SAMOA

Period of Record

Trends

The ALE/GAGE monitoring site in Samoa is located at the National Oceanic and Atmospheric Administration (NOAA) station at Cape Matatula, on a rocky promontory overlooking the Pacific ocean ~30 m above mean sea level. The ALE/GAGE operation at Samoa through 1989 was carried out under the supervision of R.A. Rasmussen and A.J. Crawford of the Oregon Graduate Institute of Science and Technology. The site is now supervised by R.F. Weiss of the Scripps Institution of Oceanography (SIO). The site receives unpolluted oceanic air almost exclusively; during the southern summer, however, conditions during the Northern Hemisphere winter often allow air from the Northern Hemisphere to reach Samoa. Measurements at the site began in July 1978 and continued as part of ALE through May 1986. Beginning in July 1985, measurements were also collected as part of GAGE. After the conclusion of ALE, measurements at Samoa continued as part of GAGE through June 1989 and then began again in late 1990.

The monthly mean mixing ratio of CFC-11 increased from 138.9 parts per trillion (ppt) in July 1978 to 240.8 ppt in June 1989. The mixing ratio of CFC-12 increased from 251.1 to 457.8 ppt during the same period. Cunnold et al. (1994) determined that the average rate of increase in atmospheric mixing ratios at Samoa from July 1978 to June 1988 was 9.2±0.1 ppt/year for CFC-11 and 17.3±0.2 ppt/year for CFC-12. For both CFC-11 and CFC-12, the trends are highly significant (P < 0.0001). In addition, annual cycles are evident for both CFC-11 and CFC-12; maximum mixing ratios are observed in late summer and minima in late winter (Prinn et al. 1983; Cunnold et al. 1994).

The time series of the monthly mean mixing ratios of N₂O is generally linear, except for an anomalously large increase during the first 4 months of record. The values show a highly significant (P < 0.0001) trend over the period of record. The monthly mixing ratio increased from 293.8 parts per billion (ppb) in July 1978 to a high of 307.6 ppb in January 1989 to 306.1 ppb in June 1989. For January 1979 to June 1988, Prinn et al. (1990) calculated that the mixing ratio of N₂O increased by an average of 0.91±0.04 ppb/year. No significant periodic oscillation is evident.

Samoa (Cape Matatula)
U.S. Territory
South Pacific Ocean
Island rock promontory
14° 15' S, 170° 34' W
42 m above MSL

Samoa Mixing Ratios Graph

• Monthly average CFC-11, CFC-12, and N₂O mixing ratios at Samoa