Ozone (O3) is an air pollutant produced by sunlight-driven reactions involving the oxides of nitrogen and volatile organic compounds. The population of many large metropolitan areas in the US is exposed to high levels of O3, particularly in the summer months. Individuals exposed to O3 levels in human experiments at higher than common ambient levels develop reversible reductions in lung function often associated with symptoms, such as airway hyperreactivity and lung inflammation. Animal models have helped characterize potential mechanisms of lung injury from O3 exposure. Defining the adverse effects of chronic exposure to ambient levels of O3 on lung function and disease have been challenging, in part due to the presence of co-pollutants, such as particulate matter. The US Environmental Protection Agency's 1997 revised standard for O3 (0.08 ppm averaged over 8 hours) is designed to provide better protection to susceptible individuals. The revised standard is being implemented following the failure of court challenges.
Department of Internal Medicine, Division of Pulmonary and Critical Care Medicine, Medical College of Wisconsin and Zablocki Veterans Affairs Medical Center, Milwaukee, Wisconsin, USA.
Correspondence to Ralph M Schapira, MD, Milwaukee Veterans Affairs Medical Center, Section of Pulmonary and Critical Care, CC-111, 5000 West National Avenue, Milwaukee, WI 53295, USA; e-mail: firstname.lastname@example.org