The downtown Phoenix skyline is easier to see Tuesday as fewer motorists in Arizona are driving. (Ross D. Franklin/AP)

The coronavirus pandemic has put much of the world into lockdown, with factories going idle and city streets turning into eerily empty walkways. With the case count and death toll still climbing, it’s unlikely that countries will be able to flick a switch and rapidly return to pre-pandemic economic activity.

But one unintended upside to this crisis has been improved air quality, particularly in the hardest-hit areas where the most draconian measures have gone into force. This has been evident in Asia, including China’s Hubei province, where this virus began spreading among humans. It’s also a trend observed in Italy, another devastated region with several thousand deaths.

Now, given that all but a handful of states have implemented stay-at-home orders, the air-quality shifts are also being seen in the United States. This offers a rare — and unintended — large-scale experiment for scientists to see how human emissions contribute to hazardous air quality and analyze the effectiveness of particular policy ideas.

These maps show the amounts of nitrogen dioxide in the atmosphere, a key ingredient in smog, between March 1 and April 5, 2019, when compared to the same period this year. They show the subtle decreases in NO2 in much of the country, including the Mid-Atlantic, Northeast, Ohio Valley and Southwest.


According to Yifang Zhu, a professor at UCLA’s Fielding School of Public Health, the Los Angeles region, long notorious for its traffic and smog, has seen improvements in air quality in recent weeks that can be partly tied to the coronavirus response.

Before stay-at-home orders were issued March 16, Zhu said, the EPA’s Air Quality Index, which incorporates multiple air pollutants, including NO2 and PM2.5 (fine particulate matter), was about 60, or in the “moderate” category. Since then, it has improved by about 20 percent and recorded the longest stretch of “good” air quality in March seen since at least 1995.

The region has seen around a 30 percent decrease in PM2.5. This form of pollution, composed of particles smaller than a strand of human hair, are a health hazard because they get into a person’s lungs and bloodstream. Lung disease, difficulty breathing and heart ailments have been linked to this form of pollution.

Zhu says the average levels of PM2.5 for the L.A. area dropped from about 16 micrograms per cubic meter to about 12 micrograms per cubic meter.

“This is significant,” she said. “This is a dramatically changed air-quality level from medium to good.”

Zhu noted that emissions and meteorology are playing a role in improving Los Angeles’s air quality, as the weather at this time of year favors less stagnant air conditions, while factories and other emissions sources, such as cars and trucks, have decreased.


There’s a growing recognition that the coronavirus can be more harmful to those with greater exposure to air pollution, making it a potential risk factor along with such underlying health conditions as diabetes, asthma and high blood pressure.

A study published this week from researchers at Harvard’s T.H. Chan School of Public Health concludes a small increase in long-term exposure to fine particulate air pollution causes a large increase in the risk of dying of covid-19, the disease caused by the coronavirus.

“The study results underscore the importance of continuing to enforce existing air pollution regulations to protect human health both during and after the COVID-19 crisis,” the study states.

For example, the study, which examined more than 3,000 U.S. counties, found that each increase in long-term exposure to fine particulate pollution of one microgram per cubic meter is associated with a 15 percent greater likelihood of dying of covid-19. This stark difference may be explained by the lung damage such pollution causes over time. Covid-19 targets the lungs and can cause patients to develop pneumonia.


In addition to cuts in NO2 emissions, the coronavirus lockdowns have caused the relentless climb in carbon dioxide emissions to have a temporary hiccup, and the cancellations of tens of thousands of flights also could have consequences for our planet by reducing planet-warming emissions and high-altitude cirrus cloud formations.

Ryan Stauffer, a specialist in air pollution at NASA, said additional studies are needed to determine how the coronavirus-related mitigation measures have affected air pollution. “We all have this hunch” about how air pollution has changed, Stauffer said, adding, “The longer this goes on, the more we will see.”


Los Angeles daily Air Quality Index values from 1995 through April 2020, showing the low levels of air pollutants in March and April of this year (lower left). (EPA)

He said in an interview that NO2 emissions have been declining in the country overall in recent years because of air pollution regulations and that spring tends to be a period of relatively low concentrations because NO2 breaks down easily in the presence of sunlight.

It will take time for scientists to sort out how much of the variations in NO2 levels in 2020 are from to coronavirus-related changes in human activities, such as reduced driving, compared to changes in weather patterns. However, data NASA released Thursday suggests that the human signal during this pandemic is significant.

Drawing on data from one of its satellites, the agency found that, for the Mid-Atlantic and Northeast, March 2020 had the lowest monthly atmospheric NO2 levels of any March since at least 2005.

Zhu, of UCLA, said the observed air-quality improvement in Los Angeles linked to the coronavirus should not be looked at as only possible during a disaster but rather something that society should strive for during normal times.

“There are technological tools and policy tools to make our society more sustainable,” she said. “We don’t need to have a pandemic just to bring clean air to everybody.”

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