Southern hemispheric data (1978-1998) on four halons are reported. Halon-derived bromine increased by a factor of 10 from 0.6-0.7 parts per trillion (ppt) in 1978 to more than 7 ppt in early 1998, currently growing at 3% yr. In 1997 the mixing ratios were 4.0 (CBrClF, H-1211), 2.1 (CBrF, H-1301), 0.4 (CBrFCBrF, H-2402), and 0.04 ppt (CBrF, H-1202), contributing ∼60, 30, 10 and 1% respectively to halon-derived bromine (40% of background tropospheric bromine). The halons exhibit different growth patterns: CBrClF continues linearly (0.20 ppt yr), CBrF slows significantly (0.03 ppt yr, early 1998), CBrFCBrF stops and CBrF increases (17% yr in early 1998). CBrF shows a photochemically driven annual cycle. CBrClF and CBrF emissions (1963-2100) have been estimated from past and future production figures, in developed and developing countries, and from release estimates from the various halon banks. Mixing ratios have been calculated from a two-dimensional model incorporating seasonal transport and halon photochemistry and a latitudinal source function. The model-derived atmospheric lifetimes are 17 (CBrClF), 62 (CBrF), 20 (CBrFCBrF), and 2.9 (CBrF) years. Calculated and measured mixing ratios of CBrF agree reasonably but not for CBrClF in recent years. The model has been used to derive independently halon emissions that are consistent with the observed atmospheric trends. The continued growth of CBrClF in the background atmosphere could be due to enhanced production and emission in the Peoples' Republic of China, which may also explain the recent acceleration in growth of CBrF, a by-product of CBrClF manufacture. The recent atmospheric growth of CBrF may also be due to increased direct usage. The expected long-term recovery of stratospheric ozone could be delayed if the current halon growth continues into the next decade.
|Number of pages||15|
|Journal||Journal of Geophysical Research|
|Publication status||Published - 20 Jul 1999|