Kiera Jefferson
The United States is one of the world's largest emitters of greenhouse gases, with human activities accounting for almost all of the increase in greenhouse gas emissions in the country over the last 150 years. In 2021, the US emitted 6.34 billion metric tons of greenhouse gases, with carbon dioxide accounting for 79% of these emissions. The largest sources of greenhouse gas emissions in the US are the burning of fossil fuels for electricity production, transportation, and industrial activities. In 2021, the transportation sector was the largest emitter, responsible for 28.5% of emissions, followed by the electric power sector at 25% and the industrial sector at 23.5%. While total US emissions decreased by 2.3% between 1990 and 2021, they increased by 1% in 2022 compared to the previous year, driven largely by a rise in CO2 emissions from fossil fuel combustion.
| Characteristics | Values |
|---|---|
| Percentage of CO2 emissions globally | 15.5% in 2019 |
| CO2 emissions in 2019 | 5.28 billion tons |
| Average CO2 emissions over the course of 2009-2019 | 5.44 billion tons |
| CO2 emissions in 2007 | 6.13 billion tons |
| Percentage of Americans living in places with unhealthy levels of air pollution in 2014 | 47% |
| Percentage of the population living in counties with unhealthy levels of air pollution from 2013 to 2015 | 38.9% |
| Top 10 cities most polluted by short-term particle pollution | Bakersfield, Visalia-Porterville-Hanford, Fresno-Madera, Modesto-Merced, Fairbanks, San Jose-San Francisco-Oakland, Salt Lake City-Provo-Orem, Logan, Los Angeles-Long Beach, Reno-Carson City-Fernley |
| Top 10 cities most polluted by year-round particle pollution | Visalia-Porterville-Hanford, Bakersfield, Fresno-Madera, San Jose-San Francisco-Oakland, Los Angeles-Long Beach, Modesto-Merced, El Centro, Pittsburgh-New Castle-Weirton, Cleveland-Akron-Canton, San Luis Obispo-Paso Robles-Arroyo Grande |
| Percentage of emissions from transportation in 2018 | 28% |
| Percentage of emissions from industrial production of materials in 2018 | 22% |
| Percentage of emissions from commercial and residential sectors in 2018 | 12% |
| Percentage of emissions from agricultural activities in 2018 | 10% |
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What You'll Learn
Air pollution from out-of-state emissions
According to a 2020 study by MIT's Laboratory for Aviation and the Environment, half of the air pollution in the United States comes from out-of-state emissions. The study, which focused on the years between 2005 and 2018, tracked the combustion emissions of various polluting compounds from various sectors, including electric power generation, road transportation, marine, rail, aviation, and commercial and residential sources. The researchers found that while air pollution may be generated in one state, half of those pollutants are carried by winds across state boundaries, affecting the health of residents in other states and increasing their risk of early death.
Electric power generation is the greatest contributor to out-of-state pollution-related deaths. For example, in 2005, deaths caused by sulfur dioxide emitted by power plant smokestacks occurred in another state in over 75% of cases. The study also found that emissions travelling out of state could affect the health of residents beyond immediate neighbouring states. For instance, NOx emissions from road transportation in Arizona in July can impact human health in Texas.
The findings highlight the complex nature of air pollution and the need for a comprehensive approach to address it. While the study focuses on the impact of out-of-state emissions, it is important to recognise that air pollution is a multifaceted issue influenced by various factors, including industrial activity, technological developments, fuel consumption, and vehicle miles travelled.
Despite the challenges, there has been progress in improving air quality in the United States. According to the US EPA, emissions of common air pollutants and their precursors have been reduced substantially since 1980, with a 30% decrease between 2008 and 2017. The implementation of regulations such as the Clean Air Act has played a significant role in reducing emissions and improving air quality. However, there is still work to be done, as nearly half of Americans continue to live with unhealthy levels of air pollution, according to the 2025 State of the Air report by the American Lung Association.
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Marine pollution and debris
Marine debris is defined as any persistent solid material that is manufactured or processed and directly or indirectly, intentionally or unintentionally, disposed of or abandoned into the marine environment or the Great Lakes. Plastics are one of the most extensive types of marine debris, with the variety and quantity of plastic items found in the marine environment increasing dramatically as society develops new uses for them. Plastics break down into smaller components called microplastics, which can be too small to be seen with the human eye. Other common types of marine debris include metals, rubber, paper, textiles, derelict fishing gear, and abandoned vessels.
Marine debris can have significant negative impacts on marine and coastal wildlife, habitats, and human activities. It can injure or kill wildlife, damage habitats, interfere with navigation, cause economic losses to fishing and maritime industries, degrade the quality of life in coastal communities, and threaten human health and safety. Bird species, for example, can become entangled in carelessly discarded fishing lines and netting, and they sometimes use these items as nesting material, which can lead to the entanglement of chicks and parents. Seasonal storms and high tides can also wash derelict lobster traps and other gear onto shorelines, posing threats to breeding birds that nest on these shores.
The United States has implemented measures to address marine pollution and debris. Some highly toxic pollutants, such as DDT and PCBs, have been banned for manufacture or use, and ambient levels of these pollutants have been decreasing in most U.S. marine environments. Advances in waste treatment have kept pace with increases in waste volume, and this trend is expected to continue. The NOAA Marine Debris Program funds projects across the United States and its territories to remove marine debris from shorelines, research the issue, and prevent debris from entering the ocean.
However, challenges remain. High concentrations of persistent contaminants in bottom sediments require careful management during dredging operations or in-place management. The overenrichment of coastal ecosystems by nutrients, particularly nitrogen, has emerged as the most widespread and measurable effect of pollution on living marine resources and biodiversity in the United States. To address this, feasible measures include advanced treatment of municipal wastewaters, reducing nitrogen oxide emissions from power plants and vehicles, controlling ammonia emissions from animal feedlots, improving fertilizer and manure use efficiency, and restoring wetlands and floodplains that act as nutrient traps.
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Water pollution from toxic chemicals
Water pollution occurs when harmful substances contaminate bodies of water, including streams, rivers, lakes, and oceans, degrading water quality and rendering it toxic and unsafe for human or environmental use.
In the United States, water pollution from toxic chemicals is a significant issue, with a particular focus on PFASs (polyfluoroalkyl and perfluoroalkyl substances). PFASs are synthetic chemicals used in a wide range of applications, including food packaging, clothing, non-stick cookware, and firefighting foams. These chemicals have been linked to adverse health effects, including an increased risk of certain cancers, hormone disruption, high cholesterol, and obesity.
A 2016 study by Reuters Health found that the drinking water supplies of more than six million Americans contained unsafe levels of PFASs. The study examined concentrations of six types of PFASs in over 36,000 water samples collected by the U.S. Environmental Protection Agency (EPA) from 2013 to 2015. The highest levels of PFASs were detected near industrial sites, military bases, and wastewater treatment plants, where these chemicals are commonly used or present.
The persistence of PFASs in the environment is a unique concern. Due to their slow breakdown, they are often referred to as "forever chemicals." The U.S. Geological Survey (USGS) estimates that at least 45% of the nation's tap water contains one or more types of PFASs. The EPA regulates public water supplies, but the presence of PFASs in private water supplies is a concern, as homeowners are responsible for testing and treatment.
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Particle pollution in cities
Particle pollution, also known as PM2.5 or soot, is a serious health threat in the United States, with nearly half of the population exposed to dangerous levels of air pollution. According to the American Lung Association's "State of the Air" report, which covers data from 2021 to 2023, several cities in the US have recorded unhealthy levels of particle pollution.
Particle Pollution in Bakersfield, California
Bakersfield, California, has consistently ranked as one of the most polluted cities in the country for both short-term and year-round particle pollution. In the 2025 report, Bakersfield topped the list for the worst short-term particle pollution for the third year in a row and was the worst for year-round particle pollution for the sixth consecutive year. The city's pollution is likely due to a combination of factors, including industrial facilities, vehicle emissions, and wildfires.
Particle Pollution in Los Angeles, California
Los Angeles, California, has also been identified as one of the most polluted cities in the country, specifically for its high levels of ozone pollution. In the 2024 report, the Los Angeles-Long Beach-Riverside area ranked as the most ozone-polluted city, the 6th most polluted by annual particle pollution, and the 11th most polluted by 24-hour particle pollution. The pollution in Los Angeles is attributed to diesel engines, ports, motor vehicles, and industries. The natural geography of the city, with mountains to the north and west, also traps pollutants in the Los Angeles basin.
Particle Pollution in Other US Cities
In addition to Bakersfield and Los Angeles, several other cities across the US have been identified as having high levels of particle pollution. These include Visalia, Fresno-Madera-Hanford, and Delano in California; Eugene-Springfield in Oregon; and Detroit-Warren-Ann Arbor in Michigan. These cities have experienced episodic spikes in particle pollution, often driven by wildfires or sudden extreme heat events.
Health Impacts of Particle Pollution
Particle pollution has significant health impacts on vulnerable populations, including children, older adults, and people with lung diseases. It can trigger asthma attacks, harm lung development in children, and contribute to premature birth and lower birth weight in newborns. Additionally, air pollution has been linked to cognitive developmental delays and central nervous system health problems, including neuroinflammation and short-term memory disturbances.
Efforts to Address Particle Pollution
Despite the concerning levels of particle pollution in many US cities, there have been efforts to improve air quality. The Clean Air Act has successfully driven pollution reduction for over 50 years, and the Environmental Protection Agency (EPA) plays a critical role in monitoring and regulating air pollution. However, recent rollbacks in environmental regulations and funding challenges threaten the progress made in improving air quality.
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Greenhouse gas emissions
In the United States, it has historically been challenging to track how pollution from one state affects another due to the large number of states. However, modern computational tools have made it possible to assess the impact of each state's emissions on the health outcomes of other states. According to a study by MIT's Laboratory for Aviation and the Environment, half of the air pollution-related deaths in the US are caused by out-of-state emissions. This is due to the long-range travel of emissions, which can affect states over 1,000 miles away. Electric power generation has been identified as the greatest contributor to out-of-state pollution-related deaths, with sulfur dioxide emissions from power plants causing the majority of these deaths in other states.
On a more local level, New York City has implemented Local Law 97 of 2019 (LL97), which aims to reduce greenhouse gas emissions from buildings, as they account for over two-thirds of the city's emissions. The law requires most buildings over 25,000 square feet to meet new emissions limits, with the goal of reducing emissions from the city's largest buildings by 40% by 2030 and reaching net zero by 2050.
While there have been improvements in air quality across the nation, particle and ozone pollution remain serious issues. The American Lung Association's 2017 "State of the Air" report found that 125 million Americans (38.9% of the population) lived in counties with unhealthy levels of ozone or particle pollution between 2013 and 2015. The top US cities with the highest levels of short-term particle pollution include Bakersfield, Visalia-Porterville-Hanford, and Fresno-Madera, all in California.
To address greenhouse gas emissions and air pollution, it is essential to transform energy systems, industries, and food systems. Technological advancements, such as the decreasing costs of solar, wind, and batteries, can help provide cheap, clean energy for everyone. Political change is also crucial to support rapid decarbonization and create a sustainable future.
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Frequently asked questions
The primary sources of pollution in the USA are transportation, energy generation, and industrial processes. The EPA reports that 75% of carbon monoxide emissions nationwide come from vehicle exhaust, with that number rising to 95% in cities. Other sources include coal mining, sprays and chemicals, and marine debris.
According to a report by the American Lung Association (ALA), nearly half of all Americans live in areas with unhealthy levels of air pollution. This includes major metropolitan areas such as Los Angeles, Houston, Washington-Baltimore, and New York City.
The problem of air pollution in the USA has been increasing since the early 1700s when coal mining began. However, in recent years, there have been efforts to reduce emissions and improve air quality. For example, between 2010 and 2012, 18 of the 25 US cities with the worst particulate pollution saw a drop in year-round particle pollutants due to cuts in emissions from coal-fired power plants. Despite these improvements, climate events such as wildfires, droughts, and extreme heat continue to worsen air quality and pose challenges for pollution control.
