What’s the air quality in New Delhi, Jakarta or Buenos Aires? Until Tuesday, the United States Embassy in those cities could have told you.

But the Trump administration has effectively shut down a global air quality monitoring program, ending more than a decade of public data-collection and reporting from 80 embassies and consulates worldwide.

The information has supported research, helped thousands of foreign service officers working abroad to decide if it was safe to let their children play outdoors, and has directly led to air quality improvements in countries like China.

The State Department said in an email that the program was being suspended “due to budget constraints.”

Health officials and environmental experts said ending air quality monitoring would hurt Americans overseas, particularly those who work for the U. S. government.

“Embassies are situated sometimes in very difficult air quality circumstances,” said Gina McCarthy, who led the Environmental Protection Agency in the Obama administration.

She, along with John Kerry, who was secretary of state at the time, expanded globally what had been a limited but transformational air monitoring effort in China.

“You can’t send people in risky areas without information,” Ms. McCarthy said. “We generally think of risky areas as war zones or something like that. But it’s equally important to look at whether their health is deteriorating because they are in a place with such poor air quality.”

In 2008, United States officials in Beijing installed air quality monitors on the roof of the American Embassy and eventually began posting data hourly about levels of one of the most dangerous types of air pollutants, tiny particulate matter known as PM 2.5. The particles can enter the lungs and bloodstream and have been linked to respiratory problems, heart attacks and other serious health effects.

The information revealed what local residents already knew: that pollution was far worse than the Chinese government would acknowledge.

“All hell broke loose,” Ms. McCarthy recalled. The Chinese government tried unsuccessfully to pressure the American Embassy to stop making the data public, calling the readings illegal and attacking the quality of the science, she and others said.

Ultimately, Chinese officials relented. They put in place their own monitoring system, increased the budget for pollution control and eventually began collaborating with the United States on air quality projects.

In 2015, Ms. McCarthy and Mr. Kerry announced that they would expand air monitoring across American diplomatic missions, arguing that air pollution, like climate change, required global data and solutions.

A 2022 study published in the Proceedings of the National Academy of Sciences found that when U.S. embassies began tracking local air pollution, host countries took action. The study found that, since 2008, there had been substantial reductions in fine particulate concentration levels in cities with a U.S. monitor, resulting in a decrease in the risk of premature death for more than 300 million people.

Dan Westervelt, a research professor at Columbia University’s Lamont-Doherty Earth Observatory, said many countries did not have public air quality monitoring and that the data from the embassies provided researchers with reliable information.

Dr. Westervelt said he had been working on a project through the State Department using air quality data from embassies in five West African countries, but received a stop-work order when President Trump took office in January.

“In my opinion it puts the health of foreign service officers at risk,” he said. “But they’re also hindering potential research and policy.”

The data had appeared on AirNow, a website that was managed by both the E.P.A. and the State Department, and also on ZephAir, a mobile application run by the State Department. On Tuesday the website was offline and no data was being shown on the app.

The State Department said the air monitors at embassies would continue to run for an undetermined length of time but would not be sending live data to the app or other platforms “if/until funding for the underlying network is resolved.”

Embassies and other posts would be able to retrieve historical data through the end of the month, according to an internal email viewed by The New York Times.