Half of U.S. states export air pollution to neighboursA new study has used an airshed approach to track how air pollution crosses state lines, revealing that over half of all U.S. states are net exporters of pollution-linked premature deaths, while around a third contribute zero net pollution to neighbouring states. In contrast, Western states with mountain barriers, like California, see more localised pollution impacts, though they can still receive significant pollution from neighbours like Nevada. Using population and pollution exposure data, the team calculated which states are net contributors or receivers of harmful PM₂.₅. Florida is the largest exporter of cross-state pollution, particularly affecting Georgia and the Carolinas, followed by Vermont and Iowa. Marcantonio said: ‘Our analysis gives states an evidence-based way to demonstrate when cross-state pollution exceeds safe thresholds and threatens public health.