Getty Images/iStockphoto Carbon dioxide gets the fame and attention, out of the greenhouse gases. But there are others that are even more effective at trapping heat; they just exist in much smaller concentrations, so they don’t usually face the same level of scrutiny or regulation. The United States is finally taking aim at an important type of these lesser-known superpollutants: hydrofluorocarbons, or HFCs, which are used in air conditioners and refrigerators. The Environmental Protection Agency announced a rule on Monday, first reported by the New York Times’s Lisa Friedman, that it will phase out the coolant’s use by 85 percent over the next 15 years. The EPA estimates the rule would cut down on the equivalent of 4.7 billion metric tons of carbon dioxide from 2022 to 2050 — about equal to three years of US power sector pollution.