The U.S. Environmental Protection Agency today will announce standards for soot pollution that are 20 percent tighter than the current rule, according to a person briefed on the matter.

The annual standards for particulate matter, or microscopic particles released from automobile exhausts, power plants or factories, will be set at 12 micrograms per cubic meter, down from 15 micrograms now, the person said. The EPA faces a court- set deadline to announce the standards today, and the person declined to discuss the rule publicly before the agency’s public announcement.

To contact the reporter on this story: Mark Drajem in Washington at mdrajem@bloomberg.net

To contact the editor responsible for this story: Jon Morgan at jmorgan97@bloomberg.net