How smog, soot, greenhouse gases, & other đứng top air pollutants are affecting the planet—and your health.

What Is Air Pollution?

Air pollution refers to lớn the release of pollutants into the air—pollutants which are detrimental khổng lồ 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- & 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 lớn safeguard public health by regulating the emissions of these harmful air pollutants.

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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 “Burning fossil fuels releases gases & chemicals into the air.” và in an especially destructive feedback loop, air pollution not only contributes to climate change but is also exacerbated by it. “Air pollution in the khung 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 & there’s more ultraviolet radiation.” Climate change also increases the production of allergenic air pollutants, including mold (thanks lớn damp conditions caused by extreme weather & increased flooding) and pollen (due khổng lồ a longer pollen season).

“We’ve made progress over the last 50 years improving air chất lượng in the United States thanks lớn the Clean Air Act,” says Kim Knowlton, senior scientist and deputy director of the Science Center. “But climate change will make it harder in the future to meet pollution standards, which are designed to lớn 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 và 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 và 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 & trigger asthma attacks. The tiniest airborne particles in soot, whether gaseous or solid, are especially dangerous because they can penetrate the lungs và bloodstream and worsen bronchitis, lead to lớn heart attacks, và 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 & long-term exposure lớn fine particulate matter & illuminating an environmental justice issue.

Because highways and polluting facilities have historically been sited in or next to low-income neighborhoods & 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 và 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, và benzene. “These are also most often emitted during gas or coal combustion, incinerating, or—in the case of benzene—found in gasoline,” Walke says. Benzene, classified as a carcinogen by the EPA, can cause eye, skin, & lung irritation in the short term & blood disorders in the long term. Dioxins, more typically found in food but also present in small amounts in the air, can affect the liver in the short term & harm the immune, nervous, and endocrine systems as well as reproductive functions. Mercury attacks the central nervous system. In large amounts, lead can damage children’s brains and kidneys, và even minimal exposure can affect children’s IQ & ability to lớn learn.

Another category of toxic compounds, polycyclic aromatic hydrocarbons (PAHs), are by-products of traffic exhaust and wildfire smoke. In large amounts they have been linked to lớn eye & lung irritation, blood and liver issues, and even cancer. In one study, the children of mothers exposed lớn PAHs during pregnancy showed slower brain-processing speeds and more pronounced symptoms of ADHD.

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Greenhouse gases

By trapping the earth’s heat in the atmosphere, greenhouse gases lead lớn warmer temperatures, which in turn lead khổng lồ the hallmarks of climate change: rising sea levels, more extreme weather, heat-related deaths, and the increased transmission of infectious diseases. In 2018 carbon dioxide accounted for 81 percent of the country’s total greenhouse gas emissions, và methane made up 10 percent. “Carbon dioxide comes from combusting fossil fuels, and methane comes from natural and industrial sources, including large amounts that are released during oil & gas drilling,” Walke says. “We emit far larger amounts of carbon dioxide, but methane is significantly more potent, so it’s also very destructive.” Another class of greenhouse gases, hydrofluorocarbons (HFCs), are thousands of times more powerful than carbon dioxide in their ability khổng lồ trap heat. In October 2016 more than 140 countries reached an agreement lớn reduce the use of these chemicals—which are found in air conditioners & refrigerators—and develop greener alternatives over time. Though President Trump was unwilling to sign on to lớn this agreement, a bipartisan group of senators overrode his objections in 2020 & set the United States on track lớn slash HFCs by 85 percent by 2035. According lớn David Doniger, senior strategic director of’s Climate và Clean Energy program, “the agreed-to HFC phasedown will avoid the equivalent of more than 80 billion tons of carbon dioxide over the next 35 years.”

Pollen và mold

Mold and allergens from trees, weeds, and grass are also carried in the air, are exacerbated by climate change, and can be hazardous lớn health. Though they aren’t regulated & are less directly connected to human actions, they can be considered a form of air pollution. “When homes, schools, or businesses get water damage, mold can grow và can produce allergenic airborne pollutants,” Knowlton says. “Mold exposure can precipitate asthma attacks or an allergic response, và some molds can even produce toxins that would be dangerous for anyone khổng lồ inhale.”

Pollen allergies are worsening because of climate change. “Lab & field studies are showing that pollen-producing plants—especially ragweed—grow larger and produce more pollen when you increase the amount of carbon dioxide that they grow in,” Knowlton says. “Climate change also extends the pollen production season, và some studies are beginning khổng lồ suggest that ragweed pollen itself might be becoming a more potent allergen.” If so, more people will suffer runny noses, fevers, itchy eyes, và other symptoms.

Air pollution is now the world’s fourth-largest risk factor for early death. According to the most recent State of Global Air report—which summarizes the latest scientific understanding of air pollution around the world—4.5 million deaths were linked khổng lồ outdoor air pollution exposures in 2019, and another 2.2 million deaths were caused by indoor air pollution. “Despite improvements in reducing global average mortality rates from air pollution, the world’s most populous countries, India and China, continue lớn bear the highest burdens of disease,” says Vijay Lamaye, staff scientist at the Science Center. “This report is a sobering reminder that the climate crisis threatens khổng lồ worsen air pollution problems significantly if we fail khổng lồ act to cut carbon pollution.”