7. Houston, TX
Major Causes of Pollution: 4 (Oil Industry, Traffic Congestion, Cattle Industry, Processing Industry)
Houston is an oil center for the entire country and millions of gallons are refined from the city each year. These refinements contribute to chemicals in the environment. It is also one of the largest cities in North America and the high rate of vehicle congestion here contributes to air pollution heavily. Texas is also a center for the cattle industry, and processing of meat involves a lot of chemicals aside from the pollution that these large animals already cause naturally.
