Mexico City was once known for its smoggy landscape with industrial eyesores such as the 18 de Marzo Refinery spewing ozone-forming emissions such as sulfur dioxide. The cloud of contaminants hanging over the capital played into an apocalyptic reputation for pollution, crime, and overpopulation; and it fueled urban myths, like the one about birds dropping dead mid-flight because of the poor air quality.
But the refinery – named for the day Mexico expropriated its oil industry – was ordered closed in 1991, and converted into a park commemorating the country's 2010 bicentennial. It is but one example of industry exiting Mexico City and the steps taken to improve air quality over the past two decades in this megalopolis of more than 20 million people.
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.