The Iowa Department of Natural Resources says it is investigating one of thehighest levels of air pollution recorded in the state at a site in MasonCity. D-N-R Air Quality Specialist Brian Button says the pollution Fridaywas unique because it involved two substances.Sulfur dioxide gas and microscopic particles of dust and soot were both atunhealthy levels. It marked the first time in years there were unhealthylevels of two pollutants in the air at the same location. Button says twocement plants that have had previous pollution problems may be part of thelatest problem.Button says the D-N-R wants to find out how the levels developed they waythey did.Button says it’s too early to tell if there will be any fines or other actiondue to the pollution violation.