Multipollutant air quality management.

On the basis of a recent NARSTO assessment, this review discusses the factors involved in the implementation of a risk- and results-based multipollutant air quality management strategy applicable to North America. Such a strategy could evolve from current single-pollutant regulatory practices using a series of steps that would seek to minimize risk of exposure for humans and ecosystems while providing for a quantitative evaluation of the effectiveness of the management process. The tools needed to support multipollutant air quality management are summarized. They include application of a formal risk analysis, accounting for atmospheric processes, ambient measurements, emissions characterization, air quality modeling of emissions to ambient concentrations, and characterization of human and ecological responses to ambient pollutant exposure. The new management strategy would expand the current practice of accountability that relates emission reductions and attainment of air quality derived from air quality criteria and standards. Conceptually, achievement of accountability would establish goals optimizing risk reduction associated with pollution management. This expanded approach takes into account the sequence of processes from emissions reduction to resulting changes in ambient concentration. Using ambient concentration as a proxy for exposure, the resulting improvement in human and ecosystem health is estimated. The degree to which this chain of processes and effects can be achieved in current practice is examined in a multipollutant context exemplified by oxidants, as indicated by ozone, particulate matter, and some hazardous air pollutants. Achievement of a multipollutant management strategy will mostly depend on improving knowledge about human and ecosystem response to pollutant exposure.