Air pollution in the United States

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Looking down from the Hollywood Hills, with Griffith Observatory on the hill in the foreground, air pollution is visible in downtown Los Angeles on a late afternoon.

Air pollution is the introduction of chemicals, particulate matter, or biological materials that cause harm or discomfort to humans or other living organisms, or damages the natural environment into the atmosphere. Ever since the beginning of the Industrial Revolution in the United States, America has had much trouble with environmental issues, air pollution in particular. According to a 2009 report, around "60 percent of Americans live in areas where air pollution has reached unhealthy levels that can make people sick".[1] Pollution in the United States has plummeted in the recent decade, with pollutants such as nitrogen dioxide decreasing despite the fact the number of vehicles on the road isn't. This is due to better regulations, economic shifts, and technological innovations. With respect to nitrogen dioxide, NASA reported a 32% decrease in New York City and a 42% decrease in Atlanta between the periods of 2005-2007 and 2009-2011. California has the worst air quality of any state, and in most surveys the cities in California rank in the top 5 or top 10 of most polluted air in the United States.[2][3]

Clean Air Acts[edit]

In the 1960s, 1970s, and 1990s, the United States Congress enacted a series of Clean Air Acts which significantly strengthened regulation of air pollution. Individual U.S. states, some European nations and eventually the European Union followed these initiatives. The Clean Air Act sets numerical limits on the concentrations of a basic group of air pollutants and provide reporting and enforcement mechanisms.

In 1999, the United States Environmental Protection Agency (EPA) replaced the Pollution Standards Index (PSI) with the Air Quality Index (AQI) to incorporate new PM2.5 and Ozone standards.

The effects of these laws have been very positive. In the United States between 1970 and 2006, citizens enjoyed the following reductions in annual pollution emissions:[4]

  • carbon monoxide emissions fell from 197 million tons to 89 million tons
  • nitrogen oxide emissions fell from 27 million tons to 19 million tons
  • sulfur dioxide emissions fell from 31 million tons to 15 million tons
  • particulate emissions fell by 80%
  • lead emissions fell by more than 98%

In an October 2006 letter to EPA, the agency's independent scientific advisors warned that the ozone smog standard “needs to be substantially reduced” and that there is “no scientific justification” for retaining the current, weaker standard. The scientists unanimously recommended a smog threshold of 60 to 70 ppb after they conducted an extensive review of the evidence.[5]

The EPA has proposed, in June 2007, a new threshold of 75 ppb. This is less strict than the scientific recommendation, but is more strict than the current standard.

Some industries are lobbying to keep the current standards in place. Environmentalists and public health advocates are mobilizing to support the scientific recommendations.[citation needed]

International pollution[edit]

An outpouring of dust layered with man-made sulfates, smog, industrial fumes, carbon grit, and nitrates is crossing the Pacific Ocean on prevailing winds from booming Asian economies in plumes so vast they alter the climate. Almost a third of the air over Los Angeles and San Francisco can be traced directly to Asia. With it comes up to three-quarters of the black carbon particulate pollution that reaches the West Coast.[6]

In the United States unhealthy levels of pollution are measured by the Environmental Protection Agency and independent researchers or agencies, like the American Lung Association. Federal limits and pollution standards are set by the Clean Air Act.

Los Angeles Air pollution[edit]

Los Angeles has some of the most contaminated air in the country. With a population of roughly over 10 million, the Los Angeles area is a large basin with the Pacific Ocean to the west, and several mountain ranges with 11,000-foot peaks to the east and south. Diesel engines, ports, motor vehicles, and industries are main sources of air pollution in Los Angeles. Frequent sunny days and low rainfall contribute to ozone formation, as well as high levels of fine particles and dust.[7]

Air pollution in Los Angeles has caused widespread concerns. In 2011, the Public Policy Institute of California (PPIC) Survey on Californians and the Environment showed that 45% of citizens in Los Angeles consider air pollution to be a “big problem”, and 47% believe that the air quality of Los Angeles is worse than it was 10 years ago.[8] In 2013, the Los Angeles-Long Beach-Riverside area ranked the 1st most ozone-polluted city, the 4th most polluted city by annual particle pollution, and the 4th most polluted city by 24-hour particle pollution.[9]

Both ozone and particle pollution are dangerous to human health. The Environmental Protection Agency (EPA) engaged a panel of expert scientists, the Clean Air Scientific Advisory Committee, to help them assess the evidence. The EPA released their most recent review of the current research on health threat of ozone and particle pollution.[10][11]

EPA Concludes Ozone Pollution Poses Serious Health Threats

  • Causes respiratory harm (e.g. worsened asthma, worsened COPD, inflammation)
  • Likely to cause early death (both short-term and long-term exposure)
  • Likely to cause cardiovascular harm (e.g. heart attacks, strokes, heart disease, congestive heart failure)
  • May cause harm to the central nervous system
  • May cause reproductive and developmental harm

- U.S. Environmental Protection Agency, Integrated Science Assessment for Ozone and Related Photochemical Oxidants, 2013. EPA/600/R-10/076F.

EPA Concludes Fine Particle Pollution Poses Serious Health Threats

  • Causes early death (both short-term and long-term exposure)
  • Causes cardiovascular harm (e.g. heart attacks, strokes, heart disease, congestive heart failure)
  • Likely to cause respiratory harm (e.g. worsened asthma, worsened COPD, inflammation)
  • May cause cancer
  • May cause reproductive and developmental harm

-U.S. Environmental Protection Agency, Integrated Science Assessment for Particulate Matter, December 2009. EPA 600/R-08/139F.

Helping the area to meet the national air quality standards and improve the health of local residents continues to be a priority for the EPA. One of EPA's highest priorities is to support the reduction of diesel emissions from ships, trucks, locomotives, and other diesel engines.[12] In 2005, Congress authorized funding for the Diesel Emissions Reduction Act (DERA), a grant program, administrated by the EPA, to selectively retrofit or replace the older diesel engines most likely to impact human health. Since 2008, the DERA program has achieved impressive out outcome of improving air quality.[13] The EPA also works with state and local partners to decrease emissions from port operations and to improve the efficient transportation of goods through the region. Both the EPA and the Port of Los Angeles are partners of the San Pedro Bay Ports Clean Air Action Plan, a sweeping plan aimed at significantly reducing the health risks posed by air pollution from port-related ships, trains, trucks, terminal equipment and harbor craft.[14] For environmental justice, air pollution in low-income LA communities has received more attention. In 2011, the “Clean up Green up” campaign was launched to designate four low-income LA communities- Pacoima, Boyle Heights and Wilmington. This campaign aims to push green industries through incentives, including help obtaining permits and tax and utility rebates.[15]

Although Los Angeles air pollution level has declined for the last few decades,[16] citizens in Los Angeles still suffer from high level air pollution.[17]

Pollution level rankings[edit]

Most polluted US cities by short-term particulate matter[18]
Rank City
1 Bakersfield-Delano, CA
2 Fresno-Madera, CA
3 Hanford-Corcoran, CA
4 Los Angeles-Long Beach-Riverside, CA
5 Modesto, CA
6 Salt Lake City-Ogden-Clearfield, UT
7 Pittsburgh-New Castle, PA
8 Merced, CA
9 Fairbanks, AK
10 Logan, UT-ID
Most polluted US cities by ozone levels

Rank City
1 Los Angeles-Long Beach-Riverside, CA
2 Visalia-Porterville, CA
3 Bakersfield-Delano, CA
4 Fresno-Madera, CA
5 Hanford-Corcoran, CA
6 Sacramento—Arden-Arcade—Yuba City, CA-NV
7 Houston-Baytown-Huntsville, TX
8 Dallas-Fort Worth, TX
9 Washington-Baltimore-Northern Virginia, DC-MD-VA-WV
10 El Centro, CA
Most polluted US cities by year-round particulate matter
Rank City
1 Bakersfield-Delano, CA
2 Merced, CA
3 Fresno-Madera, CA
4 Hanford-Corcoran, CA
5 Los Angeles-Long Beach-Riverside, CA
6 Modesto, CA
7 Visalia-Porterville, CA
8 Pittsburgh-New Castle, PA
9 El Centro, CA
10 Cincinnati-Middletown-Wilmington, OH-KY-IN

See also[edit]


  1. ^ "Top Polluted U.S. Cities With the World Air". ABC News. 
  2. ^ "June 26, 2014". NASA. 
  3. ^ "Watch: NASA Says U.S. Air Pollution Has Plummeted". TIME. 
  4. ^ Wall Street Journal article, May 23, 2006 on
  5. ^ American Lung Association, June 2, 2007
  6. ^ Wall Street Journal article, July 20, 2007
  7. ^ U.S. EPA., 2013.
  8. ^ PPIC Statewide Survey: Californians and the environment, 2011.
  9. ^ American Lung Association, Most Polluted Cities, 2013.
  10. ^ American Lung Association, Ozone Pollution, 2013.
  11. ^ American Lung Association, Particle Pollution, 2013.
  12. ^ American Lung Association, Most Polluted Cities, 2013.
  13. ^ U.S. EPA., 2012.
  14. ^ U.S. EPA., 2013.
  15. ^ L. A. Times, Jan 21, 2012
  16. ^ Pollack, Ilana; Ryerson, Thomas (13 June 2013). "Trends in ozone, its precursors, and related secondary oxidation products in Los Angeles, California: A synthesis of measurements from 1960 to 2010". Journal of Geophysics Research: Atmospheres. 118 (11): 5893–5911. doi:10.1002/jgrd.50472. 
  17. ^ Marziali, Carl (4 March 2015). "L.A.'s Environmental Success Story: Cleaner Air, Healthier Kids". USC News. Retrieved 16 March 2015. 
  18. ^ American Lung Association, Most Polluted Cities, 2013.

External links[edit]