"We're making progress, but there are areas and places where these levels are high and still increasing," he said. "People living near very busy roadways are disproportionately affected and have not seen much benefit from the Clean Air Act."
The Clean Air Act directs the EPA to reduce air pollution.
Since it took effect, levels of fine particulate matter have fallen in most areas, but in some areas, air pollution remains too high.
Bhatia, in an accompanying journal commentary, called for more air monitors near busy roadways to compel state governments and regional planning agencies to take steps to reduce pollution near those sources.
"If you don't have monitors near roadways, they are not forced to take action," Bhatia said.
Another study in the same journal by researchers at Brown University found that more people were admitted to a Boston hospital for ischemic stroke on days when levels of fine particulate air pollution were high. Ischemic stroke occurs when a blood vessel leading to the brain becomes blocked.
Ischemic stroke risk was 34 percent higher on days with "moderate" pollution levels than days with "good" levels, according to the EPA's Air Quality Index, the researchers found.
The U.S. Environmental Protection Agency has more on air pollution.
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