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Photochemical Reactivity And Sources Of Individual VOCs In Mexico City


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V. Mugica, E. Vega, H. Ruiz, G. Sánchez, E. Reyes & A. Cervantes


Volatile organic compounds (VOCs) play a very important role in the photochemical production of atmospheric ozone. To developing cost-effective strategies aimed reducing ozone levels, the CMB model has been used to estimate the source contribution to the presence of total VOCs. Nevertheless, the photochemical importance and the origin of VOCs are not the same for all of them. In this paper, the relative contribution of VOCs to photochemical formation of ozone was examined in three sites of the Mexico City by ranking the VOCs according to their average concentration and the maximum incremental reactivity coefficients of each species. The most important compounds in the ozone formation in order of decreasing importance were: meta/para xylene, ethylene, toluene, 3methyllbutene, isopentane, 124 trimethylbenzene, propene, orthoxylene, toluene, nbutane, propane, 135 trimethylbenzene, and 1 butene. On the other hand, an assessment of the contribution of different sources to the observed concentration of the most abundant individual VOC was made by the application of the CMB model. Exhaust of gasoline and diesel powered vehicles were the most important sources to acetylene, ethylene, pentanes, nhexane, toluene and xylenes, although evaporative gasoline emissions contributed with more of 20% of npentane and isopentane. The major contributor to propane, nbutane and isobutane was the handling and distribution of LP gas. Food cooking contributed also to the presence of acetylene, ethylene, propane and butanes. Painting operations were emitters of toluene and nhexane. The results also showed that asphalting operation was an important source of xylenes and toluene.