PM2.5 particulates are fine, inhalable particles or droplets with a diameter of 2.5 microns or smaller. These fine particulates, which are about 30 times smaller than the width of a human hair, can travel deeply into the lungs and cause both short-term and long-term health effects. While larger PM10 particulates can compromise respiratory and cardiac health, smaller particulate matter (PM2.5) poses the greatest risk because it can penetrate deeply into the lungs where it can cause inflammation and damage to the lung tissue.
Air Quality Standards
The Environmental Protection Agency (EPA) develops health-based National Ambient Air Quality Standards (NAAQS) to protect public health and the environment. The EPA revises these health-based standards as more data become available to ensure the standards remain sufficiently protective of public health for the most sensitive individuals.
State Implementation Plans
Within two years after setting or revising NAAQS for criteria pollutants, EPA must designate areas as meeting (attainment) or not meeting (nonattainment) the air-quality standard. EPA’s final designations are based on the most recent three years of air-quality monitoring data, recommendations from the state, and additional technical information. State recommendations are made by the governor and take into account air-quality data, emissions inventories, meteorology, topography, and jurisdictional boundaries.
If an area is not meeting the standard, the state is required to prepare a State Implementation Plan (SIP). The SIP is a comprehensive document that identifies how the state will attain or maintain the NAAQS to comply with the provisions of the Clean Air Act. The SIP includes regulatory and non-regulatory control measures for reaching attainment by a specific deadline. Control measures typically include requirements for Reasonably Available Control Technology (RACT) for industrial sources, rules governing emissions limits for area sources, restrictions on wood-burning, and reliance on improvements in the motor vehicle emission standards.
In 1997, the EPA strengthened the 24-hour standard for PM2.5, lowering it from 65µg/m3 to 35µg/m3. Prior to this change, Utah was in compliance with the 24-hour standard, likely due to the state’s 1991 PM10 SIPs. This new standard went into effect in December 2006. In November 2009, the EPA determined that three areas in Utah were unable to meet the revised 24-hour PM2.5 standard, which required the state to prepare State Implementation Plans (SIPs) for each nonattainment area. These plans ultimately became Utah’s Moderate Area SIPs.