EPA Declares Plumas County Attained Fine Particulate Standard
The Portola nonattainment area in California met the 2012 annual fine particulate matter standard by the 2025 deadline.
The Environmental Protection Agency has finalized a determination that the Portola nonattainment area in Plumas County, California, attained the 2012 annual fine particulate matter (PM 2.5) national ambient air quality standard. The area met this standard by the December 31, 2025 "Serious" area attainment date.
This finding relies on ambient air quality monitoring data collected from 2023 through 2025. The EPA also finalized a clean data determination based on that same three-year window and an evaluation of preliminary monitoring data from 2026.
To qualify for redesignation to attainment, the Portola area met Clean Air Act requirements, which included an approved maintenance plan. This plan must demonstrate that the area will continue to meet the 1997 annual PM 2.5 standard for 10 years.
The rule becomes effective September 14, 2026.