PROGRAM TITLE:	Global Tropospheric Chemistry Program (GTCP)
ACTIVITY STREAM:	Process, Observe, Model, Data
SCIENCE ELEMENT: 	Biogeochemical Dynamics


SCIENTIFIC MERIT:  The Global Tropospheric Chemistry Program is a 
focused atmospheric chemistry program designed to provide a better 
understanding of how substances of natural or anthropogenic origin enter the 
atmosphere, are physically and chemically transformed, and ultimately 
removed.  The overall objective of this program is to measure, understand, 
and thereby predict changes in the chemistry of the global atmosphere with 
particular emphasis on changes affecting the radiative properties and 
oxidizing capacity of the atmosphere and the atmospheric component of 
biogeochemical cycles.  This objective is to be accomplished through field and 
laboratory investigations as well as theory aided by appropriate statistical and 
mathematical modeling.  Augmentation of the base is required to permit NSF 
supported scientists at the Universities and the National Center for 
Atmospheric Research to participate in major international regional field 
experiments in FY 1995 through FY 1999 and to identify, analyze, and develop 
mathematical and statistical models of atmospheric chemistry that can be 
used for process understanding and climate prediction purposes.  Laboratory 
investigations of the mechanisms and rates of key chemical reactions will 
also be supported under this program.  A portion of the program's funds will 
be used to help offset the costs of development, procurement and evaluation 
of advanced instrumentation required for future observational projects.  
Major GTCP activities, including aircraft and land-based field observations to 
investigate the atmospheric cycles of carbon, nitrogen, sulfur, and oxidant 
species, and the development of tropospheric chemistry models, have been 
and are currently being planned and scheduled for the period 1995-1999.  
GTCP participation in multi-agency and international field projects scheduled 
for 1995 and beyond include studies of surface exchange processes in the 
tropics; photochemistry experiments in the atmosphere over the Atlantic and 
Pacific oceans; and studies of the role of atmospheric sulfur compounds on 
the distribution of aerosols and cloud physical properties.  
STAKEHOLDERS:  The NSF GTCP is part of a multi-agency and international 
tropospheric chemistry research effort.  NASA, NOAA and NSF have 
assumed the initial responsibility for nurturing a U.S. atmospheric chemistry 
research program focused on Global Change issues and ensuring a long-term 
support base.  DOE and EPA are also planning to make significant 
contributions to this global research effort.  An international research effort, 
the International Global Atmospheric Chemistry (IGAC) Programme, that is 
responsive to the needs of the IGBP has been developed by the ICSU 
International Association of Meteorology and Atmospheric Physics' 
Commission on Atmospheric Chemistry and Global Pollution (CACGP).  
IGAC was adopted as the first core project of the IGBP in 1989 and the focused 
IGAC projects contributing to the research programme were published in 1990 
in IGBP Report 12 and IGBP Report 13.  Project implementation plans for 
several IGAC campaigns were published in 1993.  The IGAC activities are 
focused on international atmospheric chemistry experiments that will 
provide knowledge of the sources and sinks of greenhouse gases and aerosols 
and the processes that control their distributions and lifetimes in the 
atmosphere.  The Global Tropospheric Chemistry Program is the NSF's 
contribution to the IGAC Programme.  
POLICY RELEVANCE:  In the short-term, field, laboratory, and theoretical 
tests will allow identification of greenhouse gas sources, sinks and lifetimes, 
the role of anthropogenic sulfate aerosols in offsetting trace-gas greenhouse 
warming, and an improved understanding of the factors which control the 
oxidizing capacity of the atmosphere.  This new knowledge will support U.S. 
environmental commitments, for example, in climate change, global 
warming, and stratospheric ozone.  Over the longer term, incorporation of 
these and other chemical processes in global chemistry and climate models 
will allow improved predictions and assessments of future changes in 
atmospheric composition and the resulting impact such changes may have 
on climate forcing.
PROGRAM CONTACT:  Jarvis Moyers, Atmospheric Chemistry Program