The study followed nearly 450,000 people for two decades in 96 metropolitan regions. It analyzed the risk of death from two common parts of air pollution - ozone and fine particulate matter.

The study found that people living in areas like Los Angeles with high concentrations of ozone had a 25 to 30 percent greater annual risk of dying from respiratory diseases including pneumonia and chronic pulmonary disease than those living in the Midwest where ozone levels are low.

Ozone is one of the most widespread pollutants in the world, is formed by a chemical reaction between vehicle exhaust and industrial emissions with sunlight. Authors of the study said the findings justify stronger air quality regulations.