PROGRAM TITLE:	Atmospheric Chemistry Project (IGAC) 
ACTIVITY STREAM:	Process Research
SCIENCE ELEMENT:	Biogeochemical Dynamics


DESCRIPTION:  The Project focuses global measurements, lab studies, and 
theory on improving the understanding of greenhouse gas budgets and 
stratospheric ozone depletion.   Greenhouse Gases.  (i) NOAA's global 
baseline observatories are characterizing the atmospheric trends of major 
greenhouse gases, e.g., CO2, CH4, N2O, halocarbons, and tropospheric ozone.  
These studies have recently discovered that the growth rates of CH4 and the 
halocarbons have slowed.  Over the next few years, work will focus on 
characterizing the terrestrial CO2 sink and the emerging trends of the CFC 
replacements.  (ii) Lab studies are defining the chemical removal reactions 
(sinks) of radiatively important gases.  The residence time (hence Global 
Warming Potential, GWP) of CH4 was found to be 25% larger than thought, 
and perfluorocarbons have been shown to be powerful greenhouse gases, 
with residence times of millennia.  (iii) Radiative forcing calculations have 
discovered that depletion of ozone can cause less radiation to the surface-
troposphere system, thereby lowering the CWP's of the CFCs et al.  Future 
calculations are focusing on quantifying, within a year, the effect of  ozone 
depletion on surface temperature and on calculating the net GWPs of the 
CFCs.  Ozone Depletion.  (i) Lab studies are providing the atmospheric 
lifetimes that are needed to determine accurate Ozone Depletion Potentials 
(ODPs) of the CFC and Halon substitutes and methyl bromide.  (ii) Theoretical 
investigations are developing a refined method of calculating ODPs using 
atmospheric measurements, rather than purely models.  An Overall 
Performance Measure. A substantial fraction of the new discoveries noted in 
the Executive Summary of the 1992 IPCC assessment supplement were results 
from this Project [see pp. 8-9, NOAA Contributions to the 1995 IPCC 
Assessments (1993)].

STAKEHOLDERS:  The Project provides:  USGCRP.  Ground truth for 
NOAA/NASA satellites.  Collaboration with NSF in studying global chemical 
sinks and with DOE in tropospheric ozone formation.  Partner with NASA in 
polar ozone campaigns.  International.  Leader of the North Atlantic Regional 
Experiment (greenhouse ozone formation) of IGAC and major contributor of 
two other IGAC efforts.  Assessments.  Overall assessment, cochair and chairs 
of 2 chapters of the 1994 Ozone Assessment for the UN Montreal Protocol, 
cochairs of 2 of the 5 chapters of the 1994 IPCC assessment, and science advisor 
to the US for the IPCC and Climate Convention.

SHORT-TERM  POLICY PAYOFFS:  Climate Change.  Better global trends, 
sinks, and variations of greenhouse gases, providing insight into budgets and 
future scenario projections for the Climate Convention.  Quantified CFC 
cooling effect, yielding more accurate predictions of surface-temperature 
changes.  Characterizing tropospheric (greenhouse) ozone, which will help 
define the relation between pollution abatement and  greenhouse-gas 
abatement.  Ozone Depletion.  Defining the atmospheric trend response to 
CFC emission reductions, which can be used to evaluate global compliance.  
Sounder ODPs for the UN Montreal Protocol and the US Congress, yielding 
better choices for managing the maximum ozone depletion around the year 
2000.  Early evaluation of CFC substitutes for industry, thereby avoiding costly 
plant-investment errors.

PROGRAM CONTACT:  Dan Albritton, Environmental Research 
Laboratory,325 Broadway, Boulder, CO 80303, (303-497-5785) and Joel Levy, 
Office of Global Programs, 1100 Wayne Avenue, Suite 1225, Silver Spring, MD 
20910,  (301-427-2089 X756).