Environmental chamber studies for development of an updated photochemical mechanism for VOC reactivity assessment
Environmental chamber studies for development of an updated photochemical mechanism for VOC reactivity assessment
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发表时间：
1997
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通讯作者：
W. Carter
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作者：
W. Carter
进行了一系列室内环境箱实验，以填补数据库中的空白，所需的气相光化学机制的评估挥发性有机化合物（VOCs）的排放对环境空气质量的影响进行评估。采用两个大型双模式室内聚四氟乙烯袋室，一个用黑光灯照射，另一个用氙弧灯照射。评价了用于测量这些腔室中的光强度的替代方法。结果发现，石英管NO_2的光量计提供了令人满意的数据为黑光室，但Cl_2正丁烷照射提供了一个更好的方法为氙弧室。研究了不同湿度对室内实验结果和重现性的影响。结果发现，干运行和运行在约50%RH之间的差异很小，不应显着影响机制评估结果，但运行湿度接近100%RH可能会有问题。增量反应性实验，其中测试化合物被添加到代表环境污染的反应性有机气体（ROG）替代物的NOx-空气辐照，进行了使用氙弧室的代表性化合物。这些都是需要补充更大的数据库增量反应性实验在黑光室。结果是一致的模型预测和增量反应性实验在黑光灯室的大数据库，如果芳烃的机制进行了修改，以说明光源的差异。使用两种光源进行了一系列广泛的单一芳香族氮氧化物实验，以提供开发、调整和评估苯、甲苯、乙苯、邻、间和对二甲苯以及所有三种三甲基苯异构体的机制所需的数据。详细的SAPRC机制（SAPRC-93）的当前版本没有正确解释异构体的差异，往往低估了氙弧室中的反应性。更好的拟合可以得到，如果两个集总裂解产物，代表不同的光解作用光谱的产率分别为每个异构体进行优化。然而，这样的调整仍然不能提供令人满意的苯拟合，并且不能在所有方面模拟其他芳烃的数据。本研究所获得的数据库将是评价正在开发的最新机制的重要资源。
A series of indoor environmental chamber experiments were conducted to fill gaps in the data base needed for evaluation of gas-phase photochemical mechanisms for assessing the effects of emissions of volatile organic compounds (VOCs) on ambient air quality. Two large dual-mode indoor Teflon bag chambers, one irradiated by blacklights and the other by xenon arc light, were employed. Alternative methods for measuring light intensity in these chambers were evaluated. It was found that quartz tube NO2 actinometry provides satisfactory data for the blacklight chamber, but that Cl2 n-butane irradiations provide a better method for the xenon arc chamber. The effects of varying humidity on results and reproducibility of chamber experiments were examined. It was found that differences between dry runs and runs at ~50% RH were minor and should not significantly affect mechanism evaluation results, but that runs with humidities approaching 100% RH may have problems. Incremental reactivity experiments, where a test compound is added to NOx-air irradiations of reactive organic gas (ROG) surrogates representing ambient pollution, were conducted for representative compounds using the xenon arc chamber. These were needed to supplement the much larger data base of incremental reactivity experiments in blacklight chambers. The results were consistent with model predictions and the large data base of incremental reactivity experiments in blacklight chambers, if the aromatics mechanisms was modified to account for differences in light source. An extensive series of single aromatic NOx experiments were carried out using both light sources to provide data needed to develop, adjust, and evaluate mechanisms for benzene, toluene, ethylbenzene, o-, m-, and p-xylenes, and all three trimethylbenzene isomers. The current version of the detailed SAPRC mechanism (SAPRC-93) did not correctly account for isomeric differences and tended to underpredict reactivities in the xenon arc chamber. Much better fits could be obtained if yields of two lumped fragmentation products, representing different photodecomposition action spectra, are optimized separately for each isomer. However, such adjustments still did not provide satisfactory fits for benzene, and could not simulate the data for the other aromatics in all respects. The data base obtained in this study will be an important resource for evaluating updated mechanisms which are under development.