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 ConsultantPaul J. Smith, PE ▪ Principal Consultant

BREEZE SOFTWARE 12700 Park Central Drive,

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October 28, 2009

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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

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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.

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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)

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• 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

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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.

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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

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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 3.6350x50 1,021.3 307.5 3.32100x100 668.5 190.2 3.51200x200 370.6 97.9 3.78

AERMOD Maximum 24-hr PM10

Concentration, μg/m3

Ratio of Volume to

Area Source24-hr

Concentrations

SourceSize

(mxm)

Volume Source Area Source

10x10 148.3 57.5 2.5850x50 98.0 44.3 2.21

100x100 67.2 33.9 1.98200x200 38.4 20.9 1.84

AERMOD Maximum Annual PM10

Concentration, μg/m3

Ratio of Volume to

Area Source Annual

Concentrations

SourceSize

(mxm)

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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

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Volumes

Areas

AERMOD Maximum24-hr PM10

Concentration(μg/m3)

ISCST3 Maximum24-hr PM10

Concentration(μg/m3)

Ratio of AERMOD to

ISCST324-hr

Concentrations

AERMOD Maximum 24-hr

PM10

Concentration(μg/m3)

ISCST3 Maximum 24-hr

PM10

Concentration(μg/m3)

Ratio of AERMOD to

ISCST324-hr

Concentrations

10x10 1,538.2 1,247.1 1.23 423.2 511.8 0.8350x50 1,021.3 688.1 1.48 307.5 272.7 1.13100x100 668.5 411.2 1.63 190.2 188.3 1.01200x200 370.6 213.3 1.74 97.9 104.7 0.94

Volume Sources Area Sources

SourceSize

(mxm)

AERMOD Maximum

Annual PM10

Concentration(μg/m3)

ISCST3 Maximum

Annual PM10

Concentration(μg/m3)

Ratio of AERMOD to

ISCST3Annual

Concentrations

AERMOD Maximum

Annual PM10

Concentration(μg/m3)

ISCST3 Maximum

Annual PM10

Concentration(μg/m3)

Ratio of AERMOD to

ISCST3Annual

Concentrations

10x10 148.3 120.8 1.23 57.5 43.7 1.3150x50 98.0 55.4 1.77 44.3 30.5 1.45100x100 67.2 31.7 2.12 33.9 20.8 1.63200x200 38.4 82.4 0.47 20.9 37.1 0.56

SourceSize

(mxm)

Volume Sources Area Sources

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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.

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ISCST3 Areas

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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 3.4650x50 1,021.3 993.2 262.1 1.03 3.90

100x100 668.5 647.3 165.3 1.03 4.04200x200 370.6 352.2 80.2 1.05 4.62

Annual 10x10 148.3 138.2 80.6 1.07 1.8450x50 98.0 96.2 47.5 1.02 2.07

100x100 67.2 64.5 28.1 1.04 2.39200x200 38.4 35.5 12.9 1.08 2.98

SourceSize

(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 0.9550x50 307.5 314.2 294.9 0.98 1.04

100x100 190.2 190.1 185.8 1.00 1.02200x200 97.9 102.9 98.3 0.95 1.00

Annual 10x10 57.5 63.3 63.7 0.91 0.9050x50 44.3 46.8 41.1 0.95 1.08

100x100 33.9 34.6 26.7 0.98 1.27200x200 20.9 20.4 14.2 1.02 1.47

Averaging Period

SourceSize

(mxm)

Area Sources

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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

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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

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