Manufacturers of phosphoric acid, a key ingredient in fertilizer, now have until 2018 to reach two compliance deadlines for hazardous air pollutants, the EPA said in a final rule.

Previously, the Environmental Protection Agency had set an August 2016 deadline for phosphoric acid producers to include emissions of hydrogen fluoride and other fluorides from a process that turns raw phosphorus into phosphoric acid in their calculations of how much of the fluorides they emit. Hydrogen fluoride is extremely...