Use of episodic and seasonal controls to lower ozone concentrations : their impact and cost effectiveness

Episodic ozone controls are used temporarily when high concentrations of ozone are predicted to occur. More than 40 cities in the United States have implemented episodic control programs that are designed to educate the public about air pollution, attain and maintain air quality standards, and protect human health. No program has quantified the impact of episodic controls on ozone concentrations or their cost effectiveness as a control measure. To quantify the impact of episodic controls in the East Tennessee Modeling Domain, the Urban Airshed Model was used to predict ozone concentrations resulting from a variety of control scenarios that simulated typical NO_x reduction technologies for point sources and area and mobile sources. Because ozone formation in the southeastern United States is NO_x -limited, only NO_x reductions were analyzed. A cost analysis was performed to estimate the cost effectiveness of the various control technologies in lowering ozone concentrations. For peak ozone concentrations, NO_x emission reductions from elevated point sources made the largest impact on 1-hour and 8-hour average concentrations. Point source NO_x reductions were more cost effective in reducing peak ozone concentrations than were area and mobile source NO_x reductions. A 10 percent reduction in NO_x from area and mobile sources had no measurable impact of ozone concentration. For a maximum difference in ozone, occurring anywhere in the modeling domain, elevated point sources again made the largest impact on ozone concentration, about twice the impact predicted for 50 percent NO_x reductions from area and mobile sources. Cost effectiveness of achieving maximum differences in ozone concentrations was about the same for all the control technologies analyzed. Each agency should perform a modeling analysis similar to the one in this research before implementing an episodic control program in order to determine which control techniques are most effective in achieving their goals under the controlling conditions in their region.