Gas Phase Bromine in Ozone Depleted Air Over the Arctic Ocean

In situ measurements of ozone and photochemically active bromine compounds over the Arctic Ocean near Alaska in April 2008 are used to examine the causes and geographical extent of arctic ozone depletion. Data were obtained from the NOAA WP-3D aircraft during the Aerosol, Radiation, and Cloud Processes affecting Arctic Climate (ARCPAC) study and the NASA DC-8 aircraft during the Arctic Research of the Composition 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 chemical ionization mass spectrometer (CIMS) instruments, and soluble bromide was measured by a mist chamber. The CIMS instruments also detected Br2 that was likely formed from atmospheric HOBr that rapidly converts to Br2 on Teflon inlets. This detected Br2 is identified as active bromine and represents a minimum of the sum HOBr + Br2. In the marine boundary layer over the Arctic Ocean, active bromine was consistently elevated and ozone was depleted (Figure 1). Ozone depletion was confined to the marine boundary layer that was tightly capped by a temperature inversion at 200-500 m altitude (Figure 2). Figure 1. Map of Alaska showing the flight tracks of the NOAA WP-3D aircraft on 5 days in April, 2008 during the ARCPAC study. Ozone mixing ratios less than 20 ppbv are shown as symbols.

Figure 2. 1 s measurements of ozone, CO, and potential temperature, and 10 s averages of bromine, measured during a descent of the NOAA WP-3D aircraft over the Arctic Ocean within 30 km of the Alaskan coast on 15 April 2008.