In a final notice published in the Federal Register on April 18th, the U.S. Environmental Protection Agency (EPA) published a final rule retaining the current standards of the primary National Ambient Air Quality Standards (NAAQS) for oxides of nitrogen (NOx). The U.S. EPA published this final rule without a revision of the current standard. This final action becomes effective May 18, 2018.
There are two primary standards for oxides of nitrogen:
An annual standard, originally set in 1971, at a level of 53 parts per billion (ppb) based on annual average NO2 concentrations; and
A 1-hour standard, established in 2010, at a level of 100 ppb based on the 98th percentile of daily maximum 1-hour NO2 concentrations, averaged over 3 years.
Section 108 and 109 of the Clean Air Act requires the EPA to periodically review the science upon which the NAAQS are based. According to the EPA, this review of the NO2 NAAQS was conducted pursuant to these statutory requirements. Consistent with the review completed in 2010, the current review was focused on the health effects associated with gaseous oxides of nitrogen and on the protection afforded by the primary NO2 standards.
According to the EPA, this decision was based on a careful consideration of the full body of scientific evidence and information available. Based upon these considerations, the EPA reached the conclusion that the current body of scientific evidence directs the EPA Administrator to identify and list certain air pollutants. The EPA reached the conclusion that the current body of scientific evidence and the results of quantitative analyses support the judgment that the combination of the current 1-hour and annual primary NO2 standards are requisite to protect public health with an adequate margin of safety. For this reason, the EPA is retaining the current 1-hour and annual NO2 primary standards.
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