Since 1977 five different sampling programs within The Halocarbons and other Atmospheric Trace Species (HATS) group have measured chlorofluorocarbon-12 (CFC-12). These programs include three flask systems and two in situ programs. Flask measurements started in 1977 with six locations and another nine added over the years. CFC-12 mass spectrometer measurements were added to the HATS flask program in 2010 (M3 instrument).
The in situ program began in 1986 (called RITS) with a pair of gas chromatographs located at Mauna Loa, Hawaii and the South Pole observatories. The stations at Barrow, Alaska, American Samoa, and Niwot Ridge, Colorado added instrumentation over the following years. The HATS group developed a four channel gas chromatograph in the late 1990s (called CATS) to upgrade and expand the in situ measurement program. The CATS gas chromatographs are currently deployed at five field sites and make hourly measurements.
A combined data set has been developed to incorporate HATS monthly mean measurements made by different measurement systems. The combined data set is calculated by taking weighted averages of co-located measurements from background NOAA/GML air measurement programs (listed below). All programs are on the same NOAA scale (NOAA 2008 scale for CFC-12), and every attempt is made to correct known biases between measurement programs; however, there may be small differences that are not understood and characterized.
When comparing measurements from station to station, be aware that not all locations are composed of the same measurement programs. The hemispheric and global means in the combined data set are our best measure of long-term trends and are used for international and national assessments for background air measurements. Displayed below are the data sets used to produce the combined data set as well as several figures.
|CFC-12 measurement programs||Start||Finish|
|HATS old flask instrument||1977||1995|
|HATS current flask instrument (OTTO)||1995||Current|
|HATS in situ (RITS program)||1987||1999|
|HATS in situ (CATS program)||1998||Current|
|HATS MSD flasks (M3 instrument)||2010||Current|
Current HATS programs (green rectangles) and discontinued programs (orange rectangles) are used in the combined data set. Click on a rectangle for a link to a specific program's data files.
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/GML data set (black line). The combined data is calculated by first interpolating missing data at sampling location for each measurement program. A weighted average is subsequently calculated where there are co-located measurements from two or more programs. The gap filled station measurement is then smoothed with the Savitzky-Golay 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-12 data set is used in NOAA's Annual Greenhouse Gas Index (AGGI) and NOAA's Ozone Depleting Gas Index (ODGI).
Global history of CFC-12 as a function of latitude (y-axis) and time (x-axis).