Atmospheric Chemistry and Physics
www.atmos-chem-phys.net
1680-7316
1680-7324
6
10
2006
10.5194/acp-6-2847-2006
http://www.atmos-chem-phys.net/6/2847/2006/
http://www.atmos-chem-phys.net/6/2847/2006/acp-6-2847-2006.html
http://www.atmos-chem-phys.net/6/2847/2006/acp-6-2847-2006.pdf
2847
2863
2006-07-12
20th century trends and budget implications of chloroform and related tri-and dihalomethanes inferred from firn air
D. R. Worton
d.worton@uea.ac.uk
W. T. Sturges
J. Schwander
R. Mulvaney
J.-M. Barnola
J. Chappellaz
School of Environmental Sciences, University of East Anglia, Norwich, UK
Physics Institute, University of Berne, Berne, Switzerland
British Antarctic Survey, Natural Environment Research Council, Cambridge, UK
CNRS Laboratoire de Glaciologie et Geophysique de l'Environnement, Saint Martin d'Heres, France
Four trihalomethane (THM; CHCl<sub>3</sub>, CHBrCl<sub>2</sub>, CHBr<sub>2</sub>Cl and
CHBr<sub>3</sub>) and two dihalomethane (DHM; CH<sub>2</sub>BrCl and CH<sub>2</sub>Br<sub>2</sub>)
trace gases have been measured in air extracted from polar firn collected at
the North Greenland Icecore Project (NGRIP) site. CHCl<sub>3</sub> was also
measured in firn air from Devon Island (DI), Canada, Dronning Maud Land
(DML), Antarctica and Dome Concordia (Dome C), Antarctica. All of these
species are believed to be almost entirely of natural origin except for
CHCl<sub>3</sub> where anthropogenic sources have been reported to contribute
~10% to the global burden. A 2-D atmospheric model was run for
CHCl<sub>3</sub> using reported emission estimates to produce historical
atmospheric trends at the firn sites, which were then input into a firn
diffusion model to produce concentration depth profiles that were compared
against the measurements. The anthropogenic emissions were modified in order
to give the best model fit to the firn data at NGRIP, Dome C and DML. As a
result, the contribution of CHCl<sub>3</sub> from anthropogenic sources, mainly
from pulp and paper manufacture, to the total chloroform budget appears to
have been considerably underestimated and was likely to have been close to
~50% at the maximum in atmospheric CHCl<sub>3</sub> concentrations around
1990, declining to ~29% at the beginning of the 21st century.
We also show that the atmospheric burden of the brominated THM's in the
Northern Hemisphere have increased over the 20th century while
CH<sub>2</sub>Br<sub>2</sub> has remained constant over time implying that it is
entirely of natural origin.
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