MEXICO CITY – Mexico's capital city measures its notorious air quality the way the U.S. Department of Homeland Security used to measure the country's terrorist threat level: with a color-coded alert.
Today's prognosis: Red. Muy mala.
That's not the worst, though. The color code runs from green ("good" air quality) to purple ("extremely bad" air quality). There is no color for "great," but the city has been been enjoying more days in the green zone in recent years.
The sky is cleaner and clearer than it has been in decades, as the city has become increasingly strict about curbing traffic, promoting lower-emissions vehicles and improving public transportation.
Last year, the city registered 211 days with an ozone level below the official threshold (less than 110 parts per billion). That means that 58 percent of the days met the "good" breathability standard. 2010 was a record with 216 days at an ozone level below that threshold.
Five years ago, the sprawling metropolis saw only 151 "good" air days.
The days of heavy particulates contamination also decreased to 91 days in 2011 versus 94 days a year earlier.
Although the air is still bad a lot of the time, the successes are noteworthy in a city where just 20 years ago birds dropped dead out of the sky from the pollution, said Martha Delgado, head of Mexico City's environmental department.
"Cities like ours have experienced environmental crises that impact millions of people," said Delgado in a 2010 interview. "In this city, we are living the consequences of imbalance, and we're now the principle leaders of the transformation" toward a more sustainable metropolis.
Mexico City is preparing to inaugurate a new metro line, its twelfth. The low-emissions Metrobus rapid bus system has been expanding, with two new lines in the past four years. (The Metrobus website reports that the system saves the city from roughly 100,000 tons of greenhouse gases annually.) The city has also been lauded for its progressive bicycle-lending program, modeled on successful programs in Europe.
Mexico City recently added five atmospheric monitoring stations to an existing system of two dozen stations in the metropolitan area. Mayor Marcelo Ebrard said in a recent statement that the stations will register how well the city's environmental programs are working to improve air quality.
Air pollution has been linked to memory loss, respiratory ailments and heart failure.
When the ozone and particulate levels do rise to dangerous levels – as determined by the city's air quality monitoring system – the city goes on alert, raising the threat level to orange, red or purple and prompting a warning in local media recommending not going outside, exercising, driving or smoking.
Anyone who misses the warning in the media can just look to the horizon. If the mountains ringing Mexico City are all but browned out, it's probably a bad air day.
"Before" photo of Mexico City in 2003 by Tjeerd Wiersma
"After" photo of Mexico City in 2010 by Gary Denness