In situ measurements of ozone, photochemically active bromine compounds, andother trace gases over the Arctic Ocean in April 2008 are used to examinethe chemistry and geographical extent of ozone depletion in the arcticmarine boundary layer (MBL). Data were obtained from the NOAA WP-3D aircraftduring the Aerosol, Radiation, and Cloud Processes affecting Arctic Climate(ARCPAC) study and the NASA DC-8 aircraft during the Arctic Research of theComposition of the Troposphere from Aircraft and Satellites (ARCTAS) study.Fast (1 s) and sensitive (detection limits at the low pptv level)measurements of BrCl and BrO were obtained from three different chemicalionization mass spectrometer (CIMS) instruments, and soluble bromide wasmeasured with a mist chamber. The CIMS instruments also detected Br.Subsequent laboratory studies showed that HOBr rapidly converts to Bron the Teflon instrument inlets. This detected Br is identified asactive bromine and represents a lower limit of the sum HOBr + Br. Themeasured active bromine is shown to likely be HOBr during daytime flights inthe arctic. In the MBL over the Arctic Ocean, soluble bromide and activebromine were consistently elevated and ozone was depleted. Ozone depletionand active bromine enhancement were confined to the MBL that was capped by atemperature inversion at 200–500 m altitude. In ozone-depleted air, BrOrarely exceeded 10 pptv and was always substantially lower than solublebromide that was as high as 40 pptv. BrCl was rarely enhanced above the2 pptv detection limit, either in the MBL, over Alaska, or in the arcticfree troposphere.
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