Although green roofs have been widely adopted in urban areas to reduce the heat island effect and stormwater runoff, Mexico City is hoping that vegetative rooftops can also reduce the city’s air pollution.
Green roofs are increasingly being installed on schools and other buildings in the megalopolis of 21 million people to absorb smog and metal particles in the air. More than 236,000 sf of green roofs adorn the environment about the cityscape as the government continues to invest in the concept.
Last year, Mexico City spent almost $1million on the green roofs project, bringing the total area of green roofs in hospitals, schools and government buildings. This year, the investment is expected to rise by a third.
Unhealthy air can be so severe, that the government sometimes imposes a no-driving ban for a percentage of vehicles identified by license plate color or numbers. The city has made progress in removing air pollutants by moving refineries outside city limits and introducing cleaner buses, but more needs to be done, officials say.
(http://www.theguardian.com/global-development/2014/apr/24/mexico-city-roof-gardens-pollution-smog)