Mexico City has previously held a bad reputation for air quality. In 1992, the United Nations declared that the city had the most polluted air on the planet. Population and industrial growth, as well as an abundance of cars, led to the city being dubbed “the most dangerous city in the world for children” in 1998.

A few years later, things still looked bad.

As the USGS writes: “Left: April 9, 2001. Right: December 5, 2001. Mexico City lies just above the center of each of these images. The haze covering the city in the December image demonstrates that air quality can worsen in winter, when temperature inversion layers (areas where warm air holds down cool air) keep polluted air close to the surface.”

Luckily, the Mexican government has since made important strides in cleaning up its air. In 2010, Martha Delgado of the Mexico City environment office told AFP, “In recent years we have beat the records for most days with passable ozone readings. In 2009 there were 185 in the acceptable range and we have started out 2010 with the greatest number of clean days, 50 out of the first 60.” 

In a 2011 list of the world’s most polluted places, Mexico City was not among them. 

Photo courtesy of NASA/GSFC/LaRC/JPL,MISR Team