MAPPING CRITICAL LEVELS OF OZONE, SULFUR-DIOXIDE AND NITROGEN-DIOXIDEFOR CROPS, FORESTS AND NATURAL VEGETATION IN THE UNITED-STATES

Air pollution abatement strategies for controlling nitrogen dioxide, s ulfur dioxide, and ozone emissions in the United States focus on a 'st andards-based' approach. This approach places limits on air pollution by maintaining a baseline value for air quality, no matter what the ec osystem can or cannot withstand. In this paper, we present example cri tical levels maps for the conterminous U.S. developed using the 'effec ts-based' mapping approach as defined by the United Nations Economic C ommission for Europe's Convention on Long-Range Transboundary Air Poll ution, Task Force on Mapping. This approach emphasizes the pollution l evel or load capacity an ecosystem can accommodate before degradation occurs, and allows for analysis of cumulative effects. We present the first stage of an analysis that reports the distribution of exceedance s of critial levels for NO2, SO2, and O3 in sensitive forest, crop, an d natural vegetation ecosystems in the contiguous United States. We co nclude that extrapolation to surrounding geographic areas requires the analysis of diverse and compounding factors that preclude simple extr apolation methods. Pollutant data depicted in this analysis is limited to locationally specific data, and would be enhanced by utilizing spa tial statistics, along with converging associated anthropogenic and cl imatological factors. Values used for critical levels were derived fro m current scientific knowledge. While not intended to be a definitive value, adjustments will occur as the scientific community gains new in sight to pollutant/receptor relationships. We recommend future analysi s to include a refinement of sensitive receptor data coverages and to report relative proportions of exceedances at varying grid scales.