Air pollution contributes to more than 2 million premature deaths globally each year, according to new research published Friday in the journal Environmental Research Letters.
That number is much smaller than some previous estimates, which put the number around 3 million.
Scientists used mathematical models to estimate the effects of fine particulate matter, such as soot, and ozone, the main component of smog.
West and his colleagues concluded that about 470,000 people die each year from ground level ozone, produced by human industrial activities.
Authors concluded that an additional 2.1 million deaths were caused by fine particulate matter resulting from human activity. Many of these common particles have long been linked to cancer and a number of respiratory diseases.
"Our estimates make outdoor air pollution among the most important environmental risk factors for health," said study coauthor Jason West, an assistant professor of environmental science at the University of North Carolina. "Many of these deaths are estimated to occur in East Asia and South Asia, where population is high and air pollution is severe," he said.
The authors noted ways in which climate change could affect air quality, including more or less ozone depending on how wet or arid a region is.
Although different climate models resulted in widely differing forecasts, when these models were averaged together, the effects of climate change were found to be small. The authors wrote that "It cannot be clearly concluded that past climate change has increased air pollution mortality."