HR: 1340h
AN: B13C-0244 [Abstracts]
TI: Stable carbon isotope signatures of chloromethane in emissions from decaying organic matter and its
implications for constraining the atmospheric chloromethane budget
AU: Kalin, R M
EM: r.kalin@qub.ac.uk
AF: Environmental Engineering Research Centres, Queen's University Belfast, David Keir Building
Belfast BT9 5AG, Belfast, BT9 5AG
United Kingdom
AU: * Keppler, F
EM: f.keppler@qub.ac.uk
AF: Environmental Engineering Research Centres, Queen's University Belfast, David Keir Building
Belfast BT9 5AG, Belfast, BT9 5AG
United Kingdom
AU: * Keppler, F
EM: f.keppler@qub.ac.uk
AF: Queen's University Belfast, Newforge Lane, Belfast BT9 5PX, Belfast, BT9 5PX
United Kingdom
AU: Harper, D B
EM: david.harper@dardni.gov.uk
AF: Queen's University Belfast, Newforge Lane, Belfast BT9 5PX, Belfast, BT9 5PX
United Kingdom
AU: McRoberts, C W
EM: colin.mcroberts@dardni.gov.uk
AF: Queen's University Belfast, Newforge Lane, Belfast BT9 5PX, Belfast, BT9 5PX
United Kingdom
AU: McRoberts, C W
EM: colin.mcroberts@dardni.gov.uk
AF: Department of Agriculture and Rural Development for Northern Ireland, Newforge Lane, Belfast BT9 5PX,
Belfast, BT9 5PX
United Kingdom
AU: Redeker, K R
EM: k.redeker@qub.ac.uk
AF: Environmental Engineering Research Centres, Queen's University Belfast, David Keir Building
Belfast BT9 5AG, Belfast, BT9 5AG
United Kingdom
AU: Hamilton, J T
EM: jack.hamilton@dardni.gov.uk
AF: Queen's University Belfast, Newforge Lane, Belfast BT9 5PX, Belfast, BT9 5PX
United Kingdom
AU: Hamilton, J T
EM: jack.hamilton@dardni.gov.uk
AF: Department of Agriculture and Rural Development for Northern Ireland, Newforge Lane, Belfast BT9 5PX,
Belfast, BT9 5PX
United Kingdom
AB:
Atmospheric chloromethane plays an important role in stratospheric ozone destruction, but many uncertainties exist regarding
strengths of both sources and sinks and in particular the processes leading to formation of this naturally occurring gas.
Previously, we have identified a new source of chloromethane (Hamilton et al. 2003), which can explain chloromethane
formation in a variety of terrestrial environments. We have shown that chloromethane can be produced abiotically during decay
of organic matter (e.g. leaf litter) at both ambient and elevated temperatures.
A potentially useful tool in validating chloromethane emission flux estimates is comparison of the carbon isotope ratio of
atmospheric chloromethane with those of chloromethane originating from various sources and sinks (Harper et al. 2001,
Thompson et al. 2002, Harper et al. 2003, Keppler et al. 2004).
We present carbon isotope signatures of chloromethane in emissions from various plant species. The effect of temperature
($40\deg$-$300\deg$C) on emission rate and isotope fractionation was investigated. In most cases $\delta$$^{13}$C values of
chloromethane were extremely depleted relative to bulk biomass. The most depleted $\delta$$^{13}$C values were found for
emissions of chloromethane released by C3 plants at the lowest temperature of $40\deg$ ($\delta$$^{13}$C values were in the
range of $-110\permil$ to $-150\permil$).
We suggest that, if decaying plants contribute to the bulk of atmospheric chloromethane, (which has an isotopic composition
of around $-36\permil$, Thompson et al. 2002) there must be either a huge microbial sink for chloromethane in soil or a very
large kinetic isotope effect associated with the reaction of chloromethane and OH radicals in the atmosphere.
These observations are of potential biogeochemical significance in the application of carbon isotope ratios to constrain the
atmospheric chloromethane budgets.
REFERENCES
Hamilton J.T.G., McRoberts W.C., Keppler F., Kalin R.M.,
Harper D.B., Science 301, 206-209 (2003).
Harper D.B., Kalin R.B., Hamilton J.T.G., Lamb C., Environ. Sci. Technol. 35, 3616-3619 (2001).
Harper D.B. et al., Chemosphere 52, 433-436 (2003).
Keppler F., Kalin R.M., Harper D.B., McRoberts W.C., Hamilton J.T.G.,
Biogeosciences Discussions 1, 393-412 (2004).
Thompson A.E., Anderson R.S., Rudolph J., Huang L., Biogeochemistry 60, 191-211 (2002).
DE: 1030 Geochemical cycles (0330)
DE: 1040 Isotopic composition/chemistry
DE: 0315 Biosphere/atmosphere interactions
DE: 0400 Biogeosciences
SC: Biogeosciences [B]
MN: 2004 AGU Fall Meeting