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 O3, 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, H202 and PAN in comparison with measurements. Peak O3 and concurrent NOy from helicopter measurements was used as a basis for evaluating individual model scenarios. Scenarios were developed with different O3 NOx- ROG sensitivity, but only the NOx- sensitive scenarios are consistent with measured O3, NOy and isoprene.