臭氧層破洞的光化學:過氧化氯的紫外線吸收截面積及其溫度效應

Photochemistry of the Ozone Hole: Ultraviolet Absorption Cross Sections of ClOOCl and Their Temperature Effects

林衛彥(Wei-Yen Lin)

指導教授 ： 李遠哲

國立臺灣大學/理學院/化學研究所/碩士(2009年)

https://doi.org/10.6342/NTU.2009.00531

摘要

過氧化氯(ClOOCl)分子在臭氧層破洞的形成機制中扮演著重要的角色，其吸收截面積決定了臭氧層被破壞的速率。以往科學家利用測量光線經樣品槽的衰減量來計算吸收截面積，但由於過氧化氯分子極不穩定，並且在製備過程中會產生雜質，使量測的吸收光譜會有雜質的貢獻，導致在計算臭氧層破壞的速率時產生極大誤差。尤其，Pope等人[J. Phys. Chem. A 111, 4322 (2007)]在2007年發表的過氧化氯分子吸收截面積遠小於先前學界接受的值，若將此數據代入現有的大氣化學模型中，約有一半的臭氧層消失無法被解釋。本論文採用全然不同的方法，把不純的樣品利用質譜儀篩選質量後，偵測過氧化氯分子受雷射光照射後的衰減量來計算吸收截面積。此方法可確保過氧化氯分子的訊號不受雜質干擾，所以能得到準確且可信的數據。本論文測量了過氧化氯分子在溫度160K~250K下248、308及351奈米的吸收截面積，此吸收截面積遠大於2007年Pope等人的結果，將此數據代入大氣化學模型中，便可以妥善解釋臭氧洞的形成以及大氣中相關物質如氧化氯與過氧化氯的實測濃度，證實了現有的大氣化學模型仍然可行。此外使用本方法所測得的數據具有極佳的準確性，因此我們能夠測量不同溫度下過氧化氯分子吸收截面積的變化，此為過氧化氯分子吸收截面積溫度效應的首次研究。

關鍵字

Ozone Hole ； ClOOCl ； absorption cross section ； molecular beam ； temperature dependence

並列摘要

Chlorine peroxide (ClOOCl) plays an important role in the formation of the Ozone Hole. The absorption cross section of ClOOCl is a key parameter for determining the polar ozone loss rate. Conventionally, scientists determine the absorption cross sections by photo-absorption method. But all synthesized gas-phase ClOOCl samples contain impurities. Thus, there are large discrepancies in the absorption cross sections of ClOOCl. The new data published by Pope et al. [J. Phys. Chem. A 111, 4322 (2007)] are much smaller than previously accepted values. If Pope’s data are correct, about half of the observed ozone loss can not be explained. Unlike other groups, we measured the attenuation of ClOOCl molecular beam after laser irradiation by a mass detector. Therefore impurities would not contribute to the signal of ClOOCl. We determined the absorption cross sections of ClOOCl at 248, 308, 351 nm unambiguously. The cross sections we measured are much lager than Pope et al.’s data. Using our results, the current atmospheric model can well explain the observed ozone loss and concentrations of ClO and ClOOCl. Our results indicate the current model for the ozone loss is still valid. In addition, we can measure the temperature dependences of the absorption cross section of ClOOCl due to good precision of this method. This work is the first measurement for temperature effects of the absorption cross sections of ClOOCl.

並列關鍵字

Ozone Hole ； ClOOCl ； absorption cross section ； molecular beam ； temperature dependence

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