We propose, over a three year period, to assess direct and indirect effects of anthropogenically generated aerosols on surface fluxes of UVA (320-400 nm), UVB (280-320 nm), and PAR (photosynthetically active radiation,400-700 nm). Studies will include use of three-dimensional, model-generated sulfate aerosol fields resulting from emission estimates. Estimates of indirect effects will include responses of tropospheric and stratospheric ozone to aerosol induced radiative changes. The indirect effects of aerosols on cloud optical propertes will be parameterized based on results from separate modeling studies and observations. Finally, studies of the sensitivity of crops to spectral radiative changes will be used to estimate the agricultural and ecological impacts resulting from increased aerosol abundances.

The primary studies will incorporate zonally averaged, seasonally varying, anthropogenic aerosol distributions into a 2-D chemistry-radiation-dynamic (CRD) model for the calculation of the UVA, UVB, and PAR surface fluxes. Major results will include seasonal limits of the aerosol induced variation in these radiation fluxes for various latitude regions. Additional aerosol scenarios will include zonal averages taken from observations and scenarios that reflect the magnitude of zonal inhomogeneities. Final studies will use limited, available (NASA, LLNL) 3-D chemical-radiation-transport (CRT) model analyses for non-interactive assessment of the effects of zonal inhomogeneities in aerosol, cloud, and ozone distributions. Coupling between changes in aerosol loading, and ozone chemistry, via changes in photolysis and heating rates, will be investigated via 2-D modeling studies. Estimated effects of increased aerosol on cloud reflectivities, via changes in particle number densities and size distributions, will be included. Current models and experimental determinations of UV and PAR radiation effects on particular crop yields will be used to determine whether the aerosol scenarios considered have meaningful consequences for crop yields.

These studies will primarily be conducted by Faculty Members, Masters degree graduate students, and undergraduate scholars at the Timbuktu Academy at Southern University and A & M college, Baton Rouge, La. in colloboration with scientists at NASA and the Lawrence Livermore National Laboratory. This collaboration will produce important scientific results, while providing increased educational and computational opportunities for staff and students at Southern University.