title: Blue Skies Bluer?
abstract: The largest U.S. environmental health risk is cardiopulmonary mortality from ambient PM2.5. The concentration-response (C-R) for ambient PM2.5 in the U.S. is generally assumed to be linear: from any initial baseline, a given concentration reduction would yield the same improvement in health risk. Recent evidence points to the perplexing possibility that the PM2.5 C-R for cardiopulmonary mortality and some other major endpoints might be supralinear: a given concentration reduction would yield greater improvements in health risk as the initial baseline becomes cleaner. We explore the implications of supralinearity for air policy, emphasizing U.S.
  
  
  CONCLUSIONS
  If C-R is supralinear, an economically efficient PM2.5 target may be substantially more stringent than under current standards. Also, if a goal of air policy is to achieve the greatest health improvement per unit of PM2.5 reduction, the optimal policy might call for greater emission reductions in already-clean locales-making "blue skies bluer"-which may be at odds with environmental equity goals. Regardless of whether the C-R is linear or supralinear, the health benefits of attaining U.S. PM2.5 levels well below the current standard would be large. For the supralinear C-R considered here, attaining the current U.S. EPA standard, 12 μg m(-3), would avert only ~17% (if C-R is linear: ∼ 25%) of the total annual cardiopulmonary mortality attributable to PM2.5.
authors.affiliation: Department of Civil, Environmental, and Geo-Engineering, University of Minnesota , Minneapolis, Minnesota 55455, United States.
authors.forename: Julian D
authors.initials: JD
authors.lastname: Marshall
authors.affiliation: Department of Civil, Architectural and Environmental Engineering, University of Texas at Austin , Austin, Texas 78712, United States.
authors.forename: Joshua S
authors.initials: JS
authors.lastname: Apte
authors.affiliation: Department of Applied Economics, University of Minnesota , St. Paul, Minnesota 55108, United States.
authors.forename: Jay S
authors.initials: JS
authors.lastname: Coggins
authors.affiliation: Department of Applied Economics, University of Minnesota , St. Paul, Minnesota 55108, United States.
authors.forename: Andrew L
authors.initials: AL
authors.lastname: Goodkind
mesh_terms: D000397:Air Pollution / Q000331:legislation & jurisprudence / Q000517:prevention & control*; D002318:Cardiovascular Diseases / Q000209:etiology / Q000401:mortality*; D058735:Environmental Policy; D006801:Humans; D008171:Lung Diseases / Q000209:etiology / Q000401:mortality*; D052638:Particulate Matter / Q000032:analysis / Q000633:toxicity; D011634:Public Health; D014481:United States / Q000453:epidemiology
chemical_list: D052638:Particulate Matter