On March 10, 2015, the Environmental Protection Agency (USEPA) issued a proposed rule regarding the implementation of the 2012 PM2.5 national ambient air quality standard (NAAQS). The proposed rule provides details on how the local air agencies shall meet the statutory state implementation plan (SIP) requirements that apply to areas designated nonattainment for any PM2.5 NAAQS. It also clarifies the specific attainment planning requirements that would apply to PM2.5 NAAQS nonattainment areas based on their classification (either Moderate or Serious), and the process for reclassifying Moderate areas to Serious. Areas in Arizona that are currently designated as nonattainment for the 2006 PM2.5 NAAQS are West Central Pinal County and Nogales.

USEPA is seeking comments on three potential approaches regarding PM2.5 precursors. These three approaches call for attainment planning analyses and technical demonstrations through which states can demonstrate that a particular PM2.5 precursor does not need to be regulated for attainment purposes. However, states may also choose not to conduct any analysis and instead require controls for all PM2.5 precursors, including sulfur dioxide (SO2), oxides of nitrogen (NOx), volatile organic compounds (VOC) and/or ammonia (NH3).

USEPA also proposed to revoke the 1997 primary annual PM2.5 NAAQS and transition to the 2012 primary annual PM2.5 NAAQS. USEPA did not propose to revoke the 1997 secondary annual PM2.5 NAAQS in this action.

This proposed rule has not been published in the Federal Register yet. Public comments will be accepted within 60 days from the date of publication in the Federal Register.