A State Department decision to end air-quality monitoring at U.S. embassies and consulates was followed by a sharp increase in pollution across dozens of cities, according to a study published this week in the Proceedings of the National Academy of Sciences. Researchers examined satellite measurements from 46 cities before and after the program ended in March 2025. They found no significant pollution trend during the 300 days before the shutdown. About three to four months after U.S. reporting stopped, pollution levels increased by an average of about 30%, with estimates ranging from 24% to 33%. The study’s satellite measurements are not a direct replacement for ground-level monitoring. The researchers estimated that the increase corresponded to roughly a 4% rise in exposure to PM2.5, fine particles that can travel deep into the lungs and enter the bloodstream. PM2.5 exposure is associated with cardiovascular and respiratory disease and other serious health problems. The largest increases occurred in Southeast Asian cities, including Manila in the Philippines, Yangon in Myanmar and Vientiane in Laos. Pollution rose more in places with few alternative monitoring systems, the researchers reported. The State Department ended the initiative, which officials launched in Beijing in 2008, citing its cost. The program eventually expanded to more than 80 embassies and consulates around the world. In countries with limited air-quality infrastructure, the publicly available readings gave residents, regulators and researchers information that otherwise might not have existed. Eric Zou, an environmental economist at the University of Michigan who has studied the effect of pollution information, said the Beijing monitor helped many residents recognize that what they had considered fog or bad weather was dangerous air pollution. Public readings, he said, can increase demand for cleaner air and create pressure for government action. The findings also suggest that monitoring may affect pollution even when it does not directly regulate emissions. Zoe Yiyuan Zhou, a climate researcher at Columbia University and a co-author of the study, said U.S. monitors may have served as an outside accountability mechanism in countries where local systems were weak. Without scrutiny, businesses may have fewer incentives to pay for pollution controls, she said. Pollution levels appeared to decline somewhat after reaching a peak several months after the shutdown, although researchers said it is too soon to know whether that improvement will last. Zhou said the decrease could reflect local governments or residents establishing other monitoring systems after the U.S. withdrawal. Andrea La Nauze, an environmental economist at Deakin University in Australia who was not involved in the research, called the study high quality and said it raised concerns that gains in air quality may not continue when monitoring disappears. The State Department did not provide a response before publication. The study’s broader lesson is that environmental information is not merely a record of harm. When pollution data is public, communities can use it to demand cleaner air, challenge official assurances and press polluters to change. When that information vanishes, those forms of accountability become harder to sustain.