Environmental Protection Agency
The EPA recently finalized changes to the data handling conventions and computations necessary for determining when the annual and 24-hour national ambient air quality standards (NAAQS) for fine particles (generally referring to particles less than or equal to 2.5 micrometers ([mu]m) in diameter, PM<INF>2.5</INF>) are met. These changes were made in support of revisions to the NAAQS for particulate matter (PM) that were finalized in the same rulemaking. After publication, EPA discovered an inadvertent omission in the rule text explaining the procedures for calculating the key statistic (98th percentile) involved with determining compliance with the 24-hour PM<INF>2.5</INF> standard in locations where extra samples of PM<INF>2.5</INF> in ambient air were taken above the specified sampling frequency. If the error in the regulatory text is left unchanged, the resulting statistic for calculating compliance with the 24-hour PM<INF>2.5</INF> standard would be biased low at some samplers, leading to potentially incorrect determinations that an area was attaining the NAAQS. In this direct final action, EPA is correcting this error. The correction involves the replacement of the currently used statistical formula and instructions with a simpler look-up table approach which is easier for readers to understand and which retains the intended numerical consistency with EPA's historic practice.
Document Headings Document headings vary by document type but may contain the following: the agency or agencies that issued and signed a document the number of the CFR title and the number of each part the document amends, proposes to amend, or is directly related to the agency docket number / agency internal file number the RIN which identifies each regulatory action listed in the Unified Agenda of Federal Regulatory and Deregulatory Actions See the Document Drafting Handbook for more details. Environmental Protection Agency 40 CFR Part 50 [EPA-HQ-OAR-2001-0017; FRL-8502-3] RIN 2060-AO59 AGENCY: Environmental Protection Agency (EPA). ACTION: Direct final rule. SUMMARY: The EPA recently finalized changes to the data handling conventions and computations necessary for determining when the annual and 24-hour national ambient air quality standards (NAAQS) for fine particles (generally referring to particles less than or equal to 2.5 micrometers (μm) in diameter, PM 2.5 ) are met. These changes were made in support of revisions to the NAAQS for particulate matter (PM) that were finalized in the same rulemaking. After publication, EPA discovered an inadvertent omission in the rule text explaining the procedures for calculating the key statistic (98th percentile) involved with determining compliance with the 24-hour PM 2.5 standard in locations where extra samples of PM 2.5 in ambient air were taken above the specified sampling frequency. If the error in the regulatory text is left unchanged, the resulting statistic for calculating compliance with the 24-hour PM 2.5 standard would be biased low at some samplers, leading to potentially incorrect determinations that an area was attaining the NAAQS. In this direct final action, EPA is correcting this error. The correction involves the replacement of the currently used statistical formula and instructions with a simpler look-up table approach which is easier for readers to understand and which retains the intended numerica…
Other Federal Register documents from the same docket.
Interpretation of the National Ambient Air Quality Standards for PM2.5-Correcting and Simplifying Amendment
National Ambient Air Quality Standards for Particulate Matter
Availability of Additional Information Related to the Review of the National Ambient Air Quality Standards for Particulate Matter
Public Hearings for Proposed Rules-National Ambient Air Quality Standards for Particulate Matter and Revisions to Ambient Air Monitoring Regulations
Citation: 73 FR 1497
