The Role of Br2 and BrCl in Surface Ozone Destruction at Polar Sunrise
Krishna L. Foster,1
Robert A. Plastridge,2
Jan W. Bottenheim,3
Paul B. Shepson,4
Barbara J. Finlayson-Pitts,1
Chester
W. Spicer2*
Bromine atoms are believed to play a central role in the
depletion of surface-level ozone in the Arctic at polar sunrise. Br2, BrCl, and HOBr have been hypothesized as bromine atom
precursors, and there is evidence for chlorine atom precursors as well,
but these species have not been measured directly. We report here measurements of Br2, BrCl, and Cl2 made using
atmospheric pressure chemical ionization-mass spectrometry at Alert,
Nunavut, Canada. In addition to Br2 at mixing ratios up to
~25 parts per trillion, BrCl was found at levels as high as ~35
parts per trillion. Molecular chlorine was not observed, implying that
BrCl is the dominant source of chlorine atoms during polar sunrise,
consistent with recent modeling studies. Similar formation of bromine
compounds and tropospheric ozone destruction may also occur at
mid-latitudes but may not be as apparent owing to more efficient mixing
in the boundary layer.
1 Department of Chemistry, University of
California, Irvine, CA 92697-2025, USA.
2 Battelle,
505 King Avenue, Columbus, OH 43201-2693, USA.
3 Environment Canada, 4905 Dufferin Street, Toronto,
Ontario M3H 5T4, USA.
4 Department of Chemistry and
Department of Earth and Atmospheric Sciences, Purdue University, West
Lafayette, IN 47907-1393, USA.
*
To whom correspondence should be addressed. E-mail:
spicerc{at}battelle.org
