9612282 Jacob In this project, 3-dimensional chemical models will be used to investigate issues in tropospheric chemistry. (1) The export of nitrogen oxides from North America to the global atmosphere in different seasons, and the role played by non-methane hydrocarbons in modifying this export, will be quantified. Large amounts of nitrogen oxides are emitted by fossil fuel combustion in North America, but only a fraction of this material is exported out of the continental boundary layer where it affects tropospheric chemistry on a global scale. (2) The contribution of fossil fuel combustion in North America to concentrations of nitrogen oxide in the remote troposphere will be determined by expanding the scale of the 3-dimensional model from continental-scale to the northern hemisphere. The ultimate fate of the nitrogen oxides exported from North America, and its influence on global tropospheric chemistry, will be investigated. (3) The factors controlling the concentration of nitrogen and hydrogen oxide radicals in the upper troposphere will be studied. These chemical factors are currently poorly understood. A comprehensive theoretical study will be conducted, supported by data from recent and upcoming aircraft campaigns, in order to define the different regimes and to examine the sensitivity to chemical and meteorological variables. (4) The sources of atmospheric acetone are currently not known quantitatively. A 3-dimensional model study of acetone and its non-methane hydrocarbon precursors will be conducted. Detailed comparisons of simulated and observed atmospheric concentrations in different regions will be carried out.
