The Public Health Air Quality Act of 2025 seeks to enhance public health protection by significantly expanding air quality monitoring and data accessibility. It directs the Environmental Protection Agency (EPA) to establish a Health Emergency Air Toxics Monitoring Network , requiring fenceline monitoring of hazardous air pollutants at not fewer than 100 high-priority stationary sources. These sources are identified based on their contribution to health risks, such as cancer or noncancer hazards, or their proximity to vulnerable communities. The EPA must ensure that monitoring begins within 18 months and continues for at least six years, with data made publicly available online within seven days of collection. The bill mandates the use of the best available emissions measurement systems, including continuous, real-time monitoring for the highest-emitting or riskiest sources. It also requires the EPA to regularly review, update, and approve new test methods to ensure effective monitoring of all relevant pollutants. Furthermore, the bill compels the EPA to promulgate regulations for specific source categories, requiring continuous emissions and fenceline monitoring to ensure compliance with hazardous air pollutant standards. These regulations will establish corrective action levels at fencelines, triggering root cause analyses and remedial actions if exceeded. All monitoring equipment must be regularly maintained, and owners or operators must report measured emissions data and any exceedances, which will be publicly accessible. The legislation also strengthens the National Ambient Air Quality Standards (NAAQS) monitoring network by requiring the deployment of 80 additional NCore multipollutant monitoring stations, with at least 40 located in vulnerable communities. It also mandates 100 additional Federal reference method monitors in unmonitored or undermonitored areas to detect nonattainment. The EPA must assess the status of existing ambient air quality monitors and develop a plan for their repair or replacement. To further enhance monitoring, the bill directs the EPA to facilitate the use of satellite monitoring data for determining compliance with NAAQS for certain pollutants. It also requires the deployment of at least 1,000 low-cost community air quality systems in disproportionately impacted areas. If these systems detect pollution levels nearing NAAQS thresholds, Federal reference method monitors must be installed in those locations. Finally, the Act requires the EPA to amend regulations to expand reporting requirements for hazardous air pollutants, including perfluoroalkyl and polyfluoroalkyl substances (PFAS), from all major and non-major sources. It also mandates the restoration or creation of a nationwide geospatial mapping tool, similar to EJSCREEN, to integrate and provide public access to all collected air quality data. The bill authorizes significant appropriations for these monitoring and reporting initiatives, emphasizing that no exemptions from compliance will be granted under its provisions.