Reconstructed histories of the annual mean atmospheric mole fractions for the halocarbons CFC-11, CFC-12, CFC-113 and Carbon Tetrachloride
Updated 7th May 2009
- Stephen J. Walker (sjwalker AT ucsd.edu)
- Ray F. Weiss (rfw AT gaslab.ucsd.edu)
- Peter K. Salameh (peter AT gaslab.ucsd.edu)
Please note that there has been a change in the calibration scale
for the mixing ratios listed on this website. This has resulted in
small changes in the estimated concentrations for all compounds.
See 2. Calibration Scale below.
The ASCII .m files in this directory contain annual mean atmospheric
mixing ratios for the halocarbons CFC-11, CFC-12, CFC-113 and carbon
tetrachloride. These data have been reconstructed from a combination
of direct atmospheric measurements and box model simulation. The most
recent measurements for each gas are determined from monthly mean
direct tropospheric measurements made by the ALE/GAGE/AGAGE group of
atmospheric scientists (Prinn et al., 2000). For a detailed
description of how these annual mean mixing ratios were obtained, see
Walker et al., 2000.
2. Calibration Scale The ALE/GAGE/AGAGE group have
updated the calibration scale against which all atmospheric mixing
ratios are measured. Previous measurements were made against either
the SIO-93 or SIO-98 scales, while the new scale is SIO-05. This has
meant that all reported mixing ratios have changed very slightly. In
all cases the change is less than one percent. Specifically, the
ratio of SIO-05 to SIO-98 for these halocarbons is as follows:
The ratio of SIO-98 to SIO-93 for these halocarbons is also reported (Prinn et al., 2000)
To convert mixing ratios made against SIO-93 to the corresponding
value on SIO-98, multiply by the appropriate value for each compound
as listed in the table above.
3. File structure
Each ASCII .m file contains the annual mean mixing ratios, centered at
July 1st, for the Northern and Southern hemispheres. Also included is
an estimate of the uncertainty in each annual mean mixing ratio. A
header in each file describes the data layout. The files are actually
structured as matlab .m functions which may be conveniently called
from matlab or alternatively the ASCII data may simply be extracted
for use in other applications.
Mixing ratios measured against the SIO-05 calibration scale through 2008
As a convenience, we are maintaining copies of the old histories which
were measured against SIO-98 and SIO-93. The SIO-93 values appeared in
Walker et al., 2000. However, neither the SIO-93 nor SIO-98
values will not be updated with additional mixing ratios past 1998 and
Mixing ratios measured against the SIO-98 calibration scale through 2003
Mixing ratios measured against the SIO-93 calibration scale through 1998
5. Journal references
Prinn, R. G., R. F. Weiss, P. J. Fraser, P. G. Simmonds,
D. M. Cunnold, F. N. Alyea, S. O'Doherty, P. Salameh, B. R. Miller,
J. Huang, R. H. J. Wang, D. E. Hartley, C. Harth, L. P. Steele,
G. Sturrock, P. M. Midgley, and A. McCulloch, A hisotry of chemically
and radiatively important gases in air deduced from ALE/GAGE/AGAGE
J. Geophys. Res., 105, 17,751-17,792, 2000.
Walker, S. J., R. F. Weiss and P. K. Salameh, Reconstructed histories of the annual mean atmospheric mole fractions for the halocarbons CFC-11, CFC-12, CFC-113 and carbon tetrachloride J. Geophys. Res., 105, 14,285-14,296, 2000.
6. Data usage
Please feel free to take copies of all these files for use in your
research work. Also please feel free to forward
the address of this web site to colleagues whom you feel may be
interested in the data.
As more data becomes available from the ALE/GAGE/AGAGE group I will
update these files with the latest annual mean mixing ratios.