America's Air Is Cleaner,
But Still Kills
Air pollution has declined in America since 2000,
but thousands still die every year from related causes
by Mike Feldman

Fine particulate air pollution, or PM2.5 for short, is the general term for inhalable particles that are 2.5 micrometers or smaller (over 30 times thinner than a human hair). It can be emitted from natural or humanmade sources, including cars, power plants, and wildfires, and can be composed of hundreds of different chemicals.

Due to its small size, inhaling PM2.5 can allow it to enter the lungs and bloodstream, which can cause significant damage over time. Decades of research has linked PM2.5 exposure with premature death in people with heart or lung disease, poor health indicators such as aggravated asthma, decreased lung function, and nonfatal heart attacks, and many other adverse outcomes.

In the United States, average PM2.5 levels have declined steadily since 2000. However, because research has not identified a ‘safe’ level of PM2.5, even lower levels can result in thousands of deaths every year. The Centers for Disease Control and Prevention (CDC) estimates that if PM2.5 levels had been 25 percent lower across the US each year between 2001 and 2014, nearly 500,000 deaths could have been avoided (scroll down for more). For context, in 2019 Environmental Protection Agency (EPA) staff scientists recommended tightening the EPA’s PM2.5 air quality standards from 12 to 9 micrograms per cubic meter (µg/m3), which would have been a 25 percent reduction. (The EPA under the Trump administration ultimately rejected this change).

2001

In 1997, the EPA created national air quality standards for PM2.5 for the first time.

The annual standard was set at 15 µg/m3, meaning that an area would be in violation if its annual average concentration fell above that level.

The 24-hour standard was set at 65 µg/m3. Lawsuits were soon filed against the standards and settled by early 2002.

In 2006, the EPA retained its annual PM2.5 standard of 15 µg/m3 and tightened the 24-hour standard from 65 to 35 µg/m3.

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2008

The onset of the Great Recession in 2008 brought further reductions in PM2.5 concentrations across the US.

In late 2012, the EPA tightened the annual PM2.5 standard from 15 to 12 µg/m3, citing health effects linked to long- and short-term exposures.

2013

2014

2014

However, these death estimates do not reflect the full public health impact of PM2.5. First, as explained above, no safe level of PM2.5 has yet been found, and the CDC's death estimates only assume PM2.5 reductions of up to 25 percent. If PM2.5 levels were reduced even further, more deaths would have likely been avoided. Further, recent developments in the research literature on PM2.5 have focused on its neurological effects. Evidence suggests that fine particulates impair children's cognitive development and negative affect their academic performance. PM2.5 has also been linked to increased risk of dementia, Alzheimer's disease, and Parkinson's disease.

This burden of PM2.5 is not felt evenly across the US. Certain regions experience much more acute air quality problems than others:

US

Southern California

Of the 10 counties with the highest PM2.5 concentrations, 8 are in California (led by Kern County in the San Joaquin Valley). All had annual average concentrations of at least 14 µg/m3 in 2016, 2 micrograms above the EPA standard.

Major ongoing contributors to this pollution include cow manure from feedlots, vehicle exhaust, oil fields, debris from almond farming, and wood stoves and barbecue pits. In recent years, wildfires have made an overwhelming contribution.

Midwest
(Pennsylvania, Ohio, Indiana, Illinois, southern Michigan, southeastern Wisconsin)

A disproportionate reliance on manufacturing and industrial sectors and coal-fired power means these Midwestern states maintain PM2.5 levels higher than their neighbors. This has occasionally been a source of tension, as particulates originating from these states cause premature deaths in others.

Southeast
(Georgia, Alabama, South Carolina)

Prescribed fires drive this region’s elevated PM2.5 emissions, contributing about 30 percent of all PM2.5 regional emissions. About 70 percent of all prescribed fire in the US from 1998 to 2018 was completed in the Southeast.

Hawaii

According to CDC data, the island of Hawaii experienced the second-highest annual average PM2.5 concentration in the country in 2016, at 15.8 µg/m3. The primary source of PM2.5 here is not manmade, but rather volcanic emissions.

US

Despite the copious evidence on the adverse effects of PM2.5, its regulation is controversial in the United States.

Over its four years, the Trump administration weakened national auto emissions standards, attempted to repeal power plant emission restrictions, rejected tightening the national PM2.5 air quality standards, passed a new rule changing which studies can be used to inform those standards, and proposed a new methodology for calculating the health risks of PM2.5 that would predict fewer deaths caused by air pollution. This came after the Obama administration enacted national auto and power plant emission standards and implemented stricter standards on PM2.5.

Because PM2.5 is not a hot-button topic of political discourse in the United States, these actions can be easy to miss. But even though the topic may be arcane, and though the United States has made progress over the decades in reducing PM2.5, thousands of lives every year still hang in the balance.
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If you are interested in exploring more air quality and other public health-related metrics, please visit the Data Explorer tool hosted by the CDC


The GitHub repository including all code for this project is here


Data Sources:

Both the PM2.5 concentrations and the mortality estimates were downloaded via the CDC Data Explorer tool. You can find the raw data file with 2001-2016 PM2.5 concentrations here and the file with the 2001-2014 mortality estimates here


Code sources:

The scrollama library for scrollytelling
Mike Bostock on how to choropleth map in D3
Xavier Gimenez on how to create a waffle plot in D3
d3-graph-gallery on how to implement transitions in D3