air pollution, taking into account other factors such as reduced resistance to disease and climate extremes

• Develop methods to combine data from various sampling designs (for example, data assimilation and meta-analysis)

• Technological improvements in ozone measurement for biologically relevant ozone data (for example, appropriate temporal and spatial resolution)

• Modeling of the spatial distribution of dry deposition and ozone concentrations as a function of source, terrain, and meteorology. Mesoscale meteorological models require improved treatments of surface-atmosphere interactions, simulations in complex terrain, and simulation of flows under stagnating conditions often associated with ozone episodes.

• Develop coupled ecological process modeling and air quality modeling for evaluating responses spatially and temporally, and for scenario testing. The atmospheric modeling can provide spatial information on air quality to the ecosystem process models, which provide estimates of response to air pollution.

• Monitoring data are needed for verification of model predictions of exposure, particularly in rural areas.

• Continued studies on bioaccumulation of pollutants in aquatic and terrestrial ecosystems, and terrestrial/aquatic interactions.

• Exposure, transfer, and bioaccumulation of mercury in terrestrial and aquatic ecosystems. Studies on the effects of mercury on soil microbial processes and subsequent effects on plant processes in terrestrial ecosystems, including deposition in forests, terrestrial accumulation, transport to aquatic ecosystems and conversion of inorganic mercury to methyl mercury.

2. Improve process-based models of ecosystem response to pollutants for regional assessments.

Development and testing of spatially-explicit ecosystem models need to be accelerated for determining response at scales of air pollutant exposure. In terrestrial ecosystems, field studies should be linked with improved modeling of ecosystem exposure and responses to multiple controlling factors, cumulative stress, and plant community dynamics. This includes interaction of multiple cumulative effects of air pollutants and climatic factors on physiology of receptor plants (e.g., photosynthate allocation) and below-ground processes, differential sensitivities of species, and linking shifts in biogeochemical processes to changes in community dynamics and species composition.

3. Develop and test tools for assessing impacts of pollutants on biological species, populations, and ecosystems.