What traps air pollution in Mexico Cityt?

Answer 1

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.

Answer 2

Mexico City sits on a valley, surrounded by hilly and mountainous terrain. These hills and mountains prevent winds from blowing away the polluted air.