Environmental officials say the winter storm has helped clear the air over eastern Iowa. Fine particle pollution levels in excess of the EPA’s health threshold were measured Tuesday in Muscatine. The Iowa DNR had recommended that children, the elderly and those with health problems limit their time outdoors. The state agency says other parts of eastern Iowa also saw increased fine particle levels, but that health standards were not expected to be exceeded. They say stagnant air prevents particles from automobile exhaust and other combustion sources from dispersing.