External Industrial Sources Affect Regional and Local SO2 and O3 Levels in Mexico City

Researchers reaffirm the importance of emission source identification for accurate modeling.

The Science

A recent study determined how strongly various emission sources affect air quality in areas of the Mexico City metropolitan area.

The Impact

Air quality in megacities can be influenced by both local emission sources and more distant external global- and regional-scale emission sources. Studying emission sources can provide important insights into attribution of atmospheric sources for enhancing model integrity as well as applications such as improving air quality.


Since the number and sizes of megacities are projected to increase in the future, properly representing them in global atmospheric models is important. A research team, including Department of Energy scientists from Pacific Northwest National Laboratory, evaluated an observed sulfur dioxide (SO2) peak at a suburban supersite and at ambient air quality monitoring stations located in the Mexico City metropolitan area (MCMA) during the 2006 Megacity Initiative: Local and Global Research Observations (MILAGRO) field campaign. The researchers found that this peak could be related to an important episodic emission event originating northeast of the MCMA. Because regional SO2 emission sources were not considered in previous studies, the episodic emission suggests the possibility of “overlooked” emission sources that could influence MCMA air quality. The research found that cement plants in the state of Hidalgo and Mexico can account for about 42 percent of the SO2 levels in the northeast region of the MCMA basin and 41 percent at the suburban supersite T1; at some monitoring stations the contribution can be even higher than the contribution from the Tula Industrial Complex (TIC). A modeling study suggests a low contribution to the MCMA (1 to 4 ppb) and a slightly higher contribution at the suburban T1 (6 ppb) and rural T2 (5 ppb) supersites. However, the contributions could be as high as 10 ppb in the upper northwest region of the basin and in the southwest and south-southeast regions of the state of Hidalgo. The research also presents a first estimate of the potential contribution from flaring activities to regional ozone levels. Results suggest that up to 30 percent of the total regional ozone from TIC could be related to flaring activities. The combination of emission reductions in power plant, refinery, and local sources in the MCMA could result in higher reductions in the average SO2 concentrations, which tend to have a more significant impact on the northern part of the basin, while reductions of urban sources in the megacity tend to diminish SO2 levels substantially in the central, southwest, and southeast regions.

Principal Investigator(s)

Jerome Fast
Pacific Northwest National Laboratory

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This work was supported by the U.S. Department of Energy’s Atmospheric System Research Program under contract DE-AC06-76RLO 1830 at PNNL. Additional support was provided by the National Science Foundation under award AGS-1135141.


Almanza, V. H., L. T. Molina, G. Li, J. Fast, and G. Sosa. 2014. “Impact of External Industrial Sources on the Regional and Local SO2 and O3 Levels of the Mexico Megacity,” Atmospheric Chemistry and Physics 14, 8483-99. DOI:10.5194/acp-14-8483-2014