A federal appeals court says the Environmental Protection Agency acted reasonably in deciding not to change the primary air quality standard for carbon monoxide.

Three environmental and wildlife organizations want the public health standard toughened.

But the appeals court says in a 3-0 ruling that the private groups cannot challenge the lack of a secondary air quality standard for carbon monoxide. The EPA decided not to have one, based on a finding that the connection between carbon monoxide and climate change was tenuous.

The court ruled Friday that the groups failed to show that the absence of a secondary standard would worsen global warming.

Carbon monoxide is an odorless, colorless gas in motor vehicle exhaust.