氣膠的潮解與光學效應對於臺灣都會區大氣能見度的影響

The Influences of Deliquescence and Optical Effects of Aerosols on the Atmospheric Visibility in Taiwan Metropolitan Area

林建皓(Chien-Hao Lin)

指導教授 ： 張士昱

中山醫學大學/健康管理學院/公共衛生學系/碩士(2021年)

https://doi.org/10.6834/csmu202100276

摘要

大氣消光係數與能見度會受到粒徑小於2.5 μm氣膠(PM2.5)、相對濕度(RH)、氣膠化學組成與含水量等因素影響。本研究在中山醫學大學使用現址式空氣組成量測設備(Air Composition Measuring Equipment In-situ 2100, ACME In-situ-2100)量測逐時PM2.5水溶性無機離子，使用ISORROPIA模式模擬氣膠含水量，並結合臺北、臺中與高雄三大都會區同步濾紙氣膠化學成分組成與逐時散光、消光係數，探討氣膠結構組成、含水量變化趨勢與影響臺灣都會區大氣能見度的因素。氣膠含水量在相對濕度高且PM2.5污染嚴重時，氣膠中的水量會急遽增加，而[NH4+]/[SO42-] > 1.5時，由於大量二次氣膠生成，此時氣膠含水量由硫酸銨與硝酸銨主導。大氣散光、消光係數亦受PM2.5與RH影響，與PM2.5相關性佳(R2分別為0.70、0.61)，並隨著PM2.5上升而增加，雖然其與RH相關性不佳(R2分別為0.15、0.10)，但可以觀察到隨著RH上升，PM2.5的散光與消光能力也明顯提高。在小港測站相對濕度影響相對輕微(RH ≤ 75 %)且PM2.5低於24小時平均濃度標準(PM2.5 ≤ 35 μg m-3)狀況下，硝酸鹽與氣膠含水量的相關性高於硫酸鹽，且硝酸鹽的濃度與氣膠含水量比板橋及西屯(忠明)高出許多，再加上硝酸鹽的潮解點低，使小港氣膠大量潮解導致小港能見度的大幅衰減。若將氣膠化學組成套入revised IMPROVE公式中可發現，消光係數的主要貢獻來源為硫酸鹽與硝酸鹽，二次鹽類的貢獻在三站約占總消光係數的39 % ~ 58 %，其中NO3-在高污染事件中幾乎占總貢獻一半以上。計算消光係數推估值與實際觀測值的相對誤差，結果顯示三站的相對誤差皆大於20 %，可能原因為revised IMPROVE的相對濕度條件或是氣膠化學組成比例皆不同於臺灣，因此相關修正參數fS、fL(RH)、fSS(RH)也可能不適用於臺灣，若要計算更為準確的推估值可能需要發展本土濕度修正參數。而透過比較逐時量測系統與濾紙採樣組成的相對誤差發現，逐時數據比濾紙採樣推估的消光係數更為準確，且在時間解析度上遠勝於濾紙採樣。

關鍵字

逐時水溶性離子 ； 硝酸鹽 ； 硫酸鹽 ； 氣膠含水量 ； 消光係數

並列摘要

Atmospheric extinction coefficient and visibility were affected by factors such as PM2.5, RH (relative humidity), aerosol chemical composition and liquid water content. In this study, the hourly measurement of inorganic soluble ions in PM2.5, conducted with the ACME In-situ-2100 (Air Composition Measuring Equipment In-situ 2100), were combined with ISORROPIA model to simulate aerosol liquid water content (ALWC) at Chung Shan Medical University. The chemical compositions of filter samples and the hourly scattering/extinction coefficient were used to investigate the compositions of aerosols, the changing trend of aerosol liquid water content, and the factors of affecting the visibility in Taiwan metropolitan areas. The aerosol liquid water content was increased quickly as the increasing of RH and PM2.5. Ammonium sulfate and ammonium nitrate, the predominated species of secondary aerosols, contributed a large amount of aerosol liquid water content when [NH4+]/[SO42-] > 1.5. The scattering and extinction coefficient were correlated well with increasing PM2.5 (R2 is 0.70 and 0.61, respectively). The R2 between RH and scattering coefficient and extinction coefficient were 0.15 and 0.10, respectively. However, it was observed that the scattering and extinction ability of PM2.5 increased significantly under high RH. Under RH ≤ 75 % and PM2.5 ≤ 35 μg m-3 (the 24-hour average concentration standard of PM2.5) at Xiaogang station, the correlation of ALWC was higher with nitrate than that with sulfate. And the concentrations of the nitrate and ALWC at Xiaogang were much higher than that at Banqiao and Xitun (Zhongming). In addition, the lower deliquescence RH of nitrate enhanced the aerosol deliquesce abundantly. It may be one of the major reasons for the visibility decreasing at Xiaogang. The simulations of the revised IMPROVE indicated that the main contributions of the extinction coefficients were sulfate and nitrate. The total extinction coefficient contribution of secondary salts accounted for 39 % ~ 58 %, which nitrate accounted almost half in pollution events. By comparing the relative error of the hourly in-situ measurements and the daily filter measurements, it was found that the hourly extinction coefficients were more accurate than the daily result. The measured ratio of the scattering coefficients to the extinction coefficients was not as high as the theoretical ratio. The parameters of the revised IMPROVE (fS, fL(RH), fSS(RH)) may not be applicable to evaluate the extinction and scattering coefficient in Taiwna metropolitan areas.

並列關鍵字

water-soluble ions ； ACME ； aerosol liquid water content ； ISORROPIA ； extinction coefficient ； revised IMPROVE ； visibility

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