Over the past 50 years, tremendous progress has been made in reducing air pollution under the Clean Air Act. Nevertheless, while air quality has improved greatly for much of the nation, there are still places where the goal of attaining national standards has still not been reached. This is often true in urban locations that are affected by multiple pollution sources; typically, these areas are also environmental justice communities. Recent events have called attention to the urgent need for concrete action to address the many problems of these communities.