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How America solved its first air pollution crisis — and why solving the next one will be harder

The history of American air pollution, explained.

Manhattan covered in heavy smog The Environmental Protection Agency’s Program to Photographically Document Subjects of Environmental Concern, Chester Higgins
Rachel DuRose is a Future Perfect fellow, covering climate change, housing, mental health, and more. Rachel previously wrote about the workplace, hiring, and executive leadership for Business Insider.

The toxic air pollution that wafted over the Northeast earlier this month may have shocked some Americans unaccustomed to the smoky conditions that regularly plague Western states. But the air in cities like Washington, DC, and New York hasn’t always been as clean as it generally is today.

In the 1960s, the consequences of industrial activity, factory pollution, and automobiles were visible in the country’s polluted water and air. Yellow smog and falling ash coated American cities. The air in New York City was so polluted you could touch it, the New York Times reported, and “killer smog” events — short periods of heavy air pollution — were far too common. In the 1950s and ’60s, hundreds of people in NYC died from exposure to air pollution.

A series of ecologically damaging events and increasing education spurred activists and politicians to action and ultimately culminated in the modern environmental movement. The start of the next decade, 1970, marked the first Earth Day, followed soon by some of the most consequential forms of air pollution regulation in the country to date.

Those efforts bore fruit: The significant strides made by the US in the 20th century to combat its environmental crisis succeeded, both visibly in the air throughout major cities and in the health of Americans. Those laws prevented an estimated 230,000 premature deaths over 50 years. And lawmakers have continued to build on the last century’s policies. Just last year, Congress passed the Inflation Reduction Act, which invested over $270 million in clean air measures, including increased monitoring of air quality.

But now a growing source of pollution — wildfire smoke — jeopardizes much of this progress.

Smokey Sunrise in New York City
The New York City skyline due to smoky air on June 8, 2023.
Gary Hershorn/Getty Images
Manhattan covered in heavy smog
The Manhattan skyline is covered in heavy smog in 1973.
The Environmental Protection Agency’s Program to Photographically Document Subjects of Environmental Concern, Chester Higgins

Extreme fire events — like the one that caused this month’s record-breaking air pollution in New York and elsewhere — are exacerbated by climate change, and are “essentially erasing” decades of progress in improving air quality, said David Lu, the co-founder of Clarity Movement, a company providing air quality monitoring solutions. Human-led deforestation, farming, and the burning of fossil fuels are warming our planet, making the climate hotter, drier, and more prone to fires.

“Historically, we were really targeting air pollution coming from man-made sources,” Lu said. “That’s something we can control. Wildfires are a natural disaster.”

In the 20th century, the sources of air pollution were industrial. The country regulated these emissions — making cars and even power plants cleaner. Wildfires are a different beast. A number of factors influence where and how severe a fire is, but we know from our previous progress that social pressure and legislative action can work.

The stakes are too high not to take preventive and reactive measures. Air pollution still kills 7 million people annually, and there is a very real risk that this number could rise.

“Air quality is really just like a canary in the coal mine for climate change,” said Lu. “Getting everybody on board to combat climate change is hard. But everybody, no matter what your political affiliation, cares about air quality because we all are breathing this air.”

An era of change

After 1945, when World War II ended, the US experienced rapid population growth — going from a population of a little over 132 million people in 1940 to over 179 million people in 1960. Simultaneously, America further urbanized and industrialized, and enthusiastically took to the roads and highways. In 1945, there were 26 million automobiles on American roads. By the end of the 1960s, there were 100 million vehicles.

Throughout the 1950s and ’60s, car exhaust, power plant pollution, and landfill-related smog blanketed US cities coast to coast, including Los Angeles and New York City. In the US, human-made sources emitted over 92 million tonnes of emissions of nitrogen oxide, non-methane volatile organic compounds, and sulfur dioxide into the air in 1970. Air pollution, especially at this severe level, can cause respiratory infections, heart disease, and lung cancer. And is especially dangerous for children, the elderly, and those with preexisting conditions, like asthma.

To address the public health crisis air pollution poses, Congress enacted federal legislation, targeting the sources, first via the 1963 Clean Air Act — which spurred research into air pollution monitoring and control — and then again through a series of amendments, most notably the 1970 amendment. This amendment authorized the Environmental Protection Agency (EPA), which President Richard Nixon created that same year, to regulate air pollutant emissions.

The regulations resulted in tremendous progress and lowered certain types of air pollutants, including sulfur dioxide, significantly. Since 1970, emissions from nitrogen oxide, non-methane volatile organic compounds, and sulfur dioxide have declined by 63.7 million tonnes to just over 29 million tonnes. The EPA lowered levels of air pollutants by investing in the enforcement of emission-lowering technology, including what Lu calls the “game-changing” implementation of catalytic converters. California tightened the emission standards for vehicles, and by 1975, lead gas had been banned by the federal government for use in cars.

“The stationary sources — factories and power plants — and mobile sources — cars and trucks — all emit much less air pollution than they did back in 1970,” said John Dernbach, a professor of environmental law and sustainability at Widener University Commonwealth Law School and director of the school’s Environmental Law and Sustainability Center. The Clean Air Act is “an incredible success story.”

In the mid-1900s, factories and power plants produced copious amounts of sulfur dioxide, which can cause acid rain. Between 1995 and 2022, the national level of sulfur dioxide emissions decreased by over 90 percent. Levels of lead (a toxic metal) in the air decreased even more significantly — dropping 98 percent between 1980 and 2014.

The Clean Air Act also proved an economic benefit, said Dernbach. In the 20 years following the 1970 Clean Air Act, the EPA estimated the measures saved anywhere between $5.6 trillion and $49.4 trillion in health, welfare, environmental, and productivity costs. Contrary to doom-and-gloom projections, the economy kept growing, cars kept being developed, and we still have access to electricity (the average American household used the same amount of energy it used in the 1970s in 2010, despite increased efficiency).

“Part of the story that we hear is that if you protect the environment, you’re going to hurt the economy,” said Dernbach. “The air pollution story, based on the Clean Air Act, is a story to the contrary. It’s a story where we’ve had substantial economic growth and improved human quality of life and improved public health.”

The smokier future ahead

In accordance with the Clean Air Act, the EPA monitors six primary air pollutants that adversely affect human health and the environment: particulate matter (PM), ozone, carbon monoxide, sulfur dioxide, nitrogen dioxide, and lead.

While legislation in the 20th century significantly lowered the level of most of these pollutants, particulate matter remains a large and still-growing problem.

Particulate matter, PM, is composed of solid particles and liquid droplets emitted by a number of sources, including electric utilities, boilers, metal smelters, petroleum refineries, and fires. These teeny-tiny particles can also form from chemical reactions in the atmosphere prompted by other forms of pollutants that are released by power plants and cars (such as sulfur dioxide and nitrogen oxide).

Some types of PM are visible to the human eye. But other types, including the dangerous PM2.5, are not visible. These particles are 2.5 micrometers and smaller, or 30 times smaller than the diameter of a single piece of hair. Humans can inhale them without ever noticing, and given their size, they can penetrate deep into our lungs and bloodstream.

Because human activity caused much of the country’s air pollution when lawmakers created the Clean Air Act, the EPA targeted human-made polluters (factories, cars, etc), said Lu. The agency prioritized pollutants from these sources and overlooked particulate matter. The EPA did not begin monitoring PM until 1996.

Since 1999, PM2.5 emissions from human-induced sources of pollution have declined. But the threat of particulate matter is only worsening with the rise of extreme fire events. The average annual acreage burned by wildfires in the US has more than doubled over the past few decades, in part due to climate change. Between 2000 and 2022, an average of over 7 million acres of land burned each year, compared to approximately 2.9 million acres per year between 1983 and 1999, according to data from the National Interagency Fire Center. Experts warn that extreme fire events are an inevitable part of the planet’s future.

“Obviously wildfires occur in nature, but their frequency and their severity and everything else is affected by us, by human activity,” said Neil Donahue, a professor of chemistry and director of the Steinbrenner Institute for Environmental Education at Carnegie Mellon University. Emissions from natural sources are called “biogenic” emissions, and emissions from human sources are called “anthropogenic emissions,” he added. “Wildfires are kind of this weird middle other, because they’re from a natural source — in other words, burning trees — but that fire is there in some way or another because of humans.”

“Unfortunately, until we deal with climate change, we’re gonna see more fire and more smoke,” said Michael Flannigan, the research chair for predictive services, emergency management, and fire science at Thompson Rivers University in Canada.

What needs to change now

Today, PM2.5 is likely the “most harmful” air pollutant the EPA regulates, said Lu. But some consequences, especially the long-term effects, remain uncertain. “There’s actually still a very underdeveloped understanding of the health impact of, specifically, wildfire smoke on our health,” said Lu.

Given our underdeveloped knowledge of the pollutant, the EPA continues to update its guidelines on PM2.5 regularly. Earlier this year, the agency tightened its maximum allowable concentration of PM2.5 micrograms per cubic meter in the ambient air from 12 micrograms to between 9 and 10 micrograms. The agency estimates this change could save up to 4,200 lives annually.

Legislative action saved America’s air quality in the past, and today policies exist that we know could help combat PM2.5 emissions.

For example, prescribed burns, community-based fire management, and fuel reduction are all techniques already used by forest management professionals to reduce the severity and risk of PM2.5-causing wildfires. And in 2019, the Environmental Law Institute published Dernbach and co-author Michael Gerrard’s guide on decarbonizing the US, which identifies more than 1,000 legal routes addressing climate change’s effects.

Compared to the 1960s, the public mindset on climate change is actually one of the biggest hurdles to putting these pollutant-reducing actions into effect, said Dernbach.

“Much of the narrative about climate change is about how action to reduce greenhouse gas emissions will limit personal freedom,” he said. “The wildfires, and the intense public health issues that they’ve created, should make clear to everyone that there are many ways in which growing greenhouse gas emissions in a changing climate will limit personal freedom.”

One of the reasons the US was able to address air pollution in the past was the sources and solutions were straightforward. Cars create smog, so the US changed the regulations around their fuel consumption and type. Power plants made smog, so the US further managed their outputs. The results of these measures were easily visible.

The sources, solutions, and visible results of the planet’s warming future, while clear, are not as immediate. But worsening wildfire seasons are a visible manifestation of climate change, and one that could spur more needed action on air pollution.

“Air quality is a really terrific method to get people on board with the idea that we have to do something that reduces the speed of climate change,” said Lu. “It’s a Trojan horse, almost.”

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