A proposal to strengthen the ambient (fine particulate matter) PM 2.5 air quality standard has been put forth by the Environmental Protection Agency. In addition, the EPA has also proposed a revision for other aspects related to PM standards, like monitoring requirements and the Air Quality Index (AQI). The National Ambient Air Quality Standards (NAAQS) were previously reviewed in 2020, under the prior U.S. administration, at which time the EPA upheld the existing standards of PM 2.5 and PM 10. In June of 2021, under the current administration, the agency announced it would be re-examining these PM standards.
Source: https://dieselnet.com/