Southern hemispheric halon trends and global halon emissions, 1978–2011
1School of Environmental Sciences, University of East Anglia, Norwich, UK
2National Centre for Atmospheric Science, School of Environmental Sciences, University of East Anglia, Norwich, UK
3Centre for Australian Weather and Climate Research, CSIRO Marine and Atmospheric Research, Aspendale, Victoria, Australia
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 throughout the record. These trends are compared to those reported by NOAA (National Oceanic and Atmospheric Administration) and AGAGE (Advanced Global Atmospheric Experiment). The continued increase of H-1301 mixing ratios means that the contribution of the halons to total tropospheric bromine is not declining. 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 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). Additionally results are presented that suggest that H-1202 emissions are linked to H-1211 emissions rather than H-1211 production. Finally revised steady state atmospheric lifetimes are reported as 14 yr for H-1211, 75 yr for H-1301, 17 yr for H-2402 and 2.6 yr for H-1202. These revised lifetimes would reduce the estimated existing bank of H-1211 by over 80% to 10 Gg while increasing the H-1301 bank by 15% to 49 Gg.