University of California Transportation Center

Significant accomplishments in air pollution emissions control have occurred over the past twenty years. Emissions have been substantially reduced by both industrial and transportation sources; over the ten year period 1977-86, the U.S. Environmental Protection Agency (EPA) reports improvements in each of the six air pollutants for which health-based national ambient air quality standards (NAAQS) exist -- lead, sulfur dioxide, ozone, carbon monoxide, nitrogen dioxide, and particulates. Yet major problems remain: