4. Los Angeles, CA
Major Causes of Pollution: 5 (High Population Density, Traffic Congestion, Farming Industry, Manufacturing Industry, Chemical Emissions)
Los Angeles is one of the biggest cities in North America. As you might expect with a city this size, the contribution of a large population towards pollution can be heavy. Air pollution here is very high and smog is released by vehicles and facilities daily. Emissions and other particle pollutants like chemicals from farms and factories also expel out into the environment. As such LA is also considered as one of the most heavily polluted in the country.
