Data from a three-dimensional pollutant mapping program, conducted in the Los Angeles basin, wereanalyzed to obtain "grand average" vertical profiles sampled on 24 summer days in 1973. Morning andafternoon profiles at four locations show an erosion of the nighttime radiation inversion, increased temperatures, more intense mixing in the inland areas, and a semi-permanent subsidence inversion at higher levels.High values of primary pollutant parameters (NO, and condensation nuclei) are seen in the western part ofthe basin at Hawthorne. Secondary pollutant parameters (Os and light scattering coefficient) were dominating at the inland receptor site, Riverside. Ozone concentrations in the morning were consistently higheraloft. The deficit near the surface is attributed to ozone scavenging by primary emissions.