Polluted air causes roughly 200,000 early deaths each year across the United States, researchers from the Massachusetts Institute of Technology conclude after tracking emissions from industrial smokestacks, vehicle tailpipes, marine and rail transport, and commercial and residential heating.

Emissions from road transportation are the most deadly, causing 53,000 premature deaths a year, followed by power generation, with 52,000 deaths, finds the study by MIT’s Laboratory for Aviation and the Environment.

Lead researcher Steven Barrett, an assistant professor of aeronautics and astronautics at MIT, said that a person who dies from an air pollution-related cause typically dies about a decade earlier than he or she otherwise might have.

“In the past five to 10 years, the evidence linking air-pollution exposure to risk of early death has really solidified and gained scientific and political traction. “There’s a realization that air pollution is a major problem in any city, and there’s a desire to do something about it,” Barrett said.

California suffers the worst health impacts from air pollution, with about 21,000 early deaths annually, mostly attributed to road transportation and to commercial and residential emissions from heating and cooking, the researchers learned from their state-by-state analysis.

Of the 5,695 U.S. cities where the scientists mapped local emissions, they found the highest emissions-related mortality rate in Baltimore, where 130 out of every 100,000 residents is likely die in a given year due to long-term exposure to air pollution.

The team based its research on emissions data from the U.S. Environmental Protection Agency’s National Emissions Inventory, a catalog of emissions sources nationwide. The researchers collected data from the year 2005, the most recent data available at the time of the study.

While the data reflects conditions in 2005, Barrett says the results likely represent today’s pollution-related health risks.

Barrett’s team divided the raw data into six emissions sectors: electric power generation; industry; commercial and residential sources; road transportation; marine transportation; and rail transportation.

They fed the emissions data from all six sources into an air-quality simulation of the impact of emissions on particles and gases in the atmosphere.

To determine where emissions had the greatest impact, they removed each sector of interest from the simulation and observed the difference in pollutant concentrations.

The team then overlaid the resulting pollutant data on population-density maps of the United States to see which populations were most exposed to pollution from each source.

To explain why 53,000 early deaths a year were attributed to car and truck exhaust while only 52,000 premature deaths annually were blamed on power plants, the researchers reasoned that “vehicles tend to travel in populated areas, increasing large populations’ pollution exposure, whereas power plants are generally located far from most populations and their emissions are deposited at a higher altitude.”

Pollution from electricity generation had the greatest impact on premature death in the east-central United States and in the Midwest because Eastern power plants tend to use coal with higher sulfur content than Western plants, the researchers said.

Most premature deaths due to commercial and residential pollution sources, such as heating and cooking emissions, occurred in densely populated regions along the East and West coasts.

Pollution from industrial activities was highest in the Midwest, roughly between Chicago and Detroit, as well as around Philadelphia, Atlanta and Los Angeles.

Industrial emissions also peaked along the Gulf Coast region because the largest oil refineries in the United States are located there.

Southern California saw the largest health impact from shipping and port activities, with 3,500 related early deaths a year.

Emissions-related deaths from rail activities were comparatively slight, and spread uniformly across the east-central part of the country and the Midwest.

Jonathan Levy, a professor of environmental health at Boston University who was not involved in the research, says Barrett’s calculations for the overall number of premature deaths related to combustion emissions agree with similar conclusions by the Environmental Protection Agency.

“A public-health burden of this magnitude clearly requires significant policy attention, especially since technologies are readily available to address a significant fraction of these emissions.” said Levy.