- 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.
1. Contents
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:| SIO-05/SIO-98 | |
| CFC-11 | |
| CFC-12 | |
| CFC-113 | |
| Carbon tetrachloride |
The ratio of SIO-98 to SIO-93 for these halocarbons is also reported (Prinn et al., 2000)
| SIO-98/SIO-93 | |
| CFC-11 | |
| CFC-12 | |
| CFC-113 | |
| Carbon tetrachloride |
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.
4. Data
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 2003 respectively.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.
7. Updates
As more data becomes available from the ALE/GAGE/AGAGE group I will update these files with the latest annual mean mixing ratios.