Air pollution crossing U.S. state lines, causing premature deaths

The Rocky Mountains are pictured as a layer of air pollution hangs over Denver, Colorado

By Julie Steenhuysen

(Reuters Health) - A study 11 years in the making has found that half of premature deaths related to air pollution in U.S. states are caused by pollution that originated from another state, U.S. researchers reported on Wednesday.

The study, published in Nature, is the first to calculate how pollution crossing state lines impacts early deaths in each state, said coauthor Steven Barrett, an associate professor of aeronautics and astronautics at Massachusetts Institute of Technology in Cambridge.

Globally, an estimated 4.2 million premature deaths are linked to outdoor air pollution, mainly from heart disease, stroke, lung disease, and acute respiratory infections in children, according to the World Health Organization.

Efforts to address outdoor air pollution have largely focused on relationships between local sources of pollution and local air quality. What Barrett and colleagues found is that cross-state pollution accounts for about half of all premature, pollution-related deaths.

"Pollution is even less local than we thought," Barrett said in comments emailed to Reuters Health.

The computer model his team developed for the study took weather patterns and atmospheric chemistry processes into account and tied those to data on human exposures and health risks. They used this to track how each state in the contiguous U.S. affects pollution and health outcomes in every other state.

The model included data from 2005, 2011 and 2018 on different sources and types of pollutants, such as sulfur dioxide, ozone and fine particulates, from seven emissions sectors, including electric power generation, road transportation, marine, rail, aviation, and commercial and residential sources.

The team found that electric power plants - which emit sulfur dioxide from smokestacks - were the biggest contributor to deaths related to pollution from other states. In 2005, sulfur dioxide from power plants was involved in 75% of cases of premature deaths from out-of-state pollutants.

One bright note is that regulatory changes to curb emissions since 2005 have reduced the number of early deaths related to air pollution by 30%.

The team also found the proportion of premature deaths from out-of-state emissions is dropping - falling from 53% in 2005 to 41% in 2018.

Not all states contribute to the problem equally, the study showed. Many states in the northern midwest, such as Wyoming and North Dakota, are "net exporters" of pollution-related health impacts, in part because of their low populations relative to the amount of emissions they generate.

States on the east coast, where winds sweep emissions eastward, are "net importers" of air pollution. New York is hit especially hard, with 60% of early deaths related to air pollution arising from out-of-state emissions.

Dr. Peter Muennig, who studies health effects of air pollution at Columbia University's Mailman School of Public Health in New York City, applauded the work.

"This is a great study," Muennig, who was not involved in the research, said in an email.

"Because this study looks at changes over time and geographic region, it goes far beyond simple correlation," he said.

A key limitation, he said, is that the data are based on models, which can be complex and prone to error.

Barrett said the researchers tried to quantify areas of uncertainty in the models.

"Like with climate change, not knowing the exact number doesn't mean you don't take action, because uncertainty cuts both ways and reality could be worse than our central estimates, as well as better," he said.

Barrett said the team has a big archive of data that policymakers could use to curb some of these deaths.

SOURCE: Nature, February 12, 2020.