30 May 2023
 | 30 May 2023

Observations of cyanogen bromide (BrCN) in the global troposphere and their relation to polar surface O3 destruction

James M. Roberts, Siyuan Wang, Patrick R. Veres, J. Andrew Neuman, Michael A. Robinson, Ilann Bourgeois, Jeff Peischl, Thomas B. Ryerson, Chelsea R. Thompson, Hannah M. Allen, John D. Crounse, Paul O. Wennberg, Samuel R. Hall, Kirk Ullmann, Simone Meinardi, Isobel J. Simpson, and Donald Blake

Abstract. Active bromine (e.g., Br2, BrCl, BrO, HOBr) promotes atmospheric ozone destruction and mercury removal. Here we report a previously unidentified participant in active-Br chemistry, cyanogen bromide (BrCN), measured during the NASA Atmospheric Tomography (ATom) mission. BrCN was confined to polar boundary layers, often appearing at concentrations higher than other Br compounds. The chemistry of BrCN determines whether it promotes or inhibits ozone and mercury removal. This dataset provides evidence that much of the BrCN was from atmospheric Br chemistry involving surface reactions with reduced nitrogen compounds. Since gas phase loss processes are known to be relatively slow, surface reactions must also be the major loss processes, with vertical profiles implying a BrCN atmospheric lifetime in the range 1–10 days. Liquid phase reactions of BrCN tend to convert Br to bromide (Br¯) or C-Br bonded organics, constituting a loss of active Br. Thus, accounting for BrCN chemistry is crucial to understanding polar Br cycling.

James M. Roberts et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2023-860', Anonymous Referee #1, 19 Jun 2023
  • RC2: 'Comment on egusphere-2023-860', Anonymous Referee #2, 11 Jul 2023

James M. Roberts et al.

James M. Roberts et al.


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Short summary
We measured cyanogen bromide (BrCN) in the troposphere for the first time as part of a series of survey flights around the globe. BrCN is found to be a product of the same active bromine chemistry that destroys ozone and removes mercury in polar surface environments, and so is a previously unrecognized participant in this chemistry. Accounting for BrCN chemistry is an important part of understanding polar Br cycling.