What Is Air Pollution?

Air pollution refers to the release of pollutants into the air—pollutants which are detrimental to human health and the planet as a whole. According to the World Health Organization (WHO), each year air pollution is responsible for nearly seven million deaths around the globe. Nine out of ten human beings currently breathe air that exceeds the WHO’s guideline limits for pollutants, with those living in low- and middle-income countries suffering the most. In the United States, the Clean Air Act, established in 1970, authorizes the U.S. Environmental Protection Agency (EPA) to safeguard public health by regulating the emissions of these harmful air pollutants.

What Causes Air Pollution?

“Most air pollution comes from energy use and production,” says John Walke, director of the Clean Air Project, part of the Climate and Clean Energy program at NRDC. “Burning fossil fuels releases gases and chemicals into the air.” And in an especially destructive feedback loop, air pollution not only contributes to climate change but is also exacerbated by it. “Air pollution in the form of carbon dioxide and methane raises the earth’s temperature,” Walke says. “Another type of air pollution, smog, is then worsened by that increased heat, forming when the weather is warmer and there’s more ultraviolet radiation.” Climate change also increases the production of allergenic air pollutants, including mold (thanks to damp conditions caused by extreme weather and increased flooding) and pollen (due to a longer pollen season).“We’ve made progress over the last 50 years improving air quality in the United States thanks to the Clean Air Act,” says Kim Knowlton, senior scientist and deputy director of the NRDC Science Center. “But climate change will make it harder in the future to meet pollution standards, which are designed to protect health.”

Effects of Air Pollution:

The effects of air pollution on the human body vary depending on the type of pollutant and the length and level of exposure—as well as other factors, including a person’s individual health risks and the cumulative impacts of multiple pollutants or stressors

Smog and soot:

These are the two most prevalent types of air pollution. Smog (sometimes referred to as ground-level ozone) occurs when emissions from combusting fossil fuels react with sunlight. Soot (also known as particulate matter) is made up of tiny particles of chemicals, soil, smoke, dust, or allergens—in the form of either gas or solids—that are carried in the air. The sources of smog and soot are similar. “Both come from cars and trucks, factories, power plants, incinerators, engines, generally anything that combusts fossil fuels such as coal, gas, or natural gas,” Walke says.Smog can irritate the eyes and throat and also damage the lungs, especially those of children, senior citizens, and people who work or exercise outdoors. It’s even worse for people who have asthma or allergies: these extra pollutants can intensify their symptoms and trigger asthma attacks. The tiniest airborne particles in soot, whether gaseous or solid, are especially dangerous because they can penetrate the lungs and bloodstream and worsen bronchitis, lead to heart attacks, and even hasten death. In 2020 a report from Harvard’s T. H. Chan School of Public Health showed COVID-19 mortality rates in areas with more soot pollution were higher than in areas with even slightly less, showing a correlation between the virus’s deadliness and long-term exposure to fine particulate matter and illuminating an environmental justice issue.Because highways and polluting facilities have historically been sited in or next to low-income neighborhoods and communities of color, the negative effects of this pollution have been disproportionately experienced by the people who live in these communities. In 2019 the Union of Concerned Scientists found that soot exposure was 34 percent higher for Asian Americans, on average, than for other Americans. For Black people, the exposure rate was 24 percent higher; for Latinos, 23 percent higher.

Hazardous air pollutants:

A number of air pollutants pose severe health risks and can sometimes be fatal even in small amounts. Almost 200 of them are regulated by law; some of the most common are mercury, lead, dioxins, and benzenes.

Traffic-Related Air Pollution (TRAP), from motor vehicle emissions, may be the most recognizable form of air pollution. It contains most of the elements of human-made air pollution: ground-level ozone, various forms of carbon, nitrogen oxides, sulfur oxides, volatile organic compounds, polycyclic aromatic hydrocarbons, and fine particulate matter.

Ozone, an atmospheric gas, is often called smog when at ground level. It is created when pollutants emitted by cars, power plants, industrial boilers, refineries, and other sources chemically react in the presence of sunlight.

Noxious gases, which include carbon dioxide, carbon monoxide, nitrogen oxides (NOx), and sulfur oxides (SOx), are components of motor vehicle emissions and byproducts of industrial processes.

Particulate matter (PM) is composed of chemicals such as sulfates, nitrates, carbon, or mineral dusts. Vehicle and industrial emissions from fossil fuel combustion, cigarette smoke, and burning organic matter, such as wildfires, all contain PM.

PM 2.5) is 30 times thinner than a human hair. It can be inhaled deeply into lung tissue and contribute to serious health problems. PM 2.5 accounts for most health effects due to air pollution in the U.S.

Volatile organic compounds (VOC) vaporize at or near room temperature—hence, the designation volatile. They are called organic because they contain carbon. VOCs are given off by paints, cleaning supplies, pesticides, some furnishings, and even craft materials like glue. Gasoline and natural gas are major sources of VOCs, which are released during combustion.

Polycyclic aromatic hydrocarbons (PAH) are organic compounds containing carbon and hydrogen. Of more than 100 PAHs known to be widespread in the environment, 15 are listed in the Report on Carcinogens. In addition to combustion, many industrial processes, such as iron, steel, and rubber product manufacturing, as well as power generation, also produce PAHs as a by-product. PAHs are also found in particulate matter.

Whom does air pollution affect the most?

ChildrenThe NIEHS-funded Children’s Health Study at the University of Southern California is one of the largest studies of the long-term effects of air pollution on children’s respiratory health. Among its findings:Higher air pollution levels increase short-term respiratory infections, which lead to more school absences.Children who play several outdoor sports and live in high ozone communities are more likely to develop asthma.Children living near busy roads are at increased risk for asthma.Children with asthma who were exposed to high levels of air pollutants were more likely to develop bronchitis symptoms.Living in communities with higher pollution levels can cause lung damage.

Other studies on women and children:

NIEHS-funded researchers from the University of California, Davis, Environmental Health Sciences Center are conducting the Bio-Specimen and Fire Effects (B-SAFE) Study. This ongoing project seeks to discover if and how recent wildfires and their smoke affected pregnant women and their babies. Begun in 2017, study participants are pregnant women who were living in Northern California when the 2018, 2019, or 2020 wildfires occurred there.Breathing PM 2.5, even at relatively low levels, may alter the size of a child’s developing brain, which may ultimately increase the risk for cognitive and emotional problems later in adolescence.Prenatal exposure to PAHs was associated with brain development effects, slower processing speed, attention-deficit and hyperactivity disorder (ADHD) symptoms, and other neurobehavioral problems in urban youth.In New York City, prenatal exposure to air pollution may play a role in childhood ADHD-related behavior problems.Prenatal exposure to particulate matter was associated with low birth weight.Women exposed to high levels of fine particulate matter during pregnancy, particularly in the third trimester, may have up to twice the risk of having a child with autism.Second and third trimester exposure to PM 2.5 might increase the chance of those children having high blood pressure in early life.In California’s agricultural San Joaquin Valley, women who were exposed to high levels of carbon monoxide, nitrogen oxide, or nitrogen dioxide during their first 8 weeks of pregnancy were more likely to have a baby with neural tube defects.In Marietta, Ohio, home to a ferromanganese refinery, manganese concentrations in blood and hair, a biomarker of air pollution exposure, were associated with lower child IQ scores.

Older adults:

Alzheimer’s disease and related dementias are a public health challenge for aging populations. NIEHS-funded researchers at the University of Washington identified a link between air pollution and dementias. This well-conducted study adds considerable evidence that ambient air fine particles increase risk of dementias.Air pollution was linked to a greater chance of developing several neurological disorders, including Parkinson’s disease, Alzheimer’s disease, and other dementias. Hospital admissions data from 63 million older adults in the U.S., obtained over 17 years (2000-2016), was analyzed along with estimated PM 2.5 concentrations by zip code to conduct the study.In older adults, long-term exposure to TRAP may significantly hasten physical disabilities. The risk is more pronounced among racial minorities and lower-income people.PM 2.5 air pollution is also associated with accelerated memory problems and Alzheimer’s-like brain declines, which was seen among women 65 years of age and older.Nutrients may counter some harmful effects from air pollution. A 2020 study found omega-3 fatty acids, obtained by eating certain fish, may protect against PM 2.5-associated brain shrinkage in older women.

Rural dwellers:

An NIEHS-funded study found that concentrations of PM 2.5 in rural Washington State were comparable to urban Seattle. In this study, as regional PM 2.5 increased, there were increased asthma symptoms, such as limitation of activities, more wheezing, and more nighttime waking, in rural children.In the rural U.S., large-scale animal feeding operations might compromise regional air quality through emission of pollutants, such as ammonia gas. A study found acute lung function problems in children with asthma in such areas.

Different genes:

Your genes play a role in respiratory health. NIEHS-funded research discovered that people with specific gene variants, which made them more likely to have lung inflammation, had a greater chance of suffering from asthma if they lived close to major roadways.

Why improving air quality matters:

Among children in Southern California, decreases in ambient nitrogen dioxide and PM 2.5 were associated with fewer cases of asthma.An NIEHS-funded study found that a mixture of several B vitamins may protect DNA from changes attributable to PM 2.5 air pollution.Bronchitis symptoms declined as pollution levels dropped in the Los Angeles region.Improving air quality may improve cognitive function and reduce dementia risk, according to studies supported in part by NIH and the Alzheimer’s Association.When fossil-fuel power plants close, nearby air pollution is reduced. A study found the incidence of preterm births went down within 5 kilometers of retired coal and oil-powered plant locations.