Gas stations in seven southern and coastal counties in Maine will be required to sell cleaner-burning “reformulated gas” beginning June 1 as part of an agreement between the state and federal governments. The U.S. Environmental Protection Agency announced Monday that only reformulated gas – a blend designed to reduce emissions of air pollutants – can be sold in York, Cumberland, Sagadahoc, Androscoggin, Kennebec, Knox and Lincoln counties starting in June. Maine opted out of the federal government’s reformulated gas program in the late 1990s because of contamination caused by methyl tertiary-butyl ether, MTBE, which was one of the additives at the time.