Air pollution is not a new phenomenon. From the Great Smog of London in 1952 to the recent shutdown of Beijing, air pollution has long been a staple component of the industrial city. It is a major contributor to respiratory illness, cardiovascular disease and heart conditions such as strokes, and there is a strong connection between air pollution and lung cancer.
In March 2014, the World Health Organization (WHO) estimated that 7 million people die annually as a result of exposure to air pollution. That’s roughly one in eight total global deaths, making air pollution the single largest environmental health risk. In cities where there is enough comparable data, the WHO reports that air quality is becoming worse. About half of the world’s monitored urban population is exposed to air pollution 2.5 times higher than recommended levels.
Fortunately, municipalities around the world are beginning to take air pollution seriously. Mexico City, which has struggled for decades with dangerous air quality, has become a global leader in combating ambient air pollution. In 1992, the United Nations described Mexico City’s air as the most polluted on the planet. Since then, the city has enacted stringent pollution control measures to improve its reputation and quality of life.
Part of their solution: azoteas verdes , the creation of city-wide rooftop gardens.
The Greening of City Roofs
Green roof technology is neither new nor unique to Mexico. In May 2009, Toronto became the first city in North America to adopt a bylaw requiring the construction green roofs on new developments. But it is the subsequent scale of green roof implementation that makes Mexico City exceptional.
By 2014, the 20 million-person metropolis had installed over 21,000sq meters of rooftop vegetation, mainly on government and public buildings such as schools and hospitals. In the subsequent year, the $1M investment increased by one third.
Green roofs are often built as an extension of an existing structure. It involves the creation of a system of layers that provides adequate waterproofing, root repellent, and proper drainage and filters in order to successfully support plant life.
Moreover, the additional installation cost, advocates claim, more than pays for itself. Vegetation on green roofs provides oxygen and helps to filter carbon dioxide and particulate matter from the air. It helps to regulate storm water runoff from buildings; moderates the heat island effect, reducing overall urban temperature during the summer; provides new amenity space for employees or residents; and improves the energy efficiency of buildings through heat retention and the mitigation of sunlight. In some contexts, green roofs can even speed up the recovery of hospital patients.
“In a city like ours,” states Tanya Müller, Mexico City’s environment secretary, “where urban development puts pressure on the space we have at the ground level, we have to take advantage of our rooftops to create a green urban infrastructure.” Both new and existing residential buildings are currently eligible to receive a 10% reduction in their property taxes for the installation of an approved green roof.
The strategy is a major part of Mexico City’s aim to improve overall air quality and reduce greenhouse gas emissions by 50% below 2000 levels by 2050.
One Solution to a Complex Problem
Today, Mexico City continues to face many large environmental challenges; green roofs being only part of the solution. In a city of 3.5 million cars and the continued use of industrial factories, the project and its benefits appear to only scratch the surface.
Despite regulations on private cars, a hugely successful public biking program and the introduction of cleaner buses, Mexico City still has far to go, observers claim.
“Although 80% of the population uses public transport,” Müller explains, “the city is still very car-orientated…what we’re trying to do is make people conscious of how you use your car: it has to be in a much more rational and responsible manner.”
And that may be the hidden benefit of the continued expansion and presence of green roofs: residents are starting to become more aware.
Green roofs, as British journalist Sam Jones observed, have “captured the public’s imagination.” Children learn about nature and gardening in these spaces at school, and “people are starting to think about how they travel.” It’s not going to solve the problem on its own, but green roofs also serve an educational purpose.
For more information on global air pollution and Mexico City’s green roofs initiative, listen to this podcast from the Guardian, or watch the promotional video below.