Since 1977 four different sampling programs in The Halocarbons and other Atmospheric Trace Species (HATS) group have measured chlorofluorcarbon-11 (CFC-11). The programs include two flask systems and two in situ programs. Flask measurements started in 1977 with six stations and continue today sampling at 12 remote locations. The in situ program started in 1986 (called RITS) with a couple of gas chromatographs located at Mauna Loa, Hawaii and South Pole observatories. The following few years instruments were added at Barrow, Alaska, American Samoa, and Niwot Ridge, Colorado. A four channel gas chromatograph was developed in 1998 (called CATS) and replaced the RITS in situ instrumentation. The CATS gas chromatographs are currently deployed at six field sites and make hourly measurements.

Hemispheric and global means are calculated by assimilating measurements from the flask and in situ programs. The HATS CFC-11 data is on the NOAA 1992 scale.

Combined HATS CFC-11 data file

The figure above shows the different measurement programs' calculated global means and illustrates the overlap amongst programs (current programs are solid lines, dashed lines are discontinued programs). Measured monthly means from the different programs are statistically combined to create a long-term NOAA/ESRL GMD data set (black line). The combined data is calculated by first interpolating missing data at a sampling location for each measurement program. A weighted average is subsequently taken where there are co-located measurements from two or more programs; followed by a three month wide box smooth algorithm.

Zonal means are calculated for four northern (solid lines) and three southern (dashed lines) bins.

Hemispheric and a global mean are calculated from the zonal averages where sampling locations are weighted by the cosine of their latitude. This combined CFC-11 data set is used in NOAA's Annual Greenhouse Gas Index (AGGI) and NOAA's Ozone Depleting Gas Index (ODGI).

Global history of CFC-11 as a function of latitude (y-axis) and time (x-axis).

The Combined HATS CFC-11 Data File uses monthly data from the following programs:

• Original flask program: Monthly
• Current flask program: Monthly, Global
• RITS in situ program: Hourly, Daily, Monthly, Global
• CATS in situ program: Hourly, Daily, Monthly, Global