The Court will consider whether Congress, by enacting a vague statutory provision, gave EPA regulatory powers so unbridled that they amount to an unconstitutional delegation to EPA of Congress's law-making powers. Moreover, the Court will evaluate EPA's efforts to promulgate health-based standards in the face of scientific uncertainty about the nature and gravity of the health risks caused by air pollutants. Those standards represent the maximum levels of certain air pollutants allowable in outdoor air. State governments are required to set and enforce limits on the emissions of those pollutants from specific stationary sources to ensure the allowable pollutant levels are not exceeded. The standards also influence the controls placed by EPA upon emissions from mobile sources such as cars, trucks, trains, airplanes, boats, snowmobiles, and even lawn mowers.
Ozone is formed by the reaction in sunlight of nitrogen oxides and volatile organic compounds.
The 1997 revised standard was 0.08 parts per million averaged over an eight-hour period. Particulate matter takes many forms. Typically, coarse particulate matter consists of larger particles often created by travel on gravel and dirt roads and landscape grading. Fine particulate matter is often created by combustion. The Supreme Court agreed to review the Court of Appeals' decision.