紫外光誘發粒子生成現象之探討

A Study of Particle Formation Induced by UV Irradiation

歐庭維(Ting-Wei Ou)

指導教授 ： 洪惠敏

國立臺灣大學/理學院/大氣科學研究所/碩士(2014年)

https://doi.org/10.6342/NTU.2014.01654

摘要

本研究利用實驗及模擬的方式，探討不同波段(185 nm & 254 nm)的紫外光及氣流中添加不同氣體，對於光化反應和產生新粒子現象的影響，實驗所產生的粒子使用掃描式電動度粒徑分析儀(SMPS)進行粒子的粒徑、數量進行測量。實驗結果顯示，本研究中要產生新粒子必須要有OH自由基存在才行，此外，沒有水氣或沒有提供紫外光皆無法產生粒子。當相對濕度上升時，由於OH自由基產量上升，使得新生粒子的總數量、總體積增加。然而，添加臭氧、過氧化氫、甲醇等氣體於氣流中卻觀察到新粒子的數量、體積有減少的現象。藉由模擬實驗中包含的光化反應及氧化反應得知，實驗產生新粒子的現象可能與硫酸、甲醇的生成有關。當相對濕度上升時，硫酸與甲醇的產量增加，產生的硫酸及甲醇最高分別為濃度為0.12 ppb、0.45 ppb。於氣流中添加臭氧的模擬則得知硫酸的產量維持不變0.12 ppb，但甲醇的產量隨臭氧濃度增加而減少至5.38 ppt。添加過氧化氫的模擬中，過氧化氫濃度增加至1.78 ppm開始有明顯的影響，當添加的過氧化氫濃度超過1.78 ppm後，硫酸與甲醇的產量有明顯的下降。添加甲醇於氣流中的模擬則得知，添加甲醇的濃度超過17.86 ppm後，由於甲醇會消耗OH自由基，使得硫酸的產量下降。因此，本研究觀察到粒子生成的現象可能與硫酸與有機物質例如甲醇的生成有關。

關鍵字

紫外光 ； OH自由基 ； 相對溼度 ； 臭氧 ； 過氧化氫 ； 甲醇

並列摘要

The effect of different wavelengths (λ=184.9 nm and λ=254 nm) and carrier gases on particle nucleation via. photochemical reactions nucleation were investigated using a flow tube and a scanning mobility particle sizer (SMPS) to measure the size-number distribution of new particles. The experimental results suggested that the new particle formation in our study only happened with presence of hydroxyl radical (OH). The total number and volume of new particles increased with relative humidity (RH) due to more OH production. However, the new particle production significantly decreased when extra ozone or hydrogen peroxide (H2O2) or methanol was added into the flow. The simulation composed with various chemical reactions including photolysis and oxidation reactions, suggested that new particle formation is related to the concentration of produced H2SO4 and methanol. At higher RH and the provided light source, the overall concentration of H2SO4 and methanol reached the maximum concentration 0.12 ppb and 0.45 ppb. As the ozone concentration was increased, H2SO4 was at maximum concentration but methanol was decreased to5.38 ppt. When extra H2O2 was added into the system, the simulation showed no significant product variation until [H2O2] > 1.78 ppm. At [H2O2] >1.78 ppm, H2SO4 and methanol were significantly decreased. If CH3OH was added into the flow, it consumed most OH and lead to lower H2SO4. Overall, the new particle formation in this study is likely associated with the formation of H2SO4 and possible organic species such as methanol.

並列關鍵字

UV light ； OH radical ； relative humidity ； ozone ； hydrogen peroxide ； methanol

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