Southern Hemispheric halon trends (1978–1998) and global halon emissions

Abstract

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−1. In 1997 the mixing ratios were 4.0 (CBrClF2, H‐1211), 2.1 (CBrF3, H‐1301), 0.4 (CBrF2CBrF2, H‐2402), and 0.04 ppt (CBr2F2, H‐1202), contributing ∼60, 30, 10 and 1% respectively to halon‐derived bromine (40% of background tropospheric bromine). The halons exhibit different growth patterns: CBrClF2 continues linearly (0.20 ppt yr−1), CBrF3 slows significantly (0.03 ppt yr−1, early 1998), CBrF2CBrF2 stops and CBr2F2 increases (17% yr−1 in early 1998). CBr2F2 shows a photochemically driven annual cycle. CBrClF2 and CBrF3 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 (CBrClF2), 62 (CBrF3), 20 (CBrF2CBrF2), and 2.9 (CBr2F2) years. Calculated and measured mixing ratios of CBrF3 agree reasonably but not for CBrClF2 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 CBrClF2 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 CBr2F2, a by‐product of CBrClF2 manufacture. The recent atmospheric growth of CBr2F2 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.