Policy-making and the role of simplified models: An air quality planning example

Abstract

Urban areas with serious air quality problems need to use complex models in air quality planning. Such models are unwieldy and expensive to use and they focus on a multitude of details but lack scope and perspective. Work with air quality planners in Denver, CO shows that simplified models can play an important role in redressing many of these problems. Designing the simplified model to be a model of the complex models was found to be important to make the results of the simplified model acdeptable in the planning process. The simplified model developed for Denver was inexpensive to run and could easily be altered to test a variety of future conditions and planning strategies. It provided perspective beyond that of the complex models. For example, it showed that significant trade-offs between health and haze benefits must be faced in choosing between pollution control strategies. It also showed the difficulty of maintaining air quality over the long term, and the relative ineffectiveness of transportation controls compared to vehicle emission controls for long-term air quality maintenance. The simplified model was shown to be an aid to decision-making in several ways: by providing planners with the capability to achieve a broader understanding of the relevant issues; by helping planners to address issues that the complex models could not; and by augmenting the capabilities of the complex models. This case shows that the combined use of complex and simplified models offers the opportunity for an overall improvement in policy analysis.