US EPA

This draft document provides EPA’s evaluation and synthesis of the most policy-relevant science related to the health effects of oxides of nitrogen. When final, it will provide a critical part of the scientific foundation for EPA’s decision regarding the adequacy of the current primary (health-based) national ambient air quality standards for nitrogen dioxide.

The references considered for inclusion in or cited in the first and second external review drafts of the ISA are available at https://hero.epa.gov/oxides-of-nitrogen.

Oxides of nitrogen are one of six principal (or criteria) pollutants for which EPA has established national ambient air quality standards (NAAQS). For oxides of nitrogen, the NAAQS are specified in terms of nitrogen dioxide (NO2). The Clean Air Act requires EPA to periodically review the scientific basis for these standards by preparing an Integrated Science Assessment. These reviews play a significant role in EPA’s commitment to ensuring a clean and healthy environment for the public.

The second draft ISA is part of the Agency’s periodic review of the primary (health-based) NAAQS for NO2. Overall, findings from recent studies strengthen the conclusions from the previous NAAQS review, which was completed in 2010. Results from recent studies strengthen the body of evidence indicating that short-term exposure to NO2 can cause respiratory effects, in particular, effects related to asthma exacerbation. Recent results also strengthen the evidence that the respiratory effects of short-term NO2 exposure are independent of the effects of many other traffic-related pollutants. There is now stronger evidence for a relationship between long-term exposure to NO2 and respiratory effects, particularly the development of asthma in children. Results suggest that short-term exposure to NO2 may be associated with cardiovascular effects and related metabolic effects and premature mortality and that long-term exposure may be associated with cardiovascular and related metabolic effects, poorer birth outcomes, premature mortality, and cancer; however, it is uncertain whether these effects of NO2 exposure are independent from the effects of other traffic-related pollutants.

The Clean Air Act (CAA) requires EPA to periodically review and revise, as appropriate, existing air quality criteria and NAAQS. The CAA also requires an independent scientific committee to review the criteria and to advise the Administrator regarding any recommended revisions to the existing criteria and standards, as may be appropriate. The Clean Air Scientific Advisory Committee (CASAC) of EPA’s Science Advisory Board serves as this independent scientific committee. The ISA is one of the four major elements of the NAAQS review process that will inform the Agency’s final decisions; other components of the process are an integrated plan highlighting the key policy-relevant issues; a risk/exposure assessment if warranted; and an advance notice of proposed rulemaking (ANPRM) reflecting the Agency’s views regarding options to retain or revise the NO2 NAAQS based on the evaluation of key information contained in the ISA and Risk/Exposure Assessment, as well as additional appropriate technical analysis.

This draft will be reviewed by the Clean Air Scientific Advisory Committee (CASAC) at a public meeting announced in the Federal Register. A future Federal Register notice will inform the public of the exact date and time of that CASAC meeting. In revising and finalizing the ISA, EPA will take into account CASAC advice and recommendations as well as public comments. The final assessment, will be posted on EPA’s website, and will provide a critical part of the scientific foundation for the primary NAAQS for nitrogen dioxide.

U.S. EPA. Integrated Science Assessment (ISA) for Oxides of Nitrogen – Health Criteria (Second External Review Draft, 2015). U.S. Environmental Protection Agency, Washington, DC, EPA/600/R-14/006, 2015.

Included for public review is the draft Integrated Science Assessment for Oxides of Nitrogen - Health Criteria (Second External Review Draft). Comments on this document may be submitted and reviewed using the e-Government Regulations.gov Web site. From the site, select Environmental Protection Agency and the keyword EPA-HQ-ORD-2013-0232 (for the docket ID) to comment on this report.