Congress may examine wide-ranging air pollution issues as it deliberates legislation and conductsoversight of the U.S. Environmental Protection Agency (EPA). Oversight of EPA's air pollution work has historically received significant attention in Congress. Such oversight has often examined whether EPA's programs meet the statutory objective to protect human health and the environment from air pollution, how evolving scientific understanding informs Clean Air Act (CAA) decisionmaking, and the degree to which potential tradeoffs exist between public health benefits and compliance costs. Some Members of Congress have also raised concerns about potential disproportionate impacts on communities located near sources of emissions, and related concerns about whether CAA standards are protective of vulnerable individuals (e.g., children, pregnant women, the elderly, and persons with preexisting health conditions).Congress may also consider legislation to address air pollution issues and EPA's CAA authority. Recent Administrationshave interpreted CAA authority in different, and sometimes conflicting, ways. Historically, many of EPA's CAA regulationshave been challenged in court, both by industry and by public health and environmental groups, with various statessupporting each side.Some prominent air topics of potential interest in the 117th Congress are air quality standards, wildfire smoke, hazardous airpollutant standards, and permits. Related issues, such as greenhouse gas (GHG) emissions or other climate change topicsrelevant to the CAA, are not addressed herein.Air Quality StandardsThe CAA requires EPA to review national ambient air quality standards (NAAQS) for common pollutants every five years.The NAAQS review process has evolved over time. In recent years, EPA restructured the NAAQS review process bycompressing the schedule and disbanding a pollutant-specific scientific review panel that has historically advised agency staffduring their reviews. In December 2020, EPA completed its particulate matter and ozone reviews, and finalized rules to retain the current PM and ozone standards. While some supported EPA's efforts to streamline NAAQS reviews, others voicedconcerns that procedural changes compromised the agency's review of the latest science. Congress may consider whetherEPA's review process meets the CAA objectives to review in a timely manner the NAAQS and the science upon which theyare based.Wildfire SmokeWildfire smoke can temporarily increase ambient levels of particulate matter and other air pollutants. These increases may bemeasured by the national network of stationary air monitors. Given the need for real-time air quality information duringwildfire events, monitoring strategies may include some combination of stationary monitors, mobile sensors, or computermodeling to estimate pollution levels. Congress may consider which monitoring strategies effectively inform smokemanagement and public health responses. Congress may also examine how CAA requirements factor into forest management and fire prevention strategies.Hazardous Air PollutantsThe CAA requires EPA to set and periodically review standards limiting hazardous air pollutants (HAPs). Congress mayconduct oversight of EPA's statutorily mandated reviews of regulations to limit HAPs such as ethylene oxide. Another CAAissue involves the potential tension between incentivizing pollution prevention and limiting cumulative emissions. Under a2020 EPA rulemaking, major sources of HAPs can reclassify as "area sources," which are typically subject to lesser controls, after meeting conditions to limit emissions below major source thresholds. Congress may consider the health andenvironmental implications of this rule, including how potential HAP increases may contribute to cumulative exposures incommunities with relatively high environmental burdens.