We turn next to the question of defining a research strategy that addresses the primary Research Imperatives:
Stratospheric ozone and UV radiation. Define and predict secular trends in the intensity of UV exposure that the Earth receives. Document the concentrations and distributions of stratospheric ozone and the key chemical species that control its catalytic destruction and elucidate the coupling between chemistry, dynamics, and radiation in the stratosphere and upper troposphere.
Greenhouse gases. Determine the fluxes of greenhouse gases into and out of the Earth 's systems and the mechanisms responsible for the exchange and distribution between and within those systems. Expand global detection techniques to elucidate the processes that control the abundances and variability of atmospheric CO2, CH4, N2O, and upper-tropospheric/lowerstratospheric O3 and water vapor.
Photochemical oxidants. Develop the observational and computational tools and strategies that policy makers need to effectively manage ozone pollution and elucidate the processes that control and the relationships that exist among ozone precursor species, tropospheric ozone, and the oxidizing capacity of the atmosphere.
Atmospheric aerosols and UV/visible radiation. Document the chemical and physical properties of atmospheric aerosols and elucidate the chemical and physical processes that determine the size, concentration, and chemical characteristics of atmospheric aerosols.
Toxics and nutrients. Document the rates of chemical exchange between the atmosphere and ecosystems of critical economic and environmental import and elucidate the extent to which interactions between the atmosphere and biosphere are influenced by changing concentrations and depositions of harmful and beneficial compounds.
The research strategy recommended here addresses such questions and hypotheses, which have been selected in view of their intrinsic scientific merit, particularly regarding the Earth's ability to sustain life. The recommended research strategy is also based on a plan of attack that relies on a flexible array of experimental and theoretical analyses. The objective is to test the most important questions expeditiously and efficiently. The selected manifold of state-of-the-art techniques reflects the use of new technical developments and diagnostic calculation methods, along with recognition of the distinction between establishing secular trends and determining the fundamental processes responsible for global-scale