20 Most Polluted Cities in America

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20. St. Louis-St. Charles-Farmington, MO-IL
> High ozone days per year:
19.2 days
> Number of days with unhealthy particle pollution: N/A
> People with asthma: 286,090
> Population: 2,910,387

There are 19.2 days on average each year of dangerously high ozone air pollution (smog) in the St. Louis-St. Charles-Farmington metro area, tied with three other urban regions for the 18th most polluted city in the country. During the high ozone level days, residents can inhale harmful pollutants that can increase the risk of aggravated asthma, difficulty breathing, cardiovascular-related health problems and ultimately an untimely death.

19. Grand Rapids-Wyoming-Muskegon, MI
> High ozone days per year:
19.2 days
> Number of days with unhealthy particle pollution: N/A
> People with asthma: 152,906
> Population: 1,421,374

The level of smog in the Grand Rapids area would not be nearly as high as it is if the metro area were not located downwind from Chicago, where ozone pollution is also among the highest in the country. Particulates are blown from Chicago to Grand Rapids, where they combine in a photochemical reaction that creates ozone, Billings explained. For this reason, the ozone pollution in Grand Rapids is actually worse than it is in Chicago, which the ALA ranked 21st worst for ozone pollution, barely missing the cut for this list.

18. Tulsa-Muskogee-Bartlesville, OK
> High ozone days per year:
19.2 days
> Number of days with unhealthy particle pollution: N/A
> People with asthma: 116,872
> Population: 1,140,635

The Tulsa-Muskogee-Bartlesville, Oklahoma area ranks among the worst polluted cities in the country. Like a number of other metro areas, however, there are fewer high ozone pollution days compared with last year’s “State of the Air” report. Of the 8.6 million area residents, 116,872 people, including 83,664 children, have asthma. These individuals are at greater risk to the negative health effects of pollution.

17. San Jose-San Francisco-Oakland, CA
> High ozone days per year:
19.5 days
> Number of days with unhealthy particle pollution: 19 days
> People with asthma: 690,097
> Population: 8,607,423

The San Francisco metro area is more densely populated than any U.S. area except for New York City. Motor vehicle exhaust is one of the major drivers of pollution. The sheer number of cars, higher likelihood of traffic congestion, and greater industrial activity in the San Jose-San Francisco area largely explains its ranking as one of the smoggiest cities. The level of particle pollution in the air around the city reaches potentially hazardous levels during 19 days in a single year, the eighth highest of cities reviewed.

16. El Paso-Las Cruces, TX-NM
> High ozone days per year:
19.5 days
> Number of days with unhealthy particle pollution: 5.5 days
> People with asthma: 75,755
> Population: 1,050,120

The high level of smog in the El Paso-Las Cruces area, which reaches unhealthful levels 19.5 days out of the year on average, is exacerbated by the hot, dry climate. Like other areas in the Mid- and Western United States, El Paso-Las Cruces is also vulnerable to wildfires, which contribute to short-term spikes in PM pollution in particular. The Whitewater-Baldy Complex wildfire, one of the area’s largest in recent memory, burned nearly 300,000 acres in the Gila National Forest north of Las-Cruces in 2012.