EPA/600/A-93/075
Measurement of Biogenic Emissions from Corn
Sarah A. Meeks, Bru« W. Gay, Jr., and Beverly
E. Til ton*
Atmospheric Research and Exposure Assessment
Laboratory and *EnvironmentaI Criteria and
Assessment Office, U.S. Environmental
Protection Agency, Research Triangle Park, NC 27711
A pilot study was conducted to determine whether techniques for measuring biogenic emissions from tree
saplings, branches, and leaves could be adapted to the measurement of biogenic emissions from individual
plants of agricultural species. Measurements were then made to determine possible biogenic emissions
from corn (Zea mays L.), an agricultural crop of significant economic importance in the United States as
well as in other parts of the world. Biogenic emissions from corn were expected to be low, based on work
of other investigators; but corn biomass represents a substantial fraction of agricultural land-use in the
United States, such that the total impact on air quality could be appreciably more than expected from the
reported emission rate alone. Measurements were made of emissions from mature single corn plants and
from corn seedlings, using a modification of the established branch enclosure technique. Air samples
from the Tenon* plant enclosure chamber were collected at an exit port by means of gas-tight syringe,
and transferred into Tedlar* bags for temporary storage and tranport to the laboratory for cryogenic
preconcentration and analysis by GC-FID. To look at potential emissions of biogenic aldehydes, samples
were also drawn from the enclosure chamber directly through cartridges containing DN?H-coated silica,
for subsequent analysis by IIPLC. Experimental enclosure and measurement procedures are presented,
along with preliminary results.
The effects of air pollutants on vegetation have been extensively and systematically studied. Conversely,
the effects of vegetation on air pollution have not been studied nearly as extensively or systematically.
Increasing recognition of the need to understand better the role of biogenic emissions of nonmethaue
hydrocarbons (NMHCs) in atmospheric chemistry has prompted a number of investigations of emission rates
from vegetation over the past decade or so. In some cases, the investigations have taken the form of
geographically localized emission inventories or surveys. In other cases, individual species of plants known to
have agricultural or ecological importance have been studied to determine emission rates using static or flow-
through enclosure chambers.
The study reported here was a pilot study conducted to determine the feasibility of adapting techniques
for measuring biogenic emissions from tree saplings, branches, and leaves to the measurement of biogenic
emissions from individual plants of agricultural species. Measurements were then made to determine biogenic
emissions from com, an agricultural crop of significant economic importance in the United States as well as in
other parts of the world. Biogenic emissions from com were expected to be low, based on work of other
investigators; ' but com biomass represents a substantial fraction of agricultural land-use in the United States,
such that emission fluxes from corn could be large. Corn is one of (he most important food crops in the
western hemisphere and is grown in abundance in the United States, Canada, and Latin America.
Few measurements of biogenic emissions from com have been made. Iamb et al. ' measured biogenic
emissions from com, tobacco, alfalfa, clover, and mixed forage by means of the bag enclosure technique. They
reported that "isoprene was not emitted in significant amounts by any members of the group. Compounds
eluting near the monoterpenes appear to be the major emission components. In all cases, individual compound
concentrations were very low and consequently identification of individual species was not attempted". They
reported NMHC emission rates of 2.0 jtg/g dry matter/hr from corn. '
2 4
Winer et al. reported total emissions over a 6-hr sampling period of 68 ppb C, consisting of tens of ppb
C each of an unknown (molecular weight of 100), 1-decene, 1-dodeccne, 1-tetradecene, and an unknown
sesquiterpene (molecular weight of 204). In the final report of that study, however, Winer et al. presented no
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biogenic emissions from com and noted that com was sampled but did not undergo the full sampling and
measurement protocol because of its very low emission rate. A temperature-adjusted emission rate of 2.2
dry matter/hr is used for com in the U.S. EPA Biogenic Emission Inventory System (BETS).
Objectives of the study reported here were to modify previously used enclosure techniques for the study
of biogenic emissions from single corn plants, to measure total nonmethane hydrocarbon emissions from corn,
and to identify species of NMHCs emitted if possible.
Experimental Methods
The study was conducted from early June through late September 1992. Com seeds (Zaz mays L.)
(cv. P3140) obtained from the Agricultural Research Service, U.S. Department of Agriculture (Raleigh, NC,
office) were planted in commercial potting soil in containers and kept outside the U.S. EPA research building in
Research Triangle Park, NC. Seeds, seedlings, and mature plants were watered daily and a complete fertilizer
(20-20-20) was applied once per week during early growth and twice per week during more rapid growth and
maturation of the plants.
For measuring biogenic emissions, enclosure chambers of 2 mil Teflon* (from E.I. duPont de Nemours
and Co.) were constructed to fit the plants at respective stages of growth, since the size of the plants changed
rapidly during the growing season. Chambers were altered to fit the plants since emissions were expected to be
low and unnecessary chamber space was undesirable. The static enclosure technique was chosen over the flow-
through chamber technique to maximize the collection of emissions, which in turn would increase the possibility
of identifying compounds measured. Contaminants from the Teflon* film used for the static enclosure chamber
might also be increased with this technique, but such contamination is a significant problem in the use of now-
through chambers as well (discussed below).
In one attempt at enclosing a mature corn plant, the Teflon* enclosure chamber was placed over plants
and containers. This method was abandoned, however, because of the difficulties of getting an air-tight seal.
Jn subsequent experiments, the Teflon* enclosure chamber was placed over a single plant only and sealed with
tightly wound cording at the base of the cornstalk. Care was taken to avoid damage to plants, since terpene
emissions are known to be sensitive to physical damage to leaves. Plants were grown in full sun but were
generally enclosed and sampled in shade to reduc* heat buildup, since a 30-min sampling period would have
resulted hi temperatures that could have damaged the plants, i.e., >44 "C, as reported by Tingsy et al.
Insolation and temperature were recorded.
Three separate experiments were conducted to determine the possibility of biogenic emissions from corn:
(1) sequential sampling from the same bag enclosure (four 1-min samples taken in the first 5 min of enclosure),
to look at possible increases in emissions over time; (2) short-term sampling, at the end of 4 min; and
(3) longer-term sampling, at the end of 30 min. The 4- and 30-min sampling experiments both employed
previously used enclosure bags. The sequential sampling experiment used bags made of new film.
Within-expcriment replications (multiple samples from the same bag) were performed in this study, but no
attempt was made to replicate individual experiments, largely because of negative results (see below) and
because outgassing rates from bags vary from batch to batch of film and also differ between new and used bags
(Lonneman et al., 1981), which makes between-expcriment replications less meaningful. Ambient air was used
in the enclosures for the 4-min and sequential sampling experiments. Zero air with CO2 added to slightly above
ambient (to allow for plant uptake over the course of the exposure) was used in the 30-min-exposure
experiment. The 30-min sampling period was used in an attempt to determine the possible emission of
aldehydes, expected to be emitted, if at all, at even lower rates than the nonoxygenated hydrocarbons.
Control samples of air from chambers without plants were obtained by (a) flushing the bag with zero air,
refilling it with zero air plus added CO2, and sampling as in the experimental protocol; or (b) flushing the bag
with ambient air, refilling it with ambient air, and sampling as in the experimental protocol.
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Samples were removed from the bag enclosures with a 1-L gas-tight syringe equipped with a Swagelok*
quick-connect. The samples were transferred to Tedlar* bags for transport to the laboratory and temporary
storage until analysis by GC-FID. Air samples from both control and experimental bags were analyzed for
nonmethane hydrocarbons oa a Hewlett-Packard 5890 gas chromatograph using the system and method
described by Seila et al.
Samples for determination of possible aldehyde emissions, from mature corn exposed in zero air, were
taken after 30 min from the bag enclosure, using a vacuum pump to pull a 3O-L air sample directly into DNPH-
coated silica cartridges (DOW commercially available from Waters Co.)- Cartridges were subsequently analyzed
by the HPLC procedure reported by Kuntz et al.
To calculate emission rate data on the basis of leaf dry matter, leaf dry mass was determined by
removing all the leaves from the cornstalk measured and drying them to constant weight in a forced-air oven at
60 °C.
Results and Discussion
Results of this preliminary series of measurements of biogenics from com are negative. No differences
between control and experimental samples were found in these experiments.
Figure 1 shows the results of measurements made in August 1992 of total NMHC from mature
cornstalks. Note that there is no difference statistically between the amount of total NMHC, as ppb C, in
control samples and the amount in samples from the enclosed cornstalks. Sequential sampling was done to help
overcome the problem of the high background of volatile carbon species found both in zero and ambient air in
Tedlar* and Teflon* enclosure chambers. In a separate study in this lab, for example, the rate of production
of isoprcne was such that sequential samples easily showed the accumulation of emissions in the chamber.
Here, there was no change with time. The variations in total volatile organics measured from 1.5 to 4.5 mir.
(Figure 1) are not significant. Based on the emission rate for com used in the U.S. EPA biogenic emissions
inventory (BHS) of 2.2 ^g/g dry matter/hr, as reported by Pierce and Waldruff, 157 ppb C should have been
produced during the sampling period from the biomass present in this experiment. Note the high level of
volatile organics found in control samples, which is discussed later.
Figure 2 shows results of sampling and analysis for low-molecular-weight aldehydes, as well as total
NMHC in respective experiments, in July 1992, using mature corn. As Figure 2 shows, findings in these
experiments were also negative, both for aldehydes and for total NMHC. Note especially that acetaldehyde was
higher in the control samples than in the experimental. Note also that total NMHCs were approximately 100
ppb C less in this experiment (both in the control and experimental samples) than in the experiment depicted in
Figure 1 (see discussion below).
Results of measurements of total NMHCs from com seedlings are given in Figure 3. Note again the
occurrence of high background NMHCs in the control sample and the lack of difference in total NMHCs
between the control and the experimental samples. Again, using the emission rate of biogenics from corn of
2.2 fuglg dry matter/hr, 34 ppb C should have been produced during the 4-min sampling period by the biomass
present in this experiment.
Data shown in Figures 2 and 3 were obtained with bag enclosures that had been used previously. Data
shown hi Figure 1 were obtained with bags made from new film. These data emphasize the demonstrated
importance of bag outgassing and variations in outgassing as a function of commercial batch and of use history,
as reported by Lonneman et al. (1981). Because results were attributed to outgassing and interpreted as
negative, and consistently negative across three separate experiments, no replications of the separate experiments
were conducted.
Table I shows compounds reported or assumed to occur in biogenic emissions from com. The U.S. EPA
BEIS assumes a split of terpenes, oxygenates, and unreactive hydrocarbons in vegetation for which emission
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factors have been reported. 'li Lamb et al. ' reported 2.0 ^ig/g dry matter/br of unidentified NMHCs. Winer
et al. reported a preliminary identification of 1-decene, 1-dodecene, 1-tetradecene, and two unknowns—one of
them a sesquiterpene—in emissions from corn. None of these compounds was detected in this study. It should
be pointed out that some of the emissions from Teflon* film, in the absence of plants in the enclosure chamber,
have retention times close to those of some of the monoterpenes; but that retention times have been checked, on
our system by means of authentic standards. No accumulation of isoprene or terpenes over initial ambient air
levels was observed in ambient-air-exposure experiments. Nor was emission of these compounds observed in
the zero-air experiments. Conditions in these experiments were within the ranges of environmental conditions at
which emission of these biogenics has been reported. ' '
The high level of volatile organics found in the control and in the experimental samples appears to result
from outgassing from the Teflon* film used for the chamber. While some variations in total amounts can be
attributed to experimental error, random differences in outgassing across the sampling periods appear to account
for variations among respective experimental samples and between control and experimental samples. A
measurement made in a flow-through Teflon*-film chamber in May 1991 in this laboratory, as part of another
study, showed 524 ppb C, with 83 peaks in the GC-FID chrornatograrn. Emissions from the Teflon* film of
the flow-through chamber were calculated, based on the flow rate and surface area, to give a film emission rate
of 2.9 ^g/g of film/hr.
Experiments done in this same laboratory on problems with outgassing from bags made of Teflon* film';
were reported in 1981. That study, by Lonneman et al., showed unequivocally that high levels of total
volatile organics, including high levels of reactive organics, are released by Teflon* bags containing clean air
(zero air). Furthermore, that study showed variability from bag to bag in total amounts of volatile organics
produced from outgassing, along with variations in the kinds of compounds occurring. Additionally, gas
chromatographic-mass spectrophotometric techniques were used to identify the largest VOC peak, which turned
out to be perfluoropropylene; and to show tentatively, based on ion fragmentation patterns, that the lesser peaks
from outgassing contamination were probably from fluorinated carbon compounds.
Likewise, in the Lonnemau et al. study, Teflon*-film bags showed decreased emission of contaminants
with age and use of the bag, and with heat treament of the bags prior to use. Heat treatment reduced use-life of
the bags, however. In the study reported here, the lower levels of NMHCs seen in two experiments, around
510 to 520 ppb C, compared to the levels seen in the third experiment, around 650 to 680 ppb C, are attributed
to the fact that prc-used, older bags were employed in those two experiments.
1 3
Additional possible sources of differences between findings of this study and those of Lamb et al. ' and
the preliminary work of Winer ct al." include the use of different cultivars of com for study. For example,
Winer et al. ' used cv. Pioneer 3183; we used cv. P3140. The culdvar of field-grown com measured by
Lamb et al. ' was not reported. Also, cultivation methods differed. Lamb et al. ' measured com growing in
a field in Pennsylvania under natural agricultural conditions. Winer et al. ' measured containerized com
grown on the campus at Riverside, CA. We grew the corn in containers, watered frequently, and applied a
complete agricultural fertilizer once a week.
Enclosure and sampling methods also differed. Winer et al. ' used a flow-through Teflon* chamber and
Tenax* cartridge adsorption, thermal desorption, and analysis by GC-FID and GC-MS. Lamb et al. ' used a
Tedlar* static enclosure method and GC-FID analysis. We used a Teflon* static enclosure chamber and GC-
FID analysis.
13 24
Finally, differences in results from Lamb et al., ' Winer et al., ' and this study could have resulted
from the condition of the com plants. Turlings find Tumlinson, for example, have reported the systemic
release of terpinoids (e.g., linalool) from com seedlings following injury to leaf surfaces by mechanical damage
and application of macerated gut contents from beet armyworm larvae that are known herbivores.
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Summary and Condusioas
Measurements were made of mature single com plants and of corn seedlings, using a modification of the
established branch enclosure technique. Air samples from the plant enclosure chamber were collected at an exit
port by means of gas-tight syringe, and transferred into Tedlar* bags for temporary storage and transport to the
laboratory for cryogenic preconcentration and analysis by GC-FID. To look at potential emissions of biogenic
aldehydes, samples were also drawn from the enclosure chamber directly through cartridges containing DNPH-
coated silica, for subsequent analysis by HPLC.
Results of this study fail to confirm the biogenic emissions from com that have been reported in the
literature and used in the U.S. EPA Biogenic Emissions Inventory System (BHS). Variable numbers of peaks
were seen among control and experimental samples and GC-FID runs. Likewise, variable retention times were
observed among samples and GC-FID runs. The most likely source of peaks in both control and experimental
samples is outgassing from the Teflon* film used in the enclosure chambers. This likelihood is bornt out from
the essentially negative results from two studies, this one and the study of Winer ct al., ' with results from
both studies verified by use of authentic standards; and from the lack of identification and assignment of peaks
reported by Lamb et al., ' although the peaks were thought at that time to be biogenic emissions.
A quotation from the Lonneman et al. paper is appropriate here: "One should suspect at least low
levels of outgassing contamination in any system Qiat includes Teflon materials. The problem will be most
serious for trace-level analyses."
Finally, the preliminary results reported here are exactly that, and should not preclude other attempts to
resolve the issue, using different methodologies, of emissions from com. The high-background VOC levels
seen in this study can be logically attributed to Teflon® outgassing, given the evidence of such high but variable
outgassing amassed in the Lonneman et al. study. Differences between the results of this study and other
reports could, however, also be a product, conceivably, of differences in the corn cultivars measured; in
sampling and analytical methodologies; in plant cultivation methods', and in the condition of the plants
measured. Research on different enclosure materials or techniques should be conducted before further studies to
measure biogenic emissions from corn are attempted.
Disclaimer
This paper has been reviewed in accordance with the U.S. Environmental Protection Agency's peer and
administrative review policies and approved for presentation and publication. Mention of trade names or
commercial products does not constitute endorsement or recommendation for use.
References
1. Lamb, B.K.; Westberg, H.H.; Quarles, T.; and Flyckt, D.L. "Natural hydrocarbon emission rate
measurements from sekctcd forest sites." Prepared by Washington State University, Pullman,
Washington, under EPA Grant No. 807053. Environmental Sciences Research Laboratory, U.S.
Environmental Protection Agency, Research Triangle Park, North Carolina 27711. Report No.
EPA-600/3-84-001, 1983. 115 p.
2. Winer, A.M.; Arey, J.; Aschmann, S.M.; Atkinson, R.; Long, W.D.; Morrison, L.C.; and Olszyk,
D.M. "Hydrocarbon emissions from vegetation found in California's central valley." Prepared by
Statewide Air Pollution Research Center, University of California, Riverside, CA, under Contract
No. A732-155. California Air Resources Board, Sacramento, CA. Final Report, 1989.
3. Lamb, B.K.; Guenther, A.; Gay, D.; and Westberg, H. "A national inventory of biogenic hydrocarbon
emissions." Atmos. Environ. 21(8): 1695-1705 (1987).
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4. Winer, A.M.; Arey, J.; Atkinson, R.; Aschmann, S.M.; Long, W.D.; Morrison, L.C.; and Olszyk,
D.M. "Emission rates of organics from vegetation in California's central valley." Atmos. Environ.
26(A14): 2647-2659(1992).
5. Pierce, T.E.; and Waldruff, P.S. "PC-BEJS: A personal computer version of the biogenic emissions
inventory system." J. Air Waste Manage. Assoc. 41(7): 937-941 (1991).
6. Tingey, D.T.; Manning, M.; Grothaus, L.C.; and Burns, W.F. "Influence of light and temperature on
monoterpene emission rates from slash pine." Plant Physiol. 65: 797-801 (1980).
7. Tmgey, D.T.; Manning, M.; Grothaus, L.C.; and Bums, W.F. "The influence of light and temperature
on isoprene emission rates from live oak." Physiol. Plant. 47: 112-118 (1979).
8. Seila, R.L.; Lonneman, W.A.; and Meeks, S.A. 'Determination of C-2 to C-12 Ambient Air
Hydrocarbons in 39 U.S. Cities from 1984 through 1986." U.S. Environmental Protection Agency,
Research Triangle Park, North Carolina 27711. Report No. EPA-600/3-89-058, 1989. Appendix B.
9. Tejada, S.B. "Evaluation of silica gel cartridges coated in situ with acidified 2,4-dinitrophenylhydrazinc
for sampling aldehydes and kctones in air." Int. J. Environ. Anal. Chem, 26: 167-185 (1986).
10. Kuntz, R.; Lonneman, W. A.; Namie, G.; and Hull, L.A. "Rapid determination of aldehydes in air
analyses." Anal. Letters. 13(A16): 1409-1415(1980).
11. Meeks, S.A.; Gay, B.W., Jr.; and Tilton, B.E. "Isoprene emissions from willow oak trees."
In: Proceedings of the 1992 U.S. EPA/A&WMA International Symposium, Measurement of Toxic and
Related Air Pollutants. Air & Waste Manage, Assoc., Pittsburgh. In Press.
12. Roselle, S.J.; Pierce, T.E.; and Schere, K.L. 'The sensitivity of regional ozone modeling to biogenic
hydrocarbons." J. Geophys. Res. 96(D4): 7371-7394(1991).
13. Guenther, A.B.; Monson, R.K.; and Fall, R. "Isoprene and monoterpcne emission rate variability:
Observations with Eucalyptus and emission rate algorithm development." J. Geophys. Res. 96(D6):
10,799-10,808(1991).
14. Lonneman, W.A.; Bufalini, J.J.; Kuntz, R.L.; and Meeks, S.A. "Contamination from fluorccarbon
films." Environ. Sci. Technol. 15(1): 99-103 (1981).
15. Turlings, T.C.J.; and Tumlinson, J.H. "Systemic release of chemical signals by herbivore-injured com."
Proc. Natl. Acad. Sci. USA. 89: 8399-8402 (1992).
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1.5 1.5 2.S 3.i 4.5 4.5
Sampling Time after Enclosure, Minutes
August 25, 1992; serial samples.
Figure 1. Measurement of total nonmethane hydrocarbons from mature com.
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600
June 5, 1992; 4-mlnute semples.
Figure 3. Measurements of tola] nonmelhane hydrocarbons from corn seedlings.
Table I. Some expected or reported bjogenic emissions from com.11
Compound
Q-Pinene
Decene-1
Dodecene-1
Tetrad ecene
Retention Time of Standards**
26.353
27.55
32.11
36.53
This Study
n.d.
n.d.
n.d.
n.d.
*For example, Lamb et al.;1 Roselle et al.;12 Pierce and Waldruff;" and Winer et al.
**CD-FID analytical system reported by Seila et al.
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TECHNICAL REPORT DATA
1. REPORT NO.
EPA/600/A-93/075
3.
4. TITLE AND SUBTITLE
MEASUREMENT OF BIOGENIC EMISSIONS FROM CORN
5.REPORT DATE
6.PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
Sarah A. Meeks, B.W. Gay Jr., B.E. Tilton*
8.PERFORMING ORGANIZATION REPORT NO.
9. PERFORMING ORGANIZATION NAME AND ADDRESS
Atmospheric Research and Exposure Assessment Lab
Office of Research and Development
U.S. Environmental Protection Agency
Research Triangle Park, N.C. 27711
10.PROGRAM ELEMENT NO.
11. CONTRACT/GRANT NO.
In House
12. SPONSORING AGENCY NAME AND ADDRESS
Same as above
13.TYPE OF REFCST AND PERIOD COVERE
Symposium Proceedings
14. SPONSORING AGENCY CODE
EPA/600/09
15. SUPPLEMENTARY NOTES
* Environmental Criteria and Exposure Assessment Office
Presented at Emissions Inventory Conference, Durham, N.C.
Oct. 21, 1992
A pilot: study was conducted to determine whether techniques for measuring biogenic
emissions from tree saplings, branches, and leaves could be adapted to the
measurement of biogenic emissions from individual plants of agricultural species.
Measurements were then made to determine possible biogenic emissions from corn (Zea
mays L.), an agricultural crop of significant; economic importance in the US as well
as in other parts of the world. Biogenic emissions from corn were expected to be
low, based on work of other investigators; but corn biomass represents a
substantial fraction of agricultural land-use in the US, such that the total impact
on air quality could be appreciably more than expected from the reported emission
rate alone. Measurements were made of emissions from mature single corn plants and
from corn seedlings, using a modification of the established branch enclosure
technique. Air samples from the Teflon plant enclosure chamber were collected at
an exit port by means of a gas-tight syringe., and transferred into Teflon bags for
temporary storage and transport to the laboratory for cryogenic preconcentration
arid analysis by GC-FID. To look at potential emissions of biogenic aldehydes,
samples were also drawn from the enclosure chamber directly through cartridges
containing DNPH-coated silica, for subsequent: analysis by HPLC. Experimental
enclosure and measurement procedures are presented, along with preliminary results.
17.
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