U.S. proposal would tighten soot standards: report WASHINGTON (Reuters) - The U.S. government plans on Friday to announce a proposal to strengthen standards for regulating air pollution from soot that could offer health benefits over time but require some industries to make new anti-pollution investments, The Washington Post reported. The Environmental Protection Agency will propose to tighten annual exposure to fine-particle soot to between 12 and 13 micrograms per cubic meter of air from 15 micrograms, according to people briefed on the plan, the report said. Industry officials and environmentalists said the proposal to be finalized by the end of the year would have implications for both the U.S. economy and public health, the Post said. The EPA was under a court order to deliver a plan by this week for improving air quality standards for soot in response to a lawsuit by health and environmental groups. Soot can come from burning wood, car exhaust and industrial sources and can cause respiratory and heart ailments, experts say.