Why is pollution a problem in Mexico City?

Overpopulation, irresponsible consumer habits and geography create a "perfect storm" in Mexico City that allows air pollution to be the problem it is there.

The city sits in a valley surrounded by mountains. Smog from manufacturing and chemical plants as well as vehicle exhaust fumes get trapped by the surrounding mountains due to lack of any powerful-enough winds. This makes up the layer of gloom that sits over the valley due to a "cook-pot effect".

This smog can cause burning in the eyes and throat of visitors not used to it within a few days, especially in those with sensitivities to pollutants.