1,3,5-三甲苯生成二次有机气溶胶过程的室外光化学烟雾箱模拟研究

发布时间：2018-05-26 10:04

本文选题：1 + 3　；参考：《山东大学》2017年硕士论文

【摘要】：本文在调研与考查环境空气中VOCs污染特征的基础上,选择在环境空气中具有较高污染浓度并且具有较高二次有机气溶胶生成潜势的VOCs物种——1,3,5-三甲苯作为研究目标物种,利用中国环境科学研究院的大型室外光化学烟雾箱模拟实验系统,在接近真实环境空气条件下开展1,3,5-三甲苯的大气光化学氧化过程的模拟实验研究,重点考察[1,3,5-三甲苯]/[NOx]初始浓度比值以及气象因子对1,3,5-安甲苯大气光化学氧化过程的影响。文献调研表明典型区域环境空气中芳香烃在VOCs中占16.21%～53.73%,1,3,5-三甲苯占所观测芳香烃浓度的1.99%～9.29%,其SOAFP占具有SOAFP物种的5.01～15.23%。实际观测中,北京市典型城区环境空气中芳香烃占84种VOCs浓度的15%左右,1,3,5-三甲苯占观测期间间芳香烃浓度的2.00%,其SOAFP占具有SOAFP物种的7.02%。文献调研与实际观测表明典型城市环境空气中1,3,5-三甲苯为具有较高浓度的苯系物物种,并且为二次有机气溶胶的重要前体物,因此本文选取1,3,5-三甲苯作为目标VOCs物种开展大气光化学反应模拟实验研究。在进行1,3,5-三甲苯大气光化学氧化模拟实验之前,对烟雾箱箱体的密闭性、混合性和壁效应等性能进行表征。CO在3.5 min即可混合均匀;O3的衰减速率常数K=2.47×10-6s-1,半衰期t1/2=77.87 h;颗粒物总数浓度壁损失常数为7× 10-5 s-1,生命周期为4.0h;1 3.5-三甲苯的壁衰减反应速率常数K=6×10-6s-1,半衰期t1/2=32.08h。以上表征实验的结果表明,大型室外光化学烟雾箱模拟系统基本可以满足模拟实验的需求。本文开展10次不同污染气象条件下的1,3,5-三甲苯大气光化学氧化模拟实验,其中于夏季和冬季在不同气象条件下分别开展6次和4次实验,实验中对[1.3,5-三甲苯]/[NOx]初始浓度比进行调变,变化范围在1.08-16.47之间。1,3,5-二甲苯大气光化学氧化模拟实验结果分析表明,当[1,3.5-三甲苯]/[NOx]初始浓度比在1-2时,1,3.5-三甲苯大气光化学反应中反应物的消耗和产物的生成速率随比值的增加而增加;当[1,3,5-三甲苯]/[NOx]初始浓度比在7-16时,1,3,5-三甲苯大气光化学反应中反应物的消耗和产物的生成速率不随初始浓度比的变化而变化。夏季模拟实验中二次有机气溶胶数浓度和体积浓度随紫外辐射的延长表现出上升趋势,并在达到模拟实验中的最高值后出现小幅度下降,随后在结束模拟实验前一直呈上升趋势;冬季模拟实验中二次有机气溶胶体积浓度随紫外辐射强度的变化而变化,而二次有机气溶胶数浓度则随紫外辐射的延长而逐渐上升,当达到实验中的最高值后出现小幅度的下降,随后在关箱前一直呈上升趋势,并且冬季模拟实验的二次有机气溶胶产率高于夏季。模拟实验中的醛酮化合物产物主要包括甲醛、乙醛、丙酮、丙醛、正丁醛和m-甲基苯甲醛,1,3,5-三甲苯光氧化气态产物浓度冬季低于夏季。夏季模拟实验的二次有机气溶胶产物中含有2,4,6-三甲基苯酚、3,5-二甲基-2-呋喃、甲基乙二醛酸、2-甲基-2,3-二羟基-4-羰基-戊烯酸、2,4-二甲基-2,3,4-三羟基-5,6-二羰基-庚酸等5种化合物,冬季模拟实验二次有机气溶胶产物中则含有2,4,6-三甲基苯酚、3,5-二甲基-2-呋喃和2,4-二甲基-2,3,4-三羟基-5,6-二羰基-庚酸等3种化合物。根据对1,3,5-三甲苯大气光化学氧化过程产物的情况可以判断1,3,5-三甲苯存在分子重排现象,部分1,3,5-三甲苯发生了开环反应;产物中分子量较大的物质可能会转变为非挥发性有机物分配到有机气溶胶中;而分子量较低的物种由于具有更多官能团或不饱和键,易与OH自由基、O3和NO3发生进一步的氧化反应;另外一些高极性和低挥发性的小分子量物质也容易分配到有机气溶胶中。1,3,5-三甲苯光化学反应实验结果表明,影响1,3,5-三甲苯光化学反应过程的包括[1,3,5-三甲苯]/[NOx]初始比、温度、光辐照等因素。[1,3,5-三甲苯]/[NOx]初始比影响1,3,5-三甲苯光化学反应历程;较高的温度有利于提高二次有机气溶胶产率,但较低的温度有利于颗粒物粒径和数浓度的增长;较强的紫外辐射可以提高1,3,5-三甲苯的光化学反应速率,促进二次有机气溶胶浓度的生成。以上研究结果说明在制定环境空气中大气颗粒物控制政策时,需要高度重视VOCs/NOx的比例,即VOCs与NOx的协同控制。
[Abstract]:On the basis of investigating and examining the characteristics of VOCs pollution in the ambient air, this paper selects the VOCs species, 1,3,5- three toluene, which has high pollution concentration in the ambient air and has high two times of organic aerosol generation potential as the target species, and uses the large-scale outdoor photochemical smog box simulation of the Chinese Academy of Environmental Sciences. In the experimental system, the experimental study on the atmospheric and chemical oxidation process of 1,3,5- three toluene under the actual ambient air conditions is studied. The initial concentration ratio of [1,3,5- three toluene]/[NOx] and the influence of meteorological factors on the atmospheric photochemical oxidation process of 1,3,5- an toluene are mainly investigated. Hydrocarbons accounted for 16.21% ~ 53.73% in VOCs, and 1,3,5- trimethol accounted for 1.99% ~ 9.29% of the observed aromatic hydrocarbon concentration, and its SOAFP accounted for 5.01 ~ 15.23%. of SOAFP species. The aromatic hydrocarbons in the ambient air in the typical urban areas of Beijing accounted for 15% of the 84 VOCs concentrations, and 1,3,5- trimethol accounted for 2% of the observed aromatic hydrocarbon concentration during the observation period, and its SOAFP accounted for it. The 7.02%. literature survey and actual observation of SOAFP species show that 1,3,5- trimethol in the typical urban environment is a species with high concentration of benzene, and is an important precursor of two organic aerosols. Therefore, this paper selects 1,3,5- three toluene as a target VOCs species to carry out a simulated experimental study of large gas photochemical reaction. 1, Before the simulation experiment of 3,5- tri benzol atmospheric photochemical oxidation, the properties of the airtight, mixing and wall effect of the smoke box body were characterized by.CO at 3.5 min, and the decay rate constant of O3 was K=2.47 * 10-6s-1, the half life t1/2=77.87 h; the concentration wall loss constant of the total particles was 7 * 10-5 s-1, the life cycle was 4.0h; 1 3.5-. The reaction rate constant of the three toluene is K=6 x 10-6s-1, and the results of the half life longer than t1/2=32.08h. show that the large-scale outdoor photochemical smoke box simulation system can basically meet the needs of the simulated experiment. In this paper, the simulated experiment on the photochemical oxidation of 1,3,5- three toluene in the atmosphere under different weather conditions is carried out in this paper, in which summer is in summer. 6 and 4 experiments were carried out at different meteorological conditions in season and winter. The initial concentration ratio of [1.3,5- three toluene]/[NOx] was adjusted in the experiment. The variation range of the variation range of.1,3,5- dimethylbenzene atmospheric photochemical oxidation experiment between 1.08-16.47 showed that when the initial concentration of [1,3.5- three toluene] / [NOx] was 1-2, 1,3.5- tri methylbenzene was large The consumption of reactants and the production rate of the products increased with the ratio of the gas photochemical reaction. When the initial concentration of [1,3,5- three toluene]/[NOx] was 7-16, the consumption of reactants and the production rate of the products were not changed with the variation of the initial concentration ratio in the atmospheric photochemical reaction of 1,3,5- trimethol. In the summer simulation experiment, two organic compounds were used. The concentration and concentration of aerosol number and concentration increase with the increase of ultraviolet radiation, and then decrease slightly after the maximum value of the simulated experiment. Then, it has been increasing before the simulation experiment. In the winter simulation experiment, the volume concentration of two organic aerosols varies with the intensity of ultraviolet radiation, and two times. The number of organic aerosols increased gradually with the extension of UV radiation. When the maximum value of the experiment was reached, the number of organic aerosols decreased slightly, and then increased in front of the closed box, and the two organic aerosol yield in the simulated experiment was higher than that in the summer. The aldehyde and ketone compounds in the simulated experiment mainly include formaldehyde and acetaldehyde. The concentration of acetone, propionic aldehyde, n-butyl aldehyde and m- methyl benzaldehyde, 1,3,5- trimethyl benzaldehyde in the photooxidation of gaseous products in winter is lower than that in summer. The two organic aerosol products in the simulated experiment contain 2,4,6- three methyl phenol, 3,5- two methyl -2- furan, methyl ethyl two alalonic acid, 2- methyl -2,3- two hydroxyl -4- carbonyl pentaenoic acid, 2,4- two methyl -2,3,4- three hydroxyl -5. 6- two carbonyl - heptanoic acid and other 5 compounds. In the two organic aerosol products in winter simulation experiments, there are 3 compounds of 2,4,6- three methyl phenol, 3,5- two methyl -2- furan and 2,4- two methyl -2,3,4- three hydroxyl -5,6- two carbonyl heptanoic acid. In the presence of benzene molecular rearrangement, partial 1,3,5- trimethylamine has an open ring reaction, and the larger molecules in the products may change into organic aerosols with non volatile organic compounds, and the species with lower molecular weight have more oxidation reactions with OH radicals, O3 and NO3 because of more functional groups or unsaturated bonds. Some other high polar and low volatile small molecular weight substances are also easily distributed to the.1,3,5- trimethol photochemical reaction in organic aerosols. The results show that the effect of the initial ratio of [1,3,5- three toluene]/[NOx], temperature, and light irradiation on the initial ratio of.[1,3,5- three toluene]/[NOx] affects the initial ratio of.[1,3,5- three to 1,3,5-. The photochemical reaction process of trimethol can increase the yield of two organic aerosol, but the lower temperature is beneficial to the increase of particle size and number concentration. The strong UV radiation can increase the photochemical reaction rate of 1,3,5- three toluene and promote the formation of two organic aerosol concentration. When controlling atmospheric particulate matters in ambient air, we need to attach great importance to the VOCs/NOx ratio, that is, the coordinated control of VOCs and NOx.
【学位授予单位】：山东大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：X513;O648.18

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