The Streets Cleared; The Air Did Not

Jun 23, 2020

A reduction in traffic didn't impact local air quality, according to a new study.
Credit Wikimedia Commons


During the height of Shelby County’s coronavirus lockdown in late March and into April, Dr. Chunrong Jia, an air quality researcher with the University of Memphis, heard a common refrain.

 “Oh, I feel fresh air because I see much fewer cars on the street,” he says.

That may have appeared true, especially as traffic vanished from busy streets. But, in reality, Jia says, overall air pollution in the Memphis metro-area did not noticeably drop as a result of local “Shelter-In-Place” orders. 

His recently published study on air quality compared concentration levels for air pollutants—ground-level ozone and fine particulate matter—during Shelby County’s lockdown to the same period from the past three years. The study accounted for major variables that impact air quality, such as weather patterns and climate conditions.

It identifies several reasons why the Memphis-area’s air quality remained stable during the onset of the pandemic even as other COVID-19 shutdowns in large cities around the world resulted in some drastic, albeit temporary, reductions of air pollution.

Typically, traffic emissions are a lesser contributor to local pollution—between 10-15 percent, Jia says. This indicates that other larger industrial sources of pollution might have dwarfed the impact of fewer cars on the road. While residential travel dipped as much as 60 percent, highway traffic only fell about 20 to 30 percent, suggesting that commercial vehicles—often some of the dirtiest polluters—were still largely in operation. 

Another explanation is that Memphis’ air quality is already relatively clean for a metro area. Its pollution levels meet national standards, which is why, Jia says, smaller improvements in air quality are harder to detect than in mega-polluted cities such as in China

China's shutdown was also broad reaching. Unlike here, where essential business and industries remained open, major factories in China went offline for a time.  

“They could cause an almost 50 percent, [or a] 40 percent reduction from the already high pollution levels,” Jia says. 

Still, Michael Vandenbergh, a law professor at Vanderbilt University who studies energy and the environment, says the amount of time people spend in their vehicles still matters when it comes to both climate change and keeping air clean. 

But, he adds that in a major transportation hub⁠ like Memphis, environmental policies should focus on reducing the pollution footprint from this sector through measures such as using more electric trucks and delivery vehicles.  

“There is no one solution to the problem. Individual behavior is part of the problem, corporate behavior is part of the problem. Government is part of the problem,” he says. “We shouldn’t expect a solution just from people reducing the amount of commuting they’re doing.”