NOTICE: The project that is the subject of this report was approved by the Governing Board of the National Research Council, whose members are drawn from the councils of the National Academy of Sciences, the National Academy of Engineering, and the Institute of Medicine. The members of the committee responsible for the report were chosen for their special competences and with regard for appropriate balance.

Support for this project was provided by the U.S. Global Change Research Program, the U.S. Environmental Protection Agency, and the National Aeronautics and Space Administration. Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the authors and do not necessarily reflect the views of the sponsors.

Cover: The cover image shows the distribution of atmospheric carbon monoxide over the Western Hemisphere (at approx. 880hPa) simulated at Harvard University using GEOS-CHEM, a global three-dimensional model of tropospheric chemistry driven by assimilated meteorological observations from the Goddard Earth Observing System (GEOS) of the NASA Data Assimilation Office. Note that the color-scale of the image has been altered for use on the report cover. The original image, along with a variety of other GEOS-CHEM simulation results are available online at: http://www-as.harvard.edu/chemistry/trop/

Copyright 2001 by the National Academy of Sciences. All rights reserved.

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