The proposal, issued after a careful review of the best available science, builds on EPA efforts already under way to reduce NOx and SOx emissions, the agency said in a release Wednesday.
Nitrogen oxides are emitted from an array of sources, including vehicles, power plants, off-road equipment, and agricultural sources, while sulfur oxides are emitted from fossil fuel combustion by power plants, large industries, mobile sources, and from some industrial processes, the agency said.
EPA is already taking a number of steps to reduce NOx and SOx emissions, including the recently announced Cross-State Air Pollution Rule.
EPA first established standards for oxides of nitrogen and sulfur in 1971.
To ensure any updated standard is effective, the agency said, it is planning to conduct a field pilot program to collect and analyze additional data and information.
The EPA said it will accept comments for 60 days after the proposed rule is published in the Federal Register and will issue a final rule by March 2012.