Development of a Model to Assess the Effect of Ozone on Public Health Using Models-3/CMAQ

According to the Clean Air Act, the establishment of priorities in air pollution control should be based on benefits to public health and welfare. Given this mandate, EPA has incorporated the health effect evaluation in the regulatory impact analysis of its rulemaking, such as Tier2 sulfur gasoline reduction and HDE diesel emission reduction. The Tennessee Department of Environment and Conservation (TDEC) has identified ozone as the primary pollutant of concern. All these antecedents provided the basis for developing a decision-making tool that helps to evaluate the various regulatory options in controlling the emission of ozone precursors from a health-effects point of view.

In this context, a computer model called ORAM (Ozone Risk Assessment Model) was developed to evaluate the health-effects caused by ground level ozone exposure. ORAM was coupled with Models-3/CMAQ the EPA state-of-the-art air quality model that predicts ozone concentration and allows the examination of various emission scenarios in which emission rates of ozone precursors (basically NOx and VOC) are varied. Given that ozone is a local and regional problem, ORAM allows the health evaluation for local, regional, and continental scales. The principal analyses in ORAM are exposure model performance evaluation, health-effects calculations (expected number of respiratory hospital admissions), economic valuation, sensitivity, and uncertainty analysis through a Monte Carlo simulation.

To demonstrate the system’s effectiveness, ORAM was applied to the East Tennessee region, and the entire ozone season was simulated for a base case (actual, typical emissions) and three different emission scenarios using an available hospital admissions database. The results indicated that a synergism occurs when NOx emissions from mobile (50%) and point (70%) sources were simultaneously reduced. A 19% in reduction on hospital admissions for respiratory diseases occurs when both mobile and point sources NOx emissions are reduced versus 8% due to mobile source and 7% due to point source when these source’s emissions are applied singly.

ORAM has the flexibility to easily incorporate other health-endpoints such as mortality and minor restrictive activity days (MRAD) and also other pollutants such as particulate matter and other gases. Finally, because the equations in ORAM are for short-term effects (daily variation), the system developed can be used in a forecasting mode as a complementary tool in the ozone action programs such as Spare the Air or Ozone Action Days.