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The presence or introduction of contaminants that have negative impacts on the environment, the air, or the water constitutes pollution. Currently, 91 % of the º£½ÇÉçÇø's population lives and breathes in areas with air quality that is below WHO standards. This indicates that a sizeable population is in danger of serious health problems, such as cardiovascular and respiratory illnesses, increased possibilities of cancer, and early mortality.ÌýThe ten most polluted United States cities, according to The American Lung Association's annual "State of the Air" Report 2022, are listed below:

1. Bakersfield, California

Bakersfield and much of the valley where it is located remain among the worst polluted regions of the nation. Bakersfield is the most air-polluted city in the United States due to pollution from oil refineries and agriculture in California's Central Valley. According to the report, this smog and soot pollution can lead to health issues like respiratory problems,Ìýlung cancer,Ìýheart attacks, and even early death. The city is situated in a mountainous, dry valley where the smoggy air tends to hang around rather than fly away.Ìý

2. Fresno-Madera-Hanford, California 

Fresno consistently ranks as one of the most polluted cities in the United States due in large part to its function as a major hub for the area's agricultural industry and the intersection of several important state highways, including the California State Route 99 highway that runs directly through the city and the nearby Interstate 5 about 50 miles to the west. Farms emit dust and spray insecticides into the air, in addition to the emissions from their machinery and equipment. Additionally, there is a substantial amount of commuter and truck traffic in the area.Ìý

2. Visalia, California 

Visalia is located in the Central Valley of California, where locals burn wood fires and there is poor air quality caused by significant car and truck traffic. Smog can develop at the valley's lower altitudes due to the terrain of the heavily inhabited area, and the intense sun also contributes to the development of smog. According to the American Lung Association's 2019 study, Visalia is the second-most smoggy city in the nation, only behind Los Angeles. In 2015–17, according to the same assessment, Visalia had the fourth-worst levels of year-round particle pollution. But for more than 10 years, the Porterville-Visalia region has consistently ranked among the top five most polluted regions.Ìý

4. San Jose-San Francisco-Oakland, California

In the American Lung Association's State of the Air Report, San Jose came in fourth place for worst yearly particle pollution out of the over U.S. metropolitan areas. Transportation emissions, including those from ships, planes, and cars, are to blame for the poor air quality in the area around San Jose,ÌýSan Francisco, and Oakland. Air pollution is made worse by smoke from the region's increasingly frequent wildfires, particularly in the summer and fall.

5. Los Angeles-Long Beach, California

°Õ³ó±ðÌýLos Angeles-Long Beach metro area has some of the worst air pollutions in the nation, according to a new American Lung Association study. And with nearly 180 days of high ozone pollution since 2018, LA-Long Beach has the worst air pollution overall. In terms of ozone, yearly particle pollution, and 24-hour particle pollution, the LA-Long Beach metro area scored failing grades. Out of more than 200 metropolitan regions nationwide, it came in first, fifth, and eighth place, respectively. The situation is made worse by the occurrence of wildfires and the rise in the number of days with exceptionally high temperatures each year, both effects of worsening climate change.Ìý

6. Medford-Grants Pass, Oregon

According to a recent study, Grants Pass and Medford have some of the worst air quality in Oregon as well as the entire US. The research was taken from "State of the Air" 2019, an annual report published by the American Lung Association for the previous 20 years. Due to the increasing number of major wildfires in the area, they have been having serious problems with air pollution. As a result of climate change, which is creating more frequent and powerful fires, the fallout from the thick smoke during wildfire season is anticipated to get worse.

7. Fairbanks, Alaska

Smoke from wildfires and wood-burning stoves contribute to the poor air quality in which many Alaskans live.ÌýFairbanks, the second-largest city in Alaska, is currently the state's most particle-polluted city of the year. In and around Fairbanks, you can find some of the most polluted winter air in the United States. People burning wood in their houses to remain warm are a key cause of that.

8. Phoenix-Mesa, Arizona

A 2020 study reveals that not even the pandemic lockdown could improve the air quality in Phoenix, which has consistently been classified as one of the worst polluted cities in the nation. According to Environment America, the area had high air pollution levels for 149 days in 2020. Car emissions are the main cause of air pollution in the Phoenix area. Summer months often have the highest ozone levels, while temperature inversions in winter trap cooler, filthy air and prevent it from dissipating. The city has implemented an advanced dust control program that involves paving alleyways and shoulders, treating roads, and placing trespassing limits on undeveloped or unoccupied land in an effort to reduce particulate pollution.

9. Chico, California

Chico in California's Butte County is a fairly large city and part of the Sacramento Valley. Here, smoke generated from the chimneys of homes during winter contributes heavily to the deterioration of air quality in the city. Hence, the city's authorities have advised the residents to avoid burning wood for heating and use less polluting alternatives. Automobiles also contribute to air pollution in the city that has a heavy traffic flow being one of the Sacramento Valley region's economic hubs.

10. El Centro, California 

There were 49 days in El Centro, southern California when the ozone concentration was unsafe for sensitive populations. Although the city has started turning some city routes into pedestrian areas, a large portion of the pollution in the city is still caused by automobile emissions. El Centro's proximity to Mexico is largely to blame for the pollution in that area of Imperial County as well as its surroundings. The pollution carried over from the heavily populated city of Mexicali, which is just across the border, exacerbates the smog from vehicles and trucks. Mexicali's metro area has five times more population than Imperial County does.Ìý

The majority of the most ozone-polluted cities are still found in the West and the Midwest. With 11 of the top 25 most polluted cities, California continues to be the state with the most cities on the list. However, poor air quality is a problem º£½ÇÉçÇøwide, not just in the US. Around 90% of people on earth inhale air that is dangerously polluted. Air pollution, whether it comes from ozone or small particles, can have detrimental effects on one's health. They range from short-term impacts like asthma episodes to long-term effects like heart disease and lung cancer caused by exposure to pollution.

America's 25 Most Polluted Cities (based on annual PM in micrograms per cubic meter)