Growing up in Shanghai in the early 1990s, Eric Zou remembers the air.
"I lived a couple of miles next to a chemical plant and it was just really bad, really foggy," he says. "It's the middle of the day, but you can't see the sun."
Intensive industrial activity blanketed many cities in China during the 1990s and 2000s with extremely hazardous air. But Zou, now an environmental economist at the University of Michigan, says that many people didn't really understand this smog as air pollution, or something that could harm them.
"When you have a big smog event, people often talk about that as fog, they think it was just like bad weather," says Zou. One big key to changing that sentiment, he says, was information initially provided by the United States.
In 2008, U.S. officials installed an air quality monitor on the embassy in Beijing and began making the information public. Over time, that helped spur demand for cleaner air, says Zou. "Once you have pollution information, it tends to be that it actually helps people to realize, 'Oh, I actually value air quality.' "
Since 2008, the State Department's monitoring initiative has expanded to more than 80 embassies and consulates. Research suggests that monitoring contributed to measurable improvements in air quality, especially across many low- and middle-income countries with limited monitoring systems of their own.
But in March 2025, the Trump administration shuttered that program, citing monetary costs. Research out this week suggests the move had health costs for the people living in those countries. Over the several months following the shutdown, air pollution levels measured via satellite increased by 24-33%, researchers reported Monday in the journal PNAS.
The State Department did not respond to a request for comment in time for publication.
"It's a great study, high quality. And it's a real pity," says Andrea La Nauze, an environmental economist at Deakin University in Australia who has researched the benefits of the program, but wasn't involved in this study. The program "led to sustained improvements in air quality that were continuing to increase after 10 years," she says.
She says this new research suggests those improvements aren't guaranteed if monitoring stops.
Measuring the consequences of not measuring
When Zoe Yiyuan Zhou first heard the news that the Trump administration was shuttering the embassy air quality monitoring, it struck her as a research opportunity.
"It's such a rare case to study this drawback," says the Columbia University climate researcher. While there's ample evidence of the benefits of increased monitoring, she says there aren't many examples of a sudden falloff of surveillance.
Zhou and her colleagues decided to compare air pollution levels before and after monitoring ceased across 46 cities. Since they didn't have on-the-ground measures of air quality for the latter part of that comparison, they used satellite data for both.
The team found no significant trends in air pollution over the 300 days preceding the end of U.S. reporting. But about three to four months after reporting ended, pollution had gone up, on average by about 30%. Satellite data isn't a perfect substitute for monitors that can measure on-the-ground pollution. The researchers estimate their satellite measurements translate to about a 4% increase in PM2.5 — the small suspended particles that can enter the lungs and bloodstream and cause health problems.
"That magnitude is certainly concerning," says La Nauze. "Particulate matter is a serious and dangerous thing, and being exposed to it is not good."
The increase was highest in Southeast Asian cities, including Manila, in the Philippines, Rangoon in Myanmar and Vientiane in Laos, says Zhao. Pollution also spiked more in cities with fewer monitoring alternatives.
The study can't say why pollution increased after monitoring stopped.
For countries with nonexistent or nascent monitoring programs, U.S. data may have prompted more regulatory action, says Zou. "Maybe the U.S. Embassy was a really strong force, in terms of a third-party auditing mechanism, and once that's removed, people are like 'Now I can just pollute, right?'"
In many industries, it costs money to cut down on pollution, says Zhou. When monitoring stops, companies may see it as an opportunity to cut those costs.
But the researchers did find some potentially hopeful news. Pollution levels seemed to go back down somewhat after peaking about three or four months after monitoring stopped.
It's difficult to say why this decrease happened, Zhou says, or whether the trend will continue. She suspects that it may reflect other forms of monitoring, by individuals or local governments, coming online in the wake of the U.S. withdrawal.
But not all areas may have the ability to readily make up for what's been lost, she says, especially in regions where air quality monitoring is new.
"Data is just so important," says Zhou. "Having access to information is necessary to make sure that these previous gains can continue. Public information creates accountability."
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