PROGRAM TITLE: Atmospheric Physics and Chemistry Studies ACTIVITY STREAM: Process SCIENCE ELEMENT:Biogeochemical Dynamics SMITHSONIAN INSTITUTION SMITHSONIAN ASTROPHYSICAL OBSERVATORY (SAO) SCIENTIFIC MERIT: At its most fundamental level, global change is driven by the complex interactions between the earth and its atmosphere due to the actions of mankind and the Sun. Because human activities can make inadvertent changes in the composition of the atmosphere which negatively affect the delicate balance of constituents and thereby threaten the natural life support systems, it is clearly necessary to have accurate predictive models of the atmosphere which make essential contributions to the formulation of government policy. In order to develop accurate models, the detailed composition of the atmosphere, the absorption and transmission of radiation, and the many complex chemical processes which occur must be understood. Much of the available data needed in these models is of very limited accuracy. Significant advances can be made in the predictive capabilities of atmospheric models through a combination of atmospheric remote-sensing measurements, laboratory spectroscopy and theoretical studies. A prime objective of this program is the development, refinement and testing of atmospheric chemistry models which have excellent predictive capabilities. SAO scientists are engaged in an on-going program to carry out remote- sensing measurements of trace species in the stratosphere which play an important role in the ozone chemistry. Such measurements test the current models and aid in their refinement. SAO scientists are also developing instruments to fly on satellites to monitor global ozone concentrations and to quantify pollutants in the troposphere. At SAO, accurate laboratory measurements of the photoabsorption cross-sections of atmospheric species are being made in order to provide reliable data for atmospheric models. Investigation of couplings of the various regions of the atmosphere, and of perturbations, both anthropogenic and natural, to the atmosphere are carried out. Using a high-resolution Fourier-transform spectrometer (FIRS-2) that operates in the far and mid infrared, SAO scientists measure the stratospheric concentration of ozone as well as a number of trace, reactive chemicals that are involved in ozone layer photochemistry. This SAO program is the only one in the world that simultaneously (in space and time) measures abundances of complete families of chemical species related by complex chemical reactions. The satellite instruments currently under development operate in the ultraviolet, visible and infrared and will measure stratospheric chemistry, as well as sources, sinks and distributions of greenhouse gases and atmospheric pollutants. STAKEHOLDERS: Laboratory measurements in support of the far infrared measurements are on-going. The satellite measurement programs include (1) The Global Ozone Monitoring Experiment (GOME) funded by the European Space Agency as a core instrument on their ERS-2 satellite scheduled for 1994 launch and (2) The SCanning Imaging Absorption spectroMeter for Atmospheric CHemistrY (SCIAMACHY) and on the ESA polar platform in 1997. The 6.65 m. spectrometer located at Harvard-Smithsonian has been used to generate the most accurate absorption coefficients to date on a variety of atmospheric species (O2, O3, NO, etc.) and photochemically active compounds such as CH4 and H2CO. POLICY RELEVANCE: The proposed program of remote sensing measurements of the atmosphere and the troposphere addresses a large number of the key milestones in the Atmospheric Chemistry and Circulation section of the USGCRP Implementation Plan. The remote sensing measurements in the stratosphere and troposphere address a number of key objectives in the IGAC established Core Project of the IGRP as well as in the STIB Core Project of the IGBP. An understanding of the transmission properties of the atmosphere, which depend on the photoabsorption coefficients of the ambient species, and the radiative balance of the stratosphere are research priorities in the STIB Core Project of the IGBP. Over the years there has been strong NASA support for the research programs mentioned above and extensive international collaboration at all levels. PROGRAM CONTACTS:SI SGCR Representative: Ted A. Maxwell NASM MRC 315 Smithsonian Institution Washington, D.C. 20560 202 357 1424 FAX: 202 786 2566 Email: tmaxwell@ceps.nasm.edu Bureau Representative: Kate Kirby Smithsonian Astrophysical Observatory 60 Garden St. MS-14 Cambridge, MA 02138 617 495 7237 or 9524 FAX: 617 495 5970