Criteria pollutants The first air-quality issues the nation addressed were the obvious ones. Switching to unleaded gasoline largely eliminated lead in the air. Cutting emissions from power plants, refineries and factories, and improving vehicle emissions brought the other five pollutants within the standards. But there's more than just the criteria pollutants in the air. Some can build up in the environment, or combine with others to form even more harmful compounds.
Recent information shows air toxic levels are too high in some parts of Minnesota.
Diesel exhaust particles are another pollutant of growing concern. California studies indicate up to 70 percent of the cancer risk from toxic air pollutants comes from this diesel exhaust. Some air toxics come from particular types of industrial facilities. But the gains we've made with cleaner-burning engines are being undercut by more vehicles driving ever more miles. For example, from 1994 to 1998 Minnesota's population grew by about four percent, but the number of miles we traveled in our vehicles grew by 11 percent.