A decline in tropospheric organic bromine

[1] Recent changes in atmospheric bromine (Br) are estimated from samples collected at ten globally distributed, ground-based sites. The results indicate that the global tropospheric burden of Br from the sum of halons and methyl bromide (CH₃Br) peaked in 1998 and has since declined by nearly 5% (or 0.8 ± 0.2 pmol mol⁻¹ or ppt). These changes are driven primarily by a decrease of CH₃Br since 1998 that is about two times larger than expected given reported declines in industrial production, a result that may suggest revisions to our understanding of the global atmospheric budget for this gas. The observations imply 25–30% larger declines in the atmospheric burden of ozone-depleting, total equivalent chlorine (ECl = Cl + Br*45) in recent years than noted previously.