Revised Air Quality Standards for Nitrogen Dioxide (NO2) and Sulfur Dioxide (SO2) Second-Hand Emissions
The Environmental Protection Agency (EPA) is currently undertaking a thorough review of the scientific criteria used to establish national air quality standards for nitrogen oxides (NOx) and sulfur oxides (SOx). This process, mandated by the Clean Air Act, focuses on the pollutants' broader environmental and welfare effects rather than direct health impacts.
The review includes an integrated assessment of NOx and SOx, as these pollutants are closely linked in atmospheric chemistry and environmental impacts. The EPA will consider the latest scientific evidence related to the impacts on soils, water, vegetation, animals, climate, visibility, and materials.
Key aspects of EPA's review process for NOx and SOx secondary standards are:
- Integrated Review of NOx and SOx Together: Because nitrogen oxides and sulfur oxides are closely linked in atmospheric chemistry and environmental impacts, EPA reviews the secondary standards for these pollutants jointly rather than individually.
- Use of Scientific and Technical Assessments: The process includes developing and updating Integrated Science Assessments that synthesize current scientific knowledge on the pollutants' welfare effects.
- Policy Assessments: EPA prepares assessments to evaluate policy implications and potential standard revisions based on the science.
- Advisory Committee Involvement: The EPA Clean Air Scientific Advisory Committee (CASAC), composed of independent experts, reviews the scientific assessments and provides recommendations.
- Public Participation: EPA issues Federal Register notices, invites public comments, responds to these comments, and addresses litigation if it arises.
- Periodic Timing: The Clean Air Act requires EPA to conduct such reviews periodically, generally every five years, to ensure standards remain appropriate given evolving scientific understanding.
The six criteria pollutants under review are nitrogen oxides, sulfur oxides, particulate matter, ozone, carbon monoxide, and lead. The EPA has not specified the exact timeline for the completion of this review.
In addition to the current review, EPA will consider Planning Documents, Integrated Science Assessments, Policy Assessments, CASAC Documents, Federal Register Notices, Response to Comments, and Litigation from previous reviews, including documents from SO Secondary Standard Reviews Completed Prior to 2010, NO Secondary Standard Reviews Completed Prior to 1996, and the NO Secondary Standard Review Completed in 2012.
The EPA recognizes that NO and SO are inextricably linked from both an atmospheric chemistry and an environmental effects perspective. This comprehensive review aims to provide a transparent, science-driven framework for setting air quality standards that protect both human health and the environment.
For more information, visit Air Quality Analysis, Air Quality Research, Air Quality Trends, Ambient Air Monitoring Networks, Criteria Air Pollutants, Design Values, Emissions Information, Nonattainment Areas, Table of Current NAAQS, Timeline of NO NAAQS, and Timeline of SO NAAQS.
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- The EPA's comprehensively revised standards for nitrogen oxides (NOx) and sulfur oxides (SOx) will not only take into account direct health impacts but also consider broader environmental and health-and-wellness implications, such as effects on soils, water, vegetation, animals, climate, visibility, and materials – aspects that are interrelated in environmental science.
- In this review process, the EPA intends to look beyond the boundaries of individual pollutants and examine the integrated impacts of NOx and SOx, acknowledging their close connection in atmospheric chemistry as well as environmental impacts, aligning with the field of environmental-science.
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