Development of ozone-precursor relationships using VOC receptor modeling

The results of a summer 1988 VOC receptor modeling study in Detroit were used in conjunction with a photochemical model to examine the effect of VOC source contributions on predicted ambient ozone. Source hydrocarbon contributions determined from receptor modeling were input to the ozone model along with initial measured concentrations of CO, NOx, O3 and with measured temperature, uv, pressure and relative humidity data. Wind trajectories were used to compare the predicted ozone concentration maximums against measured ozone maximums at downwind ozone monitoring stations. The r2 value between observed and calculated downwind ozone was 0.38 and 0.52, for the 6 a.m. and 8 a.m. starting times, respectively, and the slopes of the least squares fit lines were 0.86 and 1.05, respectively, indicating unbiased results. These comparisons are well within the accuracy guidelines specified by the U.S. Environment Protection Agency for ozone prediction models, and are also within the accuracy of similar comparisons produced from Urban Airshed Model applications. Source sensitivity analysis was carried out to see the effect of reducing source emissions on ozone formation. This modeling approach demonstrates that accurate ozone predictive modeling does not have to rely on reported source emission inventories.