Topeka ? The Kansas Department of Health and Environment says grassland burning in the Flint Hills sent ozone levels above national pollution standards in several areas this month.

KDHE says readings showed the excessive ozone Tuesday in Shawnee County and April 6 in Linn and Sedgwick counties. Higher-than-normal levels of particulate matter also were recorded.

Farmers and ranchers burn the grasslands to provide better forage for cattle and control some plant species.

Tom Gross, of the department’s air bureau, says the readings are disappointing. But Gross also says the agency believes a smoke management plan approved in December will cut down on such incidents in the future.

The plan allows ranchers to continue spring burning but restricts other burning in 12 counties in the Flint Hills and four near Kansas City and Wichita.