BARROW

Period of Record

Trends

CFC-11 and CFC-12

From January 1977 to December 1992, the monthly average mixing ratio of CFC-11 at Barrow, Alaska, U.S.A., increased from 145.4 to 279.3 parts per trillion by mole (ppt). The increase was nearly linear during 1977-84, averaging 8.6 ppt/year (R² = .99). From September 1977 to December 1992, the monthly average mixing ratio of CFC-12 increased from 271.2 to 524.5 ppt. Although a number of gaps occur in the record, the increase was again nearly linear during 1977-84, averaging 16.4 ppt/year (R² = .98). 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 Barrow; these reached average 1985-88 values of 11.9 ppt/year (R² = .97) for CFC-11 and 20.9 ppt/year (R² = .96) for CFC-12. Since 1988 the growth rates at Barrow have decreased rapidly, particularly for CFC-11: in 1992, the mean growth rate of CFC-11 was essentially zero, and the mean growth rate of CFC-12 was 11.0 ppt/year (Elkins et al. 1993). These decreases reflect the recent worldwide declines in production and emissions of CFCs (Elkins et al. 1993). The decline in CFC-11 mixing ratios at Barrow is consistent with that at the other high-latitude sites (i.e., Alert and the South Pole) in the NOAA/CMDL network but is greater than that at low- and middle-latitude sites.

The records at Barrow also show a seasonal pattern: peak mixing ratios occur during the period November-March. These peaks are the result of cold air trapped in the polar tropospheric vortex, which forms during the winter months and restricts ventilation with cleaner air from low latitudes (Elkins et al. 1993).

HCFC-22

From December 1991 to December 1992, the mixing ratio of HCFC-22 at Barrow increased from 109.2 to 115.7 ppt, averaging 5.7 ppt/year. This trend is highly significant (P = .003).

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

Over the period of record (September 1989-February 1992), the mixing ratio of H-1211 at Barrow averaged 2.27 ppt but showed no significant (at the P = .05 level) trend. Over nearly the same period (August 1989-February 1992), the mixing ratio of H-1301 averaged 1.91 ppt and showed a significant (P = .02) increase of 0.11 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.

Barrow
Alaska, U.S.A.
Arctic coastal seashore
71° 18' N, 156° 36' W
11 m above MSL

Barrow Mixing Ratios Graph

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