These images show the results of air-quality modeling for the Los Angeles air basin with initializing data from Aug. 27, 1987. The clouded volume represents ozone concentrations exceeding federal ambient air quality standards (0.12 parts per million). At 8 a.m. (above), ozone levels are below the standard except for the easternmost region of the air basin. By 2 p.m. (below), hydrocarbons from vehicle emissions have reacted with sunlight to significantly increase ozone throughout the basin. The ozone cloud is overlaid on census maps and a LANDSAT satellite image using the Geographic Environmental Modeling System (GEMS) project being developed at Carnegie Mellon by Bernd Bruegge and Erik Riedel.