The ruling, which is in favor of the federal Clean Air Act, said the law does not require the government to consider the financial cost of reducing emissions when it sets air-quality standards.
The court also ruled against industry arguments that the Environmental Protection Agency (EPA) took too much lawmaking power from Congress when it set its standards for ozone and soot limits in 1997. However, the EPA was ordered by the court to reconsider the standards it set for ozone. The court said the agency's interpretation of that section of the Clean Air Act was unreasonable.
The Clean Air Act requires the EPA to set national air-quality standards to protect the public health. The agency is to use criteria that accurately reflect the latest scientific knowledge for identifying pollution's effects on health.
The trucking industry has long argued that EPA was setting standards without clear criteria and without considering the financial costs of complying with them. Government lawyers said the EPA considers compliance costs in deciding how states will try to meet the clean-air standards, and the law is intended to drive the creation of new technology for doing so.
A federal appeals court had ruled that EPA went too far in adopting new standards in 1997 to reduce particulate matter. The court said the government interpreted the federal law so loosely that it usurped Congress' authority.
The 1997 air standards limited ozone to 0.08 parts per million (ppm) instead of .12 ppm under the old requirement. States also were required to limit soot from power plants, cars and other sources to 2.5 microns, or 28 times smaller than the width of a human hair.