A legal maneuver by environmental groups to force the EPA to amend the 43-year-old National Ambient Air Quality Standards (NAAQS) for carbon monoxide (CO) failed in the U.S. Court of Appeals for the D.C. Circuit (Communities for a Better Environment and WildEarth Guardians v. EPA). 

The three-judge panel found that the science-based arguments offered by the petitioners for revising the primary or human health NAAQS for CO did not overcome the substantial deference the court extends to the Agency in the setting and changing of the NAAQS.  A related challenge by the groups to have the EPA reestablish the secondary NAAQS for CO—which addresses public welfare, including environmental effects—because of its alleged contribution to climate change also came up empty.

The primary CO NAAQSs have been unchanged since 1971.  Also, in 1985, the EPA revoked the secondary CO NAAQS.  In 2011, the Agency reviewed the status of both NAAQSs and decided to take no action.

1989 human clinical trial

Communities for a Better Environment, WildEarth Guardians, and the Sierra Club raised four objections to EPA’s inaction on the primary CO NAAQS.

• Epidemiological studies indicate that the current NAAQS allows emissions of CO that cause adverse health effects.  The EPA countered that adverse health effects were found where CO levels were present, but there was no evidence that these effects were not caused by other pollutants.  Also, the Agency claimed that there have been no toxicological studies showing that CO levels allowed by the current primary standards cause adverse health effects.  The court found no fatal flaw in EPA’s reasoning.
• The EPA did not include several CO poisoning studies in its integrated science assessment.  But the judges concluded that the EPA reasonably explained that the studies were not focused on the effects of CO exposure at the levels permitted by the primary standards and, thus, were not helpful in determining which physical effects are caused by emissions of CO at the levels of the primary NAAQS.
• The EPA relied on a 1989 human clinical trial to the exclusion of other relevant studies.  The EPA agreed that it did rely heavily on a 25-year-old study, but added that this particular study remained the most compelling evidence of CO-induced effects on the cardiovascular system.  The court found this explanation reasonable.
• The petitioners said the EPA ignored the advice of the Clean Air Scientific Advisory Committee (CASAC).  Under the Clean Air Act, the EPA must explain why it departs from important CASAC recommendations.  In its report on the CO NAAQS, the CASAC supported either of two approaches: retaining the existing 8-hour CO standard or revising it.  “Because the Advisory Committee’s recommendation permitted the option of retaining the current primary standards, it cannot be said that EPA departed from the Committee’s recommendations in this case,” responded the court.

Climate challenge

The petitioners contended that EPA’s failure to set a secondary standard is worsening global warming, and the Agency’s establishment of an NAAQS is therefore required by law.  The EPA responded that there are significant uncertainties regarding the effect of CO in the atmosphere on the climate.  Likewise, the CASAC said the uncertainty did not favor development of a secondary standard.  Therefore, the EPA ultimately determined that it was “not possible to anticipate how any secondary standard that would limit ambient CO concentrations in the United States would in turn affect climate and thus any associated welfare effects.” 

The court found that the petitioners did not make a showing that CO at the level permitted by the EPA would worsen climate change compared to installing a standard according to law, as the petitioners view it.

Communities for a Better Environment and WildEarth Guardians v. EPA