Opponents of soot pollution took to their strollers in Philadelphia today.

Well, it would be more accurate to say the toddler were merely along for the ride as the Mom's Clean Air Force of Philadelphia marched from William J. Green Federal Building to Independence Mall.

The EPA is conducting hearings over a proposal to tighten the regulation of soot, also called particulates. Micrograms per cubic meter is a measure of the concentration of fine particles in the air. The EPA proposal would lower the standard to 12 or 13, down from 15.g