Study co-author Jason West of the University of North Carolina at Chapel Hill said some suggest a changing climate might exacerbate the effects of air pollution and increase death rates, but the study showed this has a minimal effect.
"Our estimates make outdoor air pollution among the most important environmental risk factors for health," West said in a statement. "Many of these deaths are estimated to occur in East Asia and South Asia, where population is high and air pollution is severe."
The study, published in the journal Environmental Research Letters, estimated more than 2 million die each year from human-caused ozone and fine particulate matter.
Low-level ozone is formed by the reaction of sunlight on air containing hydrocarbons and nitrogen oxides that react to form ozone directly at the source of the pollution or many miles downwind. Fine particulate matter are tiny particles suspended in the air that can penetrate deep into the lungs, causing cancer and other respiratory disease, West said.
The researchers used 14 climate models to simulate the concentrations of ozone and fine particulate matter in the years 2000 and 1850.