SOUTH POLE

Period of Record

Trends

CFC-11 and CFC-12

From January 1977 to November 1992 at the South Pole, Antarctica, the monthly average mixing ratio of CFC-11 increased from 134.3 to 270.6 parts per trillion by mole (ppt). Over much the same period (June 1977 to November 1992), the monthly average mixing ratio of CFC-12 increased from 231.0 to 500.3 ppt. Despite the sparsity of the data (measurements generally were made only during the austral summer, when the station was open), the CFC records nevertheless show nearly linear trends during 1977-84, with average increases of 8.9 ppt/year (R² = .91) for CFC-11 and 18.8 ppt/year (R² = .95) for CFC-12. The gap in the CFC-12 record during 1984-85 resulted from a gas chromatograph problem affecting only CFC-12. A surge in CFC production worldwide beginning in 1985 caused a corresponding rise in the atmospheric growth rates at the South Pole; these reached average 1985-88 values of 8.4 ppt/year (R² = .98) for CFC-11 and 15.7 ppt/year (R² = .99) for CFC-12. Since 1989 the growth rates at the South Pole have decreased rapidly, and trends for 1992 were not statistically significant (at the P = .05 level) for either CFC-11 or CFC-12. These decreases reflect the recent worldwide declines in production and emissions of CFCs (Elkins et al. 1993). The magnitudes of the declines at the South Pole are greater than those at low- and middle-latitude sites in the NOAA/CMDL network but are consistent with those at the other high-latitude sites (i.e., Alert and Barrow).

HCFC-22

From December 1991 to November 1992, the mixing ratio of HCFC-22 at the South Pole increased from 92.0 to 97.1 ppt, averaging 6.8 ppt/year. This trend is highly significant (P = .0002).

The collective results presented here for HCFC-22 from the seven monitoring sites show a mean global mixing ratio of 100 ppt for March 1992, with a mean interhemispheric ratio (Northern hemispheric mixing ratio : Southern hemispheric mixing ratio) of 1.14. The mean global growth rate of HCFC-22 over the period of record was 7% per year (Montzka et al. 1993).

H-1301 and H-1211

From January 1990 to January 1992, the mixing ratio of H-1211 at the South Pole averaged 2.15 ppt, while that of H-1301 averaged 1.62 ppt. Neither H-1211 nor H-1301 showed any significant (at the P = .05 level) trend. Comparing their data with published results from other investigators (covering the period 1978-92), Butler et al. (1992) concluded that significant declines have occurred in the growth rates of the atmospheric mixing ratios of both halons. These recent drops in growth are supported in general by industry production figures, emission estimates, and current appraisals of atmospheric lifetimes.

South Pole
Antarctica
Ice- and snow-covered plateau
89° 59' S, 24° 48' W
2841 m above MSL

South Pole Mixing Ratios Graph

• Monthly atmospheric mixing ratios of CFC-12, CFC-11, HCFC-22, H-1211, and H-1301 at the South Pole