"On November 26, 2014, the Environmental Protection Agency (EPA) announced proposed revisions to the National Ambient Air Quality Standards (NAAQS) for ground-level ozone. If finalized, the proposal would set more stringent standards, lowering both the primary (healthbased) and secondary (welfare-based) standards from the current 75 parts per billion (ppb) to somewhere in a range of 65 to 70 ppb. This report discusses the standard-setting process, the specifics of the current and past reviews, and issues raised by the proposal. NAAQS are standards for outdoor (ambient) air that are intended to protect public health and welfare from harmful concentrations of pollution. If EPA changes the primary standard for ozone to a lower level, it would be concluding that protecting public health requires lower concentrations of ozone pollution than were previously judged to be safe. In high enough concentrations, ozone aggravates heart and lung diseases and may contribute to premature death. Ozone also can have negative effects on forests and crop yields, which the secondary (welfarebased) NAAQS is intended to protect. NAAQS do not directly limit emissions of a pollutant; rather, they set in motion a long process in which states and EPA identify areas that do not meet the standards, and states prepare implementation plans to demonstrate how emissions will be lowered sufficiently to reach attainment."
CRS Report for Congress, R43092