An aerial view of Mexico City taken in 2007. It's morning, but already a layer of smog hovers over the metropolis.
An aerial view of Mexico City taken in 2007. It's morning, but already a layer of smog hovers over the metropolis.
RONALDO SCHEMIDT/AFP/AFP/Getty Images/file
Traffic routinely backs up on the multi-lane routes in and out of the city, causing massive amounts of pollution.
Traffic routinely backs up on the multi-lane routes in and out of the city, causing massive amounts of pollution.
CNN
City authorities are doing their best to encourage more people to get on their bikes to help reduce pollution. Inevitably, with so many cars on the Mexican capital's streets, dozens of cyclists are injured and many are killed -- more than 20 died in 2015.
City authorities are doing their best to encourage more people to get on their bikes to help reduce pollution. Inevitably, with so many cars on the Mexican capital's streets, dozens of cyclists are injured and many are killed -- more than 20 died in 2015.
CNN
Campaigns for safety and cleaner streets are often convened -- like this naked ride in June 2009.
Campaigns for safety and cleaner streets are often convened -- like this naked ride in June 2009.
STR/AFP/AFP/Getty Images/file
Smog envelopes skyscrapers in Mexico City in December 2015. It was considered the most polluted city in the world during the 1990s and its problems today, as this picture shows, are far from over.
Smog envelopes skyscrapers in Mexico City in December 2015. It was considered the most polluted city in the world during the 1990s and its problems today, as this picture shows, are far from over.
RONALDO SCHEMIDT/AFP/AFP/Getty Images
The arrival of Mexico's first Formula E race wasn't only for entertainment purposes. It was important for organizers to promote cleaner transport -- the cars are all powered by batteries and an electric motor. Lucas di Grassi (center) won the race but was disqualified later because his car was under the minimum weight.
The arrival of Mexico's first Formula E race wasn't only for entertainment purposes. It was important for organizers to promote cleaner transport -- the cars are all powered by batteries and an electric motor. Lucas di Grassi (center) won the race but was disqualified later because his car was under the minimum weight.
Stef Blendis/CNN
Sebastian Buemi was moved up to second behind Belgium's Jerome D'Ambrosio, and the Swiss driver leads the championship by 22 points from Brazil's di Grassi after five rounds of the 11-race series.
Sebastian Buemi was moved up to second behind Belgium's Jerome D'Ambrosio, and the Swiss driver leads the championship by 22 points from Brazil's di Grassi after five rounds of the 11-race series.
Sam Bloxham/FormulaE
Fans turned out in their thousands to watch the inaugural race held at the Autodromo Hermanos Rodriguez on March 12.
Fans turned out in their thousands to watch the inaugural race held at the Autodromo Hermanos Rodriguez on March 12.
Andrew Ferraro/Formula E