Closer Look: Coronavirus shutdown lowers air pollution almost overnight, scientists say

Tina Locurto
York Dispatch

With fewer vehicles on the roads during the coronavirus pandemic, air pollution levels are decreasing, according to atmospheric scientists.

“The strongest thing we can say right now is anywhere there's a stay-at-home order, the morning traffic has gone down,” said Albert Presto, a professor in the Department of Mechanical Engineering at Carnegie Mellon University in Pittsburgh.

More:York County's air pollution levels decreasing, report says

Presto, who serves as a member of the university's Center for Atmospheric Particle Studies with a focus in pollutant emissions, said he has been tracking real-time data that suggests the daily spike in air pollution caused by morning commuter traffic is no longer present.

“That bump doesn't exist," he said. “Emissions are probably down because there's so much less traffic. People's movement patterns have changed, and that also might have an impact."

Presto said he first noticed an "obvious change" to air quality levels, specifically for particulate matter, after March 13 — when Gov. Tom Wolf first ordered a shutdown of all nonessential businesses and closed schools throughout Pennsylvania.

Typically, morning commuter traffic in Pittsburgh created a 1.5 microgram per cubic meter spike in particulate matter pollution. Since most commuting has slowed down, however, Presto said that spike is now flat.

Though Presto's area of study is the Pittsburgh region, he said the effects of travel on air quality could be applied to any area with commuters — including York County, which has major roadways that serve travelers going to Harrisburg, Lancaster and Maryland.

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Light traffic travels through York as the pandemic shut-down continues in PA. 
Sunday, April 19, 2020.
John A. Pavoncello photo

According to PennDOT traffic data taken from three York County  locations — at Interstate 83 between the exits at Emigsville and Strinestown, Route 30 near Route 116, and Route 616 near Route 214 — approximately 87,264 vehicles passed through those areas on March 4.

As of April 8, however, total traffic in those three locations has decreased 42%. Additionally, total traffic in the Harrisburg metro area has decreased 47%, with passenger traffic and truck traffic down 53% and 13% respectively, according to Alexis Campbell, press secretary for the state Department of Transportation. 

The highest emissions are typically produced during rush hour, with fine particle pollutants being one of the most damaging to human health, said John Graham, an atmospheric chemist working for the Clean Air Task Force, a Boston-based nonprofit working for technological advancements to fight climate change. 

Light traffic travels through York as the pandemic shut-down continues in PA. 
Sunday, April 19, 2020.
John A. Pavoncello photo

According to the Environmental Protection Agency's National Emissions Inventory for 2014, 48% of carbon monoxide emissions and 2% of particulate matter primary emissions in York County came directly from the tailpipes of vehicles.

"The inventory suggests that passenger vehicles are a more substantial source of pollution," Graham said. "Generally, we expect the emissions from one big truck to be greater than one car. So I assume that there are just many more cars driving more miles than there are big trucks that account for the larger pollution numbers."

With fewer vehicles on the road, scientists have taken note of the almost-overnight effects of lower air pollution.

“There's a definite difference,” Presto said of the changes in air quality in March.  “It was like a light switch almost."

That's good news during the pandemic because adverse air quality can make people more susceptible to COVID-19 and aggravate the symptoms, said Dr. Timothy Craig, an allergist-immunologist at Penn State Hershey Medical Center. COVID-19 is the disease caused by the new coronavirus.

Closer Look

Craig cited trends showing a correlation between higher air pollution and a greater number of people becoming infected with COVID-19.

Also, as with people who smoke cigarettes, individuals who already have an inflammation in the lungs are at higher risk for "a worse outcome" if they contract the coronavirus, Craig said.

"Those areas that are more industrial, there seems to be a predisposition for the (coronavirus)," he said. 

Poor air quality also negatively affects people with other conditions, such as heart disease or asthma, said Kevin Stewart, the director of environmental health for the American Lung Association.

Specifically, particle pollution is notably dangerous because small particles can lodge themselves in the bloodstream and affect heart function, he said.

“Even though we have improved air quality, it's still not where we want it to be," Stewart said.

This is part of a monthly series at The York Dispatch. Each month, Dispatch staffers will delve into a new topic that we believe deserves a Closer Look.

— Reach Tina Locurto at or on Twitter at @tina_locurto.