SIPs for the 9 µg/m3 PM2.5 Standard

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Introduction

The Clean Air Act (Act) requires the U.S. Environmental Protection Agency (U.S. EPA) to set health-based national ambient air quality standards (NAAQS or standards) for numerous pollutants, including fine particulate matter (PM2.5). On February 7, 2024, U.S. EPA strengthened the annual PM2.5 standard from 12.0 micrograms per cubic meter (µg/m3) to 9.0 μg/m3, based on an integrated assessment of an extensive body of new scientific evidence, which improved the body of knowledge regarding PM2.5-related health effects.

Designations

The first step in addressing the 9.0 μg/m3 standard is designating regions of the State as either attaining or not attaining the new standard. CARB staff are in the process of identifying areas that are anticipated to be nonattainment, attainment after exclusion of exceptional events (e.g., wildfires), borderline attainment, or attainment/unclassifiable for the 9 μg/m3 standard. CARB designation recommendations (e.g. attainment, nonattainment and unclassifiable) will be based on 2023 annual PM2.5 design values (2021-2023 PM2.5 data). CARB will release the proposed PM2.5 designation recommendations along with the boundaries for each area in December 2024. In January 2025, CARB staff will take the PM2.5 designation recommendations to the Board prior to submitting them to U.S. EPA by the February 7, 2025, deadline. A list of nonattainment areas will be provided on this webpage as the designation process progresses.

For more information on designations, please see CARB’s designations page.

Workshop

CARB staff invite you to participate in a public workshop on the evening of September 25, 2024, to kick off the State Implementation Plan (SIP) planning efforts for the 9 µg/m3 PM2.5 standard. This workshop will be the first in a series exploring various aspects of planning for the 9 µg/m3 PM2.5 standard which the State is required to undertake pursuant to the Act. During this first workshop, CARB staff will present key background information on the 9 µg/m3 standard and the science of PM2.5. Staff will also introduce the process for initially designating regions of the State for the purpose of implementing the standard. CARB staff encourage public engagement at this workshop and throughout the planning process, leading to submittal of SIPs to U.S. EPA for designated nonattainment areas in late 2027.

The workshop will be held both in person and on Zoom. The meeting will be conducted in English with Spanish interpretation available. Workshop materials are available below.

Resources

For more information, please see the below links to CARB- and U.S. EPA-created resources on PM2.5 and the 9 ug/m3 PM2.5 standard.