cats
Most likely smog. Mexico City has a worse smog problem than Los Angeles ever had.
cats dogs pigs horses hamsters guinea pigs turtles snakes penguins
factories and cars
western
Prolly either Los Angeles or Mexico city
Beijing, Mumbai, Mexico city
There is one major issues that New Mexico City has. The one thing that is wrong in New Mexico City would pollution.
Air pollution qualifies as such. Surrounding mountains and high elevation above sea level contribute to a "cook pot effect", preventing air currents from blowing the smog away, and keeping it trapped in the Mexico City valley below.
Smog
Overpopulation, irresponsible consumer habits and geography create a "perfect storm" in Mexico City that allows 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.
Mexico city has terrible air quality. They are plagued by smog, as well as all types of chemicals in the air. This has given them a bad climate, and terrible air pollution.