"This paper explores common presumptions about fugitive source modeling techniques by examining the sensitivity of predicted PM ambient concentrations to the choice of model (AERMOD versus ISCST3), changes in source representation (volume versus area source), and variations in chosen source dimensions. "

1. Modeling Software for EHS Professionals
Sensitivity of AERMOD in Modeling Fugitive
Dust Emission Sources
Paper No. 31
Prepared By:
George J. Schewe, CCM, QEP ▪ Principal Consultant
Paul J. Smith, PE ▪ Principal Consultant
BREEZE SOFTWARE
12700 Park Central Drive,
Suite 2100
Dallas, TX 75251
+1 (972) 661-8881
breeze-software.com
October 28, 2009

2. 2
ABSTRACT
Dispersion modelers have long faced challenges estimating ambient pollutant concentrations
caused by releases from “fugitive” sources of particulate matter, such as paved and unpaved
roadways, raw material storage piles, outdoor material processing operations, agricultural
activities, or windblown dust in general. Fugitive emissions are commonly defined as those that
could not reasonably pass through a stack, chimney, vent, or other functionally equivalent
opening. Aside from their non-point release characteristics, the unsteady state nature of most
fugitive emitting activities is what makes them particularly problematic when simulated by
steady-state dispersion models. Further, there has been limited field testing completed to provide
performance evaluations that would support the models for these types of releases.
The primary regulatory guidance from the Environmental Protection Agency for modeling
fugitive emissions is given in the Guideline on Air Quality Models (40 CFR 51, Appendix W).1
Section 5.2.2.2 of the Guideline, specific to PM10 modeling, refers the user to Section 4.2.2 “for
source-specific analyses of complicated sources”, but that section says little concerning fugitive
sources. In the AERMOD user’s manual2
, methodologies are offered for modeling fugitive
sources. Many state air regulatory agencies have also prescribed specific protocols for modeling
fugitive PM sources. However, application of many of the general and/or prescribed techniques
can yield unrealistically high air concentrations relative to the nature and magnitude of
emissions, particularly when receptors are located close to fugitive sources.
This paper explores common presumptions about fugitive source modeling techniques by
examining the sensitivity of predicted PM ambient concentrations to the choice of model
(AERMOD versus ISCST3), changes in source representation (volume versus area source), and
variations in chosen source dimensions. The affect of key meteorological data parameters, such
as wind speed and land use, are also reviewed.
INTRODUCTION
The AERMOD Model2,3
was introduced to the regulatory dispersion modeling community in the
late 1990s. AERMOD was developed specifically by the AMS/EPA Regulatory Model
Improvement Committee (AERMIC) to employ best state-of-practice parameterizations for
characterizing the meteorological influences on dispersion in the planetary boundary layer. As
amended in 2005, Section 4.2.2.b of the Guideline on Air Quality Models (GAQM) 1
states that
AERMOD is the recommended model for “a wide range of regulatory applications in all types of
terrain” thus, officially replacing the Industrial Source Complex Model as the primary refined
analytical technique for modeling traditional stationary sources. Provided with the AERMOD
Model are preprocessors for preparing data sets applicable to running the AERMOD algorithms
for transport, dispersion, convective boundary layer turbulence, stable boundary layer, terrain
influences, building downwash, and land use. These are AERMAP, AERSURFACE, and
AERMET. AERMAP is used to process elevation data from digitized data sets to generate
elevations of receptors, sources, and structures as well the critical height for each receptor.
AERSURFACE uses land use land cover (LULC) data to calculate albedo, Bowen ratio, and the
surface roughness parameter, which can vary on an annual, seasonal, or monthly basis for one or
up to twelve sectors around a site. AERMET is the meteorological data processor that uses a

3. 3
combination of either surface observation data from the National Weather Service (NWS) or
onsite data if available (and meeting prescribed collection and quality assurance criteria), and
upper air data from NWS stations. AERMET analyzes this meteorological data along with
albedo, Bowen ratio, and surface roughness parameters from AERSURFACE to define the wind
field and other atmospheric characteristics used by AERMOD.
Current guidance for modeling industrial sources of fugitive PM emissions is given in Section
5.2.2.2 of the GAQM specific to PM10 modeling. This section discusses fugitive emissions from
haul roads and recommends modeling these as a line source (the line source option is not
available in AERMOD), an area source, or a volume source. The GAQM reader is also referred
to Section 4.2.2, which is for “source-specific analyses of complicated sources”, although little is
said here specific to fugitive PM sources. Further background on modeling techniques for
fugitive sources can be found in the original user’s manual for the Industrial Source Complex
Model4
(ISCST3). In Section 3.3.1 of the ISCST3 manual, Identifying Source Types and
Locations, volume sources are introduced as possible alternative source types to represent “line
sources with some initial plume depth” and area sources for “near ground level line sources”.
Later in Section 3.3.2.2, Volume Source Inputs, volume sources are noted to be used “to model
releases from a variety of industrial sources, such as building roof monitors, multiple vents, and
conveyor belts”. Area sources, on the other hand, are noted in Section 3.3.2.3, Area Source
Inputs, as appropriate “to model low level or ground level releases with no plume rise (e.g.,
storage piles, slag dumps, and lagoons)”. Essentially, the initial ISCST3 guidance left the
specific method for representing a storage pile, storage area, haul road, or a building up to the
discretion of the modeler, who was to provide the rationale for the chosen method on a case-by-
case basis.
With the release of the AERMOD Model,2
there was an expectation that the enhanced
consideration of the convective, stable, and neutral boundary layers would improve estimates of
ambient concentrations from sources. At the same time, new and updated ambient
meteorological monitoring was incorporated into the National Weather Service first order sites.
Unfortunately, the fundamental challenges inherent in modeling fugitive sources remained with
AERMOD. The guidance in Sections 3.3.2.2 of the GAQM, Volume Source Inputs, and 3.3.2.3,
Area Source Inputs, gave little that was different from prior editions. The modeler is in fact
referred to the ISC Model User’s Guide –Volume II4
for more detail on the derivation of the
initial lateral and vertical dimensions for a simulated volume source. Many states have
attempted to be more prescriptive regarding protocols for assigning the characteristics of a
volume or area source to an actual source. For example, Missouri requires all storage piles and
haul roads to be modeled as ground release area sources. Minnesota encourages the use of
square volume sources to represent combined small fugitive sources5
. Other states such as Ohio
and Kentucky allow the user to choose and justify the representativeness of one source type over
another. Alabama requires no modeling of fugitive PM sources at all. Even when state agencies
follow certain conventions for fugitive sources, with respect to regulatory-driven dispersion
modeling analyses completed as part of Prevention of Significant Deterioration (PSD) permit
applications, most states still also defer to EPA for decisions about whether one or another
representation and methodology is appropriate.

4. 4
EPA has recognized the need to provide more information to modelers covering fugitive source
modeling techniques. At the May 12, 2009 meeting of the EPA Regional/State/Local Modelers
Workshop, long time modeler, Mick Daye of EPA, Region 7 of the AERMOD Implementation
Workgroup (AIWG), Haul Roads Subcommittee presented an interactive session6
regarding the
consideration of these issues. This presentation was within the context of “haul roads”, but
certainly the concerns and issues are similar for many types of fugitive sources. The “variety of
modeling approaches” was considered within the context of four variables for a volume source
and six variables for an area source. These are listed in Table 1.
Table 1. Source Characteristics Used in Modeling a Volume or Area Source.
Volume Source Area Source
Emissions in g/s Emissions in g/s-m2
Release height – center of volume Release height above ground
Initial lateral dimension (σyo) Length of x side
Initial vertical dimension (σzo) Length of y side
Orientation angle from North
Initial vertical dimension (σzo)
Of importance in the presentation was that the selection of these variables is not as straight
forward as is alluded to in the AERMOD or ISCST3 Model user’s guides. The selection of
specific variables requires a careful consideration of the source type, the fugitive nature of the
emissions and their generation, the extent laterally of the source, and the height of release and its
vertical extent. The process of assigning these variables is best performed with a practiced eye
toward representativeness. Additional parts of the presentation dealt with volume versus area
source differences, typical modeling approaches, and areas for potential improvement. One final
feature discussed in the presentation was plume meander. This feature which was added to
AERMOD in recent years affects the plume from a volume source. This feature allows both an
average wind component during a time step in the model as a well as the addition of a random
wind component with intent of making the results of the modeling more representative of reality.
No similar component was added for an area source.
Various state, EPA, and local agency approaches for modeling volume and area sources were
described in the May 12, 2009 EPA workshop presentation for a haul road (again applicable to
storage piles, building fugitives, and other fugitive emissions). These dealt with how to set
various dimensions of the volume or area source:
• Height of source as two times the vehicle height to account for entrainment (volume)
with a release height of the height of the vehicle.
• Height of the source as 1.7 times the vehicle height to account for entrainment (volume)
with release height equal to ½ of 1.7 times the vehicle height.
• Height of source equal to 1.0 m (volume) with release height at 0.5 m.
• Height of release at ground level, 0.0 m (area)
• Initial vertical distribution based on height of source (volume and area)
• Width based on road width (area)

5. 5
• Initial lateral distribution based on road width plus 6 m
• Initial lateral distribution based on two times the road width
• Initial lateral distribution based on 10 m road width
For anyone working in multiple states or regions, this disparity leads to confusion as to which
methodology was actually intended by the model authors. Or perhaps this disparity in guidance
is as intended - that the models should be applied on a case-by-case basis and representativeness
established based on the modeled source and the agreement of the modelers.
This paper was developed to help define the sensitivity of predicted ambient concentrations to
various changes in source representations (e.g., size of the volume and area source) and
meteorological data (different assumptions about land-use). Concentrations predicted by
AERMOD versus ISCST3 for volume and area sources are also analyzed.
METHODOLOGY
The methodology utilized in this analysis is consistent with the general recommendations of the
ISCST3 and AERMOD Model user’s guides for modeling fugitive emissions. Models were run
with the regulatory default option and hourly meteorological data processed in the AERMET
program for use in AERMOD and in PCRAMMET for use in ISCST3. To minimize the effects
of other influencing modeling features, terrain was assumed to be flat in all cases, which is
reasonable for the hypothetical case of a source near Evansville, given the shallow valley
surrounding the airport.
Study Area
The hypothetical study location used was Evansville, Indiana. The area is characterized by level
to rolling terrain near the Ohio River and has a mid-continental climate with prevailing winds
from the south-southwest most of the year with occasional strong northwest winds in the winter.
Land use in the area is generally rural but also includes the downtown Evansville area and small
pockets of industrial facilities as well as the airport. The area surrounding the Evansville Dress
Regional Airport where the meteorological data was sourced consists primarily of both medium
and low intensity residential and commercial/industrial/transportation land use with smaller areas
of deciduous and evergreen forest, pasture/hay, and small grains.
Sources
Eight sources were modeled in this analysis representing four sizes of fugitive emissions. Each
of the four size fugitive emissions was modeled either as a volume source or an area source. A
constant emission rate of 1.0 g/s was assigned to each source. All sources were assumed to be
located at the center of a coordinate system located at an arbitrary set of UTM coordinates.
Parameters defining the physical characteristics of each source are shown in Table 2. The
values were selected in a manner to allow the best equal representation of the source types within
the confines of the recommendations in the ISCST3 and AERMOD User’s Guides. Even though
the initial vertical dispersion coefficient for an area source is optional, no guidance on when and

6. 6
when not to apply the σzo is given in the User’s Guides. Thus, the σzo values were selected in a
similar manner for both volume and area sources yielding identical values. In reality, the
modeler may have recognized that the area source emitting at the full height of the source (a
rooftop, the top of a storage pile, an unpaved road) would have initial dispersion above the
release height.
Table 2. Fugitive Emission Source Characteristics.
Source
Type
Source ID
Release
Height
(m)
Physical
Height
(m)
Horizontal
Dimensions
(m)
Initial
Lateral
σyo, (m)
Initial
Vertical
σzo, (m)
Emission
Rate
(g/s)
Volume VOL10 3.96 7.92 10X10 2.33 3.68 1.0
VOL50 3.96 7.92 50X50 11.63 3.68 1.0
VOL100 3.96 7.92 100X100 23.26 3.68 1.0
VOL200 3.96 7.92 200X200 46.51 3.68 1.0
Area AREA10 7.92 7.92 10X10 3.68 1.0
AREA50 7.92 7.92 50X50 3.68 1.0
AREA100 7.92 7.92 100X100 3.68 1.0
AREA200 7.92 7.92 200X200 3.68 1.0
Receptors
In each model, an array of receptors was placed around each volume and area source. The
closest receptors were those located at a pseudo-fence line (denoting the boundary between a
facility and ambient receptors), which was a linear 25-m array located at a 50-m distance
equilaterally from each side of each individual source. Thus, the north-south and east-west
distance to fence line of 50-m was held constant throughout each analysis. A 100-m grid spacing
was used from the fence line out to 2-km around each site, and a 250-m grid spacing out to 5-km.
A total of 3,000 receptors were used in the modeling.
Meteorology
For AERMOD, the AERMET program was used along with the AERSURFACE results for
albedo, Bowen ratio, and surface roughness parameter (for a 1 km radius circle around the
meteorological station at the Evansville, Indiana airport) to generate a base set of 1992 data. A
1992 data set of SCRAM formatted surface data for Evansville along with a fixed format TD-
6201 upper air profile for Nashville, Tennessee were used. In addition to the base data with
Evansville airport land use characteristics, two additional data sets were generated for a single
sector (all directions around the site) uniform land use. The first was called the Airport Site and
was assigned an albedo of 0.18, a Bowen ratio for average precipitation conditions of 1.5, and an
airport industrial/commercial surface roughness parameter of 0.1 m. The second set was called
the Non-airport Site and was assigned an albedo of 0.18, a Bowen ratio for average precipitation
conditions of 1.5, and a non-airport industrial/commercial surface roughness parameter of 0.8 m.

7. 7
Both surface roughness parameters come from the AERSURFACE User’s Guide.7
The intended
comparison between these meteorological data sets was to test the sensitivity of the AERMOD
Model concentrations for a volume and area source using the standard
AERSURFACE/AERMET procedure (base case herein) against the extremes of surface
roughness that may be encountered from a uniform, rather smooth airport and a rougher surfaced
non-airport site (such as may be encountered at industrial facility location).
For ISCST3, the same raw surface data for the Evansville airport for 1992 along with derived
mixing heights for Nashville were used to generate the required meteorological data file. This
file was used with ISCST3 to generate all concentrations for each volume and area source similar
to the procedure used in AERMOD. For ISCST3, selection of a “rural” classification for
ISCST3 was made, consistent with the airport land use.
Model Scenarios and Analysis
Each volume source and each area source were modeled using AERMOD (Version 07026) and
ISCST3 (Version 02035) along with each set of meteorological data. Concentrations were
calculated for 24hr and annual averaging periods. The concentration associated with the
meteorological data set using the NCDC 1-km radius surface roughness parameters was
considered as the baseline for each site. This baseline was selected because this scenario
followed the AERSURFACE application guidance. Concentration differences between each
scenario and the baseline were then tabulated.
RESULTS
Tables 3a and 3b present comparisons between a volume source and an area source on a 24-hour
and annual air concentration basis, respectively, from the AERMOD Model. As Table 2
described the emissions were set to 1.0 g/s (7.94 lbs/h, 34.8 tpy) for each source which for some
sources would greatly over-estimate representative emissions from a real source. Thus, some of
the impacts in the tables may be over known air quality standards but this was simply for
illustrative purposes. As can be seen in Tables 3a and 3b the volume source concentrations for a
volume source are always higher than an area source. Generally, the volume source
characterization of a fugitive emissions source results in a concentration that is 3.32-3.78 times
higher than an area source of equal dimensions on a 24-hr basis and 1.84 to 2.58 times higher on
an annual basis. Of note was that these ratios of volume to area source impacts were consistent
over all size ranges of the sources. These differences are expected in terms of the way the model
treats each source type. The volume source uses the dimensions of the source to establish an
initial lateral dimension of a virtual-point source plume at the point of release at the source. This
value is a fraction of the actual dimension of the source (source width divided by 4.3). The area
source treatment in AERMOD uses integration across the whole extent of the source thus, giving
the source a much broader plume at the initial outset of dispersion and transport. Figures 1a and
1b provide a graphical comparison of the AERMOD results showing the higher impacts of the
volume sources.
Table 3a. Comparison and Ratios of 24-hr AERMOD Concentrations For
Volume and Area Sources

8. 8
Table 3b. Comparison and Ratios of Annual AERMOD Concentrations For
Volume and Area Sources
Figures 1a and 1b. 24-hr and Annual AERMOD Concentrations For Volume and Area
Sources
Volume Source Area Source
10x10 1,538.2 423.2 3.63
50x50 1,021.3 307.5 3.32
100x100 668.5 190.2 3.51
200x200 370.6 97.9 3.78
AERMOD Maximum 24-hr PM10
Concentration, μg/m
3
Ratio of Volume
to
Area Source
24-hr
Concentrations
Source
Size
(mxm)
Volume Source Area Source
10x10 148.3 57.5 2.58
50x50 98.0 44.3 2.21
100x100 67.2 33.9 1.98
200x200 38.4 20.9 1.84
AERMOD Maximum Annual PM10
Concentration, μg/m
3
Ratio of Volume
to
Area Source
Annual
Concentrations
Source
Size
(mxm)

9. 9
1a 1b
Because the former “preferred” model by the Guideline on Air Quality Models, namely, the
ISCST3 Model had been used extensively for fugitive source modeling and the AERMOD
Model was its replacement, a comparison of the two models for volume and area sources was
conducted. Tables 4a and 4b summarize these comparisons for 24-hr and annual averages,
respectively.
Table 4a. Comparison of 24-hr AERMOD and ISCST3 Concentrations For
Volume and Area Sources
Table 4b. Comparison of Annual AERMOD and ISCST3 Concentrations For
Volume and Area Sources
As can be seen in Tables 4a and 4b the AERMOD Model generally gives higher concentrations
for both averaging periods for volume sources. The range of higher 24-hr concentrations is from
1.23 to 1.74 times higher from the smallest source to the largest for volumes. The range of
0
200
400
600
800
1000
1200
1400
1600
1800
10x10 50x50 100x100 200x200
Concentrations, ug/m3
Volume and Area Source Sizes, mxm
AERMOD 24‐hr Concentrations‐
Comparison of Volume to Area Sources
Volumes
Areas
0
20
40
60
80
100
120
140
160
1.0 2.0 3.0 4.0
Concentrations, ug/m3
Volume and Area Source Sizes, mxm
AERMOD Annual Concentrations‐
Comparison of Volume to Area Sources
Volumes
Areas
AERMOD
Maximum
24-hr PM10
Concentration
(μg/m3
)
ISCST3
Maximum
24-hr PM10
Concentration
(μg/m3
)
Ratio of
AERMOD to
ISCST3
24-hr
Concentrations
AERMOD
Maximum 24-hr
PM10
Concentration
(μg/m3
)
ISCST3
Maximum 24-hr
PM10
Concentration
(μg/m3
)
Ratio of
AERMOD to
ISCST3
24-hr
Concentrations
10x10 1,538.2 1,247.1 1.23 423.2 511.8 0.83
50x50 1,021.3 688.1 1.48 307.5 272.7 1.13
100x100 668.5 411.2 1.63 190.2 188.3 1.01
200x200 370.6 213.3 1.74 97.9 104.7 0.94
Volume Sources Area Sources
Source
Size
(mxm)
AERMOD
Maximum
Annual PM10
Concentration
(μg/m3
)
ISCST3
Maximum
Annual PM10
Concentration
(μg/m3
)
Ratio of
AERMOD to
ISCST3
Annual
Concentrations
AERMOD
Maximum
Annual PM10
Concentration
(μg/m3
)
ISCST3
Maximum
Annual PM10
Concentration
(μg/m3
)
Ratio of
AERMOD to
ISCST3
Annual
Concentrations
10x10 148.3 120.8 1.23 57.5 43.7 1.31
50x50 98.0 55.4 1.77 44.3 30.5 1.45
100x100 67.2 31.7 2.12 33.9 20.8 1.63
200x200 38.4 82.4 0.47 20.9 37.1 0.56
Source
Size
(mxm)
Volume Sources Area Sources

10. 10
annual concentrations is from 1.23 to 2.12 times higher for the three smaller volume sources but
less than half (0.47) for the largest volume. For area sources the models compare rather closely
on a 24-hr basis with neither model being higher in all cases. For annual comparisons the
AERMOD gives higher concentrations for the three smaller sources and again about half for the
largest source.
Figures 2a and 2b show the same comparisons of 24-hr concentrations in a graphical manner. As
expected, a downward trend of concentrations is noted as the source size increases and emissions
are held constant. They also show the higher concentrations of the AERMOD Model in Figure
2a for 24-hr concentrations and more equal concentrations on an annual basis in Figure 2b.
Figures 2a and 2b. 24-hr AERMOD and ISCST3 Comparisons
Likewise, Figures 3a and 3b show a graphical comparison of annual concentrations for the
AERMOD and ISCST3 models for volume and area sources. Concentrations generally decrease
with increasing source size except for the largest sources in the ISCST3 Model where
Figures 3a and 3b. Annual AERMOD and ISCST3 Comparisons
concentrations increased. These figures show generally higher concentrations in the AERMOD
Model for both volume and area sources.
0
200
400
600
800
1000
1200
1400
1600
1800
10x10 50x50 100x100 200x200
Concentrations, ug/m3
Volume Source Sizes, mxm
Comparison of 24‐hr AERMOD vs
ISCST3 Volume Sources
AERMOD Volumes
ISCST3 Volumes
0
100
200
300
400
500
600
10x10 50x50 100x100 200x200
Concentrations, ug/m3
Area Source Sizes, mxm
Comparison of 24‐hr AERMOD vs
ISCST3 Area Sources
AERMOD Areas
ISCST3 Areas
0
20
40
60
80
100
120
140
160
10x10 50x50 100x100 200x200
Concentrations, ug/m3
Volume Source Sizes, mxm
Comparison of Annual AERMOD vs
ISCST3 Volume Sources
AERMOD Volumes
ISCST3 Areas
0
10
20
30
40
50
60
70
10x10 50x50 100x100 200x200
Concentrations, ug/m3
Area Source Sizes, mxm
Comparison of Annual AERMOD vs
ISCST3 Area Sources
AERMOD Areas
ISCST3 Areas

11. 11
One conclusion that may be drawn is that the use of the ISCST3 Model previous to December
2005 and the use of the AERMOD Model after December 9, 2005 may result in quite different
permitting requirements if based on fugitive source emissions at a facility. If AERMOD
generally gives higher concentrations for volume sources over area sources and higher than the
ISCST3 Model, careful model source characterization may be critical to determining compliance
of ambient air quality impacts.
One additional test of the sensitivity of volume and area sources in the AERMOD Model was
conducted. This test was performed to include the meteorological preprocessor, AERMET. The
volume and areas source analyses described above were performed with meteorological data
based on three different sets of land use. These were 1) a base case using the land use at the
Evansville airport (12 sectors by season), 2) a uniform airport site (1 sector, annually), and 3) a
uniform, higher surface roughness non-airport site (1 sector, annually). The results of these
comparisons are presented in Tables 5a and 5b for volume sources and area sources,
Table 5a. Comparison of Volume Source Impacts in AERMOD for a Base, Uniform
Airport, and Non-uniform Airport Land Use
Table 5b. Comparison of Area Source Impacts in AERMOD for a Base, Uniform Airport,
and Non-uniform Airport Land Use
respectively. Two comparisons are made, namely, the ratio of the base case meteorological
concentrations data to the uniform airport concentrations data, and the ratio of the base case
meteorological concentrations data to the uniform non-airport concentrations data.
AERMOD
Maximum
PM10
Concentration
(μg/m3
)
AERMOD
Maximum
PM10
Concentration at
Airport
(μg/m3
)
AERMOD
Maximum
PM10
Concentration
Not at Airport
(μg/m3
)
Ratio of AERMOD
Base Case to
Airport Site
Ratio of AERMOD
Base Case to Non-
Airport Site
24‐HR 10x10 1,538.2 1,482.1 445.0 1.04 3.46
50x50 1,021.3 993.2 262.1 1.03 3.90
100x100 668.5 647.3 165.3 1.03 4.04
200x200 370.6 352.2 80.2 1.05 4.62
Annual 10x10 148.3 138.2 80.6 1.07 1.84
50x50 98.0 96.2 47.5 1.02 2.07
100x100 67.2 64.5 28.1 1.04 2.39
200x200 38.4 35.5 12.9 1.08 2.98
Source
Size
(mxm)
Averaging
Period
Volume Sources
AERMOD
Maximum
PM10
Concentration
(μg/m3
)
AERMOD
Maximum
PM10
Concentration at
Airport
(μg/m3
)
AERMOD
Maximum
PM10
Concentration
Not at Airport
(μg/m3
)
Ratio of AERMOD
Base Case to
Airport Site
Ratio of AERMOD
Base Case to Non-
Airport Site
24‐HR 10x10 423.2 448.3 445.1 0.94 0.95
50x50 307.5 314.2 294.9 0.98 1.04
100x100 190.2 190.1 185.8 1.00 1.02
200x200 97.9 102.9 98.3 0.95 1.00
Annual 10x10 57.5 63.3 63.7 0.91 0.90
50x50 44.3 46.8 41.1 0.95 1.08
100x100 33.9 34.6 26.7 0.98 1.27
200x200 20.9 20.4 14.2 1.02 1.47
Averaging
Period
Source
Size
(mxm)
Area Sources

12. 12
Review of these tables and case comparisons discerned that the meteorological data derived
using the actual land use at the airport gave just slightly higher concentrations for both averaging
periods for volume sources and just slightly lower for area sources. Examination of the
Evansville Airport land use indicated that the 1 km surface roughness conditions were generally
grasses and pavement resulting in an average surface roughness parameter of 0.051 m as
compared to the Uniform Airport site of 0.1 m. Thus, the small added roughness resulted in
better dispersion and slightly lower concentrations for the Uniform Airport site for volume
sources and concentrations nearly the same for area sources.
In similar comparisons in Table 5a for the Uniform Non-airport site, the base case concentrations
were much greater for volume sources which are apparently very sensitive to surface roughness.
The non-airport site had a uniform surface roughness of 0.8m which gave a increased amount of
turbulence to the dispersion potential of the atmosphere. Base case concentrations for volume
sources were two to three times higher. Conversely, for area sources as shown in Table 5b,
concentrations for the Non-airport site did not vary much from those at the base case except for
the larger sources on an annual basis where the base case was higher.
Figures 4a and 4b for volume sources and 5a and 5b for area sources show these results
graphically. As before in all land use cases, the concentrations decrease as a function of source
size (more dilute emissions over larger areas and volumes).
Figures 4a and 4b. Volume Source Impacts in AERMOD for Variable Land Use
Figures 5a and 5b. Area Source Impacts in AERMOD for Variable Land Use
0
200
400
600
800
1000
1200
1400
1600
1800
10x10 50x50 100x100 200x200
Concentrations, ug/m3
Volume Source Sizes, mxm
Comparison of 24‐hr AERMOD
Base, Airport and Not Airport Volume
Source Concentrations
AERMOD Base
AERMOD Airport
AERMOD Not Airport
0
20
40
60
80
100
120
140
160
10x10 50x50 100x100 200x200
Concentrations, ug/m3
Volume Source Sizes, mxm
Comparison of Annual AERMOD
Base, Airport and Not Airport Volume
Source Concentrations
AERMOD Base
AERMOD Airport
AERMOD Not Airport

13. 13
CONCLUSIONS
To be completed………………..
REFERENCES
1. Guideline on Air Quality Models. Appendix W to 40 CFR Parts 51 and 52. Federal
Register, November 9, 2005. pp. 68217-68261.
2. User’s Guide for the AMS/EPA Regulatory Model - AERMOD. U.S. Environmental
Protection Agency, Research Triangle Park, North Carolina. Revised September 2004.
3. AERMOD Implementation Guide. U.S. Environmental Protection Agency, Research
Triangle Park, North Carolina. Revised January 2008.
4. User’s Guide for the Industrial Source Complex (ISC3) Dispersion Models. EPA-454/B-
95-003a, U.S. Environmental Protection Agency, Research Triangle Park, North
Carolina. September 1995.
5. MPCA Air Dispersion Modeling Guidance for Minnesota Title V Modeling Requirements
and Federal Prevention of Significant Deterioration (PSD) Requirements, Version 2.2,
MPCA, St. Paul, MN. October 20, 2004.
6. EPA Regional/State/Local Modelers Workshop, the AERMOD Implementation
Workgroup (AIWG), Haul Roads Interactive Session, Philadelphia, PA, May 12, 2009.
7. AERSURFACE Users Guide. U.S. Environmental Protection Agency, Research Triangle
Park, North Carolina. January 2008.
KEYWORDS
0
50
100
150
200
250
300
350
400
450
500
10x10 50x50 100x100 200x200
Concentrations, ug/m3
Area Source Sizes, mxm
Comparison of 24‐hr AERMOD
Base, Airport and Not Airport Area
Source Concentrations
AERMOD Base
AERMOD Airport
AERMOD Not Airport
0
10
20
30
40
50
60
70
10x10 50x50 100x100 200x200
Concentrations, ug/m3
Area Source Sizes, mxm
Comparison of Annual AERMOD
Base, Airport and Not Airport Area
Source Concentrations
AERMOD Base
AERMOD Airport
AERMOD Not Airport

14. 14
AERMOD, fugitive dust, volume sources, area sources, dispersion, modeling