Unexplained enhancements of CH sub(3)Br in the Arctic and sub-Arctic lower troposphere during TOPSE spring 2000

Elevated concentrations of methyl bromide (CH sub(3)Br) were observed in the Arctic atmospheric boundary layer (BL) during periods of widespread BL ozone (O sub(3)) depletion episodes (ODEs: O sub(3) mixing ratios < 20 x 10 super(-9) or parts per billion by volume, ppbv) particularly during major ODEs (MODES: O sub(3) < 4 ppbv). No other organic gases measured during TOPSE (Tropospheric Ozone Production about the Spring Equinox) exhibited anti-correlations with O sub(3) during these ODEs. Methyl bromide has both natural and anthropogenic sources and contributes similar to half of the bromine (Br) to the stratosphere, where it can catalytically destroy O sub(3). Several known CH sub(3)Br sources are evaluated, but the current knowledge cannot explain the observed enhancements. If the mechanism is direct gas-phase photochemical production, a significant portion of the unknown CH sub(3)Br source may be found.