Since 1995 two different sampling programs in The Halocarbons and other Atmospheric Trace Species (HATS) group have measured sulfur hexafluoride (SF6). The programs include a flask system and an in situ program. Flask measurements started in 1995 with eight stations and continue today sampling at 12 remote locations. A four channel gas chromatograph was developed in 1998 (called CATS). The CATS gas chromatographs are currently deployed at six field sites and make hourly measurements.

Hemispheric and global means are calculated by statistically combining flask and in situ program measurements. The HATS SF6 data is on the NOAA 2006 scale.

Combined HATS SF6 data file

The figure above shows the different measurement programs' calculated global means and illustrates the overlap amongst programs. Measured monthly means from the different programs are statistically combined to create a long-term NOAA/ESRL HATS 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.

The global SF6 mean is plotted with 1-σ error bars (gray error bars). Improvements in measurement techniques and technology, as well as more sampling locations have reduced the global mean uncertainty since the mid 1990s. The red line is a linear fit to the global mean data demonstrating a fairly constant annual growth rate of 0.24 ppt per year. More recently the SF6 growth rate has been increasing.

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

The Combined HATS SF6 Data File uses monthly data from the following programs: