A 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.
The research, led by Wenxu Liao, Richard Marcantonio, and Paola Crippa from the University of Notre Dame, uses a data-driven model to map how PM₂.₅ travels across the contiguous United States.
Unlike political borders, airsheds are defined by atmospheric flow, topography and pollution concentrations, offering a dynamic view of where pollution comes from and where it ends up.
Between 1998 and 2022, while national PM₂.₅ levels fell by about 35% and overall premature deaths declined, the share of deaths caused by cross-state pollution remained stubbornly steady at around 40%, meaning that even as air quality improves overall, the burden of pollution transported from other states has not diminished.
The study identifies clear regional patterns: states in the industrial Midwest and along the East Coast – such as Indiana, Ohio and New York – often have large airsheds that export pollution far downwind. 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.
Other exporting states are concentrated across the Upper Midwest, Mid-Atlantic and Southeast, including Wisconsin, Michigan, Indiana, Ohio, Kentucky, West Virginia, Virginia, Tennessee, Mississippi, Alabama and South Carolina, as well as California, Oregon and Washington on the West Coast.
The research arrives amid ongoing legal and regulatory debates over interstate air pollution governance, including recent Supreme Court actions that have paused parts of the EPA’s ‘Good Neighbour’ provision. The authors suggest that airshed-based tools could help policymakers better quantify cross-border pollution and design more effective regional cooperation strategies.
Marcantonio said: ‘Our analysis gives states an evidence-based way to demonstrate when cross-state pollution exceeds safe thresholds and threatens public health. Rather than relying solely on an economic evaluation, policymakers can use clear data on health risks to guide decisions that protect vulnerable residents and communities.’
Crippa added: ‘Our study introduces a simpler, data-driven framework that policymakers and regulators can readily adapt. This is an important improvement upon previous studies, which have had limited scalability and adaptability.’
The full research can be read here.
Photo: Marsha Reid / Unsplash
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