The U.S. Environmental Protection Agency said the air quality has improved significantly in the area around Ashland.
The federal agency this week has re-designated Boyd County and a portion of Lawrence County to "attainment" for fine particle pollution.
In January, the state's Division for Air Quality submitted a request for the EPA to recognize the area as meeting the annual standard for fine particulate matter. The standard measures microscopic particles or droplets that are hazardous to human health because they can easily be inhaled deep into lungs.
Kentucky Energy and Environment Cabinet Secretary Len Peters said the new designation benefits the region's economic development by eliminating the need for stricter air permitting requirements.