PHOTOCHEMISTRY OF OZONE FORMATION IN ATLANTA, GA - MODELS AND MEASUREMENTS

Chemical measurements made during an air pollution event in Atlanta, GA have been compared with results from several photochemical simulations. Measurements included O-3, primary reactive organic gases (ROG), aldehydes, PAN, total reactive nitrogen (NOy) and H2O2, with vertical profiles for primary ROG. Photochemical models using two different chemical representations and a range of assumptions about winds, vertical mixing and emissions were used to simulate the event. Results show that assumptions about vertical mixing can cause a variation in simulated surface concentrations of primary hydrocarbons of a factor of two or more. A tendency to underestimate isoprene was found in comparison with measured vertical profiles. The models tend to overestimate concentrations of HCHO, H2O2 and PAN in comparison with measurements. Peak O-3 and concurrent NOy from helicopter measurements was used as a basis for evaluating individual model scenarios. Scenarios were developed with different O-3-NOx-ROG sensitivity,but only the NOx-sensitive scenarios are consistent with measured O-3, NOy and isoprene.