Air pollution is a familiar environmental health hazard. We know what we’re looking at when brown haze sits above a city, exhaust billows over a busy highway, or a plume rises from a smokestack. Some air pollution is unseen, but its pungent smell alerts you.
When the National Ambient Air Quality Standards were established in 1970, air pollution was primarily considered a threat to respiratory health. As air pollution research advanced over the following decades, the public health concern broadened to include heart disease; diabetes; obesity; reproductive, neurological and immune system disorders; and cancer. In 2013, the International Agency for Research on Cancer for the World Health Organization (WHO) classified air pollution as a human carcinogen. Over its more than 50-year history, NIEHS has been a leader in air pollution research. The institute funds studies of how air pollution affects health and the population groups that are most affected.
What is Air Pollution?
Air pollution is a mixture of hazardous substances from both man-made and natural sources. Some hazardous substances are naturally released into the air, such as ash and gases from volcanic eruptions. Other emissions can be caused by both human and natural activity, such as smoke from forest fires, which are often initiated by people; and methane, which comes from decomposing organic matter in the soil as well as animal feedlots. The primary sources of man-made air pollution are vehicle exhaust; fuel oil and natural gas for heating homes; by-products of manufacturing and power generation, especially coal-fueled power plants; and fumes from chemical production.
The Trap and its Components
Traffic-related air pollution (TRAP) from motor vehicle emissions contains most of the elements common to all air pollution, including carbon, nitrogen oxides, sulfur oxides, volatile organic compounds, polycyclic aromatic hydrocarbons, fine particulate matter, and ground-level ozone.
Noxious gases, including 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), composed of chemicals such as sulfates, nitrates, carbon, or mineral dust, is created during the combustion of fossil fuels and organic matter.
Volatile organic compounds (VOCs) are released during the combustion of fossil fuels, and given off by paints, cleaning supplies, pesticides, and even craft materials like glue.
Polycyclic aromatic hydrocarbons (PAHs) are organic compounds released during combustion, power generation, and some manufacturing. PAHs are also found in particulate matter.
Ozone, an atmospheric gas, is created when pollutants emitted by cars, power plants, refineries, and other sources chemically react in the presence of sunlight. We call this smog.
How Air Pollution Affects Health
Fine particulate matter (PM 2.5) is 30 times thinner than a human hair and can be inhaled deeply into lung tissue. It accounts for most of the health effects caused by air pollution in the U.S.3. Other important contributors and consequences follow.
1. Respiratory Disease
Air pollution can affect lung development and has been linked to emphysema, asthma and chronic obstructive pulmonary disease (COPD). PM and nitrogen oxides have been linked to chronic bronchitis. How your genes interact with the environment also plays an important role in the health of your respiratory system. NIEHS-funded research found that people with specific gene variants that made them more likely to have lung inflammation were more likely to suffer from asthma if they lived close to major roadways.
2. Cardiovascular Disease
Air pollution can aggravate your heart and cardiovascular system in several ways. PM 2.5 can impair blood vessel function and speed up calcification in arteries. Researchers also found: • Short-term daily exposure to nitrogen oxides by postmenopausal women may increase the risk of hemorrhagic stroke. • Lowering HDL cholesterol, sometimes called good cholesterol, increases their risk for heart disease.
3. Cancer
Several types of cancer are linked to air pollution. • Researchers found that occupational exposure to benzene, an industrial chemical and component of gasoline, can cause leukemia and is linked to non-Hodgkin’s lymphoma. • A long-term study, 2000-2016, found a link between lung cancer incidence and increased reliance on coal for energy production. • The risk of developing breast cancer from exposure to air pollution is of particular concern. A study of more than 57,000 women found living near major roadways may increase a woman’s risk for breast cancer.
Who does air pollution affect most?
Pregnant women and children
Air pollution has been shown to have many negative effects for pregnant women and their fetuses. • Prenatal exposure to PAHs was associated with various prenatal and childhood neurological problems, such as brain development effects, slower processing speed, and attention-deficit and hyperactivity disorder (ADHD) symptoms. • Prenatal exposure to particulate matter was associated with lower birth weight. • Women exposed to high levels of PM2.5 during pregnancy, particularly in the third trimester, may double their risk of having a child with autism. • Second and third trimester exposure to PM2.5 may increase the chances of those children having high blood pressure in early life. • In California’s agricultural San Joaquin Valley, women exposed to high levels of carbon monoxide, nitrogen oxides, or nitrogen dioxide during the first eight weeks of pregnancy were more likely to have a baby with neural tube defects.
Children’s Health
Began in 1992 at the University of Southern California, the study is the largest on the long-term effects of air pollution on children’s respiratory health. With major funding from NIEHS, it includes data collected from more than 11,000 children in 16 communities in Southern California. Published findings include: • Higher air pollution levels 20 increase short-term respiratory infections, leading to more school absenteeism. • Children who play many outdoor sports 21 and live in communities with high ozone are more likely to develop asthma. • Children who live 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 23 symptoms.
Older Adults
In older adults, long-term exposure to NETs can greatly hasten physical disabilities. 24 The risk is more pronounced among racial minorities and people with low incomes. PM 2.5 is associated with accelerated memory problems and Alzheimer’s-like brain decline, rising by 25% among women 65 and older.
Rural housing
Many people assume air pollution is an urban problem. But rural residents, especially in agricultural areas, also face health risks from air pollution. • An NIEHS-funded study found that PM 2.5 concentrations in rural Washington state were comparable to those in urban Seattle, resulting in increased asthma symptoms for rural children, including wheezing, nighttime awakenings and limitations on activities. • Large-scale animal feeding operations can compromise regional air quality through the emission of pollutants, such as ammonia gas and methane. One study found acute lung function problems in children with asthma in such areas.
NIEHS and community involvement
NIEHS has a long history of direct involvement in communities, from close collaboration with native peoples in identifying sources and impacts of pollution on tribal lands, to understanding environmental justice issues in inner cities, to citizen science initiatives that improve the quality of data for air pollution research. Among these initiatives, researchers found: • Breathing dust from mine tailings, created by active and abandoned mining operations, affects lung function.28 NIEHS grantees address health hazards in disadvantaged communities, such as those among Native American people in the West, through culturally relevant, health communications. • NIEHS also helps residents of Imperial County, California, track air pollution through a network of 40 community run monitors. In this county, long-term improvements in air quality were associated with significant lung function improvements in children29. • Community-level strategies30 can also help reduce exposure to particulates: -Using high-efficiency particulate air (HEPA) filtration. -Building land-use buffers and vegetated barriers. -Enhancing urban design with gardens, parks, and street-side trees. -Active-travel options, such as cycling and walking paths.
Why Improving Air Quality Matters
Success stories in cleaning our air demonstrate the benefits of these efforts to public health. • Among children in Southern California, decreases in ambient nitrogen dioxide and PM2.5 were associated with fewer cases of asthma. • In the Los Angeles area, bronchitis symptoms declined as pollution levels fell. • When fossil-fuel power plants shut down, nearby air pollution decreases. One study found that the incidence of preterm births went down within 5 kilometers of retired coal- and oil-fired plants. • An NIEHS-funded study found that a combination of several B vitamins may protect DNA 34 from changes caused by PM 2.5 air pollution.
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