Unexplained enhancements of CH3Br in the Arctic and sub-Arctic lower troposphere during TOPSE spring 2000

Oliver W Wingenter,Donald R Blake,F Sherwood Rowland,Brian A Ridley,Barkley C Sive

doi:10.1029/2003gl018159

Abstract

[1] Elevated concentrations of methyl bromide (CH3Br) were observed in the Arctic atmospheric boundary layer (BL) during periods of widespread BL ozone (O3) depletion episodes (ODEs: O3 mixing ratios < 20 × 10−9 or parts per billion by volume, ppbv) particularly during major ODEs (MODES: O3 < 4 ppbv). No other organic gases measured during TOPSE (Tropospheric Ozone Production about the Spring Equinox) exhibited anti-correlations with O3 during these ODEs. Methyl bromide has both natural and anthropogenic sources and contributes ∼ half of the bromine (Br) to the stratosphere, where it can catalytically destroy O3. Several known CH3Br 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 CH3Br source may be found.

Highlights

[2] Springtime Arctic ODEs have been the subject of several studies [e.g., Barrie et al, 1988; Bottenheim et al, 1990; Jobson et al, 1994; Hausmann and Platt, 1994; Ridley et al, 2003]
Observation of the rapid decay of nonmethane hydrocarbons and halocarbons, and direct observation of halogen oxides indicate that chlorine and bromine chemistry are responsible for the ODEs
[3] Methyl bromide has both natural and anthropogenic sources with most of the latter emissions occurring in the northern hemisphere (NH)

Summary

Introduction

[2] Springtime Arctic ODEs have been the subject of several studies [e.g., Barrie et al, 1988; Bottenheim et al, 1990; Jobson et al, 1994; Hausmann and Platt, 1994; Ridley et al, 2003]. [1] Elevated concentrations of methyl bromide (CH3Br) were observed in the Arctic atmospheric boundary layer (BL) during periods of widespread BL ozone (O3) depletion episodes (ODEs: O3 mixing ratios < 20 Â 10À9 or parts per billion by volume, ppbv) during major ODEs (MODES: O3 < 4 ppbv).

Results

Conclusion