2017年)及後期(2018年)，前期觀測可分為背景期間與山谷風期間，背景期間PM2.5及PM10平均質量濃度分別為3.5 ± 1.9 µg m-3和6.9 ± 3.6 µg m-3，PM2.5占PM10為58%，可視為東亞高山氣膠背景濃度。後期觀測則分成生質燃燒影響與非生質燃燒影響期間，在生質燃燒影響期間PM2.5與PM10平均質量濃度分別為17.4 ± 3.9 µg m-3與21.6 ± 4.5 µg m-3，PM2.5占PM10的80.3%，顯示中南半島傳輸至東亞的生質燃燒氣膠受細粒徑主宰，PM2.5水溶性離子以nss-SO42-、NO3-與NH4+為主要化學成分，碳成分以OC3為優勢化學成分，但OC4較非生質燃燒期間明顯增加。
後期觀測期間當量黑碳(equivalent black carbon, EBC)與PM10元素碳相關性在生質燃燒期間最好，其次為自由大氣期間，最後為人為污染期間。PM10元素碳質量吸光效率在波長880 nm與950 nm分別為17.79 m2 g-1與15.62 m2 g-1比儀器製造廠商的黑碳質量吸光效率高；另外，EC2與吸光係數相關性明顯較低，說明EC2不是主要的吸光碳成分。
利用Revised IMPROVE公式模擬鹿林山後期觀測期間的PM2.5消光係數並和自動儀器氣膠消光係數比較，相關性很好(R2>0.75)，硫酸鹽對消光係數貢獻最大，其次為有機物。在背景期間，大氣氣膠消光係數以空氣分子散光為最顯著因子，其次為硫酸鹽和有機物。在低相對濕度和非靜風狀態下，鹿林山氣膠化學成分和上層大氣氣膠光學厚度線性相關增加。
;This study observed the atmospheric aerosol at the Mt. Lulin air-quality station (2,862 m a.s.l.) in Taiwan in August and October 2017 and March and April 2018. The objective is to explore the chemical characteristics of aerosols in the atmospheric background and the transported biomass burning (BB) smoke from Indochina to East Asia.
The observation was split into front and rear observation periods in 2017 and 2018, respectively. The front period was further divided into background and valley wind periods. The background concentrations of PM2.5 and PM10 were 3.5 ± 1.9 μg m-3 and 6.9 ± 3.6 μg m-3, respectively, and PM2.5 accounted for 58% of PM10, which can be regarded as the background aerosol concentration in a high-elevation site in East Asia. In addition, the rear observation period was further divided into the periods of BB and non-BB. The average concentrations of PM2.5 and PM10 during the BB period were 17.4 ± 3.9 μg m-3 and 21.6 ± 4.5 μg m-3, respectively. PM2.5 accounted for 80.3% of PM10, which indicated that fine particlulates dominated the transported BB aerosol. Among PM2.5 chemical compositions, nss-SO42-, NO3- and NH4+ are major water-soluble inorganic ions, and OC3 is the dominant carbonaceous component with a pronounced increase of OC4 during the BB period.
The computed equivalent black carbon (EBC) correlated best with EC in PM10 during the BB period followed by those in the periods of free atmosphere and anthropogenic influence. The mass absorption efficiency of PM10 EC were 17.79 m2 g-1 and 15.62 m2 g-1, respectively, higher than the conversion values adopted by the manufacturer. Moreover, the correlation between EC2 and light absorption coefficient was low, implying that EC2 was not a significant component of light-absorbing carbon.
This study used the Revised IMPROVE formulae to computed atmospheric light extinction to come up with a good correlation (R2>0.75) with the measured values during the rear observation period. Sulfate contributed atmospheric light extinction most followed by organic matter according to the computation. In contrast, Rayleigh scattering by air molecules was the prominent factor followed by sulfate and organic matter in the front observation period. The correlation between PM2.5 chemical components and aerosol optical depth increased when the Mt. Lulin station was in low relative humidity and non-static environmental condition. |
