Impact of External Industrial Sources on the Regional and Local SO2 and O3 Levels of the Mexico Megacity

Fast, J. D., Pacific Northwest National Laboratory

Radiation Processes

Aerosol Life Cycle

Almanza VH, LT 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, 10.5194/acp-14-8483-2014.

Science

Scientists determined how strongly various emissions sources affected air quality in different areas of the Mexico City Metropolitan Area.

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 improving air quality.

Summary

A research team, including DOE scientists from Pacific Northwest National Laboratory, evaluated an observed SO2 peak at a suburban supersite and at ambient air-quality monitoring stations located in the Mexico City Metropolitan Area (MCMA) during the 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 have not been considered in previous studies, the episodic emission suggests the possibility of “overlooked” emission sources that could influence the air quality of the MCMA. The research found that cement plants in the states of Hidalgo and Mexico can contribute to the about 42% of the SO2 levels in the northeast region of the MCMA basin, and 41% 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 low contribution to the MCMA (1 to 4 ppb) and slightly higher contribution at the suburban T1 (6 ppb) and rural T2 (5 ppb) supersites. However, the contribution 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% of the total regional ozone from TIC could be related to flaring activities. The combination of emission reductions in the power plant, the refinery, and local sources in the MCMA could result in higher reductions in the average SO2 concentration, which tend to affect more 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.