How Coronavirus Closures Impacted Philly Area's Air Quality

SOUTHEASTERN PENNSYLVANIA — As coronavirus spread around the world over the past several months, scenes of eerie stillness and silence came to encapsulate the pandemic: an empty freeway in Los Angeles, quiet streets in Manhattan, locked up downtown districts in small towns and cities everywhere.

The greater Philadelphia area was no exception, with stay-at-home orders in place and government mandated closures in place for months.

But hidden amidst the stillness and economic catastrophe was an environmental boon.

Air pollution around the world decreased significantly during the shut down, and the effect was especially pronounced in densely populated areas, including the Delaware Valley.

The cumulative number of "good" air quality days thus far in 2020 is well above the average for the past five years, according to data tracked by the Environmental Protection Agency.

Specifically, particulate matter, tracked as PM2.5, has seen 99 "good days" in the greater Philadelphia metropolitan area in 2020, as of June 10. The average of the past five years for this point in time is just 70. Similarly, there have been 153 "good" days for ozone thus far this year, compared to an average of 132 on this date.

In the case of both ozone and PM2.5, 2020 separated itself from the five-year mean around mid-March, when traffic drastically decreased in the area and industrial processes slowed amid the shutdowns.

In fact, the stretch of high air quality days in the Philadelphia area is easily the best over the last 15-year period, according to the EPA. Check out the thick bars of green, indicating "good" values, running from late May through early June:

It's unclear what, if any, long-term environmental benefit this might have.

"While we might not know that the air is cleaner, our bodies actually might, actually might feel that, that difference in ways that we can’t really perceive,” Peter DeCarlo, associate professor of environmental health and engineering at Johns Hopkins University, told WHYY in a recent interview.

The notion that environmental concerns should be minimized amid the present crises is shortsighted, according to data from the Harvard T.H. Chan School of Public Health. In fact, researchers found that individuals who live in areas with poor air quality are more likely to die from coronavirus, and that poor air quality exacerbates the negative effects of coronavirus as it does other respiratory illnesses like asthma or bronchitis.

In China, it was estimated that just weeks of economic shutdown saved at least thousands of lives that would have lost due to increased air pollution, according to a study published in the medical journal Lancet. Researchers at Stanford estimated around 50,000 to 75,000 Chinese citizens were saved by mid-March, CNN reports.

Satellite footage from the National Oceanic and Atmospheric Administration's Joint Polar Satellite System underlined other sharp distinctions between March 2019 and March 2020.

In March 2019, nitrous oxide concentrations were at or over a density of 100 parts per million in Philadelphia at around 75 in much of southeastern Pennsylvania, as shown below, courtesy of NOAA:

Come March 2020, those levels dropped to around 75 just in the city, to below 50 in the suburbs, and vanished altogether in most of the rest of the state, NOAA satellite footage shows:

General air particulate levels in southeastern Pennsylvania are also down significantly.

But how long can it last? Many of the most restrictive coronavirus shutdowns have been lifted, as southeastern Pennsylvania is now in the yellow phase of the state's reopening plan and looking to the green. Industry is ramping up to pre-pandemic levels, and motorists are hitting the road throughout the region.

As evidenced by the very thin orange line in the EPA graphic above, June 9 was the first and only hint of air rated as "unhealthy" in the Delaware Valley since mid-January. The Pennsylvania Department of Environmental Protection released a Code Orange alert Tuesday, its first in months. It is important to note that air quality alerts are weather-dependent, as well.

The World Health Organization estimates that about 7 million people die every year due to air pollution.