Estimated contribution of power plants to ambient nitrogen oxides measured in Atlanta, Georgia in August 1992

Since gasoline and coal vary in sulfur content, plumes from mobile and point sources can be identified by their characteristic sulfur dioxide to nitrogen oxides ratios. In this study this fingerprint ratio is used to estimate what percentage of the total ambient nitrogen oxides intercepted by a chemical measurement station is Atlanta is attributable to specific point sources. Emission estimates of nitrogen oxides from point and mobile sources were approximately equal for a 160 × 160 km grid centered around Atlanta. Using the present method, point sources represented 15% of the total ambient nitrogen oxides for the period at the measurement site. However, this average may be misleading because nitrogen oxides from point sources were found to be regularly affecting the station most probably through the process of fumigation, typically during the peak ozone producing hours of the day. For instance, on 31 August an ozone exceedenee day, a large percentage of the total ambient nitrogen oxides were from point sources at 3 p.m. (92%). On the other hand, 10 August showed no significant evidence of point source contribution, yet exceeded the ozone standard. The importance of fumigation to ozone production in Atlanta will be the subject of future work.