The Environmental Protection Agency (EPA) is announcing the availability of a final document titled, ``Supplement to the 2019 Integrated Science Assessment for Particulate Matter (Final)'' ([EPA/ 600/R-22/028]). The document was prepared by the Center for Public Health and Environmental Assessment (CPHEA) within EPA's Office of Research and Development (ORD) as part of the reconsideration of the EPA's 2020 final action reviewing the National Ambient Air Quality Standard (NAAQS) for particulate matter (PM). The Supplement represents a targeted review of peer-reviewed studies published since the literature cutoff date (i.e., ~January 2018) of the 2019 Integrated Science Assessment for Particulate Matter (PM ISA). The Supplement and the 2019 p.m. ISA provide the scientific basis for EPA's decisions, in conjunction with additional technical and policy assessments, for the reconsideration of the EPA's 2020 review of the NAAQS and the appropriateness of possible alternative standards.