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

-------
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

-------
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.

-------
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

-------