When the US Embassy in Beijing began sharing readings from an air-quality monitor on its roof in 2008, it started a programme that would eventually give the public access to data from more than 80 US embassies and consulates worldwide.
In March 2025, the Trump administration halted the State Department monitoring programme, citing budget constraints.
Zoey Zhou, an assistant professor of climate at Columbia University and one of the authors of a new study, said: “This is such a big loss. Not only for the data, but also for the health impacts and also for accountability.”
The study, published Monday in the Proceedings of the National Academy of Sciences, found that air pollution in 46 of the cities rose by between 24 and 33 percent after the monitoring ended.
The embassy network had supplied independent data in places where local monitoring was limited. In Southeast Asia, sub-Saharan Africa and South Asia, the monitors were often the only credible source of air-quality information available to the public.
Zhou’s team found no major pollution trend during the 300 days before reporting stopped. By September 2025, aerosol optical depth around the 46 cities had increased by about 33 percent. Pollution then appeared to ease. By November 2025, it remained around 24 percent above its level before the programme ended.
The largest average increases were recorded at sites in Southeast Asia, sub-Saharan Africa and South Asia. The study pointed to cities including Manila, Rangoon and Vientiane, and found bigger increases where other monitoring options were scarce.
A 33 percent rise in aerosol optical depth corresponds to approximately 2 micrograms per cubic meter of PM2.5. These tiny particles can lodge deep in the lungs and enter the bloodstream, contributing to serious health problems. The World Health Organization’s global air quality guidelines recommend that average PM2.5 levels do not exceed 5 micrograms per cubic meter each year.
The evidence builds on earlier research into the embassy programme. A 2022 study of 50 cities where US embassies began air-quality monitoring found significantly lower pollution and more local Google searches for terms such as ‘air quality’. Andrea La Nauze, an associate professor of economics at Deakin University in Australia who wrote that study, said: “The US Embassy monitoring program provided high quality and credible information to the public about the state of their air, often where there were no other sources of such information”.
A previous study had also linked the State Department programme to lower pollution levels in the cities where it operated. The new findings show a rise after the data stream ended, though they do not set out how much of that change resulted directly from the loss of public monitoring rather than other policy changes.
The State Department did not respond to requests for comment on the findings or on whether the programme would resume. It has said it intends to restore public access to air-quality monitoring data, without giving a date.
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