EPA-450/3-76-044
December 1976
EMISSION FACTOR
DEVELOPMENT
FOR
LEAF BURNING
U.S. ENVIRONMENTAL PROTECTION AGENCY
Office of Air and Waste Management
Office of Air Quality Planning and Standards
Research Triangle Park, North Carolina 27711
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EPA-450/3-76-044
EMISSION FACTOR DEVELOPMENT
FOR
LEAF BURNING
by
Ellis F. Darley
Statewide Air Pollution Research Center
University of California
Riverside, California 92502
Contract No. 5-02-6876
EPA Project Officer: Thomas F. Lahre
Prepared for
ENVIRONMENTAL PROTECTION AGENCY
Office of Air and Waste Management
Office of Air Quality Planning and Standards
Research Triangle Park, North Carolina 27711
December 1976
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This report is issued by the Environmental Protection Agency to report
technical data of interest to a limited number of readers . Copies are
available free of charge to Federal employees, current contractors and
grantees, and nonprofit organizations - in limited quantities - from the
Library Services Office (MD-35) , Research Triangle Park, North Garolina
27711; or, for a fee, from the National Technical Information Service,
5285 Port Royal Road, Springfield, Virginia 22161.
This report was furnished to the Environmental Protection Agency by-
Statewide Air Pollution Research Center, University of California, River-
side, California 92502, in fulfillment of Contract No. 5-02-6876. The
contents of this report are reproduced herein as received from Statewide
Air Pollution Research Center, University of California. The opinions,
findings, and conclusions expressed are those of the author and not
necessarily those of the Environmental Protection Agency. Mention of
company or product names is not to be considered as an endorsement
by the Environmental Protection Agency.
Publication No. EPA-450/3-76-044
11
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Abstract
In order to develop emission factors for particulates, carbon monoxide
and hydrocarbons from the burning of street tree leaves, leaf samples from
15 species were burned in the tower at the University of California, Riverside;
a total of 131 fires was conducted. Leaves at two moisture levels, approximately
10 and 20% (dry weight basis), were arranged in conical piles and ignited either
around the periphery at the bottom or at a single spot at the top. A few samples
were arranged in windrows and ignited from one end. For one species, American
sycamore, the opportunity was presented to compare the effect of different bulk
densities on the amount of pollutants emitted.
Catalpa, magnolia, American sycamore, and California sycamore were
consistently low in yields of all three pollutants at the low moisture level.
Averaging the four species together, the yields for particulate, CO and hydro-
carbon in pounds per ton of fuel burned were about 11, 85 and 8 pounds,
respectively. Magnolia was the cleanest at about 9, 51 and 8 pounds, respectively,
although for hydrocarbons alone, the yield from California sycamore was the lowest
at 2.7 pounds. The highest yields were from black locust which produced about
68, 117 and 49 pounds of the three pollutants, respectively.
Raising the fuel moisture level generally increased the production of all
three pollutants. The increase was greatest for particulate (up to four times)
and hydrocarbon (up to three times), and the least for CO (up to 29%).
In one sample of silver maple, green leaves had fallen among the dry leaves.
The average moisture of the mix was a little higher than the high moisture level
of the standard fires, but pollutant yields were increased dramatically.
Top ignition generally reduced the pollutant emissions. In many cases this
reduction was so great that yields from the high moisture level was less than
from the bottom ignition at the low moisture level.
An increase in bulk density of American sycamore as the result of physically
compressing the leaves resulted in an increase in pollutant emissions.
There was relatively little variation in the proportion of individual or
groups of hydrocarbons within grab samples taken for hydrocarbon analysis.
Averaging all fuels at both moisture levels, the ratio of olefins to methane,
other saturates, and acetylene was 42:32:13:8.
The majority of particles from all fires sampled were submicron in size.
Mass median diameter averaged . 28y and ranged from . 05y (catalpa) to . 60y
(black locust). An increase in moisture consistently resulted in particles of
larger diameter, ranging from a few percent change in cottonwood to a six-fold
change in catalpa. Top ignition gave no real benefit in altering particle
size distribution. Increasing the bulk density of American sycamore caused the
particles to be larger.
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Emission Factor Development for Leaf Burning
Introduction
In order to determine the emissions from burning leaves from a number of
street tree species, arrangements were made between the National Data Branch,
Environmental Protection Agency, and the University of California, Riverside.
This project was an outgrowth of one carried out for the State of Illinois
where leaves from only three tree species were burned. The leaves were burned in
a special tower that had been developed for the purpose of determining pollutant
emissions from burning wastes of agricultural and forest operations. One hundred
thirty one fires were completed using 15 species of leaf samples collected in
the Riverside-Los Angeles area. One series of fires included leaves from the
previous Illinois study.
Facilities
Experimental procedures for burning fuels and sampling emissions were
carried out in an out-of-doors burning tower and adjacent instrument building
which has been described earlier by Barley jit. jd_. (1). Some important modifica-
tions have since been made and are given in some detail in a recent publication
of the National Academy of Sciences (2). A brief description of the tower is
presented here.
The facility simulates open burning but channels the combustion products
so that representative samples of gas and particles can be taken. The tower is
in the form of an inverted funnel, 16 feet in diameter at the base, decreasing
to 28 inches in a length of 20 feet, and topped with a stack 8 feet in length.
The tower is erected above a table 8 feet in diameter, which is positioned in
a scale with a maximum capacity of 125 pounds. The sample site for gases,
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particulate, and for recording temperature and airflow is in the stack about
two feet below the top. Stack gases for analysis of total hydrocarbon, CO, and
C00, are drawn through sample lines into the appropriate analyzers in the instru-
ment building to give a continuous millivolt equivalent recording of concentra-
tions. Taps on the gas sampling system lead to bottles which were used to take
grab samples at two points during the fire—the temperature peak and the hydro-
carbon peak. Grab samples were taken from 34 fires, representing 11 of the 15
species and analyzed for individual hydrocarbons.
Airflow is monitored with a 4-cup anemometer mounted in the stack. A shaft
encoder is positioned on the end of the anemometer shaft, just outside of the
stack. The encoder generates a millivolt signal by making and breaking a light
beam through an 800-slot disc. One revolution of the shaft creates 800 pulses,
and 3000 pulses per second generates the full-scale 50 mv signal. The maximum
airflow encountered during the peak of the hottest agricultural fires is
between 40-45 mv, or approximately 10,000 cubic feet per minute. A transducer
was adapted to the actuating mechanism of the scale so that a change in weight
generated a millivolt signal; 1 mv is equivalent to 1 pound and full range is
50 mv.
All recording instruments are connected to a data acquisition system which
in turn is connected to the campus computer. The computer polls each recorder
every 2.6 seconds and stores the millivolt response of each instrument on tape
or discs. A computer program has been written from which the yield of pollutants
in pounds per ton of fuel burned can be calculated using the data collected on
temperature, gas concentration, and airflow.
Particulates are collected isokinetically on standard Type A glass fiber
filters held in two modified HIVOL samplers positioned in series in the sample
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line and outside of the tower. A pneumatic controller senses differences in
airflow in the stack and continuously adjusts a globe valve in the sample line
so that isokinetic sampling is achieved. The sample volume is approximately
l/776th of the total flow through the stack. The principal use made of the
isokinetic collection system has been to determine the total weight of parti-
culate from given fuels to establish emission factors. In addition, for the
present project a Sierra Instrument Company HIVOL 5-stage cascade impactor was
usad to determine particle size distribution from 36 fires, representing all
but one of the species, The impactor was set up near the top of the tower so
that samples were taken just above the opening of the stack. Particle cut-off
sizes were determined for each stage by calculations based on the theory developed
by Marple (3). A correction was made for a 50 cfm flow and a mass density of
0.9 g/cc was selected as a reasonable approximation.
Leaf Samples and Burning Procedures
Samples of leaves from the following 15 following tree species were collected
from the Riverside Campus, City parks, and from the Los Angeles State and County
Arboretum in Arcadia:
Black ash Sweet gum
Modesto ash Black locust
White ash Magnolia
Catalpa Silver maple
Horse chestnut American sycamore
Cottonwood California sycamore
American elm Tulip
Eucalyptus
Great care was taken in all stages of collecting, transporting, and subsequent
handling of the leaves so as not to alter their bulk density from what might
have existed if the leaves had been raked into a pile on site and burned.
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Leaves were burned at two moisture levels determined on a dry weight basis.
The low level was the air-dry moisture existing in the leaves at the time the
leaves were burned and was generally between 7 and 10 percent. The high level of
moisture used was approximately 20 percent. Once the moisture content of the
air-dry leaves had been determined, the amount of water to be added to a given
weight of leaves to bring the moisture to approximately 20 percent could be
calculated. Leaves to be moistened were placed in a large polyethylene bag and
the desired amount of water was added in a fine spray in 3 to 5 aliquots,
stirring the leaves between each spraying. The bag was sealed and allowed to
equilibrate for about 16 hours; the leaves were rolled gently around within the
bag a few times during that interval. Just before the leaves were placed on
the table, a sample was taken for moisture determination.
From the previous Illinois study, it was found that a 6-pound sample of
leaves was the best quantity to use for each fire. In most cases leaves were
arranged in a conical pile; windrows were occasionally used. Piles were ignited
with small laboratory-type propane torches either around the entire periphery
at the bottom or at a single spot at the top. Windrows were lighted across
the bottom of one end. At least two fires were conducted at each moisture
level and ignition method for each of the species.
Some special fires were conducted comparing the emissions from leaves of
American sycamore collected in Riverside with those sent to us from Illinois.
The latter leaves had become quite compressed during shipping so that their
bulk density was somewhat greater than that of leaves raked into piles on site.
Piles of Riverside leaves burned quickly and completely within a few minutes,
whereas the piles of Illinois leaves had to be stirred several times to accomplish
similar burning rates.
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Results and Discussion
Emissions of Particulates, Carbon Monoxide, and Hydrocarbons
The emissions of particulate, CO, and hydrocarbons at the two moisture
levels and two ignition methods are given in terms of pounds per ton of leaves
burned in Table 1. In addition, the bulk density in pounds per cubic foot is
also given.
Particulates.—Bottom ignition is probably the most common method of
lighting piles of combustible plant material. When particulate emissions
were compared between species at the low moisture level using bottom ignition,
it was found that catalpa, magnolia, and both American and California sycamore
produced less than 15 pounds per ton of fuel burned, the low value being 9.4
pounds for magnolia. White ash and tulip produced a little less than 20
pounds while the emission value for all other species was over 25 pounds.
Those producing nearly 40 or more pounds were Modesto ash (40.4), cottonwood
(39.1), sweet gum (40.9), black locust (68.0), and silver maple (74.2).
Increasing the moisture generally increased the particulate yield, in
some cases by a factor of two and in one case (white ash) by a factor of
almost 4. Moistened horse chestnut leaves gave the highest yield at 76.3
pounds. In four species, black ash, cottonwood, silver maple, and California
sycamore, there was a slight reduction in the yield of particulate matter with
an increase in moisture. At first one might think that the reversal could be
associated with bulk density per se, since three of the species had a. bulk
density of less than .80 pounds per cubic foot. But Modesto ash, American
elm, sweet gum, and tulip leaves have a similar range of bulk densities and
in all of these cases there was a considerable increase in particulate yield
with increase in moisture.
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Table 1. Emissions of Particulate, Carbon Monoxide, and Hydrocarbon from
Burning Street Tree Leaves at Two Moisture Levels and Three
Ignition Patterns
Leaf Ignition,
Species Method-
Black ash B
Modesto B
ash
T
WR
White ash B
Catalpa B
T
WR
Horse B
chestnut
Cottonwood B
Bulk den.^, % Moisture
Ibs/cu.ft.— dry wt. basis
1.50 8.2
16.6
.89 8.4
17.7
6.7
21.9
8.1
1.40 9.8
21.0
9.6
17.3
9.5
18.3
9.5
19.2
8.1
21.5
.77 9.7
20.0
Emissions, Ibs./ton
of leaves burned
Part.
36.2
35.8
40.4
71.1
19.5
15.2
22.5
17.4
68.2
13.8
28.2
12.2
16.3
12.5
16.5
31.9
76.3
39.1
35.9
CO
111.0
143.6
139.0
166.6
190.1
122.1
178.4
103.3
122.6
85.6
99.0
87.5
88.5
85.3
86.1
145.9
148.2
93.0
86.2
HC
29.6
52.0
27.1
64.1
13.2
13.3
16.7
10.0
32.5
12.0
28.1
7.5
16.1
8.5
14.5
26.7
51.0
29.4
34.2
-^Ignition of conical piles; B, complete circle at bottom of pile, and T,
single spot at top of pile. WR; leaves piled in a window and ignited
across the bottom at one end.
b/
Bulk density was determined when the leaves were at the low moisture content.
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Table 1. (continued)
Leaf Ignition Bulk den.
Species Method Ibs/cu.ft.
American B . 82
elm
T
WR
Eucalyptus B 2.45
Sweet gum B .77
T
WR
Black B 3.00
locust
Magnolia B 1.09
Silver maple B .78
T
WR
% Moisture
dry wt.
basis
10.7s/
17.4
9.8^
17.5
8.1s7
16.5
7.3
19.5
10.3s-7
20.1
6.4
17.5
7.5
25.0
7.2
19.4
8.2
19.9
8.9^
19.4
24.1^
9.1
22.5
7.1
20.6
Emissions, Ibs./ton
of leaves burned
Part.
26.1
52.7
12.8
10.8
15.1
39.4
33.9
37.7
40.9
61.5
7.1
19.1
14.3
56.8
68.0
72.4
9.4
16.4
74.2
63.9
164.7
25.6
39.6
37.5
56.8
CO
102.9
126.0
128.7
120.1
122.2
115.4
85.4
94.1
151.2
144.9
113.0
131.6
135.6
163.6
116.7
142.7
51.1
59.4
98.7
105.7
143.3
86.8
74.8
98.2
105.5
HC
26.3
58.2
15.5
18.8
17.2
40.0
18.8
32.9
29.9
44.8
8.0
24.5
14.5
42.0
49.0
74.6
7.7
12.5
27.3
35.6
45.9
11.9
16.6
15.9
24.1
c/
— Average of 4 fires
— Average of 3 fires
e/
— Average of 7 fires
— This single fire was composed of a mix of dry leaves
and some that were still quite green, all of which
had fallen from the tree. The proportion of each
leaf type in the mix and the moisture content was
as follows: Dry - 61% at 19.1% moisture
Green - 38% at 41.9% moisture
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Table 1. (continued)
% Moisture
Leaf Ignition Bulk den. dry wt.
Species Method Ibs/cu.ft. basis
American
sycamore
California
sycamore
American
sycamore
River .
111.
Tulip
B .38 9.0
17.1
T 8.7
22.8
B .28 10.7
17.4
— Special Bulk Density Series —
B .38 9.3
T 8.9
B 1.78 10.0
T 9.7
B .65 10.5
16.6
T 7.2
26.6
WR 11.0
18.4
Emissions, Ibs./ton
of leaves burned
Part.
11.8
24.5
14.3
10.3
10.2
9.8
11.9
11.9
34.5
20.6
19.1
31.4
12.5
19.1
13.3
23.1
CO
97.6
117.9
139.5
104.1
106.3
101.3
106.9
124.7
118.5
98.6
74.0
81.5
78.5
61.8
86.1
78.5
HC
7.5
16.3
3.1
3.3
2.7
6.8
5.7
2.6
30.6
20.5
16.8
29.5
8.6
15.5
8.6
19.3
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One of the silver maple leaf fires should be mentioned. We noted that
the fallen leaves under one tree near the campus included a fairly high pro-
portion of green leaves. Such a mix could have been burned by the property
owner had our laws permitted burning. These leaves gave us an opportunity
to compare emissions of remoistened dry leaves with a mix of leaves, some of
which had not yet dried naturally. A random sample of the dry-green mix was
separated and weighed. Sixty-one percent of the sample was classed as the
dry type having a moisture content of 19.1% and 38% of the leaves were classed
as the green type having a moisture content of 41.9%. Since the leaves had
been held for a few days in a plastic collection bag, it was obvious that the
dry leaves had absorbed some moisture from the green leaves. But, fortunately,
the dry leaves in the mix were at almost the same moisture content as the
remoistened leaves with which they were being compared (19.1 and 19.4%,
respectively) and the moisture content of the dry-green mix was only a little
higher than that of the remoistened sample (24.1 and 19.4%, respectively). The
green leaves alone had 41.9% moisture. The particulate yield of the dry-green
mix was more than 2.5 times (164.7 vs. 63.9 pounds) that of the dry leaves that
had been moistened. This indicates the sheer folly of trying to burn leaves in
the green state.
Top ignition was employed with seven of the leaf species. In all cases
but one (American sycamore-low moisture), both at the high and low moisture
levels, the yield of particulate was reduced when compared with yields from
bottom ignition. In some instances, the reduction was more than 60%. It was
interesting to note also that in most cases, yield of particulate from top
ignition at high moisture was less than the yield from bottom ignition at low
moisture.
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10
The windrow arrangement for ignition was used with six of the leaf
species. At both low and high moisture levels, the yield of particulate
was intermediate between bottom and top ignition for a given species.
These results indicate that for particulate emissions, the leaves
should be as dry as feasible, preferably less than 12% on a dry weight
basis. Top ignition is by far the most desirable ignition method. Bottom
ignition is the least desirable, even when the leaves are quite dry.
The leaf species varied a great deal in bulk density, due mostly to
differences in leaf (or leaflet) size and degree of curling upon drying. The
largest and most curled leaves were the American and California sycamores,
having a bulk density of .28 and .38 pounds per cubic foot, respectively.
The most dense species were eucalyptus and black locust at 2.45 and 3.00 pounds,
respectively. The former leaf does not curl at all, and the latter, being a
compound leaf, included relatively large petioles in the collected leaf
sample. Whereas the lowest particulate yields with dry leaves were obtained
from the two sycamores with the lowest bulk density and nearly the highest
yield came from black locust which had the highest bulk density, this rela-
tionship did not occur consistently. Eucalyptus, the second most dense leaf sample,
had a yield of particulate about half that of black locust. Further, silver maple
at a density of .78 yielded more particulate than did black locust at a density
of 3.00 pounds.
Within American sycamore, where the bulk density was altered by physical
manipulation of the samples, the density did have an effect on particulate
emissions. The Illinois sample had been compressed to a density of 1.78 pounds
as compared to a normal Riverside sample of .38, and the particulate yield of
the former was almost 3 times that of the latter with bottom ignition and
twice as much with top ignition.
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11
Carbon monoxide.—Using bottom ignition, seven species (cottonwood,
eucalyptus, magnolia, silver maple, American sycamore, and tulip) yielded
less than 100 pounds of CO per ton of fuel burned at the low moisture level.
Magnolia leaf fires produced the least at 51.1 pounds. The three species
yielding the least amount of particulate (catalpa, magnolia, and American
sycamore) were among the group yielding the least CO. Sweet gum at low
moisture gave the highest yield at 151.2 pounds.
An increase in fuel moisture resulted in an increase in CO yield in all
but three species (cottonwood, sweet gum, and California sycamore); the
increase, however, was not nearly as dramatic as had occurred with particulates.
The greatest increase of CO due to moisture was 29% (black ash) whereas parti-
culate increases were often by a factor of two and even 4 in one case.
With the normal silver maple leaves, an increase in moisture resulted
in only a 7% increase in CO. However, burning the dry-green mix resulted in
a 45% increase of CO over the dry leaves and a 24% increase over the nearly
comparable wet leaves. This again illustrates the folly of burning green leaves.
Igniting the leaves at the top of the pile was not quite as beneficial as
it had been with particulate emissions. At the low moisture level, top ignition
increased CO yields in five of the seven species where this method was employed;
only with sweet gum and maple was the yield decreased. However, at the high
moisture level top ignition was always an improvement over bottom ignition.
Again, yields of CO from windrow ignition were intermediate between bottom
and top ignition.
The effect of bulk density alteration of the American sycamore leaves
had a variable effect on CO emissions. Yields from the higher density
Illinois sample were increased by 11% over the Riverside sample with bottom
ignition and were decreased by 21% with top ignition.
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12
Hydrocarbons.—Bottom ignition at low moisture levels resulted in a
range of total emissions of hydrocarbons from a low of 2.7 pounds from
California sycamore to a high of 49.0 pounds from black ash. Catalpa,
magnolia, and American sycamore were again among the species lowest in
yield as they had been with particulates and CO; white ash was also quite
low, the yield being 10.0 pounds. The yield from the remaining species
was between 16.8 and 29.9 pounds. Increasing the moisture always resulted
in an increase in hydrocarbon, at times as much as by a factor of 3.
Burning the dry-green mix of silver maple followed the same pattern
as was evident with particulates and CO. The mix produced 68% more hydro-
carbon (27.3 vs. 45.9 pounds) than did the normal dry leaves and 26% more
(35.6 vs. 45.9 pounds) than dry leaves that had been brought to nearly the
same moisture.
The effect of top ignition was about as striking in reducing hydrocarbon
emissions as the method had been in reducing particules. In every instance,
at both low and high moisture levels, the yields of hydrocarbon were lower
than from bottom ignition. Further, in all species except catalpa, the top-
wet combination gave a lower yield than the bottom-dry combination.
As had been the case with particulates and CO, windrow ignition had
no particular advantage since the yields of hydrocarbon were intermediate
between those from bottom and top ignition.
The physical alteration of bulk density of American sycamore caused
a greater increase in hydrocarbon emissions than it did with particulates.
Emission of hydrocarbon from the compressed Illinois sample was increased
by a factor of 5.5 (5.7 vs. 30.6 pounds) over the normal Riverside sample
using bottom ignition, and by a factor of 7.9 (2.6 vs. 20.5 pounds) using
top ignition.
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13
The above results on emission factors from burning of several species
of street tree leaves suggest that the factors will vary from species to
species, but that the emissions from some species are consistently low for
the three pollutants examined. Moisture content of the leaves is an important
variable and letting them dry down will keep the emission factors low. The
type of ignition should also be given serious consideration because where
there is a choice between lighting piles at the bottom or top, the latter
method results in further benefits. Limited studies on variable bulk
density within a given species strongly suggests that leaves should not
be broken, stomped on, or otherwise compressed when burning is to be the
ultimate disposal method.
Yields of Methane, Other Saturates, Olefins, and Acetylene
Gas grab samples were taken from one fire at each moisture level from
11 of the tree species as well as from fires in the special bulk density
group . Analysis of the grab samples gives the concentration of some 23
individual hydrocarbons. For convenience these have been grouped as
methane, other saturates, olefins, and acetylene. The percent yield of
these four groups were averaged for the two samples taken within one fire
at each moisture level. The results are given in Table 2. Also shown is
the amount of carbon in the grab sample expressed as a percent of the
total carbon in the peaks at the time of sampling.
By averaging all of the fires with bottom ignition only, the photo-
chemically reactive olefins constituted about 42% of the hydrocarbons in
the grab samples. In decreasing order of occurrence, methane, other
saturates, and acetylene constituted about 32, 13, and 8%, respectively.
In general, the yields of a given hydrocarbon or groups of hydrocarbons
from the several leaf species did not vary greatly from the above averages.
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14
Table 2. Percent Yield of Methane, Other Saturates, Olefins, and Acetylene
in Grab Samples Taken During the Burning of Street Tree Leaves
at Two Moisture Levels and Two Ignition Methods
Leaf
Species
Black
ash
Modesto
ash
Catalpa
Horse
chestnut
Cotton-
wood
American
elm
Eucalyptus
Sweet
gum
Black
locust
Silver
maple
%
Igni- Moisture
tion . Dry Wt.
Method-' Basis
B
B
B
B
B
B
T
B
B
T
B
B
T
8.2
16.6
8.4
17.5
9.6
17.2
8.1
21.0
9.7
19.3
9.1
17.7
8.5
17.7
7.3
19.6
10.3
20.8
6.4
17.8
7.2
19.2
7.5
18.9
9.1
24.6
% of Total
Carbon in
Grab Sample
32.0
52.0
27.0
50.5
50.5
50.5
33.0
30.5
33.0
47.5
29.0
38.0
65.5
37.5
49.0
48.0
32.0
46.0
39.5
45.0
49.5
53.5
34.0
44.0
40.0
36.0
Percent of Hydrocarbons
in Grab Sample
Meth-
ane
38.9
37.7
38.0
34.6
39.5
34.3
39.1
36.9
39.7
34.7
36.7
32.3
49.2
46.0
37.5
33.3
39.6
47.7
55.2
42.3
43.2
39.5
32.2
28.9
48.3
48.5
Other
Sat.
14.0
12.4
14.2
15.4
10.3
15.3
11.7
10.5
13.5
12.7
19.1
13.9
8.7
9.5
7.8
10.8
8.5
14.7
6.9
6.6
17.8
16.0
9.4
16.7
5.2
9.8
Ole-
fins
38.5
42.4
40.5
43.5
39.0
41.1
43.0
45.0
38.9
42.9
37.4
45.8
34.3
36.7
41.5
44.3
41.4
59.0
29.2
43.7
30.5
40.5
49.3
45.2
32.5
35.7
Acety-
lene
8.5
7.3
7.2
6.4
11.2
9.4
6.2
7.6
7.9
10.0
6.9
8.1
7.6
8.1
13.3
11.6
10.5
7.1
8.5
7.3
8.4
4.1
9.3
9.3
13.5
6.0
a. Ignition of conical piles; B, complete circle at bottom of pile, and
T, single spot at top of pile.
-------
15
Table 2 (continued)
Leaf
Species
American
sycamore
(bulk den.
series)
River .
111.
River .
111.
7
to
Igni- Moisture
tion / Dry Wt.
Method- Basis
B
T
B
B
T
T
9.0
16.6
8.7
22.7
9.3
10.0
8.9
9.7
% of Total
Carbon in
Grab Sample
51.5
50.5
51.0
48.0
67.5
59.0
58.5
51.5
Percent of Hydrocarbons
in Grab Sample
Meth-
ane
41.2
42.8
49.1
49.4
45.6
42.0
52.7
48.2
Other
Sat.
5.3
6.8
4.2
4.9
14.8
9.0
4.6
13.0
Ole-
fins
40.0
43.3
39.9
29.9
29.5
41.4
27.1
36.0
Acety-
lene
13.4
7.1
6.8
16.2
10.0
7.6
15.5
5.6
-------
16
The notable exceptions were the lower yields of other saturates from low
moisture fires of eucalyptus, sweet gum, silver maple, and American
sycamore, and the somewhat higher yield of acetylene from eucalyptus and
American sycamore.
In most cases, increasing the moisture had the effect of slightly
decreasing yield of methane and increasing the yield of olefins. For
other saturates and acetylene, increased moisture had no consistent effect
on yield, increasing in some cases and decreasing in others. It is apparent
that moisture did not have the marked influence on the varying proportion
of hydrocarbons within the sample as it did on total hydrocarbon yield as
discussed in an earlier section.
While top ignition did not have as great an influence on varying the
proportion of groups of hydrocarbons within the sample as it did in
reducing total hydrocarbon yield, there was a consistent reduction in the
yield of olefins as compared to bottom ignition. This again demonstrates
top ignition to be a better method of lighting piles of leaves.
Similarly, the physically imposed alteration on the bulk density of
American sycamore leaves did not have the effect on proportion of hydro-
carbons within the sample as it did on the yield of total hydrocarbons.
Nevertheless, the yield of the important olefins was increased by more
than 30% by burning the compressed Illinois leaves.
Particle Size Distribution
Particle size distribution was determined for one fire at both
moisture levels for all tree species except California sycamore. In
addition, this determination was also made for the bulk density fires with
American sycamore. Mass median diameter and percent of particles less
than 1 and 2 microns are given in Table 3. The particle diameters plotted
-------
17
Table 3. Particle Mass Median Diameter
ly and 2y from Burning Street
and Two Ignition Methods
and Percent of Particles Less than
Tree Leaves at Two Moisture Levels
Leaf Ignition,
Species Method —
Black B
ash
Modesto B
ash
White ash B
Catalpa B
Horse B
chestnut
Cottonwood B
American B
elm
T
Eucalyptus B
Sweet gum B
T
Black B
locust
% Moisture
dry wt. basis
8.2
16.6
8.4
17.5
9.8
21.5
9.6
17.2
8.1
21.0
9.7
19.3
10.6
17.7
12.4
17.5
7.3
19.6
10.3
20.8
17.8
7.2
19.2
Mass median
Diameter,
Microns
.30
.44
.34
.45
.13
.47
.05
.32
.41
.58
.52
.54
.33
.56
.32
.36
.14
.44
.33
.63
.25
.60
.75
Percent
of Particles
less than
iy
84
76
82
75
93
79
93
84
78
71
72
73
84
72
84
83
90
77
82
68
87
68
61
2U
94
91
94
90
98
94
97
94
92
89
89
90
95
90
95
94
96
91
93
88
96
87
82
-^Ignition of conical piles; B, complete circle at bottom of pile, and
T, single spot at top of pile.
-------
Table 3. (continued)
18
Leaf Ignition
Species Method
Magnolia B
Silver B
maple
T
American B
sycamore
(bulk den.
series)
River . B
111. B
River . T
111. T
Tulip B
% Moisture
dry wt. basis
8.2
20.6
8.1
18.9
9.1
9.0
16.6
9.3
10.0
8.9
9.7
10.5
15.9
Mass median
Diameter,
Microns
.06
.17
.33
.70
.55
.07
.20
.15
.22
.03
.35
.13
.52
Percent
of Particles
less than
iy
92
78
83
64
72
92
87
92
87
95
81
96
73
2y
96
86
94
85
90
97
95
98
95
98
93
99
89
-------
19
against cumulative mass percent less than the indicated particle diameter
are included as pages 21 through 37 at the end of the report.
The great majority of particles from all fires were submicron in
size. Those from bottom ignition fires at the low moisture level ranged
from . 05u mm (catalpa) to .60y (black locust) and averaged . 28u. Along
with catalpa, magnolia and American sycamore fires also produced particles
of very small diameter. It was these same species that had produced the
least amount of particles. Particles from horse chestnut and cottonwood
were somewhat larger than the average, their mass median diameters being
. 41y and . 52y, respectively.
An increase in moisture consistently resulted in particles of larger
diameter, ranging from a few percent change in cottonwood to a six-fold
change in catalpa.
The limited fires with top ignition indicated that there was no real
advantage in using this method if particle size were the sole criterion.
Physically compressing leaves to give a higher bulk density caused the
particles to be slightly larger when using bottom ignition at low moisture
and a great deal larger when using top ignition. Although the sampling
was limited in scope, the results do indicate that leaves should not be
altered from their natural state when being burned.
-------
20
References
1. Barley, E. F., F. R. Burleson, E. H. Mateer, J. T. Mlddleton and V. P.
Osterli. Contribution of burning of agricultural wastes to photochemical
air pollution. J. Air Pollution Control Assoc., 16(12): 685-690 (1966).
2. Barley, E. F., S. Lerman, G. E. Miller, Jr., and J. F. Thompson.
Laboratory testing for gaseous and particulate pollutants from forest
and agricultural fuels. In, "Air Quality and Smoke from Urban and
Forest Fuels—International Symposium," National Academy of Sciences,
pp. 78-89 (1976).
3. Marple, V. A. A fundamental study of inertial impactors. Ph.B. Thesis,
Mechanical Eng. Bept., Univ. of Minnesota, Becember, 1970.
-------
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-------
TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
1 REPORT NO.
EPA-450/3-76-044
3. RECIPIENT'S ACCESSIOr*NO.
4. TITLE AND SUBTITLE
Emission Factor Development For Leaf Burning
5. REPORT DATE
_December 1976
6. PERFORMING ORGANIZATION CODE
7 AUTHOR(S)
Ellis F. Darley
8. PERFORMING ORGANIZATION REPORT NO.
9. PERFORMING ORGANIZATION NAME AND ADDRESS
Statewide Air Pollution Research Center
University of California
Riverside, California
10. PROGRAM ELEMENT NO.
11. CONTRACT/GRANT NO.
Project No. 5-02-6876-1
12
.SPONSORING AGENCY NAME, AND AD.DflESS .
If.5. Environmental Protection Agency
Office of Air and Waste Management
Office of Air Quality Planning and Standards
Research Triangle Park, North Carolina 27711
13. TYPE OF REPORT AND PERIOD COVERED
Final
14. SPONSORING AGENCY CODE
15. SUPPLEMENTARY NOTES
16. ABSTRACT
This report describes the methodology used to develop emission factors for
particulates, carbon monoxide and hydrocarbons from the burning of street tree
leaves. This project was an outgrowth of one carried out for the State of Illinois
where leaves from only three tree species were burned. The leaves were burned in
a special tower that had been developed for the purpose of determining pollutant
emissions from burning wastes of agricultural and forest operations. One hundred
thirty one fires were completed using 15 species of leaf samples collected in the
Riverside-Los Angeles area. One series of fires included leaves from the previous
Illinois study.
17.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.lDENTIFIERS/OPEN ENDED TERMS
c. COSATI Field/Group
Emissions
Particulates
Carbon Monoxide
Hydrocarbons
Methane
Qlefins
Saturates
Acetylene
18. DISTRIBUTION STATEMENT
Release Unlimited
19. SECURITY CLASS (This Report)
Unclassified
21. NO. OF PAGES
38
20. SECURITY CLASS (Thispage)
Unclassified
22. PRICE
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