Fires and industrial sources account for much of the rest. Many of the larger industries are in the northern part of the valley so their emissions are blown across the city. Air pollution is not Mexico City's only environmental problem. Dust from fecal matter in areas without sewers increases skin and eye infections. The Earth offers a huge amount of resources, the problem is most resources are limited, and the Earth has more and more consumers all the time.
Geographers see three major misuses of resources.
We deplete scarce natural resources, especially petroleum, natural gas, and coal for energy production. We destroy resources through pollution of the air, water, and soil. We fail to use resources efficiently, especially the global food supply. It remains the most important in some Less Developed Countries, but during the last 200 years most of the world has converted to fossil fuels. Coal supplanted wood on the 1800's in North America and Western Europe.