It’s been hailed as a silver lining of the coronavirus lockdown: With fewer cars on the road, air quality has improved, bringing clearer skies to cities across the world.
Los Angeles had its longest streak of good air days in decades, and social media is full of photos of an unusually crisp skyline. “Coronavirus Got Rid of Smog,” proclaimed a headline in the Wall Street Journal.
So has L.A. smog been eliminated?
While there is no question the restrictions to stem the pandemic have reduced air pollution, the coronavirus lockdown does not bear full responsibility for the weeks of clean air Californians have enjoyed. Dramatic reductions in vehicle and industrial emissions contributed to lower smog levels, air quality experts say, but much of the improvement was also due to stormy spring weather.
“We have the readings that show us that the air has been better, and presumably it’s not a coincidence that it happens at the same time that people are sheltering in place and the economy is at a fraction of its normal activity,” said Mary Nichols, who chairs the California Air Resources Board. But determining how much is due to weather versus pandemic-triggered emissions reductions, she said, “will take us a while to figure that one out.”
At least for now, scientists and regulators say, the situation offers an unintended glimpse at what the nation’s smoggiest region could be like with more electric vehicles on the road.
“If I could wave my magic wand and we all had electric cars tomorrow, I think this is what the air would look like,” said Ronald Cohen, a professor of atmospheric chemistry at UC Berkeley who has been studying the effects of the stay-at-home orders on air quality.
The experience also underscores what it would take to clean Southern California’s air to federal health standards permanently, through a dramatic transition from fossil fuel combustion to zero-emission cars, trucks and power.
“There is technology that would allow us to have the clean air that we’re seeing now . . . on a permanent basis,” said Wayne Nastri, executive officer for the South Coast Air Quality Management District. “Zero-emission technology is something that we all need to pursue very aggressively so that we can maintain these clean-air benefits, to see as far as we can and take those deep breaths.”
Unfortunately, the clean air spell has already come to an end, thanks to a heat wave in recent days that generated unhealthy smog levels across Southern California. Air quality officials are predicting more bad air days to come, even with public health restrictions in effect, as the region enters a hotter, drier time of year.
L.A.'s air has been unusually clean. In March, the area enjoyed 21 straight days of air in the green, “good” category on the Air Quality Index, in what was the longest stretch in at least four decades, according to U.S. Environmental Protection Agency monitoring data going back to 1980.
While that streak sounds exceptional, it began on March 7, well before Gov. Gavin Newsom issued statewide stay-at-home orders on March 19. It’s a time of year in Southern California that typically has the cleanest air, after the winter soot season and before summer smog.
Get Boiling Point, our new newsletter exploring climate change, energy and the environment, and become part of the conversation — and the solution.
“The period in green was particularly stormy, with frequent storm systems, rain, and atypically high inversion heights,” said Nahal Mogharabi, a spokeswoman for the South Coast air district. “It is possible that this was partially due to reduced emissions, but meteorology likely played a much larger role.”
L.A. pollution levels crossed back into the “moderate” range on March 28. In the Inland Empire, where pollution is typically higher, the good air quality lasted a shorter 10 days before jumping back to moderate levels.
At least partly responsible for the recent gains, experts say, are restrictions from the pandemic that have brought abrupt and dramatic reductions in the vehicle traffic that is the biggest source of California’s air pollution.
Data from roadside monitors in Southern California show that passenger vehicle traffic has decreased by one-third under the stay-at-home orders, while trucks — which contribute a greater share of smog-forming emissions — have declined by about 20%, according to air quality officials. In the Bay Area, regulators have reported more than 60% fewer cars on the road.
Cargo volumes at the Port of Los Angeles, a major hub for polluting trucks, ships and trains, were down 31% in March compared to March 2019.
Emissions have plummeted too, with researchers detecting roughly 30% declines in nitrogen dioxide and other key air pollutants in Southern California and the Bay Area. Satellite measurements have revealed similar drops in air pollution during lockdowns in the northeastern U.S., China and India.
But in Southern California, experts say that favorable weather has made it hard to disentangle the effect of reduced emissions.
For example, an analysis of satellite measurements by Cohen and his team found a 32% decline in levels of nitrogen dioxide pollution in Southern California in the three weeks after the stay-at-home orders compared to the three weeks before. But they also found a 26% reduction between the same time periods in 2019, suggesting that spring weather played a big role.
“Driving is dramatically lower,” Cohen said, “but differences in weather between this year and last still make it hard to put numbers on how much cleaner the air is because of the shelter-in-place.”
Weather is such a dominant factor in determining the region’s smog levels, according to the South Coast air district, that it can more than double the pollutant concentrations we are breathing, even when emissions remain constant.
Other evidence is emerging, nonetheless. The South Coast air district is starting to see below-average levels of key pollutants that form ozone, as well as days where concentrations of fine-particulate matter, nitrogen dioxide or carbon monoxide are lower than any recorded within 15 calendar days before and after that date in the past five years.
“However, we still expect to have ozone exceedances this year, even if emissions are reduced throughout the summer,” Mogharabi said.
Southern California’s air quality has, in fact, reached unhealthy levels during the shutdown.
On April 1, the region logged its first bad air day since stay-at-home-orders took effect. It racked up a string of additional violations since last week as temperatures climbed into the 90s and boosted smog levels. Even under lockdown, ozone pollution has exceeded federal health standards across the region, including in downtown Los Angeles, the San Fernando Valley, Pasadena, Pomona, Riverside and San Bernardino.
How can that be? The explanation lies in how a key ingredient in L.A.'s pollution is formed. Ozone, the lung-searing gas in smog that triggers asthma attacks and other health problems, is not emitted directly, but forms when pollution — from cars, trucks, factories and other combustion sources — bakes in the heat and sunlight.
Higher temperatures boost those smog-forming chemical reactions in the atmosphere. Combine that with dry, still conditions with strong inversion layers, and you get more pollution trapped near the ground where people are breathing.
That’s why more ozone violations are sure to come as the warm season brings the more stagnant, pollution-trapping pattern that besets Southern California for much of the year. But regulators and scientists could see a clearer signal of the effect of lowered emissions as time goes on, such as bad air days that are forecast but don’t materialize.
The temporary drop in pollution has surely benefited people’s health during a time when healthy lungs are critical to confront the new coronavirus. But those gains have, of course, come at a heavy cost, including sickness, death, lost jobs and restricted freedom, that have environmentalists, scientists and regulators cautious not to celebrate.
“It’s terrible to get that view by people getting sick,” Cohen said. “It’s not at all how we would design the experiment if we had a choice.”
It’s also an unsustainable way to improve air quality, experts point out. If history is any guide, emissions will come roaring back once economic crisis fades, erasing these temporary gains.
Before the pandemic, air quality had been on the decline across the U.S. in recent years, reversing decades of improvement. Southern California has long suffered the nation’s worst ozone pollution.
Adrian Martinez, an attorney at the environmental law nonprofit Earthjustice, said he remains optimistic that experiencing what clean air actually feels like will bring a new moment of clarity and shake off any complacency over cleaning Southern California’s air.
“It’s going to change people’s frame of reference from how much worse it was in the sixties, seventies and eighties, to how do we get back to that time where we could go outside and breathe a deep breath of air and it’s safe?” Martinez said.
Environmentalists at the same time have raised alarms about the perils of loosening air quality protections during the pandemic and economic downturn.
The Trump administration has moved forward with major environmental rollbacks in recent weeks that are expected to hinder progress toward healthful air long after the pandemic wanes. California regulators are also fielding numerous requests to relax air quality rules and delay new regulations to provide relief to industries in upheaval.
South Coast air board Chairman William A. Burke vowed to continue the work of cleaning pollution while being sensitive to both business and environmental concerns, but said he fears air quality will take a nosedive once the economy reopens.
“Because I think that everybody who’s been holding all the goods that haven’t been shipping during this pandemic are going to let it go,”Burke said. “I don’t think there’s enough trucks to carry all the stuff that Americans and Californians are going to need.”
Burke predicted a surge in complaints to the district’s air pollution hotline, 1-800-CUT-SMOG, “because I think that commerce will spring back into action.”