Study finds pollution spiked after State Department ended embassy monitoring

Researchers estimate 4% PM2.5 increase in affected cities

Air pollution rose sharply in dozens of cities around the world in the months after the State Department shut down its embassy air quality monitoring program, according to a study published Monday in the Proceedings of the National Academy of Sciences. Researchers estimate the increase translates to a roughly 4% rise in PM2.5, the fine particulate matter linked to lung and cardiovascular harm.

The State Department launched its embassy air quality initiative in 2008 with a single monitor on the U.S. Embassy in Beijing. Over the following 17 years, the program expanded to more than 80 embassies and consulates, providing public data on pollution in many low- and middle-income countries that had limited or no monitoring of their own. Earlier research suggested that the program contributed to measurable improvements in air quality, especially in countries where alternative monitoring was scarce.

The Trump administration shuttered the program in March 2025, citing monetary costs. When the monitoring stopped, Columbia climate researcher Zoe Yiyuan Zhou saw an opening for a rare kind of study. “It’s such a rare case to study this drawback,” Zhou said. While there is ample evidence of the benefits of increased monitoring, she said, there are not many examples of a sudden falloff of surveillance.

Zhou and her colleagues compared air pollution levels before and after U.S. monitoring ceased across 46 cities. Because on-the-ground measurements were not consistently available for the post-shutdown period, the team relied on satellite data for both halves of the comparison.

The researchers found no significant trends in air pollution over the 300 days preceding the end of U.S. reporting. But roughly three to four months after reporting ended, pollution had increased by an average of about 30%. Satellite data is not a perfect substitute for ground-level monitors, and the researchers estimate their satellite measurements translate to approximately a 4% increase in PM2.5.

The increase was highest in Southeast Asian cities, including Manila in the Philippines, Rangoon (Yangon) in Myanmar, and Vientiane in Laos. Pollution also spiked more sharply in cities with fewer monitoring alternatives.

The study cannot determine why pollution increased after monitoring stopped. The researchers offered several possible mechanisms. For countries with nascent monitoring programs, U.S. data may have prompted more regulatory action; removing the data may have removed a form of third-party auditing that encouraged compliance; and in industries where cutting pollution costs money, the absence of public data may have created an opportunity to skip those costs.

“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?’” said Eric Zou, an environmental economist at the University of Michigan.

The researchers also found some potentially hopeful news. Pollution levels appeared to decline somewhat after peaking about three to four months after monitoring stopped. Zhou said it is difficult to determine why this occurred or whether the trend will continue. She suspects it may reflect other forms of monitoring — by individuals or local governments — coming online in the wake of the U.S. withdrawal.

Not all areas can readily replace what was lost, she said, especially in regions where air quality monitoring is new.

Andrea La Nauze, an environmental economist at Deakin University in Australia who has researched the benefits of the program but was not involved in this study, called the findings significant. “It’s a great study, high quality. And it’s a real pity,” she said. The program “led to sustained improvements in air quality that were continuing to increase after 10 years,” she added, and the new research suggests those improvements are not guaranteed if monitoring stops.

“That magnitude is certainly concerning,” La Nauze said. “Particulate matter is a serious and dangerous thing, and being exposed to it is not good.”

Zhou said the findings underscore the role of public data in environmental accountability. “Data is just so important,” she said. “Having access to information is necessary to make sure that these previous gains can continue. Public information creates accountability.”

The State Department did not respond to a request for comment in time for publication.