Organic Geochemistry 41 (2010) 263–269
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Organic Geochemistry
journal homepage: www.elsevier.com/locate/orggeochem
Chemical and carbon isotopic characteristics of ash and smoke derived from
burning of C3 and C4 grasses
Oindrila Das a,*, Yang Wang a, Yuch-Ping Hsieh b
a
b
Department of Geological Sciences, Florida State University and National High Magnetic Field Laboratory, Tallahassee, FL 32306, USA
Center for Water and Air Quality, Florida A&M University, Tallahassee, FL 32307, USA
a r t i c l e
i n f o
Article history:
Received 20 April 2009
Received in revised form 25 September
2009
Accepted 3 November 2009
Available online 6 November 2009
a b s t r a c t
C4 and C3 grasses were subjected to burning in the laboratory to determine whether there was any significant fractionation of carbon isotopes between plant material and corresponding ash and smoke produced from burning. The results show that smoke produced from C4 grasses is generally depleted in 13C
relative to the original plant, but the magnitude of the 13C depletion varies with species from <0.5‰ to a
maximum of 7.2‰. Ash derived from C4 grasses is, on the other hand, either depleted (by 0.1–3.5‰) or
slightly enriched (<1‰) in 13C relative to the original grass, depending on species. In contrast, both smoke
and ash produced from C3 plants do not show any significant deviation in d13C signature from that of the
original plant material. Our data also show that the C isotope fractionation between ash and smoke and
the original plant material depends not only on plant species and plant type but also on burning temperature. The weight percentage of C in ash and smoke decreases with increasing burning time in the temperature range 400–700 °C. Multi-elemental thermo analysis of ash, smoke and original plant material
reveals distinctly different chemical characteristics for these materials. Ash is preferentially enriched
in compounds with higher thermal stability whereas smoke contains a wide spectrum of compounds
with different stability in comparison with the original plant material. C4 grass appears to be more thermally stable than C3 grass. The results have important implications for paleoecological or ecological studies based on 13C signatures of black carbon (BC) or charcoal.
Ó 2009 Elsevier Ltd. All rights reserved.
1. Introduction
Biomass burning produces one third of the annual atmospheric
CO2 emission and aerosol particle emission, playing an important
role in the global carbon cycle and climate (Oglesby et al., 1998;
Thevenon et al., 2004). The majority of modern biomass burning
is considered to be from anthropogenic sources, though the effect
of other sources also needs to be examined, particularly their influence on d13C, d15N and atmospheric CO2 (Finkelstein et al., 2006). It
has been documented that localized burning in areas of high
amounts of biomass, such as during the Indonesian wildfires in
1997, can affect the carbon isotopic composition of the atmosphere
and the global carbon balance (Langenfelds et al., 2002; Page et al.,
1997). Ash and smoke are the major products of biomass burning
that contain black carbon (BC). Biomass burning is a major cause
of the atmospheric brown clouds that blanket much of south Asia
and affect the air quality. In the southern hemisphere, smoke from
biomass burning is also a significant source of atmospheric particles (Oglesby et al., 1998). BC in smoke and ash represents a carbon
sink in the global carbon cycle (Kuhlbusch, 1998). In the atmo-
* Corresponding author. Tel.: +1 8502648273.
E-mail addresses: [email protected], [email protected] (O. Das).
0146-6380/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.orggeochem.2009.11.001
sphere it also absorbs and scatters solar radiation, affecting atmospheric thermal structure and hence climate (Druffel, 2004;
Crutzen and Andrea, 1990). Because of the climatic effects of fires,
there has been increased interest in reconstructing the history and
dynamics of past fire regimes (Conedera et al., 2009).
The significance of BC in sediments and soils as a tracer of fire
history has been recognized (e.g. Wang et al., 2005; Preston and
Schmidt, 2006; Zhou et al., 2007; Moore and Kurtz, 2008). Stable
isotope analysis of charcoal or BC in soils and sediments has also
been used to study past changes in terrestrial ecosystems (e.g. Jia
et al., 2003). The basic assumption of this type of study is that
the d13C composition of charcoal or BC is the same as the original
biomass from which it is derived, which is supported by the 13C
values of wood charcoal produced in the laboratory (Leavitt
et al., 1982; Bird and Grocke, 1997; Schleser et al., 1999). In other
words, it has been assumed that no significant carbon isotope fractionation occurs between BC and the original vegetation during
burning. Thus, any change in the isotopic signature of BC in
sediments/soils is often assumed to reflect mixing of different
proportions of C3 and C4 plant inputs and the relative proportion
of C3- and C4-derived inputs can be calculated by using a simple
mass balance formula (Buotton et al., 1999):
%C4 ¼ ððds d3 Þ=ðd3 d4 ÞÞ 100
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O. Das et al. / Organic Geochemistry 41 (2010) 263–269
where ds, d3 and d4 represent the d13C value of the sample and
organic matter derived from C3 and C4 vegetation.
However, recent studies suggest that the stable C isotope ratios
of char or BC may not faithfully record the C isotopic signatures of
the source vegetation. For example, Leavitt et al. (1982) reported a
significant difference in d13C values of laboratory produced chars
and naturally occurring char. It has also been observed that aerosol
derived from C4 grass was depleted in 13C by up to 7‰ compared to
the original grass, whereas aerosol derived from C3 vegetation was
enriched in 13C by 2‰ (Cachier et al., 1985). Krull et al. (2003) observed a 13C depletion up to 8‰ in C4-derived chars from natural
burning, but no 13C depletion in chars from wood or C3 grasses.
Czimczik et al. (2002) reported that low temperature charring
(150 °C) caused enrichment of 13C in chars, as a result of lipid loss,
while high temperature charring (340–480 °C) led to depletion of
13
C by up to 0.8‰, as a result of loss of cellulose and enrichment
in lignin. However, in both low and high temperature experiments,
chars derived from softwood were more depleted in 13C than those
from hardwood (Czimczik et al., 2002). The isotope effect of combustion has also been measured by Turekian et al. (1998), who reported higher d13C values (by 0.5‰) for aerosol particles compared
to the source vegetation, formed during burning of C3 plants. They
also observed a 13C depletion (by 3.5‰) in aerosol particles formed
during burning of C4 vegetation relative to source plant material. In
order to use stable carbon isotopes in charcoal or BC to reconstruct
the paleovegetation (e.g. Hall et al., 2007) and to improve understanding of the C cycle, we need to better understand the effects
of burning on the chemical and C isotopic composition of charcoal
or BC.
We report the results from controlled laboratory burning experiments designed to investigate whether biomass burning induces
any significant changes in the chemical characteristics and stable
C isotope ratios of ash and smoke in comparison with the original
vegetation, and whether the laboratory burning can mimic field
burning. Our objective was to quantify the fractionation of carbon
isotopes between original vegetation and smoke and ash, and also
to determine whether the isotopic fractionation varies with vegetation type and burning conditions.
2. Materials and methods
2.1. Materials
Eight grass samples were collected from different geographic
areas in the USA, including centipede (Eremochloa ophiuroides), little bluestem (Schizachyrium scoparium), big bluestem (Andropogon
gerardii), wiregrass (Aristida beyrichiana), sugarcane (Saccharum
officinarum), black needlerush (Juncus roemerianus), sawgrass (Cladium jamaicense) and cattail (Typha domingensis). Each sample consisted of different parts of the plant (e.g. leaves, stem and roots).
Five are C4 grasses and three are C3 plants (Table 1). Grass material
was dried at 60–70 °C and then cut into small pieces and homogenized for burning and C isotope analysis. In addition to combustion
gases which escaped to the atmosphere, burning produced residues and combustion particles in the form of ash and smoke, which
were collected in the laboratory under different burning conditions
for C isotope measurements.
2.2. Laboratory burning
The homogenized grass sample was placed in a porcelain crucible and burned in a furnace at 300, 400, 500 and 700 °C for times
ranging from 10 to 100 min (Fig. 1). The furnace was connected
to a small negative-pressure pump via a glass funnel that covered
an opening on the top of the furnace, a filter holder and glass tubing (Fig. 1). A small door in the furnace was kept open during burning to allow air to enter, in order to mimic outdoor burning. Ash
was collected in a porcelain crucible and smoke emitted from the
opening on the top of the furnace was collected on a pre-combusted quartz filter paper placed in a filter holder (Fig. 1). The
weight of the grass sample before burning and the weight of the
ash after burning were measured using an electronic balance.
Ash samples were ground to a powder with an agate mortar and
pestle for stable isotope analysis. Smoke samples collected on
pre-combusted quartz filter papers were dried out in desiccators
for 20 min to remove the moisture and were then cut into equal
pieces. Burning experiments were repeated several times for the
same burning time to ensure that the results were reproducible.
Burning experiments were also performed for two grass samples (centipede and big bluestem) under more controlled conditions by adding a glass condenser between the furnace and filter
to remove moisture from the smoke particles. The glass condenser
had an inlet and an outlet that allowed cold water to continuously
pass over it (Fig. 1). The advantage of the more controlled experiment was that removal of the moisture might help minimize the
analytical error, although the same results were obtained (Fig. 2).
2.3. Mass spectrometry
For ash samples, 50–150 lg (depending on C content) of each
sample were weighed into an ultra clean tin cup, which was sealed.
For smoke samples, a small piece of the filter bearing the smoke
was wrapped in an ultra clean tin cup. The stable C isotopic composition and C content (%) of the sample were then analyzed at
the Florida State University, using a Carlo Erba Elemental Analyzer
(EA) connected to a Finnigan MAT delta PLUS XP stable isotope
ratio mass spectrometer through a Conflo III interface. Isotope
results are reported in the conventional d notation as d13C values
with reference to the international VPDB standard (Faure and
Mensing, 2005). Samples were analyzed in duplicate for d13C value.
Table 1
d13C values of original grass samples.
Sample
d13C (‰)
C (%)
C/N
Plant type
Centipede
Big bluestem
Little bluestem
Sugarcane
Wiregrass
Black needlerush
Cattail
Sawgrass
13
12.5
12.5
12.3
13.8
24.6
26.1
26.1
50
47
47
58
39
36
41
37
57
71
C4
C4
C4
C4
C4
C3
C3
C3
82
Fig. 1. Schematic diagram of the burning experimental setup.
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O. Das et al. / Organic Geochemistry 41 (2010) 263–269
Big
2 bluestem
0
Smoke (new experiment)
Δ 13C(‰)
Δ 13C (‰)
0
-2
-4
Ash
Smoke
Ash (new experiment)
Smoke (new experiment)
Ash
-4
-6
-8
-8
2 Wiregrass
0 20 40 60 80 100 120
Burning duration (min)
2
Δ 13C (‰)
0
-2
-4
-6
-8
0 20 40 60 80 100 120
Burning duration (min)
-2
-4
-8
-2
-4
-6
-8
-8
Ash
Cattail
2
Smoke
0
-6
0 20 40 60 80 100 120
Burning duration (min)
0 20 40 60 80 100 120
Burning duration (min)
20 40 60 80 100 120
Burning duration (min)
2 Sawgrass
Black needlerush
Δ 13C (‰)
0
-4
Ash
Ash
Ash
-2
-6
0
Smoke
Δ13C (‰)
-4
-6
Ash
Smoke
0
-2
-8
Sugarcane
2
Smoke
0
-2
-6
0 20 40 60 80 100 120
Burning duration (min)
Little bluestem
2
Δ 13C (‰)
2 Centipede
Ash (new experiment)
Δ 13C (‰)
Smoke
Δ 13C (‰)
Ash
Smoke
0
-2
-4
-6
-8
0
20 40 60 80 100 120
Burning duration (min)
0 20 40 60 80 100 120
Burning duration (min)
Fig. 2. D13Cash–grass (=d13Cash d13Cgrass) and D13Csmoke–grass (=d13Csmoke d13Cgrass) values derived from burning of various C4 and C3 grasses at 400 °C. Open symbols
represent results from more controlled burning. Error bars indicate 1 standard deviation from the mean.
2.4. Multi-element scanning thermal analysis (MESTA)
a
8
6
2
0
-2
-4
-6
-8
200 300 400 500 600 700 800
Burning temperature (0C)
8
3. Results and discussion
6
3.1. d13C values of ash and smoke
Our experiments show that burning resulted in variable
amounts of isotopic fractionation between the ash and smoke
and the original plant material, depending on plant type and species, as well as on burning conditions (Figs. 2 and 3).
For C4 grasses, different species displayed different C isotope
fractionation patterns during burning (Fig. 2). Smoke produced
from C4 grasses was generally depleted in the heavy C isotope relative to the original plant material, but the magnitude of the 13C
depletion varied from <0.5‰ to a maximum of 7.2‰ (Fig. 2). Smoke
4
Δ 13C (‰)
Table 1 shows the d13C values of the various C4 and C3 grass species. The values for C3 grasses varied from 24.6‰ to 26.1‰ and
those for C4 grasses from 12.3‰ to 13.8‰. The d13C values and
wt.% C content of the ash and smoke derived from burning of these
grasses under different conditions are shown in Figs. 2–4 and
Appendices.
Ash
4
Δ 13C (‰)
Selected samples were subjected to MESTA (Hsieh, 2007; Hsieh
and Bugna, 2008). The device is made up of a quartz pyrotube
which has connected compartments for sample and combustion.
The sample was placed in the sample compartment and heated
from ambient to 800 °C at a constant heating rate of 50 °C/min
and in a carrier gas of 40% O2 and 60% He. The decomposed material was carried to the combustion compartment by the carrier gas.
There, it was oxidized to CO2, NO2 and SO2 and the products passed
through detectors for C, N and S. Sample temperature and C, N and
S signals were recorded in a PC-based, online multi-channel data
logger. The C and N contents of the samples were calibrated against
cystine and glucose. Thermogram peak analysis was done using
commercial software (PeakFit) to determine the BC content of
the sample. BC was detected and quantified using the criterion proposed by Hsieh and Bugna (2008), with BC being defined as the
components decomposed at temperatures of 550 °C or higher.
Centipede
Big bluestem
Centipede (new exp.)
Big bluestem (new exp.)
Little bluestem
Sugarcane
Wiregrass
Black needlerush
Sawgrass
Cattail
2
b
Smoke
Centipede
Big bluestem
Centipede (new exp.)
Big bluestem (new exp.)
Little bluestem
Sugarcane
Sawgrass
Cattail
Black needlerush
0
-2
-4
-6
-8
200 300 400 500 600 700 800
Burning temperature (0C)
Fig. 3. Deviation in stable carbon isotope ratios of ash (a) and smoke (b) from
original grass, D13Cash/smoke–grass (=d13Cash/smoke d13Cgrass), at various burning
temperatures. Error bars indicate 1 standard deviation from the mean.
derived from centipede showed the largest 13C depletion among
the C4 grasses (Fig. 2). It appears that smoke from C4 grasses was
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O. Das et al. / Organic Geochemistry 41 (2010) 263–269
Centipede
Big bluestem
90
80
70
60
50
40
30
20
10
0
Ash 3000C
Centipede (new exp.)
Big bluestem (new exp.)
Black needlerush
Cattail
0
C % in smoke
90
80
70
60
50
40
30
20
10
0
20 40 60 80 100 120
Burning duration (min)
Ash 4000C
centipede
Sugarcane
Black needlerush
Little bluestem
Big bluestem
Sawgrass
Cattail
90
80
70
60
50
40
30
20
10
0
Centipede (new exp.)
Smoke 3000C
Big bluestem (new exp.)
Cattail
0
5
10
15
20
25
30
Burning duration (min)
Centipede
Little bluestem
90
Smoke 4000C
80
C % in smoke
C % in ash
C % in ash
Big bluestem
Big bluestem
Cattail
Sawgrass
70
Black needlerush
60
50
40
30
20
0
20 40 60 80 100 120
Burning duration (min)
10
0
5 10 15 20 25 30
Burning duration (min)
Fig. 4. C content (wt.%) of ash and smoke derived from burning of C3 and C4 grasses at 300 and 400 °C. Error bars indicate 1 standard deviation from the means.
generally more depleted in 13C than ash from the same species
(Fig. 2). Ash from C4 plants was either depleted or slightly enriched
(<1‰) in 13C relative to the original grass, depending on species.
Ash samples derived from wiregrass did not show any fractionation between ash and original grass, whereas ash from sugarcane
yielded slightly enriched (up to 0.7‰) d13C values (Fig. 2). Other C4derived ash samples were depleted in 13C by up to 4‰ relative to
the original grass. Burning of centipede grass also produced the
largest isotopic fractionation between ash and the original plant
material (Fig. 2).
Unlike C4 grasses, C3 plants did not show significant fractionation between ash, smoke, and original plant (Fig. 2). Overall, our
data show that burning of C3 grasses generally did not significantly
fractionate C isotopes (<0.7‰), confirming the results of Krull et al.
(2003). Thus, the data suggest that the d13C values of smoke and
ash produced by burning of C3 biomass generally represent the
d13C signatures of the original plants (Fig. 2).
Our data also show that the C isotope fractionation between ash
and smoke and the original plant material depended not only on
plant type and species but also on burning temperature (Fig. 3).
Burning time did not appear to have a significant effect on the
d13C of ash and smoke (Fig. 2). The magnitude of the 13C depletion
in ash and smoke derived from C4 grasses decreased with increasing temperature until 500 °C and then increased at higher temperature (i.e. 700 °C; Fig. 3).
The wt.% C content of ash and smoke also varied significantly
with burning duration and temperature (Fig. 4, Appendices 1–4).
The data show that, at 300 °C, the wt.% C of ash and smoke increased slightly with burning time, whereas at higher temperature
it decreased with burning time (Fig. 4). It can be concluded from
these data that burning above 300 °C resulted in C loss with respect
to the mineral content and at lower temperatures C loss with respect to mineral content seems to be insignificant within the time
of burning experiments (up to 80 min).
The data from our laboratory experiments show more or less
the same pattern as observed for biomass burning under natural
conditions (Wang and Hsieh, 2006). Our experimental approach
therefore can be used to study the isotope fractionation associated
with natural biomass burning (Wang and Hsieh, 2006). Widory
(2006) showed that combustion of fossil fuels (such as diesel, fuel
oil, natural gas and coal) resulted in a consistent 13C depletion by
1.3 ± 0.5‰ in CO2 in the exhaust gases but generally produced a
13
C enrichment in the resulting combustion particles except for
combustion of coal (which showed either no fractionation or a
slight 13C depletion in the resulting particles). If this C isotope fractionation pattern observed for combustion of liquid/gas fuels were
to hold for biomass burning, one would expect the ash and smoke
to be enriched in 13C relative to the plant material, but this was not
seen in our experiments. A few other studies (Cachier et al., 1985;
Turekian et al., 1998) also reported 13C depleted aerosol particles
produced from C4 vegetation burning, inconsistent with the results
from burning of liquid/gas fuels (Widory, 2006). Krull et al. (2003)
investigated the isotopic effects in C4 and C3 derived chars. They
found that C4-derived chars were consistently depleted in 13C relative to the original vegetation but there was no significant isotopic fractionation between C3 derived chars and vegetation. The
data from our experiments exhibited no significant isotopic change
in smoke and ash derived from C3 grasses, consistent with the results of Krull et al. (2003). However, our results show that burning
caused significant 13C depletion in smoke and ash derived from
some, but not all, C4 grasses. Smoke from burning C4 grasses was
consistently more depleted in 13C (up to 7‰) than ash (up to
4‰) relative to the original grass material. Our data also show that
burning duration had little effect on C isotope fractionation in ash
and smoke, whereas the degree of 13C depletion in smoke and ash
increased with decreasing burning temperature in the range 300–
500 °C, but varied among species. The 13C depletion in both ash and
smoke derived from some of the C4 grasses would imply that the
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O. Das et al. / Organic Geochemistry 41 (2010) 263–269
120
100
Loss of C %
The C loss from biomass as a result of burning can be calculated
by using the mass balance relationship:
Centipede
Big bluestem
Centipede (new exp.)
Big bluestem (new exp.)
Little bluestem
Sugarcane
Black needlerush
Sawgrass
Cattail
80
60
Carbon loss ð%Þ ¼ ½carbon in grass ðmgÞ fcarbon in ash ðmgÞ
þ carbon in smoke ðmgÞg=carbon in grass ðmgÞ
100 ð%Þ:
Our data show that C loss from biomass as a result of burning
generally increased with increasing temperature (Fig. 5, Appendix
6), suggesting that higher temperature biomass burning releases
greater amounts of C in the form of gases to the atmosphere than
low temperature burning for the same burning duration.
40
20
0
200
400
600
800
3.2. Chemical characteristics of ash and smoke
Burning temperature (0C)
Fig. 5. C loss (%) from vegetation due to burning at different temperatures. Error
bars indicate 1 standard deviation from the mean.
C or N x 10 relative atomic unit
combustion gases were enriched in 13C relative to the original biomass, opposite to that observed for burning of fossil liquid/gas
fuels (Widory, 2006). Unfortunately, we did not measure the d13C
values of CO2 and other C compounds in the combustion gases to
fully balance the C budget. Krull et al. (2003) attributed the 13C
depletion in C4-derived chars to physically protected organic matter in silicate phytoliths. Our data did not show any relationship
between the C isotope fractionation and the amount of ash or
smoke produced (Appendices 1–4). It is also unknown whether
the amount of ash/smoke reflects the amount of silica in plants
or not. However, it is well known that different biochemical fractions of plant material can be either depleted (e.g., lignin, cellulose
and lipids) or enriched (e.g. hemicellulose, sugars, amino acids and
pectin) in 13C compared to the whole plant (Deines, 1980). Thus,
another possible explanation could be the preferential loss of
13
C-enriched biochemical fractions of plants, such as hemicellulose, sugar, amino acids and pectin (Deines, 1980) during biomass
burning. This implies that C4 grasses that produced 13C-depleted
ash and smoke may have a higher proportion of lignin, cellulose
and/or lipids (relative to hemicellulose, sugar, amino acids and/or
pectin) compared to C3 plants. These alternative hypotheses can
be tested through chemical and biochemical analysis of C3 and C4
plants, which is beyond the scope of this study.
Ash and smoke produced at 400 °C were characterized by a decrease in total carbon content relative to plant, indicating that high
temperature (400 °C or above) burning releases to the atmosphere
significant amounts of C previously stored in the plant biomass.
C
2.5
Centipede
The chemical characteristics of some of the samples were
examined using MESTA (Hsieh, 2007; Hsieh and Bugna, 2008).
Grass samples produced two C and N decomposition peaks superimposed on a broad peak extending from 300 to 520 °C (Fig. 6).
The data show that centipede – a C4 grass – displayed a much
stronger high temperature peak than low temperature peak in
its C thermogram, whereas sawgrass – a C3 grass – showed an
opposite pattern (Fig. 6), suggesting that C4 grasses may be more
thermally stable than C3 grasses. Thermograms of ash samples
derived from C3 and C4 plants showed a narrow peak around
500 °C or higher (Fig. 7). LTA-20a, an ash sample derived from
centipede burned at 400 °C for 20 min, showed two peaks at
400 and 500 °C (Fig. 7a), while the same sample burned for
80 min at the same temperature had one peak at ca. 560 °C
(Fig. 7b). In contrast, thermograms from smoke samples derived
from different C4 and C3 species under various burning conditions
generally exhibited multiple C and N decomposition peaks superimposed on a very broad peak with a wide temperature range of
180 – ca. 600 °C (Figs. 8 and 9). Our data show that burning resulted in ash being preferentially enriched in components with
high thermal stability, whereas smokes contained a wide spectrum of compounds with different thermal stability. No significant difference was found between different species burned
under different conditions.
BC content of the sample was determined by measuring the
peak area above 550 °C in the thermogram from MESTA (Hsieh
and Bugna, 2008). A small amount of BC was detected in ash samples derived from centipede (5%) and sawgrass (1.4%). In contrast,
ash from big bluestem showed no detectable BC. Smoke derived
from the burning of centipede at 400 °C contained 7% BC, while
smoke samples produced from higher temperature burning
2.5
C
Sawgrass
Nx10
2
2
1.5
1.5
1
1
0.5
0.5
Nx10
0
0
0
200
400
600
Temperature (0C)
800
0
200
400
600
Temperature (0C)
Fig. 6. Thermograms of C and N for C4 (centipede) and C3 (sawgrass) grass.
800
O. Das et al. / Organic Geochemistry 41 (2010) 263–269
C or N x 10 relative atomic
unit
a
1
LTA-20a
Centipede
0.8
b
1
C
LTA-80a
Centipede
Nx10
0.8
a
C
C or N x 10 relative atomic
unit
268
Nx10
0.6
0.6
0.4
0.4
0.2
0.2
0
0
0
200
400
600
800
0
200
400
600
800
300BBS-15a
1.4
Bigbluestem
Nx10
C or N x 10 relative atomic
unit
c
C
1
0.8
0.8
0.6
0.6
0.4
0.4
0.2
0.2
0
0
0.8
0.6
0.6
0.4
0.4
0.2
0.2
0
0
200
400
600
Temperature
Nx10
200
400
600
0
200
400
600
Temperature
800
(0C)
Fig. 7. Thermograms of C and N for ash samples derived from C4 (a–c) and C3 (d)
grasses at 400 °C for burning duration of 20, 80, 60 and 40 min, respectively.
(500 °C) of the same species contained 19% BC. Smoke derived from
big bluestem under different burning conditions contained little
(1.6%) or no BC. It appears that the ash and smoke with the highest
BC content also displayed the largest 13C depletion relative to the
original plant material (i.e. centipede). However, more data are
needed in order to establish any quantitative relationship (if there
C or N x 10 relative atomic
unit
a
1.6
LTS-5a
Centipede
1.2
C
1.6
200
400
600
800
Temperature (0C)
Nx10
1.4
c
b
LTS-10a
Centipede
1.2
C
1.6
Nx10
1.4
1
1
0.8
0.8
0.6
0.6
0.6
0.4
0.4
0.4
0.2
0.2
0.2
0
0
400
600
C or N x 10 relative atomic
unit
Temperature
800
0
200
(0C)
600
Temperature
d
1.6
1.4 LTBBS-10c
1.2
400
C
LTBBS-5a
Bigbluestem
1.2
1
200
0
The C isotope signature of smoke and ash derived from biomass
burning does not necessarily represent the isotopic signature of the
original vegetation. Burning generally results in 13C-depleted
smoke and ash derived from C4 grasses, but the same effect was
not observed for C3 grasses. The isotope fractionation for C4-derived ash and smoke appears to be species dependent, as different
C4 species gave different isotopic signatures for ash and smoke
samples. Isotopic differences among ash, smoke and plant most
likely reflect differences in their chemical make up, as revealed
by MESTA. Thermograms show that C4 grass appears to be more
thermally stable than C3 grass and that smoke contains a wide
range of compounds with various thermal stabilities, while ash is
enriched in compounds with higher thermal stability compared
0.8
0
0
4. Conclusions
(0C)
1.4
800
(0C)
is any) between BC content and C isotopic composition of the
samples.
0
800
Nx10
Fig. 9. Thermograms of C and N for smoke samples derived from C4 grasses at
300 °C (a) and 500 °C (b) for burning duration of 15 and 5 min, respectively.
C
LTSGA-40a
Sawgrass
Nx10
LTSCA-60b
Sugarcane
0.8
d
1
C
500S-5a
Centipede
1.4
1
Temperature
1
b
1.6
1.2
1.2
Temperature (0C)
Temperature (0C)
C
1.6
Nx10
0
800
0
(0C)
200
400
600
800
Temperature (0C)
e
C
1.6
Nx10
1.4
Bigbluestem
C
LTSGS-5a
Sawgrass
1.2
1
1
0.8
0.8
0.6
0.6
0.4
0.4
0.2
0.2
Nx10
0
0
0
200
400
600
Temperature (0C)
800
0
200
400
600
800
Temperature (0C)
Fig. 8. Thermograms of C and N for smoke samples derived from C4 (a–d) and C3 (f) grasses at 400 °C for burning duration of 5, 10, 5, 10, 20, 15 and 5 min, respectively.
O. Das et al. / Organic Geochemistry 41 (2010) 263–269
to original plant material. A small amount of BC, as traditionally
defined, was observed in the smokes and ashes. High temperature
biomass burning releases more C to the atmosphere than low temperature burning for a given burning time. The results have important ramifications for ecological and paleoecological studies using
d13C signatures of BC or charcoal in soils and sediments. Ecological
or paleoecological studies utilizing the d13C values of BC or charcoal, without considering burning-induced C isotopic fractionation,
would underestimate the proportion of C4-derived organic matter
in modern soils or ancient sediments.
Acknowledgements
Isotope analysis was performed at the Florida State University
Stable Isotope Laboratory, supported by Grants from the US National Science Foundation (EAR-0517806 and EAR-0236357). We
thank Yingfeng Xu and G. Bugna for assistance in sample analyses.
We are grateful to E.S. Krull and an anonymous reviewer for valuable comments and suggestions.
Appendix A. Supplementary material
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.orggeochem.2009.11.001.
Associate Editor—D. Hunkeler
References
Bird, M.I., Grocke, D.R., 1997. Determination of the abundance and carbon isotope
composition of elemental carbon in sediments. Geochimica et Cosmochimica
Acta 61, 3413–3423.
Buotton, T.W., Archer, S.R., Midwood, A.J., 1999. Stable isotopes in ecosystem
science: structure, function and dynamics of a subtropical Savanna. Rapid
Communications in Mass Spectrometry 13, 1263–1277.
Cachier, H., Buat-menard, P., Fontugne, M., 1985. Source terms and source strengths
of the carbonaceous aerosol in the tropics. Journal of Atmospheric Chemistry 3,
469–489.
Conedera, M., Tinner, W., Neff, C., Meurer, M., Dickens, A., Krebs, P., 2009.
Reconstructing past fire regimes: methods, applications, and relevance to fire
management and conservation. Quaternary Science Reviews 28, 555–576.
Crutzen, P.J., Andrea, M.O., 1990. Biomass burning in the tropics: impact on the
atmospheric chemistry and biogeochemical cycles. Science 250, 1669–1678.
Czimczik, C.I., Preston, C.M., Schimdt, M.W.I., Werner, R.A., Schulze, E.D., 2002.
Effects of charring on mass and organic carbon isotope composition of wood.
Organic Geochemistry 33, 1207–1223.
Deines, P., 1980. The isotopic composition of reduced organic carbon. In: Fritz, P.,
Fontes, J.C. (Eds.), Handbook of Environmental Isotope Geochemistry, The
Terrestrial Environment, vol. I. Elsevier Scientific Publishing Company, New
York, pp. 329–406.
Druffel, E., 2004. Comments on the importance of black carbon in the global carbon
cycle. Marine Chemistry 92, 197–200.
269
Faure, G., Mensing, T.M., 2005. Isotopes: Principles and Applications, third ed. John
Wiley and Sons, New York.
Finkelstein, D.B., Pratt, L.M., Brassell, S.C., 2006. Can biomass burning produce a
globally significant carbon-isotope excursion in the sedimentary record? Earth
and Planetary Science Letters 250, 501–510.
Hall, G., Woodborne, S., Scholes, M., 2007. Stable carbon isotope ratios from
archaeological charcoal as palaeoenvironmental indicators. Chemical Geology
247, 384–400.
Hsieh, Y.P., 2007. A novel multi-elemental scanning thermal analysis (MESTA)
method for the identification and characterization of solid substances.
Journal of the Association of Analytical Communities International 90, 54–
59.
Hsieh, Y.P., Bugna, G.C., 2008. Analysis of black carbon in sediments and soils using
multi-element scanning thermal analysis (MESTA). Organic Geochemistry 39,
1562–1571.
Jia, G., Peng, P., Zhao, Q., Jian, Z., 2003. Changes in terrestrial ecosystem since 30 Ma
in East Asia: stable isotope evidence from black carbon in the South China Sea.
Geology 31, 1093–1096.
Krull, E., Skjemstad, J., Graetz, D., Grice, K., Dunning, W., Cook, G., Parr, J., 2003. 13C
depleted charcoal from C4 grasses and the role of occluded gases in phytolith.
Organic Chemistry 34, 1337–1352.
Kuhlbusch, T., 1998. Black carbon and the carbon cycle. Science 280, 1903–1904.
Langenfelds, R.L., Francey, R.J., Pak, B.C., Steele, L.P., Lloyd, J., Trudinger, C.M., Allison,
C.E., 2002. Interannual growth rate variations of atmospheric d13C, H2, CH4, and
CO between 1992 and 1999 linked to biomass burning. Global Biogeochemical
Cycles 16, 1048.
Leavitt, S.W., Donahue, D.J., Long, A., 1982. Charcoal production from wood and
cellulose: implications to radiocarbon dates and accelerator target production.
Radiocarbon 24, 27–35.
Moore, E., Kurtz, A., 2008. Black carbon in Paleocene–Eocene boundary sediments: a
test of biomass combustion as the PETM trigger. Palaeogeography,
Palaeoclimatology, Palaeoecology 267, 147–152.
Oglesby, R.J., Marshall, S., Tylor, J.A., 1998. The climate effects of biomass burning:
investigation with a global climate model. Environmental Modelling and
Software 14, 253–259.
Page, S.E., Siegert, F., Rieley, J.O., Boehm, H.-D.v., Jaya, A., Limin, S., 1997. The amount
of carbon released from the peat and forest fires in Indonesia during 1997.
Nature 420, 61–65.
Preston, C.M., Schmidt, M.W.I., 2006. Black (pyrogenic) carbon: a synthesis of
current knowledge and uncertainties with special consideration of boreal
regions. Biogeosciences 3, 397–420.
Schleser, G.H., Frielingsdorf, J., Blair, A., 1999. Carbon isotope behavior in wood and
cellulose during artificial ageing. Chemical Geology 158, 121–130.
Thevenon, F., Bard, E., Williamson, D., Beaufort, L., 2004. A biomass burning
record from the West Equatorial Pacific over the last 360 ky: methodological,
climatic and anthropic implications. Palaeogeography, Palaeoclimatology,
Palaeoecology 213, 83–99.
Turekian, V.C., Ballentine, S.R.J., Garstang, M., 1998. Causes of bulk carbon and
nitrogen isotopic fractionations in the product of vegetation burns: laboratory
studies. Chemical Geology 152, 181–192.
Wang, Y., Hsieh, Y.P., 2006. Stable carbon isotopic fractionation in smoke and char
produced during biomass burning. American Geophysical Union Fall Meeting,
San Francisco, p. 87 (Abstract B54A-03).
Wang, X., Peng, P.A., Ding, Z.L., 2005. Black carbon records in Chinese Loess Plateau
over the last two glacial cycles and implications for paleofires. Palaeogeography,
Palaeoclimatology, Palaeoecology 223, 9–19.
Widory, D., 2006. Combustibles, fuels and their combustion products: a view
through carbon isotopes. Combustion Theory and Modelling 10, 831–841.
Zhou, B., Shen, C., Sun, W., Zheng, H., Yang, Y., Sun, Y., An, Z., 2007. Elemental carbon
record of paleofire history on the Chinese Loess Plateau during the last 420 ka
and its response to environmental and climate changes. Palaeogeography,
Palaeoclimatology, Palaeoecology 252, 617–620.