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Pollution

By the 1990s Mexico City had become infamous as one of the world's most polluted cities; however, the city has since become a model for drastically lowering pollution levels. By 2014 carbon monoxide pollution had dropped drastically, while sulfur dioxide and nitrogen dioxide were at levels about a third of those in 1992. The levels of signature pollutants in Mexico City are similar to those of Los Angeles. Despite the cleanup, the metropolitan area is still the most ozone -polluted part of the country, with ozone levels 2.5 times beyond WHO -defined safe limits.

To clean up pollution, the federal and local governments implemented numerous plans including the constant monitoring and reporting of environmental conditions, such as ozone and nitrogen oxides. When the levels of these two pollutants reached critical levels, contingency actions were implemented which included closing factories, changing school hours, and extending the A day without a car program to two days of the week. The government also instituted industrial technology improvements, a strict biannual vehicle emission inspection and the reformulation of gasoline and diesel fuels. The introduction of Metrobús bus rapid transit and the Ecobici bike-sharing were among efforts to encourage alternate, greener forms of transportation.