Under the Clean Air Act (CAA), the Environmental Protection Agency (EPA) is required to conduct periodic review of the air quality standards and the science upon which they are based. The CAA requires EPA to review the ozone standard every five years. The review is a lengthy process and includes several major steps. Once the EPA has completed this review, they determine whether to take action to introduce a new standard, which triggers a proposal of the new rule and a public comment period before a new standard is adopted. To learn more about how the EPA reviews the National Ambient Air Quality Standards and proposes new standards, visit https://www.epa.gov/criteria-air-pollutants/process-reviewing-national-ambient-air-quality-standards.