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

• Published in: Atmospheric Chemistry and Physics
• Main Authors: Roberts, James M., Wang, Siyuan, Veres, Patrick R., Neuman, J. Andrew, Robinson, Michael A., Bourgeois, Ilann, Peischl, Jeff, Ryerson, Thomas B., Thompson, Chelsea R., Allen, Hannah M., Crounse, John D., Wennberg, Paul O., Hall, Samuel R., Ullmann, Kirk, Meinardi, Simone, Simpson, Isobel J., Blake, Donald
• Format: Text
• Language: English
• Published: 2024
• Subjects: Arctic
• Online Access: https://doi.org/10.5194/acp-24-3421-2024; https://acp.copernicus.org/articles/24/3421/2024/

Bromine activation (the production of Br in an elevated oxidation state) promotes ozone destruction and mercury removal in the global troposphere and commonly occurs in both springtime polar boundary layers, often accompanied by nearly complete ozone destruction. The chemistry and budget of active bromine compounds (e.g., Br 2 , BrCl , BrO , HOBr ) reflect the cycling of Br and affect its environmental impact. Cyanogen bromide ( BrCN ) has recently been measured by iodide ion high-resolution time-of-flight mass spectrometry ( I − CIMS), and trifluoro methoxide ion time-of-flight mass spectrometry ( CF 3 O − CIMS) during the NASA Atmospheric Tomography Mission second, third, and fourth deployments (NASA ATom), and could be a previously unquantified participant in active Br chemistry. BrCN mixing ratios ranged from below the detection limit (1.5 pptv ) up to as high as 36 pptv (10 s average) and enhancements were almost exclusively confined to the polar boundary layers in the Arctic winter and in both polar regions during spring and fall. The coincidence of BrCN with active Br chemistry (often observable BrO , BrCl and O 3 loss) and high CHBr 3 / CH 2 Br 2 <svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="76pt" height="14pt" class="svg-formula" dspmath="mathimg" md5hash="f9c2c577e80b58a3c7d171e37d26f4c3"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-24-3421-2024-ie00001.svg" width="76pt" height="14pt" src="acp-24-3421-2024-ie00001.png"/> </svg:svg> ratios imply that much of the observed BrCN is from atmospheric Br chemistry rather than a biogenic source. Likely BrCN formation pathways involve the heterogeneous reactions of active Br ( Br 2 , HOBr ) with reduced nitrogen compounds, for example hydrogen cyanide ( HCN / <svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="8pt" height="14pt" class="svg-formula" dspmath="mathimg" md5hash="5c3774ab0600a2f03e83f0e636ae5ed2"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" ...