From the Summary: "On October 1, 2015, the Environmental Protection Agency (EPA) finalized revisions to the National Ambient Air Quality Standards (NAAQS) for ground-level ozone. The rule sets more stringent standards, lowering both the primary (health-based) and secondary (welfare-based) standards from 75 parts per billion (ppb) to 70 ppb. This report discusses the standard-setting process, the specifics of the most recent reviews, and issues raised by the final rulemaking."
CRS Report for Congress, R43092
Federation of American Scientists: http://www.fas.org/sgp/crs/index.html