The subject of the chapter is the interplay between science, which spells out the effects of air pollution on biological diversity, and policy-making, which determines how society will respond. Specifically: How should scientists design their research--through the questions that they ask and the biotic quantities that they measure--so as best to inform the regulatory decision process, and so to advance the goal of conserving biological diversity. Scientists must be willing to propose ecological priorities. While idealized science strives for value-neutrality, ecological scientists cannot afford neutrality. Their insights and their aesthetic perceptions are essential, if society is to act wisely in resolving the biodiversity crisis.