The United States Environmental Protection Agency (“EPA”) announced on January 6 a proposed rule that will strengthen the National Ambient Air Quality Standard (“NAAQS”) for fine particulate matter.
The EPA previously announced on June 10, 2022 that it was reconsidering the Trump administration’s earlier decision to keep the prime minister2.5 NAAQS Clean Air Act. Note that the particulate standard includes both fine particles (PM2.5) and coarse particles (PM10).
Particulate matter (“PM”) is an umbrella term for a large class of chemically and physically diverse substances that exist as discrete particles (liquid droplets or solids) in a wide range of sizes. It is made up of two main components.
Primary particulate matter or soot is emitted directly into the atmosphere. Secondary particles can also be formed through a secondary process. They could be formed by the condensation of high temperature vapor from vapors generated as a result of chemical reactions involving gas-based precursors.
The largest particles (PM10) are generally the result of mechanical, evaporative and suspension processes. Particulate designated PM2.5 they typically consist of sulfates, nitrates, elemental carbon, organic carbon, compounds, and metals. Due to their small size, these particulates can remain in the air for long periods of time.
Sections 108 and 109 of the Clean Air Act require EPA to identify air pollutants using certain criteria and establish NAAQS for each. Particulate matter is one of six air pollutants currently designated as criteria air pollutants and subject to NAAQS. Section 109 requires EPA to promulgate the primary NAAQS for the pollutants identified in section 108.
Article 109(b)(1) defines a primary standard as one “the achievement and maintenance of which, in the judgment of the administrator, based on the criteria and allowing for an adequate margin of safety, are requirements to protect public health”. The margin of safety requirement addresses the uncertainties associated with available inconclusive scientific and technical information, as well as providing a reasonable degree of protection against adverse effects that may have gone undiscovered.
Section 109(d)(1) of the Clean Air Act mandates periodic review of each NAAQS. Depending on the results of the review, EPA must determine whether existing air quality criteria and the NAAQS should be revised. EPA review of PM and PM2.5 is an example of this review process.
Rule proposed by EPA on Jan. 6 solicits comments on strengthening annual primary PM2.5 standard from a level of 12 micrograms per cubic meter to a level of between 9 and 10 micrograms per cubic meter. This is said to be driven by the federal agency’s belief that it reflects the most recent health data and scientific evidence. It’s also collecting comments on the full range (between 8 and 11 micrograms per cubic meter) that it says is included in the latest report from the Scientific Advisory Committee on Clean Air.
The EPA proposes maintaining the 24-hour primary PM10 standards and the current secondary standards (based on welfare) for both PMs2.5 and PM10.
The proposed rule also provides for the updating of monitoring requirements. This includes changing the PM2.5 monitor network design criteria to include the environmental justice factor. The EPA says the factor would explain the proximity of populations at higher risk of PM2.5– health effects related to sources of air pollution.
The proposal also includes revisions to data computation and other ambient air monitoring requirements that the agency says are intended to improve the quality of data used in regulatory decision-making and better characterize air quality in communities that are most affected. PM risk2.5 exposure and health risks.
Revisions are claimed to include:
- Updates in data calculations
- Approval of reference methods and equivalent methods
- Updates in QA statistical calculations to account for lower concentration measurements
- Updates to support improvements in PM methods
- Updates to the probe location and monitoring path criteria for NAAQS pollutants
Note that states are primarily responsible for ensuring that a NAAQS is achieved and maintained once EPA establishes or reviews them. Each state is therefore required to formulate, subject to EPA approval, an implementation plan (or “SIP”) to achieve each NAAQS.
The SIPs will contain the steps and actions the State proposes to take to achieve each NAAQS. These measures or actions must be implemented through state regulations and typically include emission limits that apply to certain types of stationary sources. States are generally free to make their own choices about how to reach the NAAQS through their SIPs.
You can find a link to the proposed rule before publication here.