United States
Environmental Protection
Agency
Air and Energy Engineering
Research Laboratory ,
Research Triangle Park NC 27711 '
Research and Development
EPA/600/S2-89/025 Dec. 1989
&EPA Project Summary
Effects of Burn Rate, Wood
Species, Moisture Content, and
Weight of Wood Loaded on
Woodstove Emissions
K.E. Leese and S.M. Harkins
Four woodstove operating param-
eters (burn rate, wood moisture,
wood load, and wood species) were
tested at two levels each using a half
factorial experimental test design to
determine statistically significant
effects on the emission components
CO, CO2, particulate matter, total ex-
tractable organics (TEOs), polycycllc
aromatic hydrocarbons (PAHs), Cj-C/
hydrocarbons, metals, and the Ames
plate incorporation bioassay
mutagenic potential.
Results showed that increasing
burn rate lowered CO, particulate
matter, TEO and C^-Cj hydrocarbon
emission rates. Increasing burn rate
raised emission rates of individual
PAHs and several metals, and also
the mutagenic potential of the
emissions. All of these effects were
significant at the 90% or better
confidence interval.
At the 90% or better confidence
interval, reducing wood moisture in-
creased the particulate emission
factor while concentrations of several
PAHs in the stack gas were lowered.
Changing from pine to oak in-
creased potassium emissions at the
90% confidence interval. Effects just
under the 90% confidence interval
included reductions in emission
factors for several PAHs and a
decrease in mutagenic activity.
Increasing the weight of the initial
wood load increased particulate
emissions, significant at the 90%
confidence interval. A decrease In
mutagenic activity was significant at
slightly below the 90% confidence
interval.
This Project Summary was devel-
oped by EPA's Air and Energy
Engineering Research Laboratory,
Research Triangle Park, NC, to an-
nounce key findings of the research
project that is fully documented In a
separate report of the same title (see
Project Report ordering Information at
back).
Test Conditions
This project is one of a number of
studies to characterize toxic/mutagenic
compounds emitted by residential wood
combustion units such as woodstoves.
The Integrated Air Cancer Project (IACP)
will use the information gained from this
and other such studies to determine the
contribution of toxic/mutagenic sub-
stances by residential woodburning units
to ambient air.
Specifically, this project studied the
effect of stove operating variables on
organic emissions such as polycyclic
aromatic hydrocarbons (PAHs), total
extractable organics (TEOs), particulates,
and CO. Other emissions studied in-
cluded CfC7 hydrocarbons.
A half factorial experimental test design
was used to evaluate statistically the
effects of four stove operating variables:
burn rate, wood moisture, wood load, and
fuel type on the measured woodstove
emissions. Ranges were established ac-
cording to high and low values and used
in the half factorial test matrix. Burn rate
target values were previously determined
to be approximately 2 kg/hr for low burn
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rate and 6 kg/hr for high burn rate. The
experimental averages for the low and
high burn rates were used. Wood mois-
ture contents were determined gravi-
metrically for cure and uncured woods
which were procured prior to test im-
plementation. Uncured wood remained in
log form and was cut 1 day prior to
testing to preserve the wood moisture
content. Wood loads were determined
according to the volume of the firebox.
High wood loads filled the stove to ca-
pacity initially, and low wood loads filled
the stove approximately half full. Two
wood types were tested, oak and pine.
Test variables with actual experimental
values are:
Variables High
Low
Fuel Oak Pine
Moisture Cured 16.9% Uncured 33.2%
Load High 15.2 kg Low 8.0 kg
Burn Rate High 6.56 kg/hr Low 1.75 kg/hr
Results
For this discussion, three types of
emissions are defined: concentrations are
mass of component per cubic meter of
stack gas (STP) wet (g/m3), emission fac-
tors are mass of component per mass of
wet wood burned (g/kg), and emission
rates are mass of component emitted per
hour (g/hr). All reported effects are the
result of the analyses of variance per-
formed by the half factorial statistical test
design.
Burn Rate
A. The effects of increasing burn rate
(kg wood burned/hr) at a 90% or
better confidence limit are:
1. The stove and stack gas tem-
peratures increase significantly,
as much as 140 and 170°C,
respectively. Maintaining higher
temperatures may contribute to
better combustion efficiency,
and thus, lower total extractable
organic, particulate, and CO
emissions.
2. C02 emissions are increased
while CO emissions are
decreased.
3. Particulate matter (probe and
filter catch) concentration and
emission factors decrease. At
high burn rates, particulate
concentrations and emission
factors are lower, but the stack
flow rate is higher; at low burn
rates, particulate concentrations
and emission rates are higher,
but the stack flow is lower.
These effects tend to cancel,
such that wood load has the
most significant effect on
particulate emission rates.
4. Gravimetric compounds
(>300°C b.p.) emissions
decrease.
5. TCO compounds (100-300 °C
b.p.) emissions decrease.
6. TEO emissions decrease.
7. C,-C7 concentration and
emission factors decrease.
8. H20 emission rates increase
but H20 emission factors
decrease.
9. Benzo(b)fluoranthene emission
factor (mg/kg wet wood)
increases.
10. Potassium emission increases.
11. Manganese concentration and
emission rate increase.
12. Sulfur emission increase.
13. Zinc concentration increases.
14. Mutagenic activity as measured
by TA98 + S9 increases.
B. The effects of increasing burn rate
(kg wood burned/hr) at just under a
90% confidence limit are:
1. Naphthalene, phenanthrene,
fluoranthene, pyrene, chrysene,
benzo(b)fluoranthene, and
benzo(a)pyrene emission rates
all increase.
2. Naphthalene and fluorene
emission factors (mg/kg wood)
decrease.
3. Chrysene emission factor
increases.
4. Benzo(a)pyrene concentration
increases.
5. TA98-S9 mutagenic activity
increases.
Wood Moisture
The effects of decreasing wood mois-
ture percent at a 90% or better
confidence limit are:
1. Lower stack gas moisture
concentration, but particulate
and C02 emission factors
increase.
2. Naphthalene concentration
decreases.
3. Pyrene emission factor
decreases.
4. Cadmium emissions decrease.
5. The weight percent of barium in
the ash decreases while the
weight percent of aluminum,
iron, magnesium, and strontium
increases.
6. The iron to potassium rati
the ash increases.
Wood Type
A. The effects of changing from pin
oak at a 90% or better confide
limit are:
1. Potassium emissions increas
2. Manganese emissic
decrease.
3. Zinc emission factor decreas
4. The weight percent in ash
barium, calcium, and stront
increases.
5. The weight percent in ash
aluminum, manganese, m
nesium, and zinc decreases.
6. The iron to potassium n
decreases.
B. Effects of changing from pine to
just under a 90% or better c
fidence limit are:
1. Acenaphthylene, phenanthre
anthracene, and pyre
emission factors decrease.
2. Particulate emission fac
increases.
3. Gravimetric and TCO cone*
trations and emission ral
decrease.
4. TEO concentration decreases
5. Mutagenic activity as measur
by TA98 + S9 and -!
decreases.
Wood Load
A. The effects of increasing wood lo
at 90% or better confidence lir
are:
1. Stack flow increases.
2. Particulate emission ra
increases.
B. The effect of increasing wood lo
just under a 90% confidence limit
1. Mutagenic activity (TA98-S
decreases.
U. S. GOVERNMENT PRINTING OFFIfF- 1 QRQ /7/.B_m •> /n-M o
-------
K.E, Leese and S.M. Harkins are with Research Triangle Institute, Research
Triangle Park. NC 27709
Robert C. McCrillis is the EPA Project Officer (see below).
The complete report, entitled "Effects of Burn Rate, Wood Species, Moisture
Content, and Weight of Wood Loaded on Woodstove Emissions," (Order
No. PB 89-196 828/AS; Cost: $36.95, subject to change) will be available
only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Air and Energy Engineering Research Laboratory
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
A L^rvj U.S.Pi)SIA6t
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