Name two federal regulations that govern ambient air monitoring and reporting in the United States.

• A. The Clean Air Act alone is sufficient to govern ambient air monitoring.
• B. 40 CFR Part 50 regulates NAAQS but does not cover monitoring.
• C. The Clean Air Act and 40 CFR Part 50 (National Ambient Air Quality Standards); 40 CFR Part 53 (Ambient Air Monitoring) is also relevant.
• D. Only state regulations apply; federal regulation is not required.

Answer: (C)

Ambient air monitoring and reporting in the United States are governed at the federal level by the Clean Air Act and the implementing regulations in 40 CFR Part 50 and Part 53. The Clean Air Act provides the authority to set National Ambient Air Quality Standards (NAAQS) and to require states to monitor air quality and report data. The regulations in Part 50 define the NAAQS themselves and how monitoring data are used to determine compliance, including the measurement methods and data interpretation. Part 53 adds detailed requirements for ambient air monitoring, such as method performance criteria, QA/QC, siting, and data validation. Together, these establish both the standards for air quality and the standardized, credible methods and reporting needed to track and communicate ambient air conditions. The other options miss these essential regulatory details or overstate what the Act or Part 50 covers, or incorrectly suggest federal regulation isn’t required.