Development of the map-O3 ozone model for predicting seasonal average ozone concentrations due to large point source NOx emissions

The first objective of this investigation was to demonstrate the ability of the U. S. Environmental Protection Agency's Ozone Isopleth Plotting Mechanism trajectory model (OZIPM-4) to predict ozone concentrations due to large point source NO_X emissions. The model was applied to a hypothetical case study power plant in a rural area of the southeast U. S. under a range of background conditions. Results for a 500 MW coal-fired power plant (26.2 tons NO_X/day) under high ozone conditions, (daily peak temperature of 93 °F), showed ozone formation as high as 26 ppb, after 5 to 8 hours of travel time in some plumes. A model validation exercise was performed in which ozone concentrations obtained from aircraft measurements within the plume of a large power plant were compared to predicted ozone concentrations. Results showed that the OZIPM-4 model can accurately predict plume average ozone concentrations within the plume of a large NO_X source. Furthermore, the model is capable of predicting ozone concentrations within different sections of the plume cross-section with reasonable accuracy. The second objective of this investigation was to develop an ozone model using the OZIPM-4 model and its accompanying chemical mechanism (Carbon Bond IV) that could predict ozone concentrations throughout a study area, over long-term time periods. The Mapping Areawide Predictions of Ozone (MAP-O₃) model developed to meet this objective, is a simplified model designed to meet the special needs of human health and crop and vegetation effects studies, by predicting daily peak incremental ozone concentrations over the ozone season and seasonal average 9 a.m. to 9 p. m. incremental ozone concentrations. MAP-O₃ model results for a case study of a hypothetical power plant in the southeast U. S. showed the highest increase in the seasonal average ozone concentration of 0.7 ppb occurred within 40 km of the plant. The model predicted the highest daily peak incremental ozone concentration of 25-26 ppb which occurred within 120 km of the plant. The MAP-O₃ model provides a simple tool by which researchers can assess the impact of NO_X emissions from large point sources over the entire ozone season throughout a study area.