United States
Environmental Protection
Agency
Research and Development
Air and Energy Engineering
Research Laboratory
Research Triangle Park, NC 27711
EPA/600/S7-91/006 Feb. 1992
& EPA Project Summary
Development of Seasonal and
Annual Biogenic Emissions
Inventories for the U.S. and
Canada
Lysa G. Modica and John R. McCutcheon
Historically, ozone control programs
based on reductions of known anthro-
pogenic volatile organic compound
(VOC) emissions have had limited suc-
cess in obtaining the National Ambient
Air Quality Standard. Researchers have
therefore been actively evaluating VOC
emission sources not routinely consid-
ered in ozone control strategies. One
potentially large source of reactive
VOCs is thought to be emissions from
crop and forest foliage. A biogenic
emissions inventory for the U.S. and
Canada was developed to assess the
role of biogenic emissions in ozone
formation. Emission inventories were
developed at hourly and grid (1/4 x 1/
6°) levels from input data at the same
scales. Emissions were calculated as
a function of biomass density and me-
teorological parameters (solar radiation,
cloud cover, temperature, wind speed,
and relative humidity). These factors
were applied to a forest canopy algo-
rithm that simulated processes gener-
ating biogenic emissions from foliage.
Resultant emissions were aggregated
to monthly, seasonal, and annual lev-
els and spatially to counties and states.
Approximately 50% of the biogenic
hydrocarbon emissions occur in the
summer, approximately equal amounts
(20%) in the spring and fall, and much
lower amounts in the winter. Isoprene
emissions result primarily from decidu-
ous tree species in forest canopies;
therefore, the contribution is lower in
the winter than in the other seasons
since deciduous biomass is assumed
to be zero between the first and last
frost dates. Isoprene emissions from
deciduous trees are dependent on the
incident solar radiation intensity and
therefore have a maximum emission
rate with warm temperatures and maxi-
mum solar intensity which occur dur-
ing the summer. The relative contribu-
tion of alpha-pinene and other monot-
erpenes to the total hydrocarbon emis-
sions is higher in the winter, especially
in the South where the climate is rela-
tively moderate. The relative contribu-
tion of alpha-pinene and other monot-
erpenes to total hydrocarbons in
Canada is higher than in the U.S., as
more deciduous foliage is present in
the U.S. The estimated annual biogenic
hydrocarbon budget is 18.8 Tg for the
U.S. and 6.7 Tg for Canada.
This Project Summary was developed
by EPA's Air and Energy Engineering
Research Laboratory, Research Tri-
angle Park, NC, to announce key find-
ings of the research project that is fully
documented in a separate report of the
same title (see Project Report ordering
information at back).
Introduction
A biogenic emissions inventory for the
U.S. and Canada was developed to ad-
dress research and assessment needs on
the role of biogenic emissions in ozone
formation. The seasonal and annual bio-
genic emissions inventories in this study
were developed at the hourly and grid
levels. Input data at these same temporal
and spatial scales were developed for com-
patibility with emissions algorithms.
Printed on Recycled Paper
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Since the emissions algorithms avail-
able rely on meteorological data as input,
diurnal profiles for each month were de-
veloped for a 3-year period that would
represent the meteorological conditions
around the year 1985. The representa-
tive diurnal meteorological parameters
were spatially interpolated to 1/6° latitude
by 1/4° longitude grid cells and were used
to calculate biogenic emissions using
gridded land cover data with the same
spatial resolution. The calculated emis-
sions were then aggregated spatially to
the county and state levels, and tempo-
rally to monthly, seasonal, and annual lev-
els. The resulting database provides esti-
mates of biogenic emissions that rely on
spatially and temporally variable condi-
tions, but are represented at larger spatial
and temporal scales for use in emissions
assessment evaluations comparing the
magnitude of anthropogenic and natural
sources.
A secondary objective of the research
was to process an updated version of the
county level natural paniculate data which
was developed after the completion of the
1985 NAPAP Emissions Inventory (Ver-
sion 2). The updated natural participate
data incorporated improvements to the
emissions calculation methodologies for
dust resulting from unpaved road travel in
the U. S. and improvements in the state-
to-county allocation methodologies.
Background
The National Acid Precipitation Assess-
ment Program (NAPAP) was established
by Congress in 1980 to expand the un-
derstanding of the processes that result in
acid deposition phenomena in and around
the U. S. A principal objective of NAPAP
was to develop a complete and accurate
inventory of natural and anthropogenic
emissions of acid deposition precursors.
The 1985 NAPAP Emissions Inventory
(Version 2) was delivered in February
1990. This inventory included anthropo-
genic emission data for SO,, NO, NO,
NO, VOC, THC, CO, TSP, NH3, SO_,
HCI, HF, 32 hydrocarbon reactivity classes,
and 15 classes of particulate based on
reactivity and size classes. Emissions
data were also developed for 12 classes
of natural particulate data based on reac-
tivity and size classes.
Another potentially large source of re-
active VOCs'in certain areas is thought to
be emissions resulting from biogenic pro-
cesses in forest and crop biomass. Al-
though the details regarding the emission
mechanisms and the controlling factors
affecting biogenic sources are not well
understood, significant advances have
been made in attempts to quantify these
emission source strengths.
Biogenic VOC emissions can affect the
atmospheric chemistry of urban ozone
plumes when introduced to an urban area
as a background flux. In addition, these
emissions can react with small amounts
of NOX left over from urban processes or
with additional natural sources of NOX.
The principal known sources of VOC from
natural processes are direct emissions
from the leaf surface of forest biomass
and agricultural crops. Emissions of NOX
from natural sources are thought to arise
from chemistry and biochemistry in soils
and from lightning. Natural sources of
other air pollutants may also be important
for other environmental concerns. For
example, emissions of natural particulate
can have effects on visibility, and the al-
kaline components of particulate may in-
teract in the atmospheric and cloud chem-
istry of acid rain.
The development of the emissions al-
gorithms and supporting data for the cal-
culation of biogenic emissions was not
sufficiently advanced to allow the inclu-
sion of natural hydrocarbon and NOX emis-
sions in the NAPAP Version 2 inventory.
Biogenic emissions algorithms, which de-
pend on meteorological data inputs, were
made available shortly after the comple-
tion of the NAPAP inventory. These algo-
rithms can be used to estimate emissions
of isoprene, alpha-pinene, other monoter-
penes, unknown hydrocarbons, NO, and
NO2. For this inventory, only grassland
NOX emissions were considered. Other
sources of biogenic NOX are known to
exist but have not been well quantified to
date. A methodology to apply these algo-
rithms was developed by the EPA's Atmo-
spheric Research and Exposure Assess-
ment Laboratory (AREAL) for episodic (day
specific) simulations using the Regional
Acid Deposition Model (RADM) for model
evaluation and research purposes.
While the availability of the episodic
emissions estimates were valuable for ap-
plication to the specific days selected for
the RADM evaluation simulations, it was
desirable to develop representative sea-
sonal and annual emissions estimates for
other NAPAP and EPA analyses. Earlier
efforts, performed by researchers at
Washington State University, were based
at the county level and relied on monthly
average meteorological data (e.g., tem-
perature and wind speed). The emissions
rates calculated by the emissions algo-
rithms are highly dependent op hourly tem-
perature and solar radiation data. A com-
parison of the results of this study with
earlier efforts is presented with the emis-
sions data. In general, biogenic hydrocar-
bon emissions estimated using data and
methodologies presented in this report are
lower than those reported in earlier efforts
on an annual and seasonal basis.
Biogenic Emissions Overview
The objective of the work documented
in this report is to develop county- and
state-level emissions inventories of bio-
genic hydrocarbon and NOX emissions rep-
resentative of the monthly, seasonal, and
annual temporal scales. The methodol-
ogy followed to achieve this objective was
to calculate gridded hourly biogenic emis-
sions for a representative day in each
month and sum these emissions to larger
temporal and spatial scales.
Three years of hourly surface airways
meteorological data from the National CIU
matic Data Center, reported at over 500
measurement sites in the U.S., were ob-
tained and quality checked. Data at over
130 measurement sites in Canada were
obtained from the Canadian Climate Cen-
tre of Environment Canada. These data
were used to develop diurnal profiles rep-
resentative of each month of the year at.
each reporting site. These data were
spatially interpolated to generate monthly
average diurnal profiles for the entire study
region in a grid based system defined by
grid cells of 1/4° longitude by 1/6° latitude.
Gridded land use cover data were avail-
able from the NAPAP program. Leaf bio-
mass data were available at the county
level from the Oak Ridge National
Laboratory's geoecology data base. These
data were disaggregated to the grid level
using gridded land use/cover data.
Biogenic hydrocarbon emissions were
calculated for the representative hour and
day in each grid cell for each month of the
year using the Canopy Emissions Model
developed for NAPAP by researchers at
Washington State University. The Canopy
Model considers the leaf temperature and
solar radiation gradient within the forest
canopy. Since the emissions from trees
are highly dependent on both temperature
and solar radiation, this algorithm pro-
vides more representative estimates of the
emissions rates than does a simpler treat-
ment based on the assumption that all of
the biomass is exposed to the same
unattenuated solar radiation intensity. Al-
gorithms were provided by the National
Oceanic and Atmospheric Administration
(NOAA) to calculate emissions of NOX from
undisturbed (uncultivated) grassland ar-
eas. Similar to the biogenic hydrocar-
bons, grassland NOX emissions are also
dependent on temperature. NOX emis-
sions algorithms for other land use types
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1
were not available for application to this
study. Additional emissions of NOX from
soils in forests, from agricultural lands, for
deserts, and from wetlands have been
observed in measurement programs; how-
ever, their dependencies on meteorologi-
cal and other factors were not yet deter-
mined for use in this effort.
The resulting hourly gridded emissions
calculations were aggregated to develop
monthly mean emissions magnitudes at
the grid level. Allocation factors, based
on the grid/county overlap, were used to
aggregate the gridded emissions to county
and then state totals. Finally, the monthly
averages were aggregated to seasonal
and annual totals.
The resultant emissions data indicate
that biogenic hydrocarbon emissions and
NOx are highest during the summer and
lowest during the winter. For the spring
and fall, the magnitudes of the biogenic
emissions are similar for the U.S. In
Canada, biogenic hydrocarbon emissions
are higher in the fall than in the spring.
Analysis of state-level seasonal totals in-
dicates that during the winter and sum-
mer, total State land area appears to be
the controlling factor in determining states
and provinces with the highest biogenic
hydrocarbon emissions magnitudes, al-
though emissions are also dependent on
the canopy foliage biomass. In the spring
and fall, land area as well as geographic
location appear to be important.
Report Organization
The primary objectives of this report are
to document the development of a bio-
genic hydrocarbon emissions inventory
using representative monthly diurnal pro-
files of meteorological data and the imple-
mentation of the Canopy Model software.
The calculated emissions at varying levels
of spatial and temporal aggregation are
also summarized.
The remainder of the report consists of:
Section 2: Development of Repre-
sentative Gridded Diurnal Meteoro-
logical Profiles
Section 3: Calculation of Biogenic
Hydrocarbon Emissions
Section 4: Natural Particulate and
Biogenic Emissions Data
Section 5: Summary and Recom-
mendations.
The emissions calculation methodology
and summary for grassland NOX emis-
sions are also provided in Sections 3 and
4.
&U.S. GOVERNMENT PRINTING OFFICE: 1992 - 648-080/40178
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L Modlca andJ. McCutcheon are with Alliance Technologies Corp., Lowell, MA
01852.
Christopher D. Geron is the EPA Project Officer (see below).
The complete report, entitled "Development of Seasonal and Annual Biogenic
Emissions Inventories for the U.S. and Canada," (Order No. PB92-126 796/AS;
Cost: $26.00; 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
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POSTAGE & FEES PAID
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PERMIT No. G-35
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Penalty for Private Use $300
EPA/600/S7-91/006
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