SAMOA (U.S.)

Period of Record

Trends

CFC-11 and CFC-12

From August 1977 to December 1992, the monthly average mixing ratio of CFC-11 at Cape Matatula, American Samoa, increased from 133.6 to 269.6 parts per trillion by mole (ppt). Over nearly the same period (August 1977-November 1992), the monthly average mixing ratio of CFC-12 increased from 242.1 to 500.1 ppt. During 1977-84, the increases were nearly linear, averaging 9.1 ppt/year (R² = .99) for CFC-11 and 17.6 ppt/year (R² = .99) 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 Samoa; these reached average 1985-88 values of 10.2 ppt/year (R² = .98) for CFC-11 and 18.4 ppt/year (R² = .96) for CFC-12. Since 1988 the growth rates at Samoa have decreased rapidly, particularly for CFC-11: in 1992, the mean growth rate of CFC-11 was 3.6 ppt/year, and the mean growth rate of CFC-12 was 11.5 ppt/year. These decreases reflect the recent worldwide declines in production and emissions of CFCs and are consistent with findings at other sites in the NOAA/CMDL network (Elkins et al. 1993).

The records for Samoa also show a seasonal pattern: peak mixing ratios occur during November-March, when a high frequency of northwesterly flow transports air masses enriched in CFCs from the Northern Hemisphere (Elkins et al. 1993).

HCFC-22

From November 1991 to December 1992, the mixing ratio of HCFC-22 at Samoa increased (after an anomalously high initial value of 96.2 ppt) at an average rate of 4.4 ppt/year, reaching a value of 97.5 ppt by the end of the period. This trend is highly significant (P = .02).

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 July 1989 to February 1992, the mixing ratio of H-1211 at Samoa averaged 2.12 ppt but showed no significant (at the P = .05 level) trend. Over the same period, the mixing ratio of H-1301 increased from 1.51 to 1.96 ppt and showed a significant (P = .01) increase of 0.13 ppt/year. 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.

Samoa (Cape Matatula)
U.S. Territory
South Pacific Ocean
Rocky promontory
14° 18' S, 170° 36' W
77 m above MSL

Samoa Mixing Ratios Graph

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