Trends of halon gases in polar firn air: implications for their emission distributions C. E. Reeves1, W. T. Sturges1, G. A. Sturrock1, K. Preston1, D. E. Oram1, J. Schwander2, R. Mulvaney3, J.-M. Barnola4, and J. Chappellaz4 1School of Environmental Sciences, University of East Anglia, Norwich, NR4 7TJ, UK 2Physics Institute, University of Berne, Berne, Switzerland 3British Antarctic Survey, Natural Environment Research Council, Cambridge, UK, UK 4CNRS Laboratoire de Glaciologie et Geophysique de l’Environnement, Saint Martin d’Heres, France
Abstract. Four halons (H-1301, H-1211, H-2402 and H-1202) have been measured in air
samples collected from polar firn from Dome Concordia (Dome C), Antarctica,
from Devon Island, Canada and the North Greenland Ice Core Project (NGRIP)
site, Greenland. H-2402 and H-1202 are reported for the first time in firn
air. The depth profiles show the concentrations of all four halons to be
close to zero (i.e. below the detection limit of 0.001 ppt) at the base of the firn
thus demonstrating their entirely anthropogenic
origin. This is the first evidence of this for H-2402 and H-1202. A 2-D
atmospheric model was run with emissions previously derived using
archive air measurements from the southern hemisphere mid-latitudes to
produce historical trends in atmospheric concentrations at the firn sites,
which were then input into a firn diffusion model to produce concentration depth
profiles for comparison with the firn measurements.
This comparison provides an evaluation of the model-derived
atmospheric concentration histories in both hemispheres and thus an indirect
evaluation of the emission rates and distributions used in the
atmospheric model. Atmospheric concentration trends produced using
global emissions previously determined from measurements at Cape Grim are found
to be consistent with the firn data from the southern hemisphere.
Further emissions of H-1202 in recent years (late 1980s onwards) are likely
to have come from latitudes mostly south of 40° N, but emissions prior to
that may have come from further north. Emissions of H-1211 may also have
shifted to latitudes south of 40° N during the late 1980s. Following
comparison of the atmospheric model output with the firn data, modelled
atmospheric trends of total organic bromine in the form of
halons were derived for both polar regions.
Citation: Reeves, C. E., Sturges, W. T., Sturrock, G. A., Preston, K., Oram, D. E., Schwander, J., Mulvaney, R., Barnola, J.-M., and Chappellaz, J.: Trends of halon gases in polar firn air: implications for their emission distributions, Atmos. Chem. Phys., 5, 2055-2064, doi:10.5194/acp-5-2055-2005, 2005.