Air Pollution in Mexico City has been a concerning issue to all pop people and members of the health departments for some time. In the 20th century, Mexico City's population rapidly increased as industrialization brought thousands of migrants from all over the world.". Such a rapid and unexpected growth led to the UN declaring Mexico City as the most polluted city in the world in 1992. This is perhaps due to Mexico City's high altitude (7382 ft above sea level), its oxygen levels are 25% lower and fuels do not combust completely. But it is important to mention that proliferation of vehicles, rapid industrial growth and the population boom are considered the main causes of this situation. The Mexican government has several active plans to try to reduce the emission levels that requires citi