EPA data shows that from 1990 through 2017, sulfur dioxide emissions per unit of coal-generated energy decreased by 91%, and nitrogen oxides emissions decreased by 83%. Per the U.S. Department of Energy: "While coal used to be a dirty fuel to burn, technology advances have helped to greatly improve air quality, especially in the last 20 years. Scientists have developed ways to capture the pollutants trapped in coal before they escape into the atmosphere. Today, technology can filter out 99 percent of the tiny particles and remove more than 95 percent of the acid rain pollutants in coal, and also help control mercury."