United States
Environmental Protection
Agency
Air and Energy Engineering
Research Laboratory
Research Triangle Park NC 277T1
Research and Development
EPA/600/S7-90/005 June 1990
&EPA Project Summary
Development of County-Level
Wind Erosion and Unpaved
Road Alkaline Emission
Estimates for the 1985 NAPAP
Emissions Inventory
William R. Barnard
The National Acid Precipitation
Assessment Program (NAPAP) is
developing a nationwide emissions
inventory of substances contributing
to acid precipitation. Also of interest
are substances that can neutralize
acids in precipitation. Information
from NAPAP's natural sources task
group on the emissions of alkaline
materials (calcium, magnesium,
potassium, and sodium) is available,
but the spatial resolution is not
currently in a form that lends itself to
use by either the National Emissions
Data System (NEDS) or modelers
using the NAPAP Resolved Modelers
Inventory grid system. This report
details the methods used and the
results of the conversion of alkaline
material emissions information for
wind erosion, unpaved roads,and
dust devils from their current spatial
resolution to county-level resolution.
Additionally, methods for converting
the county-level data to the NAPAP
Modelers Inventory grid system are
proposed .
This Project Summary was
developed by EPA's Air and Energy
Engineering 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
The National Acid Precipitation
Assessment Program (NAPAP) is
developing a nationwide emissions
inventory, representing the 1985 base
year, of sources that may contribute to
the formation of acid precipitation.
Among the sources of interest are area
sources, including those that emit alkaline
particulates which may play a role in
neutralizing acids in precipitation.
Information on the emissions of
alkaline material (calcium sodium,
potassium, and magnesium) from three
important area sources- wind erosion,
unpaved roads and dust devils-- :.s
available from NAPAP's natural sources
task group, but the spatial resolution is
not currently in a format that is consistent
with data submitted or other sources
included in the 1985 NAPAP Emissions
Inventory.
This report discusses both the
methodology used to convert the current
emission estimates available from the
natural sources task group into county-
level estimates that can be incorporated
into the 1985 NAPAP Emissions
Inventory, and the results of this jffort.
Additionally, a method for converting the
county-level information to the NAPAP
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Modelers Inventory grid level is
proposed.
Note that this study presents the
method used to convert the NAPAP
natural sources task group data from its
current resolution to the county level and
the results of that conversion. It does not
present the method used to develop the
original emissions estimates. Thus,
questions concerning the development of
the original emissions estimates for the
various area sources considered here
should be addressed to the original
NAPAP natural sources task group.
Availability of Data from the
Natural Sources Task Group
Data from this group include wind
erosion, unpaved roads and dust devils.
Wind Erosion
Estimates of total mass and alkaline
emissions from wind erosion for particles
less than or equal to 20 pm in diameter
have been calculated for irregularly
shaped areas known as Major Land
Resource Areas (MLRAs) by developing
emission factors (in grams per square
centimeter) for each MLRA and
multiplying by the area of the
corresponding MLRA. A map in Figure 1
shows the distribution of MLRAs across
the U.S. The emission factors calculated
for these areas have also been assigned
to modified Regional Acid Deposition
Model (RADM) grid points. This
assignment was done strictly on the basis
that the value calculated for an MLRA
was assigned to any grid points that fell
within that MLRA's boundaries. The
modified RADM grid points create grids
that are the same size (80 x 80 km) as
the original RADM grids, except that grid
points are added to the east and west of
the existing grid to include the 48 states.
As a consequence, this modified RADM
grid incorporates the original grid points
which are in their same latitudes and
longitudes. Modification of the grid
mostly reflects the renumbering of the
west- to- east grid point locations to
reflect the larger geographic coverage.
Temporal information for wind erosion
is also available as monthly emissions
based on calculations using the
MLRA/RADM grid assignment scheme
outlined above.
Unpaved Roads
Unpaved road total mass and alkaline
emissions estimates for particles less
than or equal to 10 pm are available on
the state level. No temporal information
for unpaved road total mass or alkaline
emissions is currently available. The
current unpaved road alkaline emissions
estimates represent particles that are
both soluble and capable of neutralizing
acids, not total alkaline material. Total
alkaline emissions would include both the
soluble and insoluble fractions of alkaline
material as well as compounds that would
provide no neutralizing effect (such as
gypsum or sodium chloride).
No size distribution or temporal
information is provided with the current
estimates.
Oust Devils
Both total mass and alkaline emissions
of particles less than or equal to 25 urn
from dust devils have also been
estimated. Observations made near
Tucson, Arizona were used to classify
dust devils into four size categories
(small, medium, large and extra large). A
census was made over several months to
determine the number distribution in each
category. Following this observation
period, aircraft were flown within active
dust devil cells to simultaneously
measure filter exposures and vertical air
velocities. Measurements were made at
two different altitudes. The dust exposure
measured on the filter was utilized with
the vertical air velocities to calculate the
flux from the dust devil. Each category of
dust devil was sampled and an average
value was established for the emissions
per unit area for each category.
Once the flux for each category was
established, vegetation classes and
climatic categories were used to evaluate
the potential for dust devil development
for a particular area. Based on the
potential for dust devil development and
the number distribution determined in the
Tucson studies, emissions were
estimated" for the""area". The modified
RADM grid described above was overlaid
on these areas and the emissions value
for the area in which a grid point was
located was assigned to that grid point.
Spatial Resolution Conversion
Current alkaline emissions information
cannot be readily compared with
emissions estimates of other chemical
species important in causing acid
precipitation, because the spatial
resolution of the alkaline emissions
estimates is not consistent with
emissions estimates developed for other
chemical species. Consequently, the
conversion of the natural source
emissions data from their current spatial
resolution to a level consistent with that
available for emissions estimates for
other chemical species was required.
Conversion to the county level was
chosen for several reasons: (1) it is
consistent with the current National
Emissions Data System (NEDS) reporting
level for area source information; (2) it is
likely that county-level emissions data
would be used by more researchers at
this time than would grid-level data; (3) a
method for converting county-level
information to the NAPAP Modelers
Inventory grid level has already been
developed and utilized with other
chemical species; and (4) once these
emissions have been converted to the
NAPAP Modelers Inventory grid level
they could also be converted to the
RADM grid level, although the current
RADM chemistry and kinetics modules
cannot handle alkaline particulate data.
Conversion from the NAPAP Modelers
Inventory grid level or the RADM grid
level to the county level would be less
straightforward.
Results
Study results show that unpaved road
emissions dominate the calcium and
magnesium alkaline element emissions,
but that wind erosion dominates the
potassium and sodium alkaline element
emissions. This is predominantly
because many unpaved roads (especially
in non-arid regions) are surfaced with
gravel or crushed stone. Frequently the
crushed stone used on these roads is
limestone which 'is particularly rich in
calcium and magnesium. Soils typically
have higher potassium and sodium
levels, which explains why wind erosion
dominates those elemental emissions.
Alao note that, although the
information presented here is for the
1985 NAPAP Emissions Inventory, the
wind erosion values would be the same
for any year. The method used to
calculate the wind erosion values at the
MLRA level involved calculating
emissions using 30 years of wind
information. Unpaved road emissions
represent data for 1985.
Dust devils contribute between 13 and
31% of the alkaline species but rank last
of the three sources in alkaline
emissions, except for Na where they are
second. However, they dominate the
particulate emissions with over 42% of
the total particulate emissions calculated
here.Remember, however, that unpaved
road emissions are for particles less than
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or equal to 10 pm. while wind erosion
emissions are for particles less than or
equal to 20 pm, and dust devil emissions
are for paeticles less than or equal to 25
pm. This difference is due to the way the
original data was provided, not to the
method used to assign emissions to the
county level.
Figure 1. Distribution of MLRAs across the U.S.
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W. R. Barnard is with E. H. Pechan and Associates, Inc., Durham.NC 27707.
Charles C. Masser is the EPA Project Officer (see below).
The complete report, entitled "Development of County-Level Wind Erosion and
Unpaved Road Alkaline Emission Estimates for the 1985 NAPAP Emissions
Inventory," (Order No. PB 90-172 586/AS; Cost: $23.00, 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
Official Business
Penalty for Private Use $300
EP/V600/S7-90/005
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