Advancing the Framework for Assessing Causality of Health and Welfare Effects to Inform National Ambient Air Quality Standard ReviewsAdvancing the Framework for Assessing Causality of Health and Welfare Effects to Inform National Ambient Air Quality Standard Reviews As part of its responsibilities under the Clean Air Act, the U. S. Environmental Protection Agency sets National Ambient Air Quality Standards (NAAQS) for the air pollutants carbon monoxide, lead, oxides of nitrogen, particulate matter, ozone, and sulfur dioxide. EPA uses a "weight of evidence approach" to evaluate