Environmental groups have sued the EPA to overturn its December 31st rule retaining Obama Era National Ambient Air Quality Standards (NAAQS) for ozone.  The suit alleges that the Trump EPA ignored science and mounting evidence that serious health harms occur due to ozone exposure at levels below the current NAAQS.  Litigation is likely to focus heavily on the truncated NAAQS review process used by the Trump administration which allegedly failed to properly analyze the latest science on health risk, resulting in a predetermined outcome favored by industry which did not propose tighter regulation.  The EPA, in its December rule, retained the “primary” ozone NAAQS, designed for human health, as well as the “secondary” standard designed to protect the environment.  Both standards are currently set at 70 parts per billion.  The EPA’s own Clean Air scientific Advisory Committee twice voted unanimously to support a standard within a range of 60 ppb to 70 ppb during the Obama era.