United States
Environmental Protection
Agency
Environmental Sciences Research "^
Laboratory /,
Research Triangle Park NC 27711
vVEPA
Research and Development
EPA-600/S3-82-010 June 1982
Project Summary
Measurement of Loblolly Pine
Terpene Emissions
R. L. Seila, R. R. Arnts, R. L. Kuntz,#/&4/l0wm.K. R. Knoerr, and A. C.
Dudgeon ^ *>'-•
A new method for quantifying bio-
genic hydrocarbon emission rates
without disturbing the vegetation is
presented. An energy balance/Bow-
en ratio approach was used to esti-
mate fluxes of cr-pinene from meas-
urements of net radiation and vertical
gradients of a-pinene, temperature,
and water vapor above a loblolly pine
forest canopy. The mean flux for 20
determinations ranging from 19 to 84
/ug/m2/min was 41 /ug/mVmin. This
method was compared to an enclo-
sure method, in which foliage is en-
closed with a Teflon bag for emission
rate determinations. For this compari-
son, the energy balance/Bowen ratio
flux values were converted to emis-
sion rate units of /jg a-pinene/g dry
needle mass/hr using site-specific
biomass factors. Seventeen enclosure
method determinations from mature
loblolly pine trees yielded a median
value of 4.7 /ug/g/hr over a range of
1.2 to 32 yug/g/hr. While both methods
displayed relatively high variances,
the variance of the enclosure method
was considerably higher than that of
the energy balance/Bowen ratio
method. There was no statistically sig-
nificant difference between the re-
sults of the two methods.
This Project Summary was devel-
oped by EPA's Environmental Sci-
ences Research Laboratory, Research
Triangle Park, NC. to announce 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).
Introduction :*«/
Monitoring of ambient air ozone con-
centrations in rural areas of the United
States for more than 10 years has con-
firmed that ozone concentrations above
the previous National Ambient Air Qual-
ity Standard of 80 ppb are not uncom-
mon. It has been proposed that tropo-
spheric ozone is produced by the
photochemical reactions of biogenic
hydrocarbons; the evidence is the high
ozone concentrations in rural areas.
Investigation of this hypothesis has
addressed several questions: What vol-
atile organic compounds are emitted by
vegetation? What are the emission rates
and ambient air concentrations of the
most abundant biogenic hydrocarbons7
What is the ozone production potential
of biogenic hydrocarbons? This report
addresses biogenic hydrocarbon emis-
sion rates and the methodology for
measuring such rates.
Previous methods for determining
biogenic hydrocarbon emission rates
were variations of enclosure methodol-
ogy, in which a plant or portion of a plant
was isolated in an artificial environment,
and the emission rate was determined
by measuring the increase in emissions
mass over time Emission rate measure-
ments from individual plants were then
combined with vegetative density esti-
mates to yield biogenic hydrocarbon
inventories. A potentially more accurate
method would be to directly measure
the flux of biogenic hydrocarbons over a
vegetated area and thereby obtain an
integrated measurement that includes
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emissions from leaves, ground litter,
and non-leaf vegetative surfaces.
This project was an experiment
designed to determine biogenic hydro-
carbon flux over a forested area. Experi-
mental measurements were made at a
loblolly pine plantation over a six-month
period. Due to analytical limitations,
cr-pinene, which is the most abundant
volatile organic compound emitted from
loblolly pine, was the only hydrocarbon
for which a flux was determined. By
measuring the net radiation and vertical
gradients of a-pinene, temperature, and
water vapor above the forest canopy,
the c-pinene flux could be calculated
using an energy balance/Bowen ratio
approach. Measurements were also
made by a limb enclosure technique
for comparison to the energy balance/
Bowen ratio method.
Procedure
The area of study was a uniform 19-
year-old loblolly pine plantation which
had already been intensively studied to
develop biomass and energy relation-
ship models. A very sophisticated
micrometeorological measurement sys-
tem, consisting of sampling and mea-
surement sensors on a 25-m scaffold-
ing tower (Figure 1) and analytical
instrumentation in two vans, was used
for atmospheric profile measurements
of water vapor, carbon dioxide, temper-
ature, and wind speed, at 18 levels
within and above the forest. Point mea-
surements were taken of wind direc-
tion, atmospheric pressure, and net
radiation. A minicomputer was used for
sampling control, data acquisition, and
data analysis.
A sampling system to collect air sam-
ples in Teflon® bags at six levels above
the canopy was added for the analysis of
Radiation
25 —
20
75
S
10
22 m&-
Canopy
1
Wind Speed and Direction
26.0
25.0^U
HzO, COz, Temperature, and a-Pinene
19.
18.5 fA-
77.5**-
77.0*?*-
76.5 .
75.5 i
14.5
72.5
77.5
3.5
7.5
4.5
25.0
23.0 If
21.0
6 Pumps for i
Collecting \
a-Pinene Bag I
Samples \
To
H20 and C02
Analyzers
Figure 1. Micrometeorological sampling system.
2
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cr-pinene. Stainless steel bellows
pumps withdrew sample air from exist-
ing water vapor/carbon dioxide sam-
pling manifolds through Teflon tubing
into 25-L Teflon bags. Analysis of a-
pinene was by gas-liquid chromatog-
raphy, with flame ionization detection
and cryogenic preconcentration of
sample.
Measurements were conducted at
approximately solar noon on sunny
days, when the wind speed and direc-
tion was relatively stable (westerly
winds between 1 and 5 m/s). A typical
set of concentration profiles is illus-
trated in Figure 2.
Biogenic hydrocarbon emission rates
were also determined at the site using
an enclosure method. For this method,
the limb of a tree was enclosed in a large
Teflon bag, which was secured to the
limb with tape. The bag was evacuated
using a non-contaminating pump, so
that the bag partially collapsed around
the limb. A hydrocarbon sample was
withdrawn into a separate small Ted-
lar® bag, using the same pump from the
enclosure bag; the volume of the enclo-
sure bag was visually estimated. Clean
air was added at 10 L/min for about 5
min, then another hydrocarbon sample
was collected. After sampling was com-
25
pleted, the limb was clipped, dried, and
the needles weighed. The enclosure
hydrocarbon samples were analyzed by
the same gas chromatographic method
used for the energy balance/Bowen
ratio method The hydrocarbon emis-
sion rate was equal to the mass of the
second sample minus the mass of the
first sample divided by the emission
time period and the dry needle mass.
Emission rate measurements of cr-
pinene, /3-pinene, myrcene, and d-
limonene for loblolly pine were made at
the site using this method.
Results and Discussion
Twenty determinations of #-pinene
flux were made using the energy bal-
ance/Bowen ratio method. Values rang-
ed from 19 to 84 //g/mVmin over a
temperature range of 14° to 35°C, with
most of the data collected during the
summer between a temperature range
of 28° to 35°C. The mean flux was 43
Seventeen emission rate determina-
tions on mature trees using the enclo-
sure method yielded values for a-
pinene ranging from 1 2 to 32 ^g
cr-pmene/g/dry needle mass/hr. The
*
Q>
E
o
20
15
e/0
a s
.<*>
Q
Forest
Canopy
4 Temperature
0 Water Vapor Pressure
o Carbon Dioxide
m a-Pinene
I i I I
ill I I I>||
5\25.8 26.8\-
37.2 37.8 32.6|25.S
Temperature, °C Water Vapor
Pressure, mb
•Wind Speed)
f\<
i
26.8\-2.0-1.0 0 1.0,2.^1.4 ZO2.6\150w 350
A COa. ppm a-Pinene, ug/m3 Wind Speed,
cm/sec
Figure 2. Loblolly pine forest vertical gradients, 7/18/77, 1035-1100 hrs EST.
median was 4.7/ug/g/hr. We observed
that the determinations on saplings
were much higher than the mature tree
values.
Figure 3 shows a graphical compari-
son of the two methods by a plot of log
cr-pinene versus temperature. The
regression line and 95% confidence
bounds derived by Tingey et al.* for the
cr-pinene emission rate of slash pine is
also included for reference and compar-
ison. The graph suggests three things:
the two data sets are very scattered and
indistinguishable from each other; the
enclosure method points show greater
dispersion than the energy balance/
Bowen ratio points; and neither set of
data shows a log-linear relation to
temperature.
Conclusions
Although the enclosure method mea-
surements displayed higher variances
than the energy balance/Bowen ratio
method, statistical comparison of the
two techniques indicated no significant
difference between them. Both meth-
ods displayed relatively large vari-
ances, and the enclosure method may
have yielded results biased high, due to
the unavoidable physical contact be-
tween the enclosure bag and the vege-
tation.
The chief advantage of the energy
balance/Bowen ratio method is that a
total flux, which includes emissions
from leaves, ground litter, and other
non-leaf vegetative surfaces, is deter-
mined directly, rather than from individ-
ual emission rates and biomass densi-
ties — both of which can have large
uncertainties. The disadvantages of this
method are that it is complicated and
expensive and that the analytical
method for the hydrocarbons must be
very sensitive and specific. The advan-
tage of the enclosure method is that it is
relatively easy to perform and is field-
portable. The analytical requirements
are not as stringent, because the con-
centrations of biogenic hydrocarbons in
the enclosure bag are much higher than
ambient concentrations.
Because of the variability of the flux
estimates and the lack of any simple
functional relationships with environ-
mental variables, only approximate flux
estimates can be made at this time. A
more complete set of emission data over
the seasonal range of temperatures and
a better understanding and description
of the emission surface will probably be
required before adequate predictive
emission functions can be developed.
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The EPA authors R. L. Seila. R. R. Arms, and R. L. Kuntx are with the
Environmental Sciences Research Laboratory, Research Triangle Park, NC
27711 • F. L Mowry, K. R. Knoerr, and A. C. Dudgeon are with the School of
Forestry and Environmental Studies, Duke University, Durham, NC 27706.
Joseph J. Bufalini is the EPA Project Officer (see below).
The complete report, entitled "Measurement of Loblolly Pine Terpene Emis-
sions," (Order No. PB 82-207 135; Cost: $7.50, subject to change) will be
available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Environmental Sciences Research Laboratory
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
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Environmental Protection
Agency
Center for Environmental Research
Information
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