The number of exceedances of National Ambient Air Quality Standards declined sharply in 2015 compared with 2014, due in large part to reductions in pollution emitted by Grain Processing Corporation's (GPC) corn-milling operations in Muscatine.
According to the Iowa Department of Natural Resources (IDNR) air quality report for 2015, 17 exceedances of the sulfur dioxide ambient air standards were recorded and 8 exceedances of the PM 2.5 (fine particulate) standard.
All 17 SO2 exceedances and one of the eight PM 2.5 exceedances occurred at Muscatine air monitors.