25th International Meeting on Organic Geochemistry IMOG 2011

P-466
Can molecular markers for pyrogenic carbon help to reconstruct
wildfire temperatures?
Maximilian P.W. Schneider 1 , William C. Hockaday 2 , Caroline A. Masiello 2 , Michael W.I.
Schmidt 1
1 University of Zurich, Department of Geography, Zurich, Switzerland, 2 Rice University, Department of Earth
Science, Houston, United States of America (corresponding author:maximilian.schneider@geo.uzh.ch)
The maximum temperature experienced by charcoals
strongly influences relevant properties, such as
surface area (Brown et al., 2006), sorption capacity
(Chen et al., 2008) and degradability (Bruun et al.,
2008; Zimmerman, 2010). Yet information about the
temperature during formation of natural charcoals in
the environment is difficult to obtain.
Benzenepolycarboxylic acids (BPCA) are molecular
markers specific for pyrogenic carbon (PyC) and are
used to quantify PyC in soils, sediments and oceans
(Hammes et al., 2008; Dittmar & Paeng, 2009).
Additionally to quantitative information, the
concentration of one of the marker molecules, B6CA
(mellitic acid), provides information on the degree of
aromatic condensation in charcoals and probably,
also the intensity of the heat treatment during the
pyrolysis process (Schneider et al., 2010). We
calibrated this ―molecular thermometer‖ by using a
thermosequence of charcoals (200 to 1000°C),
produced under N2 atmosphere from two different
types of biomass (grass and wood) in a tube furnace
(Schneider et al., 2011).
So far it is not clear how other factors during
pyrolysis, such as availability of oxygen, moisture and
exposition time, influence the resulting molecular
marker pattern. Here we apply the molecular marker
method to a set of 10 charcoals produced during a
controlled burn experiment, which was conducted at
the US Forest Service Silas Little Experimental
Forest, located near New Lisbon, New Jersey. The
charred samples were derived from litter and bark of
pitch pine (Pinus rigida) and inkberry (Ilex glabra)
plants. Thermo-sensitive paints were used to keep
record of the upper temperature range that a sample
experienced during the fire event. Maximum
temperatures of 260 to 650°C were monitored, which
are typical temperatures for wildfires and which is well
within the calibrated temperature range of the
thermosequence charcoals. We compare the
estimated formation temperatures derived from
molecular marker patterns with those measured by
the thermo-sensitive paints. Our results show if the
―molecular thermometer‖ can be used to estimate the
formation temperature of natural charcoals.
References
Brown, R.A., Kercher, A.K., Nguyen, T.H., Nagle,
D.C., Ball, W.P., 2006. Production and
characterization of synthetic wood chars for use as
surrogates for natural sorbents. Organic
Geochemistry 37, 321-333.
Bruun, S., Jensen, E.S., Jensen, L.S., 2008. Microbial
mineralization and assimilation of black carbon:
Dependency on degree of thermal alteration. Organic
Geochemistry 39, 839-845.
Chen, B.L., Zhou, D.D., Zhu, L.Z., 2008. Transitional
adsorption and partition of nonpolar and polar
aromatic contaminants by biochars of pine needles
with different pyrolytic temperatures. Environmental
Science & Technology 42, 5137-5143.
Dittmar, T., Paeng, J., 2009. A heat-induced
molecular signature in marine dissolved organic
matter. Nature Geoscience 2, 175-179.
Hammes, K., Torn, M.S., Lapenas, A.G., Schmidt,
M.W.I., 2008. Centennial black carbon turnover
observed in a Russian steppe soil. Biogeosciences 5,
1339-1350.
Schneider, M.P.W., Hilf, M., Vogt, U.F., Schmidt,
M.W.I., 2010. The benzene polycarboxylic acid
(BPCA) pattern of wood pyrolyzed between 200 °C
and 1000 °C. Organic Geochemistry 41, 1082-1088.
Schneider, M.P.W., Smittenberg, R.H., Dittmar, T.,
Schmidt, M.W.I., 2011. Comparison of gas with liquid
chromatography for the determination of
benzenepolycarboxylic acids as molecular tracers of
black carbon. Organic Geochemistry (in press).
Zimmerman, A.R., 2010. Abiotic and microbial
oxidation of laboratory-produced black carbon
(biochar). Environmental Science & Technology 44,
1295-1301.
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