JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 106,NO. D20, PAGES 24,143-24,155,OCTOBER 27, 2001
Emissionsof greenhousegasesand other airborne pollutants
from charcoal making in Kenya and Brazil
DavidM. Pennise,
• KirkR. Smith,
•'2Jacob
P.Kithinji,
• MariaEmiliaRezende,
4
TulioJardim
Raad,
sJunfeng
Zhang,
2'6andChengwei
Fan•
Abstract. Airborne emissionsfrom charcoal-makingkilns commonlyusedin Kenya and
Brazil were measuredduring typical operatingconditions.Emissionfactorswere determined
nonmethanehydrocarbons,
nitrogenoxides(NO.0 and total suspendedparticulates(TSP)
alongwith charcoalproductionefficiencyandcharcoalandfuelwoodcarbonandenergy
contents.The conversionof wood carbonto charcoalcarbonrangedfrom 37 to 69%,
dependingon kiln type. E•ssion factors,expressedas gramsof pollutantper kilogramof
charcoalproduced,for the eightkilns rangedfrom 543 to 3027 for CO2, 32-62 for CH4, 143373 for CO, 24-124 for total nonmethaneorganiccompounds,0.01 1-0.30 for N20, 0.00540.13 for NO.•,and 13-41 for TSP. On average,fuelwoodcarbonwas approximatelydiverted
as follows: 51% to charcoal,27% to CO2, and 13% to productsof incompletecombustion
(PIC). Due to the higher global warming potentials(GWPs) of PIC relative to CO2 on a
carbonatombasis,suchkilns can produceratherlargenet greenhousegasemissions,even
when the wood is harvestedrenewably. Basedon publishedGWPs for CO2, CH4, and N20
only, we estimatethat 0.77-1.63 kg C-CO2 (carbonas carbondioxide equivalents)is emitted
per kilogramof charcoalproduced.We estimatethat the total primary globalwarming
com•tment (GWC) of Kenyan and Brazilian charcoal-makingkiln emissionsis about2.7
and 7.5 •11ion tons(Mr) C-CO2, respectively.For comparison,the primary GWC from
fossil fuel use in the United States is almost 1700 Mt C-CO2.
dioxide,CO,_)and,becauseof the chemicalprocessas well, a
significantproductionof productsof incompletecombustion
Charcoal is a fuel commonly used for household and
(PIC). The PIC emittedduring the charcoal-makingprocess
institutional cooking and heating in certain parts of the
include carbon monoxide (CO), methane (CH4), total
developingworld, especiallyAfrica and SoutheastAsia. In
nonmethaneorganic compounds(TNMOC), and particulate
Brazil, charcoalis producedon a large scale for use in the
matter. Oxides of nitrogen (NO, NO2, and N20 ) are emitted
steeland pig iron industries.Charcoalis essentiallyproduced as well. CO2, CH4, and nitrous oxide (N20) are important
by heatingfuelwood (or any otherraw biomass)in sometype
greenhousegases(GHG) in that they directly absorbsomeof
of kiln with limited access to air, a process called
the Earth's outgoingradiation in the atmosphere. CO and
carbonization. Charcoal-making kilns can vary greatly in
TNMOC
indirectly affect global warming through
structure and size, from simple earthen mounds to
atmosphericphotochemicalreactionsthat in turn affect GHG
semipe•qnanentbrick ovens to large, permanent metal
levels. The emission of incomplete combustionproducts
structures.Carbonizationcreatesa fuel of higher quality than
(such as CH4, total nonmethanehydrocarbons(TNMHC), and
the originalfuelwood. Becauseof inherentinefficiencyin the
CO) is quite important. This is due to the fact that CH4,
process,however,there is a substantialloss of carbonand TNMHC, and CO have higher global warming potentials
energy from the starting fuelwood (primarily as carbon (GWP), or ability to cause warming of the Earth's
atmosphere,per mole or kilogram of carbon,thandoesCO2.
1Environmental
HealthSciences,
Universityof California,Berkeley, The Food and Agriculture Organization of the United
Nations(FAO) reportsthat about26 million tonsor megatons
California, USA.
2Also
atProgram
onEnvironment,
East-West
Center,
Honolulu,
Hawaii, (Mr) of charcoalwereproducedworldwidein 1995,largelyin
USA.
the developingworld [Food and Agriculture Organization
1. Introduction
3Department
ofChemistry,
UniversityofNairobi,
Nairobi,
Keny
a-
4Biocarbo
Industria
eCom•rcio
Ltd.,
Belo
Horizonte,
Brazil.
(FAO),1997]. Thisrepresents
about12%of worldwide
fuelwood
use[FAO,
1997].
A higher
estimate
oftheamount
SDepartamento
deEngenharia
Mecanica,
Universidade
Federal
deofcharcoal
produced
annually
worldwide
is100
Mt[Rosillo-
Minas Gerais,Belo Horizonte,Brazil.
6Environmental
and Occupational
HealthSciences.
Institute,
Calleetal.,1996].Thefactthatmostcharcoal
isproduced
in
Piscataway,
NewJersey,
USA.
the noncommercial
sector,and thereforenot easilytracked,
7Graduate
Program
in Environmental
Sciences,
Rutgers
University,may explain some of the large variationin the estimates.
NewBrunswick,
NewJersey,
USA.
Charcoalproductionhasincreased
in recentyears,at a rateof
approximately3% per year over the period 1991-1995 [FAO,
Copyright
2001bytheAmerican
Geophysical
Union.
Paper
number
2000JD000041.
0148-0227/01/2000JD000041509.00
1997].
TheFAO[1997]reports
theproduction
of charcoal
in
Kenya and Brazil in 1995 to be 2.2 and 6.4 Mr, respectively.
24,143
24,144
PENNISE
ET AL.: GREENHOUSE
GASES FROM CHARCOAL
About 85% of Kenya's energy needs are derived from
biomass [Senelwa and Hall, 1993]. Kenya's rural and urban
populations are nearly 100% and 75% biomass energy
dependent,respectively[Senelwaand Hall, 1993]. Charcoal
accountsfor 9% of Kenya's total energyconsumption(10.3%
of biomassend usesor 534 petajoules(PJ)) and 18.8% (1138
PJ) of biomassinputs [Senelwaand Hall, 1993]. In 1992 in
Brazil 29.2 Mt of fuelwood were used to producecharcoal,
primarily for the pig iron and steel industries. This was the
single largestuse of the total 74.0 Mt (1105 PJ) of fuelwood
consumedin Brazil, followed by household,industry, and
agriculture[Brito, 1997]. In 1993, fuelwood consumption
made up 13.3% (58,870 PJ) of Brazilian primary energyuse
[Brito, 1997]. Thus Kenyan and Brazilian charcoal-making
kilns could potentiallyaccountfor a significantpart of their
nation's
overall GHG
emissions.
Biomass burning, including charcoal productionand use,
plays an importantrole in the global carboncycle. Current
estimatesare that biomassburning accountsnot only for 2545% of the annualglobal emissionsof CO2, but also for 1550% of CO, 3-10% of CH4, and 24% of TNMOC [Levine,
1990; Crutzen and Andreae, 1990; Andreae, 1991]. A good
characterizationof biomass burning thus is important for
achievingscientificunderstanding
of the potentialfor human
activities to engender global climate change, as well as
informing the international political/economic discourses
aboutwhat GHG mitigationmeasuresare warrantedand who
should pay for them. Greenhousegas emissionissuesare
now of great concern the world over, as the scientific
community more strongly agrees that the human health,
ecological, and economic consequencesof human-induced
globalclimatechangecouldbe quite serious.
Combustionof biomassharvestedor naturally regrown
on a sustainablebasisdoes not causea net increaseof CO2
in the atmosphere. Unfortunately, through deforestation
and other nonrenewablepractices,much burnedbiomassis
not replaced. Even with completerecyclingof the carbon,
however, a biomassfuel cycle can produce a net increase
in global warming commitment (GWC, the sum of the
global warming potentials of the gases emitted in a
process)becauseof the emitted PIC. As a result of these
two factors, partially nonrenewable harvesting and
significantPIC production,there has been much work in
recent years to characterize biomass combustion of
MAKING
surfacekiln (larger round brick kiln), and one large,
industrialrectangular
kiln with tar recovery(Missouri-like,
metal and brick) in Brazil. Reportedin this paper are
emissionfactors for the productionof charcoal for the
greenhousegasesCO2, CH4, and N20, as well as CO and
TNMHC, which indirectly affect GHG levels, and total
suspendedparticulates (TSP).
Charcoal production
efficiency (yield) and charcoaland fuelwood carbon and
energy contents were determined as well.
At the
conclusionof this paper we compare our measured
emissionfactorsto the resultsof previousstudiesand
estimate
the
national
inventories
of
these
airborne
pollutantsfrom charcoalmakingin KenyaandBrazil.
2. Methods
The experimentsconductedin this study were designed
based on charcoal-makingkiln emissionsexperimentswe
conductedin Thailand. Please see Smith et al. [1999] for the
detailsof thoseexperiments(pleasecontactus if you would
like a copyof that reportandcannototherwiseobtainit).
2.1. Kilns
Tested
The majority of charcoal produced in Kenya and
throughoutAfrica is derivedfrom Earth moundkilns. Hence
we tested five Earth mound kilns in Kenya. In Brazil we
tested one hot-tail kiln, one circular brick kiln, and one
rectangularkiln with tar recovery. These three kiln types
account for about 85%, 10%, and 5% of Brazilian charcoal
production,respectively.
1. Kenyan Earth mounds (EM1 - EM5) are layers of
brush/grass,
twigs, and a final layer of dirt over a chargeof
anywherefrom about400 to 32,000 kg wood; firing time is 510 days.
2. Brazilian hot-tail (HT) is a beehive-shapedbrick kiln
with no chimney and is chargedwith about 4000 kg wood,
with a firing time of about40-50 hoursper run.
3. Brazilian round brick (surface)is a large, circular brick
kiln with chimney;it usesabout20,000 kg wood, with a firing
time of about 40-50 hours.
4. Brazilian rectangularwith tar recovery (rectangular)is
modeled after the Missouri
kiln and is metal and brick.
It has
a semiautomatedprocess,loaded with about 80,000 kg of
wood, and firing time is about80 hours.
In Kenya,EM1 andEM2 wereconstructed
andoperatedby
different
kinds in different
seasons around the world
grounds staff of the University of Nairobi who were
[Levine, 1996].
experiencedwith traditionalcharcoal-makingmethods. EM3,
Given the emission of large amounts of incomplete
EM4, and EM5 were constructedand operatedon a former
combustionproductsduring the charcoal-makingprocess,
black wattle tree (Acacia mearnsii) plantationby a team of
we might expect the use of charcoal to have a greater
migrant charcoal makers. In Brazil, on-site (plantation)
impact on global warming commitment than its share of
fuel demand. To date, however, the airborne emissions charcoalkiln workersoperatedthe three kilns usingtypical
from charcoalmaking are poorly characterizedin existing
greenhousegas emissiondatabases. This is likely due to
the fact that the charcoal-making kilns used in the
developing world are not easily monitored, as they are
typically operatedin remoteareasover many daysor even
weeksfor a singlerun. In an effort to fill this information
gap, we have collecteddata on charcoal-makingemissions
from three developing countries whose charcoal
production is large and that are representativeof their
region: Thailand, Kenya, and Brazil.
Using methods
developed and tested in Thailand [Smith et al., 1999], in
this phaseof the studywe testedfive Earth moundkilns in
Kenya, and one hot-tail kiln (brick beehive type), one
methods.
In Kenya, EM1 used Croton megalopoliswood (from the
University of Nairobi campus),EM2 used eucalyptus(from
the University of Nairobi campus),and EM3-5 used black
wattle (Acacia mearnsii) with bark removed.
In Brazil,
Eucalyptusgrandhaiswood from the plantation,harvestedat
7 years of age and air-dried, was used in each of the three
kilns tested.
2.2. Carbon Balance Approach and Determination of
Emission
Factors
Startingwith a carbonbalanceon the system,we calculated
the emissionfactorsfor each of the speciesof interest(CO2,
PENNISE ET AL.: GREENHOUSE GASES FROM CHARCOAL MAKING
24,145
Table1. Experimental
Methods
Summary
a
Ash
Kiln
Firing Sampling
Grab WoodMass Charcoal
Mass Brands
Mass Condensables
TSP
Experiment
Time, Period Samples
Determined
By Determined
By Determined
By Mass
Emissions Emissions
Days Covered,Taken
Determined Determined Determined
Days
EM 1
7.10
7.10
By
24+8
directweighingdirectweighing directweighingThai kiln
average
EM2
5.05
EM3
9.87
5.05
3.0
16
10
directweighingdirectweighing directweighingThai kiln
9.71
3.0
7
9.68
EM6t'
EM7t'
EM8t'
HT
2.0
5(est.) 1
5(est.) 1
5(est.) 1
3.29 3.29
7
1(x2)
1(x2)
1(x2)
6(x2)
1.88
1.88
Rectangular
3.25 3.29
6(x2)
7(x2)
Thai kiln
sampling
direct
woodvolume numberof bags numberof logs Thai kiln
x sampledbag x sampledlog average
direct
sampling
aveyieldof
EM3 and
numberof bags numberof logs Thaikiln
x sampledbag x sampledlog average
mass
Thai kiln
average
Thai kiln
average
direct
Thaikiln
sampling
average
mass
woodvolume numberof bags numberof logs Thai kiln
ND
ND
ND
woodvolume
average
mass
x sampledbag
x sampledlog
mass
mass
average
ND
ND
ND
ND
ND
ND
ND
ND
ND
directweighingdirectweighingThaikiln
average
Surface
direct
sampling
EM5
EM5
By
average
mass
EM4
By
woodvolume directweighingdirectweighingThaikiln
direct
sampling
ND
ND
ND
Thai/Kenya
Thai kiln
average
ND
ND
ND
Thaikiln
kiln average average
Thai/Kenyan Thaikiln
average
kiln average average
directweighing
directweighingdirectweighing
Thaikiln
Thai/KenyanThaikiln
average
kiln average average
:Abbreviations
are est.,estimated;
ND, not determined;
EM, Earthmoundkiln; HT, hot-tailkiln; surface,surfacekiln; rectangular,
rectangularkiln with tar recovery.
•One(duplicate)
grabsample
of emissions
wascollected
fromeachof theEM6,EM7,andEM8kilns.Nootherdatawerecollected
from these kilns.
CO, CH4, TNMOC, TSP, and N20 ). We will present the
emission factors in two different forms: grams of pollutant
of charcoal produced (and converting grams of carbon to
gramsof carbondioxide)or by the total massof the charcoal
carbonproduced. The emissionfactorsfor the other species
emitted per kilogram of charcoalproducedand grams of
pollutantcarbonemitted per kilogram of charcoalcarbon of interest were found via their molar emission ratios to CO2
produced.
The carbonbalancefor the charcoal-makingprocesscan be
(againon a carbonbasis).
written as follows, on a carbon mass basis:
2.3. Parameters
Measured
As many inputsand outputsas possiblewere monitoredin
wood = charcoal+ brands+ condensableliquids + ash
order to determine a detailed carbon balance for each kiln.
+ CO2+ CO + CH4 + TNMOC + TSP,
Since field conditions precluded the measurement of
condensables(tar) and ash emissions in both Kenya and
dividingthroughby CO2andrearranging
yields
1 = (wood- charcoal- brands- condensables
- ash)/CO2
Brazil
and TSP
measurements in Brazil,
we used our
experimentaldatafrom Thailandfor thoseproducts.
Concentrationsof the following airborne species were
measured in the kiln emissions as well as in the ambient air:
- (GO + CH4 + TNMOC + TSP)/CO2.
CO2, CO, CH4, TNMHC, N20, NO, NOr, and TSP (measured
for the Kenyan kilns only).
The following wood and solid product parameters were
also measured: (1)wood: mass (directly weighed or
determinedfrom wood volume); carbon,energy,and moisture
contents; (2)charcoal: mass; carbon, energy, and moisture
CO2= (wood- charcoal- brands- condensables
- ash)
contents; (3)brands (partly carbonized wood product
/(1 + K).
remaining in kiln chamber): mass; carbon and moisture
The absoluteCO2emissionfactorwasthenfoundby dividing contents. Note that carbon analyses were not able to
this total amountof CO2 emittedas carbonby the total mass performedon samplesfrom the Kenyahkilns (EM1 - EM5).
We define(CO + CH4+ TNMOC + TSP)/CO2= K. The total
amountof CO2 emitted (still in terms of carbonmass) was
foundby solvingthefollowingequation:
24,146
PENNISE ET AL.: GREENHOUSE
GASES FROM CHARCOAL
MAKING
Table 2. Net Molar EmissionRatiosof GasesandTSP to CO2a
CO/CO2 CH4/CO2TNMHC/CO2TSP/CO2NO/CO2
b NOx/CO2
b N20/CO2
b
EM 1
EM2
0.1630
0.1726
0.0485
0.0418
0.1109
0.0767
0.0304
0.0165
4.24E-05
2.66E-05
5.04E-05
4.98E-05
5.83E-05
9.80E-05
EM3
0.2108
0.0736
0.1283
0.0205
NA
2.26E-05
9.21E-05
EM4
0.2672
0.1477
0.2642
0.0494
NA
4.51E-05
7.30E-05
EM5
0.2121
0.0834
0.1387
0.0177
NA
2.31E-05
6.39E-05
EM6
0.2123
0.1249
0.1825
0.0362
NA
2.63E-05
9.45E-05
EM7
0.2286
0.1124
0.1604
0.0611
NA
3.19E-05
1.25E-04
2.02E-04
EM8
0.1672
0.0503
0.0678
0.0181
NA
3.63E-05
HT
0.3680
0.0945
0.1431
NA
NA
2.31E-05
3.24E-05
Surface
0.3818
0.1017
0.0732
NA
NA
1.03E-05
3.30E-05
Rect.
0.4672
0.1845
0.1075
NA
NA
1.15E-05
2.09E-05
Ambient- 1c 0.006
0.004
0.001
NA
3.01E-05
5.02E-05
7.47E-04
Ambient-2d 0.0016
0.0068
0.0039
0.00075
NA
1.58E-04
8.00E-04
Ambient-3 e NA
NA
0.0424
NA
NA
2.12E-04
9.27E-04
aNA,notanalyzed.
Read4.24E-05
as4.24x 10'5.
bunits:molecularratio.
CAmbient-1
corresponds
to kilnsEM 1 andEM2.
dAmbient-2
corresponds
tokilnsEM3,EM4,andEM5.
CAmbient-3
corresponds
to kilnsHT, surface,andrectangular.
2.4. Experimental Designand AnalysisMethods
Kilns were operatedusing typical methods. The massof
the wood loaded into each kiln was determinedeither by
direct weighing or from the wood volume. Wood moisture
content was determinedby weighing severalcross-sectional
log samplesbeforeand after oven drying (at least24 hoursat
105øC). Carbon content and calorific analyseswere also
performedon wood samplesfrom eachkiln.
Grab samplesof the airborne (gaseous)emissionswere
taken throughoutthe firing period of each kiln. The gas
samplingconfigurationconsistedof a ¬"ID coppersampling
tube, a TSP sampling cassetteholding a 37-mm diameter
quartz fiber filter (Whatman), a low-flow pump (SKC
Aircheck Sampler, model 224-PCXR7), and a 5-L metalreinforced Tedlar (MMT) bag. Ambient samples were
collectedwith the samesamplingconfiguration.The stability
of the gasesof interest during storagein MMT bags is
describedby Fan et al. [2001].
A Hewlett Packard6890 gaschromatographic
(GC) system
equippedwith a flame ionization detector(FID) or an electron
capture detector(ECD) was used for this study. The GC
system,equippedwith a nickel catalystmethanizerand a FID,
was usedto analyzeCO2, CO, and CH4. During the analysis,
CO2 and CO were convertedto CH4 by the nickel catalyst
methanizerand then detectedby the FID. A 10-foot x 1/8inch stainless steel column packed with 80-100 mesh
Carbosphere(Waters Associates,Inc., USA) was used to
separatethesethreecompoundsand othercompounds
present
in the samples.The cardergaswas zero-gradenitrogenwith
a flowrateof 30mLmin'•. Theoventemperature
washeldat
35øCfor9 min,ramped
upto 200øCattherateof 25øCmin'•
and held at the final temperaturefor 5 min. The injector
temperature was 35øC, the methanizer temperature was
375øC, andthe FID temperaturewas 200øC.
The GC-FID system,whenequippedwith a 2-footx ¬-inch
stainlesssteelcolumnpackedwith glassbeads(Alltech Co.,
USA) was usedfor total hydrocarbon
analysis. The carder
gaswaszero-grade
nitrogenwith a flow rateof 10 mL min-1.
The oven temperature
was 35øC for 5 min. The injector
temperaturewas 35øC and the detector temperaturewas
200øC. The concentration
of TNMHC, calculatedon a CH4
basis(ppmas CH4), wasdetermined
by subtracting
the CH4
concentration from
the THC
concentration in the same
sample.
N20 was analyzedusingthe GC-ECD system[Rasmussen
andKhalil, 1980,1981;Rasmussen
et al., 1982]. Thissystem
utilizedan 8-foot x 1/8-inchstainlesssteelcolumnpacked
with 80-100 meshHayesepQ (WatersAssociates,
Inc.) for
the separation
of N20 from othercompounds.Zero-grade
nitrogenwasusedas the carriergas,at a flow rateof 20 mL
min-t Theoventemperature
washeldat 50øCfor 3.5min,
ramped
upto 200øCat 20øCmin-•, andheldfor 9 min. The
injector and detectortemperatureswere 35øC and 350øC,
respectively.A chemiluminescent
nitrogenoxidesanalyzer
(Model 8840, Lear Siegler Measurements Controls
Corporation)wasusedto measureNO andNO2.
Whatman quartz fiber filters (37 mm diameter) were
employed for collection of TSP from the charcoal kiln
emissions.Before sampling,the filters were baked at 105øC
in anovenfor at least24 hoursandthenplacedin a desiccator
for at least 24 hours before weighing. The filters were
weighedin a 5-placebalanceimmediatelyafterbeingtaken
out of the desiccator.After sampling,the filterswereagain
placedin a desiccator
for at least24 hoursandthenweighed.
After the end of the firing, each kiln was sealed and
allowed to cool. After cooling,charcoaland brandswere
removedand weighed. Samplesof each were collectedand
later analyzedfor carboncontent(in Brazil only), calorific
value,andmoisturecontent.Table 1 givesa summaryof the
experimental
methodsusedin thisstudy.
PENNISE ET AL.: GREENHOUSE GASES FROM CHARCOAL MAKING
24,147
0.25
0.20
0.15
0.10
0.05
0.00
20
40
60
80
1 O0
120
140
160
180
Time after Firing (hours)
0.40
0.35
0.30
0.25
0.20
* EM3
0.15
= EM4
•, EM5
0.10
0.05
0.00
0
50
1 O0
150
200
250
Time after Firing (hours)
Figure 1. (a)Variationin the CO/CO2grabsampleemissionratiosthroughout
the firing of Kenyankiln EM1.
(b)Variation in the CO/CO2 grab sampleemissionratios for the three large Kenyan kilns (EM3, EM4, and
EM5).
3. Results
3.1. Molar
and Discussion
Emission
Ratios
Table 2 shows the net molar emission ratios to CO2 for CO,
CH4, TNMHC, TSP, NO, NOx, and N20 for each kiln test.
Throughouteach kiln test, grab sampleswere collectedfrom
the chimney(or other openings)from which the most smoke
was being emitted at the time of samplecollection. During
the charcoal-makingprocess,emissionsoften exit kilns from
more than one chimneyor openingat a time. In order to test
the degreeof similarityof emissionsreleasedsimultaneously
from two different chimneys or openings of a kiln, we
collectedeight setsof emissiongrab samplesfrom EM1, one
from each of the two chimneys. We found that the ratios of
the gasesemittedfrom the two different chimneyswere quite
similar. For example,therewas only a 3% percentdifference
in the averageCO/CO2 ratio betweenthe two chimneys. The
CH4/CO2 ratio was even more similar between the two
chimneys,with a 0.02% difference,while the N20/CO 2 ratio
wasthe mostdissimilar,still with only a 17% difference.
While the averagegaseousemissionratios were used in
determiningthe emissionfactorsfor a given kiln test, these
ratios vary throughoutthe charcoal-makingprocess. As an
example,Figure l a displaysthe CO/CO2emissionratiosfor
eachof the 24 grabbag samplescollectedduringthe firing of
EM1. In addition,Figure lb showsthe variationin each of
the CO/CO2 grab sampleemissionratiosfor the three large
KenyanEarthmoundkilns (EM3, EM4, andEM5).
3.2. Carbon and Energy Balances
The total mass and mass of carbon in the solid species
involved in each of the charcoal-makingexperiments(wood,
charcoal, brands, ash, condensables,and TSP) are shown in
Table 3.
The wood moisture fraction was calculated on the
wet basis: moisture fraction = (wet wood mass - oven dry
wood mass)/(wet wood mass). An average value of 5%
moisturecontentwas appliedfor the charcoalproduced.Due
to field limitations,we were not able to determinethe massof
condensable
speciesemittedfrom the kilns. Basedon two
experimentson Thai kilns (one Earth moundand one brick
24,148
Table
PENNISE ET AL.: GREENHOUSE GASES FROM CHARCOAL
Table 5. Charcoal Yields (Mass, Carbon, and
Energy Bases)
3. Solid Product Measurements
Wood In,
Wood
Charcoal
Brands
Dry Mass, Moisture Produced, Produced,
Charcoal
Charcoal Energy
kg
Yield
Carbon
Fraction
a kg
kg
EM1
EM2
782
350
0.400
0.382
EM3
25250
0.178
7452
480
186
79.5
132
14
EM4
16080
0.178
5267
500
EM5
14600
0.178
5258
550
3430
0.161
1180
45
15720
0.195
4605
965
0.128
26020
4420
HT
Surface
MAKING
Rectangular 67780
EM1
EM2
EM3
Conversion
(DryBasis)
a Yieldt'
toCharcoal
0.226
0.216
0.280
0.384 c
0.367 c
0.477 •
0.459
0.339
0.470
EM4
0.311a
0.529•
0.522
EM5
0.342
0.582 •
0.574
HT
Surface
0.341
0.287
0.521
0.504
0.461
0.403
0.689
0.571
Rectangular 0.364
aDrybasisyield= product
mass/dry
woodmass.
t'Carbon
yield= product
carbon
mass/
aDeterminedon a wet basis;moisturefraction=
(wet mass-drymass)/(wet mass).
wood carbon mass.
•Asshownin Table4, thecharcoal
percentcarbon
value usedin determiningtheseyields camefrom
data from our three tests of Thai Earth mound kilns.
aSincethe initial wood masswas not determined
for EM4, the charcoalyield for EM4 was set as the
averageof the charcoalyieldsof EM3 andEM5 (all
threekilns were constructedandoperatedsimilarly).
beehive kiln), carbon in the condensableliquid emissions
accountedfor 3% of the original wood carbon. Therefore an
averagefactor of 3% of the original wood carbonwas applied
to estimate
the amount
of condensables
carbon
emitted
in
each of thesekiln experimentsshown in Table 3. Similarly,
calculationsperformedby one of us, Rezende,basedon much
practical and theoretical experience with tar recovery from
charcoal-makingkilns in Brazil, indicate that about 3.6% of
the originalwoodcarbonis emittedas condensable
species.
Table 4 presentsthe results of the carbon content and
calorificvalueanalysesof the solidspeciesfrom the eightkiln
experiments. These carbon content values were used in
calculatingthe carbonmassesshownin Table 3. The charcoal
yields, or kiln conversionefficiencies, were determinedfor
each experiment. Thesedata are shownin Table 5. The dry
basis charcoal yield is the total mass of charcoalproduced
divided by the total dry mass of wood used in the kiln run.
The carbon yield is the mass of charcoal carbon produced
divided by the total massof carbonin the original wood used.
Energy conversionto charcoalis the ratio of the total energy
contentof the charcoalproductto that of the wood input. The
charcoalyield for the five Kenyanearthmoundkilns ranged
Table 4. CarbonAnalysesand Calorific Valuesof Solid Products
from 21.6 to 34.2%. The larger Earth mound kilns (EM3,
EM4, and EMS) had higher charcoal yields than the two
smallerEarth moundkilns (EM1 and EM2). As expected,the
large, industrialrectangularBrazilian kiln with tar recovery
outperformedthe Brazilian hot-tail and surfacekilns and the
Kenyan Earth moundkilns, with a charcoalyield of 36.4%, a
charcoalcarbonyield of 68.9%, and a charcoalenergy yield
of 57.1%.
Also shownin Table 5 are the brandsyields, on a wet mass
basis and an energy basis. Brands, which are partially
carbonized wood product, can be considereda secondary
productof charcoalproduction,becausethey are often soldas
cooking fuel, commandinga price greater than that of raw
wood, but less than that of charcoal. Brands are also often
reloaded into a kiln and fully converted to charcoal in a
secondfiring.
The emissionfactorsfor all airbornespeciesare shownin
Tables 6a and 6b. The average emission factors and
coefficientsof variation of the five Kenyan Earth mound kilns
are also shown in Table 6a.
Wood
Wood
%
Calorific
Carbon Value,
Charcoal
Charcoal
%
Carbon
kJg'•
Brands
Brands
Calorific
%
Calorific
Value,
Carbon Value,
kJg'•
kJg'•
EMI
EM2
44.0a
44.0a
15.12
19.10
74.8t'
74.8t'
30.68
30.02
52.3c
52.3c
23.00
21.21
EM3
44.0'
18.55
74.8t'
31.11
52.3•
23.00
EM4
44.0a
18.55
74.8t'
31.11
52.3c
23.00
The last columns of Tables 6a
and 6b showthe emissionfactor (EF) for all airbornespecies
(gases+TSP). The CO2 emissionfactor for the Kenyan earth
mound
kilnsranged
from1058to 3027g CO2kg-• charcoal
produced.Due to betterinsulationand greatermanageability,
the CO2 emissionfactors for the Brazilian hot-tail and surface
kilnsfell in thelowerendof thisrange. Due to its high
EM5
44.0a
18.55
74.8b
31.11
52.3•
23.00
efficiency (conversionof wood carbon to charcoal carbon),
the Brazilian rectangularkiln had the lowest or nearly the
lowest emissionfactorsfor all species. For example, its CO2
HT
48.8
20.42
74.6
27.64
55.4
21.33
EF wasonly543g kg-• charcoal
produced,
muchlowerthan
Surface
48.8
20.81
85.7
29.20
55.6
23.36
Rectangular48.7
20.04
92.2
31.46
54.5
21.20
all other kilns testedin this current study and in our testsof
Thai kilns.
The percentdistributionof the original wood carbonin the
products
of the charcoal-makingprocessis shownin Figure 2
'Thisvalueis theaveragecarboncontentof theeucalyptus
woodusedin
our Thai kiln experiments[Smithet al., 1999].
for each of the kiln tests. They range from the best
t'This
valueistheaverage
carbon
content
ofthecharcoal
produced
inour performancefor the rectangularkiln in which only 20.8% of
threetestsof ThaiEarthmoundkilns[Smithet al., 1999].
the wood carbon is diverted to PIC and CO2 to the worst,
•Thisvalueis theaverage
carboncontentof thebrandsproduced
in our
three testsof Thai Earth mound kilns [Smith et al., 1999].
EM2, in which 55.7% is lost to airborne emissions.
PENNISE ET AL.: GREENHOUSE
GASES FROM CHARCOAL
MAKING
24,149
Table 6a. EmissionFactors,Gramsof Pollutantper Kilogram CharcoalProduced(the
Averagesand Coefficientsof Variation, CV, Are Given for the Five KenyanEarth
Mound Kilns)a
CO2 CO
CH4 TNMHCb NO
NOx N20
TSPc PIC
gases+TSP
EM1
EM2
1992
3027
207
333
35.2
46.2
90.3
94.9
0.058
0.055
0.087
0.130
0.12
0.30
41•2
34.1
373
508
2365
3535
EM3
1787
240
47.9
93.8
NA
0.035
0.16
25.0
406
2193
EM4
1147
195
61.7
124.0
NA
0.045
0.084
38.7
420
1567
EM5
1058
143
32.2
60.1
NA
0.021
0.068
12.8
248
1306
HT
1382
324
47.6
80.9
NA
0.028
0.045
NA
459
1841
Surface
1533
373
56.8
45.9
NA
0.014
0.051
NA
484
2017
162
36.5
23.9
NA
0.0054 0.011
NA
229
772
EM average 1802
223
44.6
92.6
0.056 0.063 0.15
30.4
391
2193
EM CV
0.31
0.26
0.033
0.38
0.24
0.40
Rectangular 543
0.44
0.24
0.70
0.63
apIC-- products
of incomplete
combustion
- CO + CH4+ TNMHC + TSP. gases+TSP
-- CO2+ CO
+ CH4 + TNMHC + TSP. NA, not analyzed.
bAssuming
a percarbon
molecular
weightof 18.
•Determinedusingdatafrom Thai charcoal-making
experiments,
wheretheTSP emitted(as carbon)
rangedfrom 0.02 to 0.10% of the original wood carbon[Smithet al., 1999]. The carboncontentof
the TSP rangedfrom 40.0 to 54.1%.
.
Table 6b. EmissionFactors,Grams of PollutantC per Kilogram CharcoalC Produced
(the Averagesand Coefficientsof Variation, CV, Are Given for the Five Kenyan
EarthMound Kilns)•
CO2 CO
CH4 TNMHC NOb
NOxb N20b TSPc PIC
gases+TSP
765
1162
125
201
37.1
48.6
0.045
0.068
EM3
686
145
50.5
EM4
441
118
65.1
EM5
406
HT
511
Surface
498
EM1
EM2
Rectangular 170
86.2
0.038
0.036
88.0
116
0.104
0.266
23.2
19.2
270
358
1035
1520
983
NA
0.018
0.147
14.1
297
NA
0.023
0.075
21.8
321
762
NA
0.011
0o061
7.2
184
590
33.9
56.4
188
48.3
73.1
NA
0.014
0.0386
NA
314
825
190
50.7
36.5
NA
0.0060
0.0384
NA
282
781
18.2
NA
0.0023 0.0083 NA
132
302
87.0
0.037
0.033
0.131
17.1
286
0.033
0.70
0.63
0.38
0.23
79.3 31.3
EM average 692
135
47.0
EM CV
0.31
0.26
0.44
84.8
89.1
0.24
978
0.36
•PIC- products
of incomplete
combustion
= CO + CH4+ TNMHC + TSP.gases+TSP
= CO2q-CO
+ CH4 + TNMHC + TSP. NA, not analyzed.
bUnits
aregrams
of N perkilogram
ofcharcoal
C.
CDetermined
usingdatafromThai charcoal-making
experiments,
wheretheTSP emitted(ascarbon)
rangedfrom 0.02 to 0.10% of the original wood carbon[Smithet al., 1999]. The carboncontentof
the TSP rangedfrom 40.0 to 54.1%.
Table 7 presents a summary of earlier charcoal kiln
emissionstudies. Note that the Brazilian rectangularkiln with
tar recovery tested here is similar in constructionto the
Missouri kilns. As shownin Table 7, the resultsof this study
roughly validate the default values listed by the
Intergovernmental
Panel on Climate Change (IPCC) for CO
and TNMOC in that the IPCC values [Intergovernmental
Panel on ClimateChange(IPCC), 1997] fall within the range
of valuesfor the kilns monitoredhere. Comparedto the IPCC
default emission factors, the values for the Kenyan and
Brazilian kilns testedhere range from -1.5x to +l.8x for CO
and-2.1x
to +3.4x for TNMOC
(we assume TNMHC
=
TNMOC). Also comparedto the IPCC default values, this
study's resultsrangefrom +1. lx to +2. lx for CH 4 and from 56x to-2.3x for NOx. Thus, becauseof the dependenceon
kiln type, to accurately quantify global emissions from
charcoalproduction,there is a need to quantify the fraction of
charcoalproducedin eachmajor kiln type.
3.3. Global Warming Commitment
One way of examining the greenhousegas implicationsof
these charcoal-making kilns can be seen in Figures 3-5.
These figures show the carbonbalancefor the Kenyan Earth
24,150
PENNISE ET AL.: GREENHOUSE
Earth
Mound
1
Earth
Mound
2
Earth
Mound
3
Earth
Mound
4
Earth
Mound
5
GASES FROM CHARCOAL
MAKING
Hot Tail
Surface
Rectangular
0%
20%
40%
60%
80%
100%
Percent of Original Wood Carbon
ICharcoal
!•Brands
•QCondensables
I-ICO2
I•iCO
I•!CH4
!•TNMOC
mTSP
and Ash
Figure 2. Distributionof the woodcarbonin the productsof thecharcoal-making
process.
moundkilns (averageof five), the Brazilian hot-tail kiln, and the total amounts of air pollutants emitted from charcoal
the Brazilian rectangularkiln with tar recovery,respectively, productionin Kenya and Brazil were calculated. This is
as well as the greenhousegas implicationsof the airborne shownin Table 8 as megatons(Mr) of pollutant.The amount
emissions.Figures3-5 are normalizedto the productionof 1 of CO2 emittedfrom the use of fossil fuels in Kenya and
kg of charcoal. In Figures3-5, two typesof global warming Brazil is also shownin Table 8 for comparison.Also shown
are the air pollutionemissionsresultingfrom
commitments(GWC) are applied. The first, called "primary for comparison
fossil fuel use in the United States. We can see that CO2
GWC.," assumesglobal warming potentials(GWPs) only for
CO2, CH4, and N20 (respectively,1, 23, and 290 by mole for emissionsfrom charcoalmaking in Kenya are of the same
a 20-year time horizon [IPCC, 1995]). The second,"total orderof magnitudeas the CO2 from fossilfuel use in Kenya
GWC," also appliesGWPs for CO and hydrocarbons,which (3.9 versus6.7 Mr). In Brazil, CO2 from charcoalmakingis
about 3.5% of the CO2 from fossil fuel use. Table 8 shows
are less certain (respectively,4.5 and 12 for a 20-year time
horizon [IPCC, 1990]). A discussionand additional citations that charcoal making is indeed an important source of
on the GWPs of CO and hydrocarbonsare presentedby Smith greenhousegases(and other air pollutants)in Kenya and
et al. [2000].
For each the GWC is calculated under two
extremeassumptions:(1) that the kilns rely on a completely
renewable wood supply, that is, the emitted carbon is
eventually recycled back into trees and (2) that there is
completedeforestation,that is, no carbonrecyclingback into
biomass. Under assumption2, the GWC includes the full
complementfrom CO2 (GWP=I.0). Under assumption1,
there is no contributionfrom CO2 in the GWC, becauseall of
that carbon is assumedto be reabsorbedby new biomass.
Based on results from the eight kilns tested here and on
publishedGWPs (using a 20-year time horizon) for CH4 and
N20 only, we estimatethat 0.77 to 1.63 kg C-CO2 (carbonas
carbondioxide equivalents)is emittedper kilogram charcoal
produced.
In Kenya, nearly all charcoalis producedin Earth mound
kilns. We estimatedthe amountof charcoalproducedin each
type of kiln in Brazil. The amountswere basedupon charcoal
production patterns in Brazil in 1996. Using the annual
amountof charcoalproduced,the fractionaluse pattern,and
the experimentalemissionfactors determinedin this study,
Brazil.
Finally, using20-yearGWPs, the total GWCs for Kenyan
and Brazilian charcoal-makingkilns are estimatedin Table 9.
Shownfor both countriesis a two-by-twomatrix of GWCs,
dividedas discussed
earlierfor Figures3-5. We estimatethat
the total primary GWC of Kenyan and Brazilian kiln
emissionsis about2.7 and 7.5 Mt C-CO2,respectively.For
comparisonthe estimatedtotal primaryGWC resultingfrom
fossil fuel use in the United Statesis 1693 Mt C-CO2 [U.S.
Departmentof Energy (U.S. DOE), 1999; U.S. Environmental
ProtectionAgency(U.S. EPA), 1998; IPCC, 1995]; this along
with the total GWC are displayedin Table 9. Considering
that KenyaandBrazil combinedproduceaboutone quarterof
the world's charcoal, Tables 8 and 9 reveal that global
charcoalmaking is a much less major sourceof GHGs than
the use of fossil fuels in the United States.
A full analysisof the airborneemissionsresultingfrom the
charcoalfuel cycle would requireevaluationof its final end
use (e.g., combustionin cookstoves)and emissionsfrom the
alternate fate of the wood input if it were not used for
24,151
PENNISE
ETAL.'GREENHOUSE
GASES
FROMCHARCOAL
MAKING
Table7.Summary
ofCurrent
andPrevious
Charcoal-Making
KilnEmission
Studies
% Charcoal
Emission
Factors,
g ofPollutant
perkgof Charcoal
Produced
Yield
(Charcoal
TNMHC
Mass/Dry
or
Condensables
NOx
TSP
(Tars and
Oils)
Study
KilnType
Wood
Mass)CO2 CO
CH4 TNMOC N20
Present
study
Kenyan
Earth
22.6
1992 207
35.2
90.3
0.12
0.087
41.2
---
Present
study
Kenyan
Earth
21.6
3027 333
46.2
94.9
0.30
0.130
34.1
---
Present
study
Kenyan
Earth
28.0
1787 240
47.9
93.8
0.16
0.035
25.0
---
Present
study
Kenyan
Earth
31.1
1147 195
61.7 124
0.084
0.045
38.7
---
Present
study
Kenyan
Earth
34.2
1058 143
32.2
60.1
0.068
0.021
12.8
---
Present
study
Brazilian
Hot-tail 34.1
1382 324
47.6
80.9
0.045
0.028
......
Present
study
Brazilian
Surface 28.7
1533 373
56.8
45.9
0.051
0.014
......
543 162
36.5
23.9
0.011
0.0054
......
966 162
31.8
29.7
0.017
---
1.90
58 a
1235 158
21.7
19.9
0.021
---
0.69
63 a
29.4
1517 336
57.7
71.5
0.026
---
4.19
66 a
Smith
etal.[1999] ThaiEarth
mound 29.8
1140 226
27.7
95.3
0.046
---
2.25
65 a
1570 106
12.7
8.5
0.084
---
0.81
65 a
1593 254
39
Mound
1
Mound 2
Mound
Mound
3
4
Mound 5
(brick beehive)
(roundbrick)
Present
study
Brazilian
rectangular
36.4
with tar recovery
Smith
etal.[1999] Thaibrick
beehive 33.3
(ave. of 3 runs)
Smith
etal.[1999] Thaimud
beehive 30.8
(ave. of 3 runs)
Smithetal.
[1999] Thaisingle
drum
(ave. of 3 runs)
(ave. of 3 runs)
Smith
etal.[1999] Thairicehusk
mound
29.7
(ave. of 3 runs)
Brocard
etal.[1996]African
Earth
mound27.6
U.S.
EPA
[1995] Missouri
--IPCC[1997]
(World
average) 20.8
d
Shah
etal.[1992] Metal
partial32.7
550 145 55
--210 30
1192 336 ---ø
7.2(asC) 0.11
80b
51
72s
0.24
--12
--0.3
......
14 (as C) --___c
155c
___
133g
combustion kiln
•Value
derived
from
theaverage
oftwocondensable
emissions
tests
(one
ThaiEarth
mound
kilnandoneThaibrick
beehive
kiln).
bDerived
bysubtracting
CH4fromtheemission
factor
given
forvolatile
organic
compounds
(VOC).
CTSP was included in the condensables.
dConverted
to a drybasisby assuming
20%moisture
in wood.
CCH4includedin the TNMOC column.
SSum
of CH4,ethane,andethene.
gSumof tars,phenols,andfurfurals.
charcoal making, along with the emissions from its
production in kilns. This complete emissions analysis is
required for accurate comparison to the emissions
implications of other fuel cycles, such as the direct use of
fuelwood. For example, in some locations, part of the
fuelwoodmay decayanaerobicallyin the environmentleading
to considerableCH4 emissions.In sucha case,the accounting
shouldallocateonly the net changein GHG emissionsto the
charcoalfuel cycle.
are quite sensitive to errors in the measured solid masses,
especiallywood mass. It is also apparentthat the emission
factor for any one speciesis quite insensitiveto errorsin any
of the otherairbornespecies,exceptCO2.
We were not able to calculate
standard deviations
for the
valuespresentedin Tables 2, 3, 4, 5, 6a, 6b, 8, and 9, because
only one experimentwas conductedper kiln in this study.
The measurementuncertaintyor error involved in this study
includedthe following.
1. There was instrumentalerror for the gaschromatograph
3.4. Error Analysis
systemused for the gaseoussamples. Each gaseoussample
Sincethe carbonbalancemethodusedin this studyrelies was injectedinto the GC twice. If the two valuesfor any of
on measurementsof gaseousratios to CO2 and measurements the peak areasof a samplediffered by more than 10%, the
of the solid inputs and outputsto determinethe emission samplewas reinjecteduntil a differenceof lessthan 10% was
factorsof interest,the sensitivityof the calculatedemission observed. We estimate the instrumental error to be +/-5 %.
2. Therewasinstrumentalerrorfor the scalesusedto weigh
factors to potential measurementerrors is not directly
obvious. The error analysis in Table 10 shows typical the wood and charcoal in the field. We estimate this error to
percentage changes in the calculated emission factors be +/- 10%.
3. There was instrumental
error for balances used in
resulting from hypothetical 10% errors in the measured
determination of wood moisture content.
We estimate this
gaseousconcentrationsor solid masses. Data from kiln EM1
was used for this exercise.
We can see that emission factors
error to be +/-5%.
24,152
PENNISE ET AL.: GREENHOUSE GASES FROM CHARCOAL MAKING
3.64 kg Dry Wood
(1.60 kg Carbon)
(65.4 MJ)
0.10 kg Brands-C (4.5 MJ)
0.048 kg Condensables-C
1 kg Charcoal
(0.75 kg Carbon)
0.00064 kg Ash-C
(30.8 MJ)
0.012 kg TSP-C
0.49 kg CO2-C
No CO2 Recycled
PrimaryGWC = 1.35 kg C-CO2
Total GWC = 2.58 kg C-CO2
0.099 kg CO-C
0.036 kg CH4-C
0.066 kg TNMOC-C
All CO2Recycled
Primary GWC = 0.82 kg C-CO2
Total GWC = 1.89 kg C-CO2
0.00015 kg N20
Figure3. Carbon
cycleforcharcoal
making
in theKenyan
Earthmound
kilnandtheGWCresulting
from
renewable
andnonrenewable
harvesting
of thewood(MJ, megajoule).
4. There was analyticalerror in the determinationof the
carboncontentsof wood, charcoal,and brands.We estimate
the errorfor the carboncontentanalyticalmethodto be +/-
5%. Thethreecharcoal
samples
fromBrazilwereanalyzed
at
two differentlaboratories.
The averagepercentdifferenceof
thesethreepairsof valueswasonly 1.8%.
5. Errorwasassociated
with theuseof grabsampling
to
determinethe overallgaseousemissionratios. In five of the
2.93 kg Dry Wood
(1.43 kg Carbon)
(59.8 MJ)
0.021 kg Brands-C (0.82 MJ)
0.043 kg Condensables-C
1 kg Charcoal
(0.75 kg Carbon)
(27.6 MJ)
0.0057 kg Ash-C
0.0034 kg TSP-C
0.38 kg CO2-C
No CO2 Recycled
PrimaryGWC = 1.19kg C-CO2
Total GWC = 2.46 kg C-CO2
0.14kgCO-C
0.036 kg CH4-C
0.054 kg TNMOC-C
All CO2Recycled
PrimaryGWC = 0.77 kg C-CO2
Total GWC = 1.85kg C-CO2
0.000045kg N20
Figure4. Carboncyclefor charcoal
makingin the Brazilianhot-tailkiln andthe GWC resulting
from
renewable
andnonrenewable
harvesting
of thewood(MJ, megajoule).
PENNISE
ET AL.' GREENHOUSE
GASES FROM CHARCOAL
MAKING
24,153
2.75 kg Dry Wood
(1.34 kg Carbon)
(55.1 MJ)
1 kg Charcoal
(0.92 kg Carbon)
(31.5 MJ)
0.092 kg Brands-C (3.6 MJ)
0.0045 kg Condensables-C
0.0054 kg Ash-C
0.036 kg Tar-C
0.0032 kg TSP-C
recovered
0.15 kg CO2-C
No CO2 Recycled
All CO2Recycled
0.069 kg CO-C
0.027 kg CH4-C
Primary GWC = 0.77 kg C-CO2
PrimaryGWC = 0.59 kg C-CO2
0.016 kg TNMOC-C
Total GWC = 1.27 kg C-CO2
Total GWC = 1.01 kg C-CO2
0.000011 kg N20
Figure 5. Carboncycle for charcoalmaking in the Brazilian rectangularkiln with tar recoveryand the GWC resultingfrom
renewableand nonrenewableharvestingof the wood (MJ, megajoule).
kiln experimentsin our previous study of Thai kilns, we
compared the grab sampling method to the continuous
sampling method for the gaseousemissions. Unlike the
currentstudywherefrom 7 to 24 grab sampleswere taken per
kiln experiment,only 3, 4, or 5 grab sampleswere taken in
the five Thai kiln experiments. Hence the error in the grab
samplingmethodin the Thai experimentswould be expected
to be larger than that error in the current study. Nonetheless,
the percentdifferencesin the gaseousemissionratiosfor the
grab samplingmethod versusthe continuousgas sampling
method in the five Thai experiments were 12% for the
CO/CO2 ratio, 32% for the CH4/CO2 ratio, and 37% for the
TNMHC/CO2 ratio. Among all the grab samplescollected
Table
8. Estimated
Annual
Air Pollution
and analyzedin the currentstudy,there were 25 duplicates
(two bags collected sequentially). The average percent
differencesin the gaseousemissionratiosfor the 25 pairs of
samples were as follows: 14% for CO/CO2, 21% for
CH4/CO2, 38% for TNMHC/CO2, 33% for NO, 73% for NOx,
and 75 % for N20.
6. Error was associatedwith determiningthe wood mass
given the wood volume for EM3, EM4, EM5, HT, and surface
kilns only. We used a standard wood volume-to-mass
conversionfor Acacia mearnsii (black wattle) for EM3, EM4,
and EM5.
We estimate this error to be +/-5%.
surface kilns.
Emissions
We estimate this error to be +/-10%.
from Charcoal
Production
in KenyaandBrazil (1996), Comparedto Emissionsfrom FossilFuel Use in
Kenya,Brazil,andtheUnitedStates
a
CO2, CO,
CH4, TNMHC,t' NOx,
N20,
Mt
Mt
Mt
Mt
Mt
Mt
Kenyancharcoalproduction
3.9
0.49
0.097
0.20
0.00014
0.00032
Braziliancharcoalproduction
8.6
2.0
0.31
0.47
0.00016
0.00028
Kenyanfossilfuel use, 1995
6.7 c _.....
Brazilian fossil fuel use, 1995
U.S. fossil fuel use
249 c
_.....
5490d 68.66e 10.09d 9.621e
21.09e
aUsing
a totalproduction
of charcoal
of 2.2 Mt in Kenyaand6.4 Mt in Brazil.
t'Assuming
a percarbon
molecular
weight
of 18.
CDatafor 1995,from WorldResources
Institute[1998].
aDatafor 1997,fromU.S.DOE [1999].
eDatafor 1997,from U.S.EPA [1998].
We used the
volume-to-massratio of the rectangularkiln for the HT and
0.269a
24,154
PENNISE ET AL.: GREENHOUSE GASES FROM CHARCOAL MAKING
Table 9. EstimatedGlobal Warming Commitments(GWC) from Kenyan
and Brazilian CharcoalProduction(1996) Comparedto GWC from
Fossil Fuel Use in the United States (1997)
Kenyan
Kenyan
Brazilian
Brazilian
PrimaryGWCa TotalGWCa PrimaryGWCa TotalGWCa
CO2 recycled
CO2 not recycled
1.60
2.74
3.80
5.29
4.97
7.55
11.5
15.2
Primary
GWCfrom 1693
t'
U.S. fossil fuel use
Total GWC from
1903t'
U.S. fossil fuel use
aUsing20-yearglobalwarmingpotentials.UnitsareMtC asCO2equivalents.
t'Using
emissions
datafromU.S.DOE[1999]andU.S.EPA[ 1998].
Table 10. Error Analysis
A 10% Change in
CO2
GivesThisPercentChangein theFinalEmissionFactorEstimates
CO2
GO
CH4
TNMOC
TSP
NOx
N20
2.4
-6.9
-6.9
-6.9
-6.9
-6.9
-6.9
CO
- 1.2
8.7
- 1.2
- 1.2
- 1.2
- 1.2
- 1.2
CH4
-0.4
-0.4
9.6
-0.4
-0.4
-0.4
-0.4
TNMHC
TSP
Wood mass
Charcoal mass
Brands mass
Condensables mass
-0.8
-0.2
24.3
-9.7
-4.6
-0.8
-0.8
-0.2
24.3
-9.7
-4.6
-0.8
-0.8
-0.2
24.3
-9.7
-4.6
-0.8
9.1
-0.2
24.3
-9.7
-4.6
-0.8
-0.8
9.7
24.3
-9.7
-4.6
-0.8
-0.8
-0.2
24.3
-9.7
-4.6
-0.8
-0.8
-0.2
24.3
-9.7
-4.6
-0.8
7. Error in the use of sampled charcoal bag mass to
determine the total massof charcoal for EM3, EM4, and EM5
kilns only. We estimatethis error to be +/-10%.
8. Error was in the useof sampledbrand massto determine
the total massof brandsfor EM3, EM4, andEM5 kilnsonly.
We estimate this error to be +/-10%.
9. Error was associated with the use of Thai Earth mound
kiln data for carbon contents of wood, charcoal, and brands
for EM 1, EM2, EM3, EM4, and EM5 kilns only. Differences
in wood carbon contentsare expectedto be less than 5%.
Charcoaland brandscarboncontentsare primarilya function
of the carbonizationtemperature,which is, in turn, mostly
dependenton the kiln materialsand size. Given the similarity
of the kiln materials(layersof brush,twigs, and Earth) in the
Thai and Kenyan experiments,we estimatethis error to be +/10%.
Basedon this roughanalysis,we estimatethe error in the
valuespresentedin Tables2, 3, 4, 5, 6a, 6b, 8, and9 to be the
following:+/-20% for CO2,+/-25% for CO, +/-30% for CH4,
+/-40% for TNMHC and NO, +/-50% for TSP, and +/-75%
for NOx and N20.
Acknowledgments.We greatlyappreciatethe effortsandpatience
of all the kiln operatorsinvolvedin this study,at the Universityof
Nairobi, at the plantationin Soy, Kenya, and at the plantationin
Brazil. We would like to thank SusanThorneloe, U.S. EPA Project
Manager,for her faithful supportand adviceand Keith Openshawfor
his assistance with wood volume to mass conversions.
This research
was funded by the U.S. EPA througha cooperativeagreementwith
the East-West Center (CR820243). This paper has not gone through
official EPA review proceduresand thus shouldnot be consideredto
have official EPA approval.
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(ReceivedOctober16, 2000; revisedApril 12, 2001;
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