<P> It has been said that "Mexico City's air has gone from among the world's cleanest to among the dirtiest in the span of a generation ." Historic air pollution episodes of the 1950s led to acute increases in infant mortality . </P> <P> Much improvement was made in the city since 1992, when the United Nations named Mexico City "the most polluted city on the planet ." At the time pollution was thought to cause 1,000 deaths and 35,000 hospitalizations per year . </P> <P> In 2012 ozone and other air pollutants ranked at about the same level as Los Angeles . This improvement in air quality was achieved, starting in the 1980s, through the Mexican government's requirement that gasoline be reformulated, that polluting factories be closed or moved, and that drivers be prohibited from using their car one day per week . More recently there has been an expansion of public transportation . Air pollution has been a major issue in Mexico City for decades . </P> <P> However, after loosening regulations in 2015 by the Mexico City government, air pollution has steadily increased in recent years in Greater Mexico City . This regulatory change was fostered by political reasons and backed by several parties . In April and May 2016 ozone and suspended matter pollution in Mexico City had reached levels that were detrimental to health, though the criterion to signal a pollution alert is lower in 2016 than it was in the 1980s . The city's population continues to grow, to spread out, which lengthens automobile trips, and the number of autos in the city increases yearly . </P>

Mexico citys geography makes air pollution a greater problem because it is located