MAUNA LOA

Period of Record

Trends

CFC-11 and CFC-12

From January 1977 to December 1992, the monthly average mixing ratio of CFC-11 at Mauna Loa, Hawaii, U.S.A., increased from 139.9 to 275.4 parts per trillion by mole (ppt). During 1977-84, the increase was nearly linear, averaging 9.0 ppt/year (R² = .99). From May 1977 to December 1992, the monthly average mixing ratio of CFC-12 increased from 258.0 to 518.1 ppt. The increase was again nearly linear during 1977-84, averaging 15.7 ppt/year (R² = .97). 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 Mauna Loa; these reached average 1985-88 values of 10.7 ppt/year (R² = .98) for CFC-11 and 20.7 ppt/year (R² = .96) for CFC-12. Since 1988 the growth rates at Mauna Loa have decreased rapidly, particularly for CFC-11: in 1992, the mean growth rate of CFC-11 was 4.3 ppt/year, and the mean growth rate of CFC-12 was 17.1 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).

HCFC-22

From December 1991 to December 1992, the mixing ratio of HCFC-22 at Mauna Loa increased from 102.9 to 111.0 ppt, averaging 7.0 ppt/year. This trend is highly significant (P = .0007).

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 September 1989 to April 1992, the mixing ratio of H-1211 at Mauna Loa increased from 1.92 to 2.56 ppt, averaging 0.16 ppt/year (P = .06). From July 1989 to April 1992, the mixing ratio of H-1301 grew from 1.14 to 1.88 ppt, at an average of 0.11 ppt/year (P = .05). 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.

Mauna Loa
Hawaii, U.S.A.
Barren volcanic mountain slope
19° 30' N, 155° 36' W
3397 m above MSL

Mauna Loa Mixing Ratios Graph

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