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EPA Issues Final Rule Addressing Particulate Matter National Ambient Air Quality Standards

The Environmental Protection Agency on Feb. 7 issued its final rule reconsidering the particulate matter national ambient air quality standards.

EPA is revisiting the level of the primary (health-based) annual standard for fine particles (PM2.5) from its current level of 12 micrograms per cubic meter to 9 micrograms per cubic meter.

The final rule will retain all other PM standards: primary (health-based) and secondary (welfare-based) 24-hour PM2.5 standards at the level of 35 micrograms per cubic meter, the primary and secondary 24-hour PM10 standards at 150 micrograms per cubic meter and retain the secondary annual PM2.5 standard at the level of 15 micrograms per cubic meter.

EPA is also finalizing changes to the Air Quality Index (AQI) to improve public communications about the risks from PM2.5 exposures.

In addition, EPA changed the monitoring network to enhance air quality protection in communities overburdened by air pollution.

The final rule is available on EPA's website.


After EPA issues the final PM2.5 NAAQS, the agency will issue a memorandum discussing the process for designating an area in attainment or nonattainment of the revised PM2.5 NAAQS.

The memo will discuss the development and submittal of “infrastructure” state implementation plans that demonstrate states have the necessary clean air programs and authorities to meet the revised standard. Additionally, at the effective date of the final rule, all applicants for permits to construct a new major source or major modification of an existing stationary source will need to conduct an air quality analysis that considers the revised PM2.5 NAAQS.

Once the initial area designation process is complete, areas designated nonattainment have a planning obligation to demonstrate attainment and meet the new standard within six years following the nonattainment designations. The Clean Air Act also includes a pathway for states to seek additional time to attain the new standard.


The CAA’s new source review (NSR) permitting program requires industrial facilities to install modern pollution control equipment when built or when making a change that significantly increases emissions. Prevention of significant deterioration (PSD) permitting will continue to apply in existing clean areas until EPA completes the process of designating areas as meeting or not meeting the revised PM2.5 standard (likely in 2026). Only " major " sources need a major source PSD permit when constructing or expanding, and existing sources only need a permit addressing PM2.5 when an expansion project would significantly increase PM2.5 emissions. Permit applicants who received their final PSD permit before the effective date of the new standards will not need to make any adjustments.

However, Facility owners with PSD permits still in process will need to determine if their modeling already demonstrates that their planned project will not cause or contribute to an exceedance of the new standard. If there is no violation, the permit application can continue through review however, if modeling shows that the new emissions would cause or contribute to violating the revised standard, the owner can modify their planned project and what types of emission controls they install. A more detailed modeling assessment must show no violation or that impacts fall below significant levels.


Wildfires have significantly impacted air quality as they have grown in both size and severity. Consequently, the related public health impacts, including ones from smoke exposure, will continue to grow. EPA is keenly aware that states and federal land managers are increasingly seeking to use prescribed fires to lower the risk of wildfires. 

EPA recently issued a suite of tools for public comment. The tools would help air agencies evaluate the impacts of exceptional events and develop exceptional events’ demonstrations. EPA anticipates that these tools will be helpful for PM2.5 implementation, and they are expected to help states in developing exceptional events’ demonstrations for both the annual and 24-hour PM2.5 standards. The tools include the; Data visualization and comparison tools, PM2.5 Wildfire Exceptional Events Tiering Document, and Prescribed Fire Demonstration Example. 

More information about these tools is available at https://www.epa.gov/air-quality-analysis/treatment-air-quality-monitoring-data-influenced-exceptional-events.

Monitoring Network and Air Quality Information

EPA is modifying the PM2.5 monitoring network design criteria to include an environmental justice factor. For areas with additional required State or Local Air Monitoring Stations, a monitoring station will be sited in an at-risk community where there are anticipated effects from sources in the area.

EPA is updating the Air Quality Index (AQI) for PM2.5.

The AQI is EPA’s color-coded tool used by state and local governments to help inform the public about current and daily air quality and recommends steps that individuals can take to reduce their exposure to air pollution.

The AQI converts PM2.5 concentrations to a number on a scale from 0 to 500. EPA is updating some of the breakpoints to reflect the change to the annual standard and the newest scientific information.

The final rule becomes effective 60 days after publication in the Federal Register.

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