"In terms of air pollution, there are a lot of different types of pollutants, but it's the ozone," said Kabinda Shakya, an assistant professor of environmental science at Villanova University.
Shakya published a report on air pollution in the city's different neighborhoods last year.
He says the usual high volume of cars is one of the reasons the American Lung Association gave the city an F last year in its annual "State of Air" report.
That's why he says while COVID-19 has been an awful and devastating pandemic, a byproduct of the quarantine is a break for the environment.
"One of the very few positive things we have seen from this COVID-19 is improvement in air quality that has been show in China and Italy," said Shakya.
The European Space Agency released interactive satellite images that illustrate his point. One graph shows the Nitrogen Dioxide levels from December to March. Over the four month span, the pollutant appears to decrease.
"We may be seeing the same trend in the United States also," said Shakya. As he waits for the data, however, he says whatever changes will be temporary.
"As everything starts to operate, I would expect the air quality to be the same kind as before," he said.