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