Once a Paragon of Pollution, Mexico City's Residents Breathe Easier

"With urbanization advancing, economies expanding, and climate change a concern, Mexico City has emerged as an unlikely environmental example for cities in developing countries suffering similar air quality issues," says Agren.

"Mexico City recorded only eight days with air quality considered 'good' in 1992. That compares with 248 'good' air days in 2012, reflecting the success of initiatives to relocate industry, kick clunkers off the capital's streets, encourage cleaner technologies, and expand public transit and cycling options."

Despite the marked improvements, levels of particulate matter pollution and sprawling development remain a concern for public officials. Guillermo Velasco Rodríguez, director of planning and projects for the Centro Mario Molina, "acknowledges the improvement in air pollution in Mexico City but cautions against prematurely celebrating."

"It sounds good if you compare it to 1992," he says, "but it's not [yet] what we want."