Growth and distribution of halons in the atmosphere

The atmospheric burden of halons has continued to increase in recent years, despite an international ban on their production and sales in developed nations as of January 1, 1994. Halon emissions persist because of a lack of suitable substitutes for critical uses as fire extinguishants. As of January 1, 1997, halons H-1301 (CBrF3), H-1211 (CBrClF2), and H-2402 (CBr2F4) were present in the troposphere at 2.3+/-0.1, 3.5+/-0.1, and 0.45+/-0.03 pmol mol(-1). During 1995-1996 the tropospheric mole fraction of H-1301 increased at 0.044+/-0.011 pmol mol(-1) yr(-1), while that for H-1211 grew at 0.16+/-0.016 pmol mol(-1) yr(-1). These increases are significant and of concern because of the efficiency of bromine in depleting stratospheric ozone and because of the long atmospheric lifetimes of these gases. Given the current atmospheric record and the reported amount of halon produced before the ban on production, emission of H-1301 at the 1995-1996 rate could continue for another 40 years, but H-1211 would be depleted in 8-12 years. Exemptions to the ban on production may extend these periods. Tropospheric H-2402 is increasing at 9+/-1 fmol mol(-1) yr(-1), but historical data on its production and use are lacking.