Abstract
Abstract. The atmospheric records of four halons, H-1211 (CBrClF2), H-1301 (CBrF3), H-2402 (CBrF2CBrF2) and H-1202 (CBr2F2), measured from air collected at Cape Grim, Tasmania, between 1978 and 2011, are reported. Mixing ratios of H-1211, H-2402 and H-1202 began to decline in the early to mid-2000s, but those of H-1301 continue to increase up to mid-2011. These trends are compared to those reported by NOAA (National Oceanic and Atmospheric Administration) and AGAGE (Advanced Global Atmospheric Experiment). The observations suggest that the contribution of the halons to total tropospheric bromine at Cape Grim has begun to decline from a peak in 2008 of about 8.1 ppt. An extrapolation of halon mixing ratios to 2060, based on reported banks and predicted release factors, shows this decline becoming more rapid in the coming decades, with a contribution to total tropospheric bromine of about 3 ppt in 2060. Top-down global annual emissions of the halons were derived using a two-dimensional atmospheric model. The emissions of all four have decreased since peaking in the late 1980s–mid-1990s, but this decline has slowed recently, particularly for H-1301 and H-2402 which have shown no decrease in emissions over the past five years. The UEA (University of East Anglia) top-down model-derived emissions are compared to those reported using a top-down approach by NOAA and AGAGE and the bottom-up estimates of HTOC (Halons Technical Options Committee). The implications of an alternative set of steady-state atmospheric lifetimes are discussed. Using a lifetime of 14 yr or less for H-1211 to calculate top-down emissions estimates would lead to small, or even negative, estimated banks given reported production data. Finally emissions of H-1202, a product of over-bromination during the production process of H-1211, have continued despite reported production of H-1211 ceasing in 2010. This raises questions as to the source of these H-1202 emissions.
Highlights
The uncertainties for the NOAA-2006 gravimetric scale are estimated as 1 % for H-1211 and 2 % for H-1301 (Brad Hall, personal communication), those of the University of East Anglia (UEA) volumetric scale are estimated as 4 % for both H-2402 and H-1202 (Fraser et al, 1999)
42 45 48 was run with the alternative lifetimes; the cumulative emissions (1963–2010) derived for H-1211 increased by 14 Gg to 290 Gg, for H-1301 they decreased by 5 Gg to 101 Gg and for H-2402 they increased by 4 Gg to 46 Gg (Table 2)
The atmospheric mixing ratios of H-1202, H-1211 and H2402 are all declining and are likely to continue to do so due to the cessation of all halon production in 2010
Summary
Atmospheric mixing ratios of the halons increased rapidly from the late 1970s up to the late 1990s (Butler et al, 1999; Fraser et al, 1999; Sturrock et al, 2002) They have since levelled off or begun to decline, with the exception of H1301 which continues to grow (based on data reported up to 2008) (Reeves et al, 2005; Montzka et al, 2011). A two-dimensional atmospheric chemical transport model is used to derive top-down global annual emissions of the halons These derived emissions are compared to those derived by NOAA and AGAGE using a top-down approach and by HTOC (Halons Technical Options Committee) using a bottom-up approach. The current and future contribution of the halons to tropospheric bromine mixing ratios is discussed
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