The Bush administration is taking steps to cut a form of pollution that often travels long distances across many states.
At issue is the smog and soot-forming chemicals that are produced by power plants and factories.
The Environmental Protection Agency is proposing a cap on plant emissions of sulfur dioxide and nitrogen oxide -- two of the chemicals that cause this type of pollution.
The government says smog and fine soot can cause respiratory problems, especially in children and the elderly.
The new guidelines would affect plants in 30 states, most of them east of the Mississippi River.
The EPA's proposal would become final after a comment period.