Evidence for a decline in the atmospheric accumulation rate of CHCIF₂ (CFC-22)

Abstract

Concern that emissions of fully halogenated hydrocarbons may deplete stratospheric ozone through chlorine-catalysed destruction^1–3 has prompted a search for safer chemicals. CHCIF₂ (CFC-22) is a promising substitute as it contains only a single chlorine atom and is partially removed in the troposphere by reactions with hydroxyl radicals (OH) ⁴. Recognizing these facts, CFC-22 has been excluded from the controls under the Montreal Protocol²⁹. The possibility of rapidly increasing use of CFC-22 suggests a need for careful atmospheric monitoring, especially as the atmospheric lifetime of CFC-22 is long but uncertain (12–28 yr (refs 3, 5)) and absorption by the strong CFC-22 infrared bands could contribute to greenhouse warming^6,7. Here we report atmospheric CFC-22 measurements derived from ground-based solar spectra recorded between December 1980 and May 1988 which show that the CFC-22 total column increased at an average annual exponential rate of 7.8% ± 1.0% (2σ). Compared with other atmospheric data, these measurements indicate that CFC-22 is increasing at a more rapid rate than either CFC-11 or CFC-12, the two most abundant chlorofluorocarbons, but that the rate of CFC-22 increase is likely to have declined over the past few years.