Half a century ago the metropolitan area of Mexico City had a population of less than three million people. Mexico City serves as the nation capital of Mexico, but beyond that, it also serves as the industrial and financial heart of the country as well. By the year 2000, the city had grown from a population of three million to one of eighteen million, making it the second largest city in the world behind Tokyo. A swell in population of this magnitude was bound to be accompanied by additional problems, one of which was an increase in air pollution. Since this time, the air quality in the city has improved, but not to the extent that it even meets its own standards for air quality most of the time. In 2002, Mexico City air quality exceeded local standards (110 parts per billion, or ppb) on 80% of the days of the year. There are other cities, though, with higher population, massive industry, or both, such as Tokyo and Los Angeles that do not have the levels of air pollution that Mexico City experiences. Why is this? The air pollution problem in Mexico City is the result of a combination of factors that come together to create the problem as a whole. These factors include the layout of the city, transportation methods most used in the city, lax domestic air quality regulations, an economy based on industry, and even the topographic landscape surrounding the city. The problem of air pollution in Mexico City and its metropolitan area cannot be fully understood or explained without addressing all of the factors that contribute to the issue.
The economy of Mexico City is one factor that contributes to the city's air pollution problem. The city is home to more than 35,000 industries, which contribute to the forty million liter of fuel that the city consumes every day. When this fuel in burned it releases chemicals such as sulphur dioxide, nitrogen dioxide, carbon monoxide, and ozone. The sheer number of factories pumping these gases into the air makes it difficult for these gasses to dissipate and over time they continue to build up.