1. 
   It has been known for many years that the air pollution in Mexico City is much worse than that found in similar sized cities in other developing nations.
2. In 1992, the United Nations described Mexico City’s air as the most polluted on the planet. Six years later, that air earned Mexico the reputation of “the most dangerous city in the world for children” — a reputation Mexico has been working hard to improve. But despite more than a decade of stringent pollution control measures, a haze hangs over the city most days, obscuring the surrounding snow-capped mountains and endangering the health of its inhabitants.
3.