WASHINGTON — In the crystalline air of the pandemic economy, climate change researchers have been flying a small plane over Route I-95, from Boston to Washington, measuring carbon dioxide levels. Scientists have mounted air quality monitors on Salt Lake City’s light rail system to create intersection-by-intersection atmospheric profiles.
And government scientists at the National Oceanic and Atmospheric Administration have started a Covid air quality study to gather and analyze samples of an atmosphere in which industrial soot, tailpipe emissions and greenhouse gases have plummeted to levels not seen in decades.
The data, from Manhattan to Milan to Mumbai, will inform scientists’ understanding of atmospheric chemistry, air pollution and public health for decades to come, while giving policymakers information to fine-tune air quality and climate change laws and regulations in hopes of maintaining at least some of the gains seen in the global shutdown as cars return to the roads and factories reopen.
Already, Gov. Larry Hogan of Maryland, a Republican, has assigned his top environment official to use the pollution data gathered by a University of Maryland scientist in flights over Baltimore to push new policies through the state legislature this fall, expanding telework and promoting electric vehicles.
“Our goal is not just to celebrate the silver lining but to seize upon that lining and institutionalize it,” said Benjamin H. Grumbles, the head of Maryland’s environmental agency.
Policy experts say the new data could even bolster legal fights against the Trump administration’s efforts to roll back major air pollution regulations. Early studies appear to show that even as the coronavirus took more than 100,000 American lives, deaths related to more typical respiratory illnesses like asthma and lung disease fell in the clean air, boosting the case that Mr. Trump’s environmental rollbacks will contribute to thousands of deaths.
“This is a giant, global environmental experiment that has been done in a very controlled way,” said Sally Ng, an atmospheric scientist and chemical engineer at Georgia Tech, who, in the first days after the shutdown, briefly returned to her lab in downtown Atlanta to install an atmospheric monitor on the roof. “We suddenly turned the knob off, very drastically, and now we’re very slowly turning it back on.”
Three other moments in recent history have seen economies slow suddenly and the skies clear enough to create a valuable research opportunity: Sept. 11, 2001, when airplanes were grounded and the skies were briefly free of chemical airplane pollution; the 2008 Beijing Olympics, when Chinese officials shut down the city and the soot-choked air cleared for about two weeks; and the financial meltdown in the fall of 2008.
But the pandemic clearing has been more dramatic, in duration and scope.
“We were able to observe these changes in real time, all around the world, for a much longer period of time than ever before,“ said Shobha Kondragunta, a NOAA atmospheric chemist who studies smog-causing tailpipe pollutants such as nitrogen dioxide and sulfur dioxide, using images taken from satellites over the North and South Poles.
In India, where some of the most polluted skies in the world turned clear and blue for the first time in decades, Sarath Guttikunda, director of Urban Emissions.info, a New Delhi-based research organization, spent the shutdown monitoring air quality data gathered by government-operated atmospheric monitors across 122 Indian cities. “This is a really good experiment that we hope will never be repeated again,” he said. “Every day we learned something new.”
In a country where much of the population suffers under an opaque stew of pollution, the Indian government has little information about which sources of emissions — cars, power plants, factories or cookstoves — are the worst culprits, Dr. Guttikunda said. But as the shutdown cleared cars off the roads and brought factories to a halt, coal plants and cookstoves kept emitting. That allowed Dr. Guttikunda and his colleagues to develop a more precise profile of pollution, source by source, city by city, region by region.
“If you want to clean up your air pollution problem, you have to know what to target,” he said.
Other experts agreed. “These studies, particularly in India, can make it much easier to get a good bead on emissions,” said Maureen Cropper, a senior fellow at Resources for the Future, a nonpartisan environmental research organization in Washington. “You don’t want to be controlling the wrong thing.”
Among the most surprising of Dr. Guttikunda’s observations: In some cities, as vehicle traffic and tailpipe pollution declined, levels of one major smog-causing pollutant, ozone, actually shot up.
Dr. Guttikunda said the sharp rise was a real-life validation of a theory of atmospheric chemistry that says ozone — which is linked to asthma, heart disease and premature death — will increase, at least temporarily, as emissions of the tailpipe pollutants nitrogen oxide and sulfur dioxide go down.
“This is a theory that atmospheric chemists learn in class, but we haven’t seen it work in real time,” said Dr. Guttikunda.
Eight thousand miles away, scientists monitoring the air over the Los Angeles basin observed the same phenomenon.
“The spike in ozone, that’s caused a lot of interest,” said Michael Benjamin, who heads the atmospheric monitoring laboratory for California’s clean air agency.
Dr. Benjamin said that could have surprising implications for California, which has led the nation in implementing tough clean air policies. As the state continues to reduce its vehicle pollution, it may go through a period where some aspects of smog actually worsen “because of the weird air chemistry.”
Still, he expressed optimism. “This is a grand, real-world experiment that is validating what our path” to cleaner air might look like, he said.
In the northeast corridor of the United States, Xinrong Ren of the University of Maryland and Colm Sweeney of NOAA used the shutdown to help validate scientific models that are crucial in understanding the human impact on climate change and air quality.
Scientists still do not have a reliable system for measuring day-to-day changes in human-caused emissions of carbon dioxide, the main driver of global warming. But for the past two years, Dr. Ren and Dr. Sweeney have been monitoring carbon dioxide levels over Boston, New York, Philadelphia, Baltimore and Washington from a device mounted on the wings of two small airplanes that they fly up and down the East Coast. As soon as the shutdown started, the pair returned to their flying laboratories.
“A lot of policy is driven by models and guesstimates of how much we think certain things contribute to emissions,” Dr. Sweeney said. “Covid is a great opportunity to do real-life testing of those models.”
Because New York City saw a 50 percent decrease in vehicle traffic, one of the major sources of carbon dioxide pollution, the scientists could calibrate real-life impacts of auto-related emissions on the climate by comparing the shutdown measurements with those taken on their earlier flights.
“Covid-19 allows us to test the models that policy depends on,” Dr. Sweeney said.
The Obama administration used such models to justify the country’s first federal regulations to counter climate change, through stricter limits vehicle and power plant emissions. As the Trump administration weakened or wiped out those regulations, officials downplayed or disparaged climate change modeling as inaccurate or unreliable.
Now, opponents of those efforts will have new ammunition to combat them.
“This is powerful data,” said Mr. Grumbles, the Maryland environmental official. “It reinforces the policy arguments for stronger, more aggressive controls.”
Allies of the administration scoffed at the idea that three months worth of research on emissions levels could make any difference in the quality of scientific models.
“I don’t see how any of this strengthens climate models,” said Steven J. Milloy, who serves as an informal environmental policy adviser to members of the Trump administration and is author of the book “Scare Pollution: Why and How to Fix the E.P.A.”
“I know these guys want any excuse for more money and something to do,” he added, “but I don’t think this validates anything
Administration officials struck a cautious note, but were not so dismissive.
Andrea Woods, a spokeswoman for the Environmental Protection Agency, wrote in an emailed statement: “The E.P.A., along with many other federal agencies, including NOAA and NASA, are using the opportunity available during the Covid-19 outbreak to further enhance our understanding of how human activity potentially impacts air quality. Many data streams are being collected. All will require integration along with a comprehensive and systematic analyses before any models might be updated or conclusions drawn.”
Public health scientists are studying another aspect of the pandemic’s cleaner air. A working paper published by the National Bureau of Economic Research calculated that the reduction in pollution has led to about 360 fewer deaths each month in the United States from illnesses like asthma, lung disease and heart disease — a drop of about 25 percent.
“It’s certainly not a silver lining — it in no way compares to the over 100,000 deaths from Covid in the U.S.,” said Steve Cicala, an economist at the University of Chicago and an author of the paper. “But 25 percent is a lot. This is the savings of lives that would be achieved if there were a less costly way to improve air pollution.”