The Effect of Future Anthropogenic Emissions on Ozone Concentrations in the Great Lakes Region

High ozone concentrations can have an adverse effect on certain different types of vegetation. Ozone exposure estimates have typically been based on measurements made at ozone monitoring stations. However, most ozone monitoring stations are located in urban areas and the measurements made at these sites are not representative of values in remote agricultural and forested regions.

In this study, a coupled meteorological and chemical model is employed to simulate the production/destruction, turbulent mixing, transport, and deposition of ozone over the Great Lakes region during the summers (between May and September) of 1999 and 2001. The meteorological conditions during the summer of 1999 were more conducive to ozone production in the region than during 2001. The model was run in a nested grid configuration with an outer grid encompassing eastern North America with a horizontal grid spacing of 36 km and an inner grid encompassing the Great Lakes region with a horizontal grid spacing of 12 km. The meteorological predictions are evaluated with operational National Weather Service surface and upper observations, while the chemical model results are evaluated with U.S. EPA monitoring data. Using current emission rate estimates, the predicted spatial ozone distributions and the temporal ozone trends are usually similar to the monitoring data. During many episodes, ozone produced by the urban and point source emissions in the southern portion of the region is transported to the north and east into Canada. Ozone exposure is then computed to determine cumulative effect of relatively high ozone concentrations in rural areas and the impact of pollutants on vegetation.

Future ozone exposure will be affected by changes in meteorological conditions associated with regional-scale climate change and increases in anthropogenic emissions of ozone precursors. To examine the effect of increases in anthropogenic emissions on ozone exposure, we repeated the simulations of the 1999 and 2001 summer periods using projected emission rates based on EPA?s Economic Growth and Analysis System. The effect of future emission projections on the magnitude and distribution of ozone exposure is quantified as a function of meteorological conditions.