ADDENDUM

USER'S GUIDE FOR THE

AMS/EPA REGULATORY MODEL - AERMOD

(EPA-454/B-03-001, September 2004)

U.S. ENVIRONMENTAL PROTECTION AGENCY

Office of Air Quality Planning and Standards

Air Quality Assessment Division

Research Triangle Park, North Carolina 27711

June 2015
ii

PREFACE

This document provides updated user instructions for the AERMOD dispersion model, 

including modifications introduced with version 06341 and later. This addendum supplements 

and updates the information contained in the current AERMOD User’s Guide (EPA, 2004a).
iii

ACKNOWLEDGEMENTS

Portions of this Addendum to the “User’s Guide for the AMS/EPA Regulatory Model –

AERMOD” related to the PSDCREDIT option for the Plume Volume Molar Ratio Method 

(PVMRM) were prepared by MACTEC Federal Programs, Inc., Research Triangle Park, North 

Carolina. This effort was funded by the Environmental Protection Agency, Region 10, under 

Contract No. EP-D-05-096, with Herman Wong as the Work Assignment Manager (WAM).
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CONTENTS

PREFACE ..................................................................................................................................... ii

ACKNOWLEDGEMENTS ........................................................................................................iii

FIGURES...................................................................................................................................... vi

TABLES ...................................................................................................................................... vii

1.0 INTRODUCTION................................................................................................................... 1

1.1 OVERVIEW OF AERMOD REVISIONS ....................................................................... 1

1.2 BACKGROUND ON DEPOSITION ALGORITHMS................................................... 9

2.0 USER INSTRUCTIONS ...................................................................................................... 12

2.1 DISPERSION MODELING OPTIONS ......................................................................... 12

2.1.1 Modification to Urban Option for Morning Transition ............................................... 12

2.1.2 MODELOPT Keyword................................................................................................ 13

2.1.3 BETA Test Options...................................................................................................... 19

2.1.4 Averaging Time Options.............................................................................................. 20

2.1.5 Performing Multiple Year Analyses with MULTYEAR Option................................. 21

2.1.6 Processing for Particulate Matter (PM) NAAQS......................................................... 23

2.1.7 Processing for 1-hour NO2 and SO2 NAAQS.............................................................. 26

2.1.8 Specifying Multiple Urban Areas................................................................................ 28

2.1.9 BETA Options for Capped and Horizontal Stack Releases......................................... 29

2.1.10 BETA Options for Low Wind Conditions................................................................. 31

2.2 DEPOSITION ALGORITHM INPUTS AND OPTIONS ............................................ 33

2.2.1 Definition of Seasons for Gas Dry Deposition ............................................................ 34

2.2.2 Definition of Land Use Categories for Gas Dry Deposition........................................ 35

2.2.3 Option for Overriding Default Parameters for Gas Dry Deposition............................ 36

2.2.4 Specifying Source Parameters for Gas Deposition (Dry and/or Wet)......................... 36

2.2.5 Option for Specifying the Deposition Velocity for Gas Dry Deposition..................... 37

2.2.6 Specifying Source Parameters for Particle Deposition................................................ 38

2.2.7 Specifying Emission and Output Units........................................................................ 40

2.2.8 Deposition Velocity and Resistance Outputs............................................................... 40

2.2.9 Meteorological Data for Deposition Algorithms......................................................... 41

2.3 OPEN PIT SOURCE OPTION ....................................................................................... 42

2.4 LINE SOURCE OPTION ................................................................................................ 45

2.5 SPECIFYING BACKGROUND CONCENTRATIONS .............................................. 46

2.6 OPTIONS FOR MODELING NO2 ................................................................................. 51

2.6.1 Specifying Ozone Concentrations for PVMRM and OLM Options............................ 53

2.6.2 Specifying the Ambient Equilibrium NO2/NOx Ratio for PVMRM and OLM........... 58

2.6.3 Specifying the Default In-stack NO2/NOx Ratio for PVMRM and OLM ................... 58

2.6.4 Specifying In-stack NO2/NOx Ratios by Source for PVMRM and OLM ................... 59

2.6.5 Specifying Combined Plumes for OLM ...................................................................... 60

2.6.6 Specifying Ambient NO2/NOx Ratios for the ARM and ARM2 Options ................... 61

2.6.7 Modeling NO2 Increment Credits with PVMRM........................................................ 62

2.7 VARIABLE EMISSION RATES.................................................................................... 67

2.7.1 Specifying Variable Emission Factors (EMISFACT) ................................................. 67

2.7.2 Specifying an Hourly Emission Rate File (HOUREMIS)........................................... 71

2.8 OUTPUT OPTIONS......................................................................................................... 73
v

2.8.1 Output Options for 24-hour PM2.5 and 1-hour NO2 and SO2 Standards.................... 73

2.8.2 Miscellaneous Output Options..................................................................................... 76

2.9 MODEL STORAGE LIMITS ......................................................................................... 78

3.0 REFERENCES...................................................................................................................... 81

APPENDIX A. ALPHABETICAL KEYWORD REFERENCE......................................... A-1

APPENDIX B. FUNCTIONAL KEYWORD/PARAMETER REFERENCE ................... B-1

APPENDIX C. LIST OF ERROR/WARNING MESSAGES.............................................. C-1

APPENDIX D. EPA MODEL CLEARINGHOUSE MEMORANDUM DATED JULY 9, 

1993 ................................................................................................................. D-1

APPENDIX E. EVALUATION OF MODIFIED URBAN OPTION...................................E-1

APPENDIX F. EVALUATION OF LOW WIND BETA OPTIONS...................................F-1

APPENDIX G. USER INSTRUCTIONS FOR THE BUOYANT LINE SOURCE OPTION 

IN AERMOD.................................................................................................. G-1
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FIGURES

Figure Page

E-1. 1-hour Q-Q Plot for Indianapolis SF6 Study for All Stabilities.........................................E-2

E-2. 1-hour Q-Q Plot for Indianapolis SF6 Study for Convective Conditions..........................E-2

E-3. 1-hour Q-Q Plot for Atlanta NO2 Study for Monitor 0002................................................E-3

E-4. 1-hour Q-Q Plot for Atlanta NO2 Study for Monitor 3001................................................E-3

E-5. 1-hour Q-Q Plot for Atlanta NO2 Study for Monitor 0048................................................E-4

E-6. 1-hour Q-Q Plot for Atlanta NO2 Study for Monitor JST..................................................E-4
vii

TABLES

Table Page

1-1. Summary of Deposition Options in AERMOD................................................................ 11

B-1. DESCRIPTION OF CONTROL PATHWAY KEYWORDS........................................ B-3

B-2. DESCRIPTION OF CONTROL PATHWAY KEYWORDS AND PARAMETERS... B-5

B-3. DESCRIPTION OF SOURCE PATHWAY KEYWORDS......................................... B-13

B-4. DESCRIPTION OF SOURCE PATHWAY KEYWORDS AND PARAMETERS.... B-15

B-5. DESCRIPTION OF RECEPTOR PATHWAY KEYWORDS .................................... B-22

B-6. DESCRIPTION OF RECEPTOR PATHWAY KEYWORDS AND 

PARAMETERS............................................................................................................ B-23

B-7. DESCRIPTION OF METEOROLOGY PATHWAY KEYWORDS .......................... B-26

B-8. DESCRIPTION OF METEOROLOGY PATHWAY KEYWORDS AND 

PARAMETERS............................................................................................................ B-27

B-9. DESCRIPTION OF EVENT PATHWAY KEYWORDS............................................ B-29

B-10. DESCRIPTION OF EVENT PATHWAY KEYWORDS AND PARAMETERS....... B-30

B-11. DESCRIPTION OF OUTPUT PATHWAY KEYWORDS......................................... B-31

B-12. DESCRIPTION OF OUTPUT PATHWAY KEYWORDS AND PARAMETERS.... B-33
1

1.0 INTRODUCTION

1.1 OVERVIEW OF AERMOD REVISIONS

This document provides user instructions for revisions to the AERMOD dispersion 

model. The discussion provided here supplements and updates the information contained in the 

current AERMOD User’s Guide (EPA, 2004a), and it is assumed that the reader is already 

familiar with the contents of that document. Note that portions of the current AERMOD User’s 

Guide (EPA, 2004a) are no longer valid or applicable.

Several sets of AERMOD revisions are included in this Addendum:

1. The first set of revisions, first introduced with version 03273 of AERMOD, 

includes dry and wet deposition algorithms for both particulate and gaseous 

emissions (see Sections 1.2 and 2.2 for more details), and the OPENPIT source 

option, originally incorporated in the ISCST3 model (EPA, 1995a), for modeling

particulate emissions from open pit (below grade) sources, such as surface coal 

mines and rock quarries;

2. The second set of revisions, first introduced with version 04300 of AERMOD,

includes two non-DFAULT options for modeling conversion of NO to NO2: 1) the 

Plume Volume Molar Ratio Method (PVMRM) (Hanrahan, 1999a and 1999b); and 

2) the Ozone Limiting Method (OLM); 

3. The third set of revisions, first introduced with version 06341 of AERMOD, 

includes the following (additional information is provided in Model Change 

Bulletin (MCB) #1 provided on the SCRAM AERMOD webpage):

a. A new “BETA” option on the CO MODELOPT card to allow for new features 

to be added to AERMOD that are still in BETA-test status;

b. A BETA option for incorporating NO/NO2 chemistry for NO2 increment 

consumption calculations with PSD credits using the PVMRM option;

c. BETA options for capped and horizontal stack releases; 

d. An option to specify an initial default in-stack NO2/NOx ratio for the PVMRM 

and OLM options; 

e. New options for varying emissions by month, hour-of-day, and day-of-week 

(MHRDOW and MHRDOW7); 

f. An option to allow multiple urban areas to be defined in a single model run;
2

g. Updated processing to support modeling demonstrations for the National 

Ambient Air Quality Standards (NAAQS) for PM, including the 24-hour 

average design value for PM-2.5 impacts; and

h. Use of dynamic array allocation for AREAPOLY sources to allocate array 

limits for the maximum number of vertices at model runtime, replacing the 

previous fixed array limit of 20 vertices.

4. The fourth set of revisions, first introduced with version 09292 of AERMOD, 

includes the following (additional information is provided in MCB#3 provided on 

the SCRAM AERMOD webpage):

a. New options for varying emissions by hour-of-day and day-of-week (HRDOW 

and HRDOW7); 

b. Modification of the regulatory default option (DFAULT) on the CO 

MODELOPT card to impose a restriction on the urban roughness length 

parameter to be 1 meter for regulatory default applications. Any value other 

than 1 meter for the urban roughness length option on the CO URBANOPT card 

will be treated as a non-DFAULT option;

c. Removal of the TOXICS option from the MODELOPT keyword. Options 

formerly associated with the TOXICS option are still considered non-DFAULT 

options within AERMOD. The area source optimizations formerly associated 

with the TOXICS option are now selected using the new non-DFAULT 

FASTAREA option on the MODELOPT keyword;

d. A new non-DFAULT option for optimizing runtime for POINT and VOLUME 

sources based on an alternative implementation of the horizontal meander 

algorithm has been incorporated through the FASTALL option on the 

MODELOPT keyword. The FASTALL option also includes the FASTAREA 

optimizations if area sources are included in the model inputs;

e. The option for specifying hourly emissions from a separate file through the 

HOUREMIS keyword has been enhanced to allow the use of hourly varying 

release heights and initial dispersion coefficients for VOLUME and 

AREA/AREAPOLY/AREACIRC sources;

f. The OPENPIT source option has been modified to allow for use of the 

OPENPIT source for gaseous (non-particulate) emissions and with METHOD_2 

for particulate emissions;

g. The non-DFAULT option of FLAT terrain can now be specified on a source-bysource basis, allowing both FLAT and ELEV terrain treatments within the same 

model run (see Section 4.1 of the AERMOD Implementation Guide regarding 

modeling of sources with terrain-following plumes in sloped terrain);

h. A non-DFAULT option for a user-specified dry deposition velocity for gaseous 

emissions has been added under the GASDEPVD keyword on the CO pathway;

i. A new SUMMFILE option has been included on the OU pathway to output the 

summary of high ranked values to a separate file;
3

j. An option to use scientific notation for output result files has been added 

through the FILEFORM keyword on the OU pathway. The FILEFORM option 

is applicable to PLOTFILEs, plot-formatted POSTFILEs, MAXIFILEs, 

RANKFILEs, and SEASONHR files;

k. An option (WARNCHKD) has been added to the MODELOPT keyword to 

allow issuing of warning messages rather than fatal errors for non-sequential 

meteorological data files, in order to allow use of multi-year meteorological 

data files that may contain gaps between years of data under the DFAULT 

option; and

l. The maximum length of filenames specified in the ‘aermod.inp’ file has been 

increased to 200 (controlled by the ILEN_FLD parameter in modules.f), and the 

maximum input string length to 512 (controlled by the ISTRG parameter in

modules.f). Double quotes (") are also allowed as field delimiters in the 

'aermod.inp' file to support filenames with embedded spaces.

5. The fifth set of revisions, first introduced with version 11059 of AERMOD, 

includes the following (additional information is provided in MCB#4 provided on 

the SCRAM AERMOD webpage):

a. Revisions to the processing options available for 24-hour averages of PM2.5 to 

support implementation of recommendations regarding appropriate modeling 

procedures for demonstrating compliance the PM2.5 NAAQS;

b. Enhancements to support processing for the 1-hour NO2 and SO2 NAAQS, 

based on the annual distribution of daily maximum 1-hour values, averaged 

across the number of years processed, including three new output file options, 

MAXDAILY, MXDYBYYR, and MAXDCONT, and revisions to the 

RECTABLE keyword to support user-specified ranks up the 999th highest value 

to support significant contribution analyses;

c. A new option to specify uniform or temporally-varying background 

concentrations, using the BACKGRND keyword on the SO pathway;

d. A new option to specify temporally-varying background ozone concentrations, 

using the O3VALUES keyword on the CO pathway;

e. Incorporation of the default equilibrium ratio 0.90 for NO2/NOx for the OLM 

option, which was previously associated only with the PVMRM option (the CO 

NO2EQUIL option can also be used to specify a non-default equilibrium ratio 

for the OLM option);

f. Increasing the maximum length for source IDs from 8 to 12 characters;

g. An option to suppress file headers for formatted output files, using the 

NOHEADER keyword on the OU pathway;

h. A modification to the urban option to address issues with the transition from the 

nighttime urban boundary layer to the daytime convective boundary layer (a 

non-DFAULT option has been included to allow users to revert to the original 

implementation); and 
4

i. Corrections to several bugs related to the PVMRM algorithm and modifications 

to the DEBUGOPT keyword to allow user to specify only PVMRM or 

deposition (DEPOS) debug output, without the MODEL debug file, which can 

be very large.

6. The sixth set of revisions, first introduced with version 11103 of AERMOD, 

includes the following (additional information is provided in MCB#5 provided on 

the SCRAM AERMOD webpage):

a. Correction to a bug that resulted in all short-term values being 0.0 if only the 

1st-highest rank was selected for applications involving the special processing 

for daily maximum values (24hr PM25, 1hr NO2 and 1hr SO2); and

b. Additional error handling to identify potential problems with the Fortran format 

specifier for hourly ozone files and hourly background files specified on the CO 

OZONEFIL and SO BACKGRND keywords, respectively. The hourly ozone 

and/or background concentrations may have been assigned values of zero (0) in 

previous versions of AERMOD if the user-specified Fortran format included an 

integer (I) format to read the concentration values. The requirements for userspecified Fortran formats with these options has been clarified in the appropriate 

sections below.

7. The seventh set of revisions, first introduced with version 12060 of AERMOD, 

includes the following (additional information is provided in MCB#7 provided on 

the SCRAM AERMOD webpage):

a. Corrections to bugs associated with the MAXDCONT option for determining 

source contributions for the 1hr NO2, 1hr SO2 and 24hr PM25 NAAQS based 

on a distribution of daily maximum values for applications including a day-ofweek component on the EMISFACT, O3VALUES, or BACKGRND 

keywords, and for applications using an hourly emission file (SO 

HOUREMIS keyword) for at least one source, but not all sources, in a 

particular run;

b. Corrected a bug for applications with the OLM and PVMRM options under 

the EVENT processing mode when only the CO OZONEVAL keyword is 

used to specify a background ozone value, without an hourly ozone file 

through the CO OZONEFIL keyword or varying ozone values through the CO 

O3VALUES keyword;

c. Replaced subroutine LTOPG for determining PG stability class based on 

Monin-Obukhov length and surface roughness used in the FASTAREA option 

with code from the CTDMPLUS model that more closely matches the Golder 

(1972) figure;

d. Incorporated an option for users to indicate that all sources in a particular 

model run are to be treated as URBAN sources, by specifying ‘ALL’ on the 

SO URBANSRC keyword. The URBANSRC ALL option is only applicable 

for applications that include a single urban area;
5

e. Included a new option for users to specify the number of years of 

meteorological data being processed for multi-year applications of the 

MAXDCONT option, using the new NUMYEARS keyword on the ME 

pathway. This allows users with less than 5 years of site-specific met data to 

specify the number of years being processed in order to minimize memory 

storage requirements. Consistent with previous versions, the default number 

of years absent the NUMYEARS option is five (5); and

f. Includes checks of the range of ranks specified on the OU RECTABLE 

keyword when the THRESH option on the MAXDCONT keyword is being 

used, since the analysis of contributions for MAXDCONT is limited to the 

range of ranks specified on the RECTABLE keyword. A fatal error message 

will be generated if the range of ranks specified is less than or equal to the 

design value rank for the specified pollutant plus 4, i.e., a fatal error will be 

generated if the range of ranks is less than or equal to 8 for 1-hr SO2, or less 

than or equal to 12 for 1-hr NO2 or 24-hr PM2.5. A non-fatal warning 

message is also generated if the range of ranks is less than or equal to the 

design value rank plus 20, i.e., if the range of ranks is less than or equal to 24 

for 1-hr SO2, or less than or equal to 28 for 1-hr NO2 or 24-hr PM2.5.

8. The eighth set of revisions, first introduced with version 12345 of AERMOD, 

includes the following (additional information is provided in MCB#8 provided on 

the SCRAM AERMOD webpage):

a. Adjustments to wind speeds based on the assumption that input wind speeds 

are vector (or resultant) mean winds (see Eq. 112 on page 79 of the AERMOD 

Model Formulation Document (Cimorelli, et al., 2004)) have been removed. 

This is considered a formulation bug fix since current EPA guidance for sitespecific meteorological monitoring (EPA, 2000) recommends that scalar mean 

wind speeds be used in steady-state Gaussian dispersion models. Furthermore, 

all wind speeds derived from NWS or FAA airport data represent scalar mean 

wind speeds. An option has also been included on the MODELOPT keyword 

on the CO pathway (VECTORWS) that allows users to specify that input 

wind speeds are vector means, in which case the previous adjustments will be 

included. The new VECTORWS option is not linked with the DFAULT 

option, but users should be able to confirm that input speeds are vector means 

in order to justify use of the option. However, scalar mean wind speeds, if 

available, should be used based on the current guidance. 

b. Modifications to check for large negative hourly emissions (< -90), which 

may be used as missing indicators. Since AERMOD allows inputs of negative 

emissions for use in emission credit calculations, negative values used as 

missing indicators in the HOUREMIS file result in negative hourly 

concentrations in the previous versions. Warning messages are generated and 

the emission rate is set to zero (0) for these cases.

c. Two new BETA (non-Default) options have been included to address 

concerns regarding model performance under low wind speed conditions. The 
6

LOWWIND1 option increases the minimum value of sigma-v from 0.2 to 0.5 

m/s and "turns off" the horizontal meander component. The LOWWIND2 

option increases the minimum value of sigma-v from 0.2 to 0.3 m/s, and 

incorporates the meander component, with some adjustments to the algorithm, 

including an upper limit on the meander factor (FRAN) of 0.95. A new 

LOW_WIND keyword has been added to the CO pathway that allows users to 

adjust the minimum sigma-v value (within a range of 0.01 to 1.0 m/s), and the 

minimum wind speed value (within a range from 0.01 to 1.0 m/s), with a 

default value of 0.2828 m/s, consistent with the default applied in previous 

versions based on SQRT(2*SVmin*SVmin) with SVmin=0.2. The new 

LOW_WIND keyword also allows users to adjust the maximum value for the 

meander factor (FRAN) within a range of 0.50 to 1.0, inclusive, when the 

LOWWIND2 option is used. These new LowWind BETA options can also be 

used in conjunction with the new option in AERMET (v12345) to adjust the 

surface friction velocity (U*) under low-wind/stable conditions (ADJ_U*), 

based on Qian and Venkatram (2011). More details regarding these LowWind 

BETA options is provided in Section 2.1.10.

d. A new LINE source type has been included that allows users to specify linetype sources based on a start-point and end-point of the line and the width of 

the line, as an alternative to the current AREA source type for rectangular 

sources. The LINE source type utilizes the same routines as the AREA source 

type, and will give identical results for equivalent source inputs. The LINE 

source type also includes an optional initial sigma-z parameter to account for 

initial dilution of the emissions. As with the AREA source type, the LINE 

source type does not include the horizontal meander component in AERMOD. 

e. Additional range checks on hourly stack exit velocities and exit temperatures 

input through the SO HOUREMIS option. A fatal error is generated if the 

hourly exit temperature is less than 200K (about -100F), unless the hourly 

emissions are zero (0) for that hour. This may indicate that incorrect units for 

exit temperature have been used, or that the order of exit temperature and exit 

velocity may have been reversed in the HOUREMIS file. Also added a new 

warning message for exit velocities larger than 250 m/s. Comparable changes 

were incorporated in subroutine PPARM for inputs on the SRCPARAM 

keyword.

f. Modified the acceptable AERMET version date from 06341 to 11059. 

AERMOD will no longer run with met data based on version 06341 of 

AERMET. AERMOD will run using met data based on version 11059. 

However, a warning message will be generated, and users are strongly 

encouraged to update their meteorological data to version 12345 of AERMET

due to the scope of changes included in that update.

9. The ninth set of revisions, first introduced with version 13350 of AERMOD, 

includes the following (additional information is provided in MCB#9 provided on 

the SCRAM AERMOD webpage):
7

a. Incorporated new options for modeling NO2, including a Default Ambient 

Ratio Method (ARM) option and non-Default BETA Ambient Ratio Method -

2 (ARM2);

b. Incorporated options to vary background ozone (O3) data by wind sector 

(new CO O3SECTOR keyword) for use with the OLM and PVMRM options, 

and options to vary background concentrations for the pollutant being 

modeled by wind sector (new SO BGSECTOR keyword). Any of the existing 

options for specifying background data can be used with the new sectorvarying options, and will continue to work as before if no sectors are defined. 

The applicable sector is determined by the flow vector (downwind) based on 

the wind direction in the surface meteorological data file;

c. Added new "debug" output file options for the OLM option and for the new 

ARM and ARM2 options for NO2. Also added a new PRIME debug option to 

separate the debug information associated with the PRIME downwash 

algorithm from the non-PRIME related information provided under the 

MODEL debug option. Also removed all debug information from the main 

'aermod.out' file.

10. The ninth set of revisions, first introduced with version 14134 of AERMOD, 

includes the following (additional information is provided in MCB#10 

provided on the SCRAM AERMOD webpage):

a. Modified subroutine POLLID to allow for an additional user-specified field to 

disable the special processing associated with the 1-hr NO2, 1-hr SO2 and 24-

hr PM2.5 NAAQS, which are based on a multi-year average of ranked 

maximum daily values (1-hr values in the case of NO2 and SO2 and 24-hr 

values in the case of PM2.5). The optional field allowed after than pollutant 

ID can be ‘H1H’, ‘H2H’, or ‘INC’ (without the single quotes), indicating that 

the results will be processed consistent with a deterministic standard, such as 

the original 3-hr and 24-hr SO2 standards, which could be exceeded once per 

year, and consistent with PSD increments, which can also be exceeded once 

per year. These options are intended to provide a mechanism for modeling to 

demonstrate compliance with the 24-hr PM2.5 increments, and also to provide 

a mechanism to evaluate the various NO2 chemistry options incorporated in 

AERMOD without the requirement for modeling complete years of 

meteorological data.

b. Modified subroutine DEBOPT to include a new AREA/LINE debug option, 

which is output to a separate file, including an optional user-specified file 

name. This includes additional information regarding AREA/LINE (and 

OPENPIT) calculations as compared to the AREA-related debug information 

included under the previous DEBUG option. Also modified subroutines 

ACALC and PSIDE to output AREA/LINE debug information under the new 

AREA/LINE debug option. Debug information is no longer included in the 

main ‘aermod.out’ file.
8

c. Modified subroutine MEOPEN to check for flags in the header record of the 

input SURFFILE indicating that MMIF-generated meteorological inputs were 

used, which is currently treated as non-DFAULT/BETA option, and for use of 

BULKRN option, which is treated as a DFAULT option. Subroutine 

MEOPEN also checks for measurement heights in the input PROFFILE file 

and issues a warning if heights exceed 999m, which could indicate that inputs 

were based on MMIF or other gridded meteorological data that were 

processed in a manner that did not include identifying information in the 

surface file header record (e.g., processing MMIF-generated pseudo- surface 

and upper air data with user-defined surface characteristics rather than the 

AERSURF file generate by MMIF. Subroutine MEOPEN was also modified 

to include checks for blank/missing upper air, surface and/or onsite station IDs 

in the surface file header record, and issues warning messages if the respective 

station IDs specified on the ME pathway in the aermod input file are not zero 

(0).

d. Modified subroutine PRTSRC to include a table of SrcIDs for sources 

identified as urban sources under the URBANSRC keyword.

e. Modified subroutine PRTDET to include the original GrpVal concentration 

from the Non-EVENT run in the header information for the DETAIL output 

option under EVENT processing.

f. Modified subroutine PRTOPT to include additional information on the initial 

input summary page of the ‘aermod.out’ file related to the use of NO2 

options, and to identify which debug options have been selected on the CO 

DEBUGOPT keyword.

g. The “acceptable” AERMET version date has been modified to version 12345, 

and AERMOD will not run if meteorological data generated by earlier 

versions of AERMET are input. AERMOD will run if meteorological data 

from versions 12345 or 13350 are used, but a warning message will be issued 

and AERMET version 14134 should be used for regulatory applications of 

AERMOD.

11. The tenth set of revisions, first introduced with version 15181 of AERMOD, 

includes the following (additional information is provided in MCB#11 

provided on the SCRAM AERMOD webpage):

a. Included a new Plume Volume Molar Ration Method 2 non-DFAULT/BETA 

option that uses total dispersion coefficients instead of relative dispersion 

coefficients for stable conditions and relative dispersion coefficients for 

unstable conditions. The new PVMRM2 option incorporates additional 

modifications relative to the PVMRM option, including the use of downwind 

distance instead of radial distance from source to receptor to calculate the 

plume volume and moles of NOx. See the modified Model Formulation 

Document Addendum for additional details.

b. Incorporated a new LOWWIND3 BETA option to address concerns regarding 

model performance under low wind speed conditions. The LOWWIND3
9

option increases the minimum value of sigma-v from 0.2 to 0.3 m/s, consistent 

with the LowWind2 option, but eliminates upwind dispersion, consistent with 

the LowWind1 option. The LowWind3 option uses an “effective” sigma-y 

value that replicates the centerline concentration accounting for meander, but 

sets concentrations to zero (0) for receptors that are more than 6*sigma-y off 

the plume centerline, similar to the FASTALL option.

c. Included a source type option, BUOYLINE, to model buoyant line sources 

based on the BLP model.

d.

1.2 BACKGROUND ON DEPOSITION ALGORITHMS

The deposition algorithms incorporated into AERMOD are based on the draft Argonne 

National Laboratory (ANL) report (Wesely et al., 2002), with modifications based on peer 

review. Treatment of wet deposition was revised from Wesely et al. (2002) based on 

recommendations by peer review panel members (Walcek et al., 2001). A full technical 

description of the deposition algorithms implemented in AERMOD is provided in an EPA report 

(EPA, 2003). 

The deposition algorithms based on the ANL report were initially implemented in the 

AERMOD model under the non-DFAULT TOXICS option, which was selected by including the 

TOXICS keyword on the CO MODELOPT card. Beginning with version 09292 of AERMOD, 

the TOXICS option has been removed from the model. Those options in AERMOD that were 

formerly associated with the TOXICS option are still considered non-DFAULT options but no 

longer require the specification of the TOXICS option to allow their use. The other changes to 

the AERMOD model inputs associated with the deposition algorithms are limited to the CO 

(control) pathway and the SO (source) pathway. For gaseous dry deposition based on the ANL 

algorithms, the user must define the seasonal categories based on the ANL report for each of the 

calendar months, and must also define the land use category and three pollutant-specific physical 

parameters that are provided in the appendices of the ANL report. An optional keyword is also 

provided to override default values for three parameters used in the gas deposition algorithm. 

The input requirements for “Method 1” particle deposition in AERMOD are the same as for the 

particle deposition algorithm in the ISCST3 model and are described below in Section 2.2. For 
10

“Method 2” particle deposition, the user must define the fraction of the particle mass in the fine 

particle category (less than 2.5 microns) and a representative mass mean diameter for the 

particles, which are also provided for selected pollutants in Appendix B of the ANL report. The 

keywords used to define these inputs and the meteorological data requirements for deposition are 

described in Section 2.2.

Consistent with Section 7.2.7(b) of the Guideline on Air Quality Models (40 CFR Part 51, 

Appendix W), the use of “Method 1” for particle deposition in AERMOD is allowed under the 

regulatory DFAULT option. However, use of the “Method 1” particle deposition algorithms 

require quantification of the particle size distribution and should be done in coordination with the

appropriate reviewing authority. Use of the “Method 2” option for particle deposition and the 

gas deposition algorithms (both dry and wet) are considered non-DFAULT options in 

AERMOD. Table 1-1 summarizes the required keywords for the various deposition options 

within AERMOD and whether they are allowed under the DFAULT option.
11

Table 1-1. Summary of Deposition Options in AERMOD

Pollutant Type Model Output Type Required Keywords Allowed under DFAULT?

Gaseous CONC w/dry depletion

DDEP

CO GASDEPVD

 or

CO GDSEASON,

CO GDLANUSE, and

SO GASDEPOS

No

Gaseous CONC w/wet depletion

WDEP

SO GASDEPOS No

Gaseous CONC w/dry & wet 

depletion

DEPOS

CO GDSEASON,

CO GDLANUSE, and

SO GASDEPOS

No

Particulate 

(“Method 1”)

CONC w/dry and/or wet 

depletion

DEPOS

DDEP

WDEP

SO PARTDIAM,

SO PARTDENS, and

SO MASSFRAX

Yes1

Particulate 

(“Method 2”)

CONC w/dry and/or wet 

depletion

DEPOS

DDEP

WDEP

SO METHOD_2 No

 

1While “Method 1” is allowed under the regulatory “DFAULT” option within AERMOD, the use of “Method 1” for 

particulate emissions in regulatory modeling applications should follow the guidance provided in Section 7.2.7(b) of 

Appendix W.
12

2.0 USER INSTRUCTIONS

2.1 DISPERSION MODELING OPTIONS

2.1.1 Modification to Urban Option for Morning Transition

The urban option within AERMOD was modified, beginning with version 11059, to 

address potential issues associated with the transition from the nighttime urban boundary layer to 

the daytime convective boundary layer. Prior to version 11059, the enhanced dispersion due to 

the urban heat island during nighttime stable conditions was ignored once the rural boundary 

layer became convective. This could result in an unrealistic drop in the mixing height for urban 

sources during the morning transition to a convective boundary layer, which could contribute to 

overly conservative concentrations for low-level sources under such conditions. This potentially 

anomalous behavior was observed in a few cases during the application of AERMOD for the 

Risk and Exposure Assessment (REA) conducted in support of the most recent review for the 

NO2 National Ambient Air Quality Standard (NAAQS) (EPA, 2008). The potential significance 

of this issue for AERMOD applications in support of air quality permitting has increased with 

the recent promulgation of the 1-hour NO2 and 1-hour SO2 NAAQS.

To address this issue, AERMOD was modified to continue applying the urban boundary 

layer option for urban sources until the daytime (rural) convective boundary exceeds the 

population-dependent urban boundary layer height. This modification to the urban option within 

AERMOD has been evaluated using the 1985 Indianapolis SF6 field study data, and shows 

improved model performance during daytime convective conditions compared to the original 

implementation of the urban option. Model-to-monitor comparisons of 1-hour NO2

concentrations from the Atlanta NO2 REA also exhibit improved model performance with this 

modification to the urban option in AERMOD. A summary of these model evaluation results is 

provided in Appendix E.

While the urban option has been modified under the regulatory default mode beginning 

with version 11059, a non-DFAULT option to revert to the urban option as implemented prior to 
13

version 11059 has been included on the CO MODELOPT keyword (see Section 2.1.2). As with 

other non-DFAULT options in AERMOD, use of this option in regulatory modeling applications 

would require justification and approval on a case-by-case basis.

2.1.2 MODELOPT Keyword

The dispersion options are controlled by the MODELOPT keyword on the CO pathway. 

The syntax, type, and order of the MODELOPT keyword are summarized below:

Syntax:

CO MODELOPT DFAULT BETA CONC AREADPLT FLAT NOSTD NOCHKD NOWARN SCREEN SCIM PVMRM PSDCREDIT FASTALL

 DEPOS and/or or or PVMRM2 or

 DDEP ELEV WARNCHKD or OLM FASTAREA

 and/or or ARM

 WDEP or ARM2

DRYDPLT WETDPLT NOURBTRAN LOWWIND1 VECTORWS

 or or or

NODRYDPLT NOWETDPLT LOWWIND2

 or

 LOWWIND3

Type: Mandatory, Non-repeatable

Order: Must precede POLLUTID, HALFLIFE and DCAYCOEF

where:

DFAULT - Specifies that the regulatory default options will be used; note that 

specification of the DFAULT option will override some non-DFAULT 

options that may be specified in the input file, while other nonDFAULT options will cause fatal errors when DFAULT is specified 

(see below for details);

BETA - Non-DFAULT option that allows for draft, “Beta” test options to be 

used (see Section 2.1.3 for more details); currently includes the 

PSDCREDIT option (Section 2.5.6); options for capped and horizontal 

stack releases (2.1.9); the LOWWIND1 and LOWWIND2 options and 

the use of meteorological inputs based on the non-Default ADJ_U* 

option incorporated in version 12345 of AERMET that adjusts the 

surface friction velocity (U*) under low-wind/stable conditions 

(Section 2.1.10),;

CONC - Specifies that concentration values will be calculated;
14

DEPOS - Specifies that total deposition flux values (both dry and wet) will be 

calculated;

DDEP - Specifies that dry deposition flux values will be calculated;

WDEP - Specifies that wet deposition flux values will be calculated;

AREADPLT - Specifies that a non-DFAULT method for optimized plume depletion 

due to dry removal mechanisms will be included in calculations for 

area sources;

FLAT - Specifies that the non-DFAULT option of assuming flat terrain will be 

used; Note that FLAT and ELEV may be specified in the same model 

run to allow specifying the non-DFAULT FLAT terrain option on a 

source-by-source basis; FLAT sources are identified by specifying 

the keyword FLAT in place of the source elevation field on the SO 

LOCATION keyword;

ELEV - Specifies that the default option of assuming elevated terrain will be 

used; Note that FLAT and ELEV may be specified in the same model 

run to allow specifying the non-DFAULT FLAT terrain option on a 

source-by-source basis;

NOSTD - Specifies that the non-DFAULT option of no stack-tip downwash will 

be used;

NOCHKD - Specifies that the non-DFAULT option of suspending date checking 

will be used for non-sequential meteorological data files;

WARNCHKD - Specifies that the option of issuing warning messages rather than fatal 

errors will be used for non-sequential meteorological data files;

NOWARN - Specifies that the option of suppressing the detailed listing of warning

messages in the main output file will be used (the number of warning

messages is still reported, and warning messages are still included in 

the error file controlled by the CO ERRORFIL keyword);

SCREEN - Specifies that the non-DFAULT option for running AERMOD in a 

screening mode will be used;

SCIM - Sampled Chronological Input Model - used only with the ANNUAL

average option to reduce runtime by sampling meteorology at a userspecified regular interval; SCIM sampling parameters must be 

specified on the ME pathway;
15

PVMRM - Specifies that the non-DFAULT Plume Volume Molar Ratio Method 

(PVMRM) for NO2 conversion will be used; 

PVMRM2 - Specifies that the non-DFAULT Plume Volume Molar Ratio Method 2 

(PVMRM2) for NO2 conversion will be used, which uses total 

dispersion coefficients instead of relative coefficients for stable 

conditions, and relative dispersion coefficients for unstable conditions; 

OLM - Specifies that the non-DFAULT Ozone Limiting Method (OLM) for 

NO2 conversion will be used; 

ARM - Specifies that the DFAULT Ambient Ratio Method (ARM) for NO2

conversion will be used; 

ARM2 - Specifies that the non-DFAULT BETA Ambient Ratio Method - 2

(ARM2) for NO2 conversion will be used; 

PSDCREDIT - Specifies that the non-DFAULT BETA test option will be used to 

calculate the increment consumption with PSD credits using the 

PVMRM option; 

FASTALL - Non-DFAULT option to optimize model runtime through use of 

alternative implementation of horizontal meander for POINT and 

VOLUME sources; also optimizes model runtime for AREA/ 

AREAPOLY/AREACIRC and OPENPIT sources through hybrid 

approach (formerly associated with TOXICS option, now controlled 

by FASTAREA option); 

FASTAREA - Non-DFAULT option to optimize model runtime through hybrid 

approach for AREA/ AREAPOLY/AREACIRC and OPENPIT 

sources (formerly associated with TOXICS option); 

DRYDPLT - Option to incorporate dry depletion (removal) processes associated 

with dry deposition algorithms; this requires specification of dry 

deposition source parameters and additional meteorological variables; 

dry depletion will be used by default if dry deposition algorithms are 

invoked; 

NODRYDPLT - Option to disable dry depletion (removal) processes associated with 

dry deposition algorithms; 

WETDPLT - Option to incorporate wet depletion (removal) processes associated 

with wet deposition algorithms; this requires specification of wet 

deposition source parameters and additional meteorological variables; 

wet depletion will be used by default if wet deposition algorithms are 

invoked; 
16

NOWETDPLT - Option to disable wet depletion (removal) processes associated with 

wet deposition algorithms;

NOURBTRAN - Non-DFAULT option to ignore the transition from nighttime urban 

boundary layer to daytime convective boundary layer (i.e., to revert to 

the urban option as implemented prior to version 11059);

LOWWIND1 - Non-DFAULT BETA option to address concerns regarding model 

performance under low wind speed conditions. The LOWWIND1 

option increases the minimum value of sigma-v from 0.2 m/s to 0.5 

m/s, and “turns off” the horizontal meander component. The BETA 

keyword must also be specified in order to invoke the LOWWIND1 

option (note that only one of the “LOWWIND” options can be 

specified in the same model run);

LOWWIND2 - Non-DFAULT BETA option to address concerns regarding model 

performance under low wind speed conditions. The LOWWIND2 

option increases the minimum value of sigma-v from 0.2 m/s to 0.3 

m/s, and includes some adjustments to the horizontal meander 

component. The BETA keyword must also be specified in order to 

invoke the LOWWIND2 option (note that only one of the 

“LOWWIND” options can be specified in the same model run);

LOWWIND3 - Non-DFAULT BETA option to address concerns regarding model 

performance under low wind speed conditions. The LOWWIND3 

option increases the minimum value of sigma-v from 0.2 m/s to 0.3 

m/s, and uses the FASTALL approach to replicate the centerline 

concentration accounting for horizontal meander, but utilizes an 

effective sigma-y and eliminates upwind dispersion. The BETA 

keyword must also be specified in order to invoke the LOWWIND3 

option (note that only one of the “LOWWIND” options can be 

specified in the same model run);

VECTORWS - Option to specify that input wind speeds are vector mean (or resultant) 

wind speeds, rather than scalar means. Under the VECTORWS 

option, the adjustments to wind speeds based on Equation 112 of the 

AERMOD Model Formulation Document (Cimorelli, et al., 2004) will 

be applied. The VECTORWS option is not linked with the DFAULT 

option.

The DFAULT option has been modified beginning with version 09292 to impose a restriction on 

the optional urban roughness length parameter to be 1 meter for regulatory default applications. 
17

The user may select any or all of the output types (CONC, DEPOS, DDEP and/or 

WDEP) to be generated in a single model run. The order of these secondary keywords on the 

MODELOPT card has no effect on the order of results in the output files - the outputs will 

always be listed in the order of CONC, DEPOS, DDEP, and WDEP. Appropriate deposition 

parameters must be specified in order to output deposition fluxes using the DEPOS, DDEP, 

and/or WDEP keywords (see Sections 1.2 and 2.2 for more details).

Beginning with version 04300, the dry and/or wet removal (depletion) mechanisms (the 

DRYDPLT and WETDPLT options in earlier versions of AERMOD) will automatically be 

included in the calculated concentrations or deposition flux values if the dry and/or wet 

deposition processes are considered, unless the user specifies the NODRYDPLT and/or 

NOWETDPLT options. Note that dry and wet removal effects on calculated concentration 

values can be included even if deposition flux values are not being calculated. However, the 

additional data requirements for dry and wet deposition, described in Section 2.2, must be met in 

order for dry and wet removal to be included in the concentration calculations. The use of the 

NODRYDPLT and/or NOWETDPLT options will result in a more conservative estimate of 

concentrations and/or deposition fluxes for applications involving deposition processes, but the 

degree of additional conservatism will vary depending on the source characteristics, 

meteorological conditions, receptor locations and terrain influences. However, the inclusion of 

particle deposition effects may increase ground-level concentrations for some sources compared 

to the same source modeled as a gaseous emission, due to the effect of gravitational settling on 

the particulate plume. The magnitude of this effect will depend on the source characteristics 

(elevated or low-level) and particle size distribution.

The PVMRM, OLM, and ARM2 options for modeling NO2 conversion are nonDFAULT options, and the ARM2 option is also considered as a BETA option. The ARM option 

is considered to be a DEFAULT option. Only one of these options for NO2 conversion can be 

specified for a given model run, and all options require that the pollutant ID be specified as 

‘NO2’ on the CO POLLUTID card (see Section 3.2.5 of the AERMOD User=s Guide). These 

options have additional input requirements as described in Section 2.6.
18

Beginning with version 09292, the TOXICS option in no longer used in AERMOD and 

the FASTAREA option on the MODELOPT is now used to select the non-DFAULT option to 

optimize model runtime for AREA sources (including AREA, AREAPOLY, AREACIRC and 

OPENPIT source types, as well as LINE sources introduced with version 12345 (see Section 

2.4)). When the FASTAREA option is specified, the area source integration routine is optimized 

to reduce model runtime by incorporation of a three-tiered approach using the Romberg 

numerical integration, a 2-point Gaussian Quadrature routine for numerical integration, or a point 

source approximation, depending on the location of the receptor relative to the source. In the

regulatory default mode the Romberg numerical integration is utilized for all receptors. Also 

beginning with version 09292, a non-DFAULT option to optimize model runtime for POINT and 

VOLUME sources has been included, which is selected by the FASTALL option on the 

MODELOPT keyword. Specification of the FASTALL option also activates the FASTAREA 

option if AREA sources are including in the model inputs. Both FASTALL and FASTAREA 

skip receptors that are more than 80 kilometers from the source.

The FASTALL option for POINT and VOLUME sources uses an alternative 

implementation of the horizontal meander algorithm based on an effective horizontal dispersion 

coefficient (σyeff) that replicates the centerline concentration based on the full meander approach. 

Use of the effective σy allows the model runtime to be optimized by skipping receptors that are 

more than 4σyeff off the plume centerline. Based on tests conducted to date, comparisons of 

concentrations based on the FASTALL option for POINT and VOLUME sources with 

concentrations based on the DFAULT option are similar to comparisons of concentrations for 

AREA sources using the FASTAREA option. The average ratio of FASTALL concentrations to 

DFAULT values is about 1.02 for high ranked values, showing a slight bias toward 

overprediction for the FASTALL option. However, the range of ratios for high ranked values 

shows both overpredictions and underpredictions relative the DFAULT option, and differences at 

specific receptors may be much larger.

The NOURBTRAN non-DFAULT option has been included to allow users to revert to 

the urban option as implemented prior to version 11059, which ignores the transition from the 

nighttime urban boundary layer to the daytime convective boundary layer. As with other non-
19

DFAULT options in AERMOD, use of the NOURBTRAN option in regulatory modeling 

applications would require justification and approval on a case-by-case basis.

2.1.3 BETA Test Options

A 'BETA' test option switch is included on the CO MODELOPT keyword to identify and 

allow for new features to be added to the model that are still in a draft BETA-test status. The 

BETA option is a non-DFAULT option, and will result in a fatal error if the DFAULT option is 

also specified. Draft enhancements included in AERMOD under the BETA option, through 

version 13350, include:

1) Options for capped stacks (source type = POINTCAP) and for horizontal releases 

(source type = POINTHOR); 

2) The PSDCREDIT option for PVMRM to account for NO/NO2 chemistry of combined 

plumes in the computation of increment consumption with PSD credits;

3) The LOWWIND1, LOWWIND2, and LOWWIND3 options under the CO 

MODELOPT keyword to address concerns regarding model performance under low 

wind speed conditions; 

4) The ADJ_U* option incorporated in version 12345 (and later) of AERMET that 

adjusts the surface friction velocity (U*) under low wind/stable conditions (see 

AERMET User’s Guide Addendum for more details regarding the ADJ_U* option); 

and

5) The ARM2 option incorporated in version 13350 of AERMOD to estimate the 

conversion of NO to NO2. 

Inclusion of these draft BETA-test options does not imply any endorsement of their use for 

regulatory or non-regulatory applications of the model. In addition, the designation of BETA-test 

to these draft enhancements does not imply that these options have completed rigorous internal 

(“Alpha”) testing prior to being included in a public release of the model. More details regarding 

the POINTCAP and POINTHOR options are provided in Section 2.1.9; more details regarding 

the PSDCREDIT option are provided in Section 2.5.6; more details regarding the LOWWIND1, 

LOWWIND2, and LOWWIND3 options in AERMOD and the ADJ_U* option in AERMET are 
20

provided in Section 2.1.10; and more details regarding the ARM2 and PVMRM2 options for 

estimating NO2 conversion is provided in Section 2.6.

2.1.4 Averaging Time Options

The averaging periods for AERMOD are selected using the AVERTIME keyword on the 

CO (Control) pathway. The syntax and type of the AVERTIME keyword are summarized below:

Syntax: CO AVERTIME Time1 Time2 . . . TimeN MONTH PERIOD

 or

 ANNUAL

Type: Mandatory, Non-repeatable

where the parameters Time1 . . . TimeN refer to the user-specified short term averaging periods 

of 1, 2, 3, 4, 6, 8, 12, and/or 24 hours, the secondary keyword MONTH refers to monthly 

averages (for calendar months), the secondary keyword PERIOD refers to the average for the 

entire data period, and the secondary keyword ANNUAL refers to an annual average. Any of the 

short term averaging periods listed above may be selected for a given run. Since the monthly 

averages are treated as short term averages, the user can select appropriate output options, such 

as the second highest values by receptor, on the OU pathway. The location of the PERIOD or 

ANNUAL keyword in the parameter list is not critical. The order of the short term averaging 

periods (including MONTH) is also not critical, although it does control the order of the 

averaging period result tables in the main output file. Generally, it is recommended that the short 

term averaging periods be input in increasing order, unless there is a clear advantage in doing 

otherwise.

The user may specify either the PERIOD keyword or the ANNUAL keyword, but not 

both. For concentration calculations, the PERIOD and ANNUAL keywords produce the same 

results for a single year data file. However, the ANNUAL average option applies only to 

complete years of data, and for multi-year data files, the ANNUAL average output is based on 

the average of the ANNUAL values across the years of data processed. For deposition 
21

calculations, the PERIOD keyword will provide a total deposition flux for the full period of 

meteorological data that is modeled, including multi-year data files, with default units of g/m2, 

whereas the ANNUAL keyword will provide an annualized rate of the deposition flux with 

default units of g/m2/yr. Use of the ANNUAL average option for meteorological data periods of 

less than a year will result in a fatal error. For meteorological data periods of longer than a year, 

if the meteorological data file does not contain complete years of data, any data remaining after 

the last complete year will be ignored for the ANNUAL average, and a warning message will be 

generated. The treatment of short term averages with multiple-year data files is comparable to 

their treatment when the CO MULTYEAR option is used (see Section 2.1.5 below for a 

description of the MULTYEAR option).

2.1.5 Performing Multiple Year Analyses with MULTYEAR Option

The MULTYEAR keyword on the CO pathway provides an option for the user to 

perform a multiple year analysis such as would be needed to determine the "high-sixth-high in 

five years" design value for determining PM-10 impacts without the need for postprocessing of

multiple concentration files, and for multiple year analyses associated with the 24-hour PM2.5 

NAAQS and 1-hour NO2 and SO2 NAAQS which are based on concentrations averaged across 

the number of years processed. More information regarding the 24-hour PM2.5 and 1-hour NO2

and SO2 NAAQS is provided in Sections 2.1.6 and 2.1.7. Since the multiple year option makes 

use of the model re-start capabilities described in the Section 3.2.10 of the AERMOD User’s 

Guide (2004a), the MULTYEAR keyword is not compatible with the SAVEFILE or INITFILE

keywords. The model will generate a fatal error message if the user attempts to exercise both 

options in a single run. The syntax and type of the MULTYEAR keyword is summarized below:

Syntax: CO MULTYEAR (H6H) Savfil (Inifil) 

Type: Optional, Non-repeatable

where the optional H6H field, formerly used to highlight the use of the MULTYEAR option for 

determining the High-6th-High (H6H) 24-hour average for the “pre-1997” PM-10 NAAQS, is no 

longer required since the “post-1997” PM-10 NAAQS was vacated. A warning message will be 
22

generated if the H6H field is included on the MULTYEAR keyword indicating that it is not 

required. The Savfil parameter specifies the filename for saving the results arrays at the end of 

each year of processing, and the Inifil parameter specifies the filename to use for initializing the 

results arrays at the beginning of the current year. The Inifil parameter is optional, and should be 

left blank for the first year in the multi-year series of runs. The MULTYEAR option works by 

accumulating the high short term average results from year to year through the mechanism of the 

re-start save file. The model may be setup to run in a batch file with several years of 

meteorological data, and at the end of each year of processing, the short term average results

reflect the cumulative high values for the years that have been processed. The PERIOD average 

results are given for only the current year, but the model carries the highest PERIOD values from 

year to year and includes the cumulative highest PERIOD averages in the summary table at the 

end of the run.

When setting up a batch file to perform a multiple year analysis, the user would first 

create an input runstream file for the first year with all of the applicable modeling options, the 

source inventory data, the receptor locations, the meteorology options for the first year and the 

output file options. To obtain the PM-10 design value, be sure to include the SIXTH highest 

value on the OU RECTABLE card (see Section 3.7.1 of the AERMOD User’s Guide (2004a)). 

For the CO MULTYEAR card for the first year, the user would only specify the Savfil 

parameter, and may use a card such as:

CO MULTYEAR YEAR1.SAV

For the subsequent years, the user could copy the input file created for Year-1, and edit the files 

to change the year parameters and meteorology filename on the ME pathway (and possibly in the 

title information), and edit the MULTYEAR cards. For the subsequent years, both the Savfil and 

Inifil parameters must be specified, with the Savfil for Year-1 becoming the Inifil for Year-2, 

and so on. The MULTYEAR cards (one for each AERMOD run) might look like this:

CO MULTYEAR YEAR1.SAV (First year)

CO MULTYEAR YEAR2.SAV YEAR1.SAV (Second year)
23

CO MULTYEAR YEAR3.SAV YEAR2.SAV (Third year)

CO MULTYEAR YEAR4.SAV YEAR3.SAV (Fourth year)

CO MULTYEAR YEAR5.SAV YEAR4.SAV (Fifth year)

The MULTYEAR keyword option is separate from the ability of the AERMOD model to process 

a multiple-year meteorological data file in a single model run. The latter capability can be used 

for applications of the model to long term risk assessments where the average impacts over a 

long time period are of concern rather than the maximum annual average determined from five 

individual years. 

2.1.6 Processing for Particulate Matter (PM) NAAQS

2.1.6.1 Processing for Fine Particulate Matter (PM-2.5)

A NAAQS for fine particulate matter, with aerodynamic particle diameters of 2.5 

microns or less (PM-2.5), was promulgated in 1997, and the 24-hour standard was revised in 

December 2006. For attainment demonstrations, the PM-2.5 standard is based on a 3-year 

average of the 98th percentile 24-hour average and a 3-year average of the annual mean

concentration at each ambient monitor. EPA issued new recommendations in May 2014 (EPA, 

2014) regarding appropriate modeling procedures for use in modeling demonstrations of 

compliance with the PM2.5 NAAQS that is intended to supersede the earlier guidance issued in 

March 2010 (EPA, 2010a). The May 2014 guidance, which addresses the issue of secondary 

formation of PM2.5 due to precursor emissions, has modified the earlier guidance regarding use 

of the average of the first-highest 24-hour average concentrations across the number of years 

modeled to represent the modeled contribution for a cumulative impact assessment and 

recommends using the average of the eighth-highest (98th percentile) of 24-hour concentrations 

to represent the modeled contribution for a cumulative impact assessment. Use of the firsthighest 24-hour average is still appropriate for significant contribution determinations. Note that 

the use of a 3-year average for monitored design values to determine attainment of the NAAQS 

does not preempt the requirement in Section 8.3.1.2 of the Guideline on Air Quality Models (40 

CFR Part 51, Appendix W) for use of 5 years of National Weather Service (NWS) data, and the 
24

5-year average of modeled impacts serves as an unbiased estimate of the 3-year average for 

purposes of modeling demonstrations of compliance with the NAAQS. 

Based on EPA’s May 2014 draft recommendations, the 24-hour modeled contribution to 

the design value for purposes of modeling demonstrations of compliance with the PM-2.5 

NAAQS is based on the highest of the eighth-highest (H8H) concentrations at each receptor, if 

one year of site-specific meteorological data is input to the model, or the highest of the multiyear average of the eighth-highest (H8H) concentrations at each receptor, if more than one year 

of meteorological data is input to the model. In other words, the model calculates the eighthhighest 24-hour concentration at each receptor for each year modeled, averages those eighthhighest concentrations at each receptor across the number of years of meteorological data, and 

then selects the highest, across all receptors, of the N-year averaged eighth-highest values. 

Similar to the 24-hour averages, an unbiased estimate of the 3-year average annual mean 

is simply the annual mean, if only one year of site-specific meteorological data is input to the 

model, or the multi-year average of the annual means if multiple years of meteorological data are 

used. The annual design value for PM-2.5 is then based on the highest annual average across the 

receptor domain for single-year meteorological data input, or the highest of the multi-year 

averaged annual means across the receptor domain for multi-year meteorological data input.

The special processing of the 24-hour and annual averages for the PM-2.5 NAAQS is 

triggered by specifying a pollutant ID of ‘PM25’, ‘PM-2.5’, ‘PM2.5’ or ‘PM-25’ on the CO 

POLLUTID card. In this case, the model will compute the 24-hour and annual average design 

values as described in the previous paragraphs. In order for the PM-2.5 processing to work

correctly for multiple year periods, the yearly meteorological data files can be concatenated into 

a single multi-year file for input into the model, or the MULTYEAR option (Section 2.1.5) can 

be used with separate model runs for each year. There is no requirement to remove the header 

records between concatenated surface meteorological data files prior to running the model, and 

multi-year meteorological data files can also be generated by processing multi-year inputs in 

AERMET, the meteorological processor for AERMOD. (NOTE: While the MULTYEAR 

option with separate yearly meteorological data files can be used to determine the modeled 
25

design values for PM2.5, the OU MAXDCONT option (see Section 2.8.1) to determine 

contributions from other source groups to the cumulative modeled design value will not work 

with the MULTYEAR option or with separate meteorological data files for each year.) 

Processing the average of the individual annual mean values across multiple years for PM-2.5 

also requires use of the ANNUAL average option on the AVERTIME keyword, rather than 

PERIOD average. The PERIOD option computes a single multi-year average concentration for 

each receptor, which may give slightly different results than the multi-year average of individual 

ANNUAL mean concentrations due to differences in the number of calms and/or missing data 

from year to year. 

In order to comply with these processing requirements, the following restrictions are 

applied to the PM-2.5 NAAQS processing whenever a pollutant ID of ‘PM25’, ‘PM-2.5’ or 

‘PM-25’ is specified on the CO POLLUTID keyword:

1. The averaging periods on the AVERTIME keyword are limited to the 24-hour and 

ANNUAL averages. Use of the PERIOD average or use of a short-term average other 

than 24-hour will result in a fatal error message being generated.

2. The FIRST (or 1ST) highest value should be requested on the RECTABLE keyword for 

24-hour averages for estimating modeled PM2.5 contributions for compliance with the 

NAAQS. However, the model places no restriction on the ranks requested on the 

RECTABLE keyword since selection of ranks lower than the FIRST highest may be 

needed to determine whether a source or group of sources is contributing significantly to 

modeled violations of the NAAQS.

3. The model will only process meteorological data for periods of record that span complete 

years, although the meteorological data period does not need to follow calendar years 

(i.e., the data period does not need to start on January 1, hour 1). If the period of record 

spans less than one complete year of data, a fatal error message will be generated and the 

model run will be unsuccessful. If additional meteorological data remains after the end of 

the last complete year of data, the remaining data will be ignored, and a non-fatal warning 

message will be generated specifying the number of hours ignored.

4. The MULTYEAR keyword on the CO pathway can be used to calculate multi-year 

averages for the PM-2.5 NAAQS; however, the MAXDCONT option will not work 

with the MULTYEAR. Multiple year analyses are best accomplished by including 

the multiple years of meteorology in a single data file.

5. Since the 24-hour average design values for PM-2.5 analyses, based on the H1H 

averaged over N years, may consist of averages over a multi-year period, they are not 
26

compatible with the EVENT processor, and the high ranked values generated based on 

the RECTABLE keyword will not be included in the EVENTFIL. However, if the 

MAXIFILE option is used to output 24-hour averages exceeding a user-defined

threshold, these individual exceedances may be used with the EVENT processor. 

Therefore, if the EVENTFIL option is used without the MAXIFILE option for PM-2.5 

analyses, a non-fatal warning message will be generated, and the EVENTFIL option 

will be ignored.

2.1.6.2 Processing for Particulate Matter of 10 Microns or Less (PM-10) 

The 24-hour NAAQS for particulate matter with aerodynamic particle diameters of 10 

microns or less (PM-10) is in the form of an expected exceedance value, which cannot be 

exceeded more than once per year on average over a three year period for purposes of monitored 

attainment demonstrations. Modeling demonstrations of compliance with the PM-10 NAAQS 

are based on the High-N+1-High value over N years, or in the case of five years of NWS 

meteorological data, the High-6th-High (H6H) value over five years. In the AERMOD model, 

the H6H 24-hour average over five years can be modeled in one of two ways: 1) running five 

individual years and combining the results using the CO MULTYEAR option, as described 

above in Section 2.1.5; or 2) using a single five-year meteorological data file and specifying the 

SIXTH (or 6TH) highest value on the OU RECTABLE card. If applied properly, the 24-hour 

average results of these two approaches will be equivalent. The special processing consisting of 

the 99th percentile 24-hour value averaged over N years for PM-10 in versions of AERMOD 

prior to 09292, referred to as the “Post-1997” PM-10 option, has been removed since that 

standard was vacated.

2.1.7 Processing for 1-hour NO2 and SO2 NAAQS

New 1-hour NAAQS for NO2 and SO2 were promulgated in February 2010 and June 

2010, respectively. EPA has issued guidance related to dispersion modeling in support of these 

1-hour standards (EPA, 2010b; EPA, 2010c; and EPA, 2011). The form of these new 1-hour 

standards is similar, based on a percentile rank from the annual distribution of daily maximum 1-

hour values, averaged across the number of years processed. For the 1-hour NO2 standard the 

modeled design value is based on the 98th-percentile of the daily maximum 1-hour values, which
27

is represented by the eighth-highest of the daily maximum 1-hour values across the year. The 1-

hour SO2 modeled design value is based on the 99th-percentile, or fourth-highest, of the daily 

maximum 1-hour values across the year. For typical multi-year modeling analysis based on 5 

years of NWS meteorological data, the modeled design value is the 5-year average of the eighthhighest values daily maximum 1-hour values for NO2, or fourth-highest values for SO2. 

The form of these new 1-hour standards complicates the process of determining the 

modeled design value as well as the analyses that may be required to determine whether a 

particular source or group of sources contributes significantly to any modeled violations of the 

standards, paired in time and space. Several enhancements have been incorporated into 

AERMOD, beginning with version 11059, to facilitate the modeling analyses required to 

demonstrate compliance with these new standards. These enhancements are described in Section 

2.8.1. The ability of the model to exercise these new options is facilitated by specifying ‘NO2’ 

or ‘SO2’ as the pollutant ID on the CO POLLUTID keyword, with the following restrictions. 

Whenever a pollutant ID of ‘NO2’ or ‘SO2’ is specified and 1-hour averages are selected, the 

options to calculate 1-hour NO2 or SO2 design values based on the distribution of daily 

maximum 1-hour values will be allowed, unless short-term averaging periods other than 1-hour 

are also specified on the AVERTIME keyword. If other short-term averages are specified, nonfatal warning messages will be generated and the options for processing 1-hour NO2 or SO2

design values will be disabled. In that case, the 1-hour modeled design values will be processed 

the same as other short-term averages, based on the overall distribution of hourly values. Also, if 

ANNUAL or PERIOD averages are specified on the AVERTIME keyword along with 1-hour 

averages, a non-fatal warning message will be generated unless the CO MULTYEAR keyword is 

specified, since the annual NAAQS for NO2 and SO2 is based on the highest PERIOD or 

ANNUAL average from an individual year, rather than an average across the years modeled. 

However, the special processing based on daily maximum1-hour values will be still applied for 

the 1-hour averages in these cases since the ANNUAL or PERIOD averages may be appropriate 

if only 1 year of site-specific meteorological data is modeled. 
28

2.1.8 Specifying Multiple Urban Areas

The AERMOD model (beginning with the version dated 06341) includes the option to 

specify multiple urban areas within the same model run. This option may be applicable for large 

domains that encompass more than one identifiable urban area where the separation is large 

enough to warrant separate treatment of the urban boundary layer effects. Use of the option for 

multiple urban areas eliminates the need for post-processing for such applications. The multiple 

urban areas are defined using multiple CO URBANOPT cards. The syntax of the modified 

URBANOPT keyword is as follows:

Syntax: For Multiple Urban Areas:

CO URBANOPT UrbanID UrbPop (UrbName) (UrbRoughness)

For Single Urban Areas:

CO URBANOPT UrbPop (UrbName) (UrbRoughness)

Type: Optional, Repeatable for multiple urban areas

where the UrbanID parameter is the alphanumeric urban ID defined by the user (up to eight

characters) when multiple urban areas are defined, the UrbPop parameter specifies the 

population of the urban area, the optional UrbName parameter may be used to identify the name 

of the urban area, and the optional UrbRoughness parameter may be used to specify the urban 

surface roughness length. Note the UrbName must be specified if the user wants to specify the 

urban roughness length. A default value of 1.0 meter will be used for the urban roughness length 

if the UrbRoughness parameter is omitted. Beginning with version 09292, any value for the 

urban roughness length other than 1.0 meter will be treated as a non-DFAULT option. Caution 

should be used when specifying a non-default urban roughness length, and use of a non-default 

value should be clearly documented and justified. Note that the syntax of the URBANOPT 

keyword for single urban areas has not changed from the previous version of AERMOD, so that 

existing input files will not require modification.
29

The syntax of the URBANSRC keyword on the SO pathway has also been modified to 

allow for the option of specifying multiple urban areas. The syntax of the modified 

URBANSRC keyword is as follows:

Syntax: For Multiple Urban Areas:

SO URBANSRC UrbanID SrcID’s and/or SrcRng’s 

For Single Urban Areas:

SO URBANSRC SrcID’s and/or SrcRng’s

 or

SO URBANSRC ALL (to specify all sources as URBAN)

Type: Optional, Repeatable

Order: Must follow the LOCATION card for each source input

where the UrbanID parameter is the alphanumeric urban ID (up to eight characters) defined by 

the user on the CO URBANOPT keyword when multiple urban areas are defined, and the 

SrcID's and SrcRng's are the individual source IDs and/or source ID ranges that are to be

modeled with urban effects. Source ranges are described in more detail in Section 3.3.3 of the 

AERMOD User’s Guide (EPA, 2004a). As with the URBANOPT keyword, the syntax of the 

URBANSRC keyword for applications with single urban areas has not changed from the 

previous version of AERMOD, so that existing input files will not require modification. 

However, beginning with version 12060, users can specify that all sources are to be treated as 

urban sources by specifying ‘ALL’ on the SO URBANSRC keyword for applications with a 

single urban area. Since the URBANSRC ALL option is identified during the pre-SETUP phase, 

there are no restrictions on the order of the URBANSRC ALL keyword within the SO pathway.

2.1.9 BETA Options for Capped and Horizontal Stack Releases

Draft BETA test options are included in AERMOD (beginning with the version dated 

06341) for modeling releases from capped and horizontal stacks. For sources that are not subject 

to building downwash influences, the plume rise for these capped and horizontal stacks is 

simulated based on an EPA Model Clearinghouse Memorandum, dated July 9, 1993, included in 

Appendix A of this Addendum. The Model Clearinghouse procedure for these sources entails 
30

setting the exit velocity very low (0.001 m/s) to account for suppression of vertical momentum of

the plume, and using an effective stack diameter that maintains the actual flow rate of the plume. 

Maintaining the flow rate will also serve to maintain the buoyancy of the plume in order to 

provide a more realistic estimate of plume rise. The Model Clearinghouse procedure also 

addresses the issue of stack-tip downwash for these cases.

The Model Clearinghouse procedure is not considered to be appropriate for sources 

subject to building downwash influences with the PRIME downwash algorithm for the following 

reason. The PRIME algorithm uses the specified stack diameter to define the initial radius of the 

plume for the numerical plume rise calculation, and the initial radius of the plume can 

significantly influence plume rise based on the PRIME algorithm. As a result, use of an effective 

diameter adjusted to maintain the flow rate is not appropriate and could produce unrealistic 

results. For PRIME downwash sources modeled using the BETA options for capped and 

horizontal releases, the basic premise of the Model Clearinghouse procedure, i.e. that the vertical 

momentum is suppressed while the buoyancy of the plume is conserved, has been adapted for the 

PRIME numerical plume rise formulation. For capped stacks the initial radius of the plume is 

assumed to be 2 times the actual stack diameter to account for the interaction of the exiting 

plume with the cap. The initial vertical velocity of the plume is set at 0.001 m/s, and the initial 

lateral velocity of the plume is set at 25% of the initial exit velocity of the plume. For horizontal 

stacks, the initial vertical velocity of the plume is set at 0.001 m/s, and the total exit velocity of 

the plume is assigned to the initial lateral velocity, and the plume is assumed to be emitted in the 

downwind direction. Although this adaptation of the Model Clearinghouse procedure to PRIME 

downwash sources has not been validated by field tracer or wind tunnel data, analyses have 

shown that simply setting the exit velocity to 0.001 m/s without any further adjustment when 

downwash is applied, as suggested in Section 6.1 of the AERMOD Implementation Guide (EPA, 

2009), may lead to overly conservative results (EPA, 2007). 

The user selects the BETA options for capped and/or horizontal releases by specifying 

one of the new source types on the SO LOCATION card: POINTCAP for capped stacks, and 

POINTHOR for horizontal releases. For each of these options, the user specifies the actual stack 

parameters [release height (m), exit temperature (K), exit velocity (m/s), and stack diameter (m)] 
31

using the SO SRCPARAM card as if the release were a non-capped vertical point source. The 

syntax of the SO LOCATION and SRCPARAM keywords is described in Sections 3.3.1 and 

3.3.2, respectively, of the AERMOD User’s Guide (EPA, 2004a), and is also summarized in 

Appendix B of this Addendum. The AERMOD model performs the necessary adjustments 

internally to account for plume rise and stack-tip downwash. For horizontal releases, the model 

currently assumes that the release is oriented with the wind direction, and the model does not 

account for directional effects that may occur with horizontal releases. The model also does not 

account for stacks oriented at a non-horizontal angle relative to vertical. For PRIME downwash

sources, the user-specified exit velocity for horizontal releases is treated initially as horizontal 

momentum in the downwind direction. More details regarding the BETA options for capped and 

horizontal releases will be provided later, as warranted based on further testing and evaluation.

2.1.10 BETA Options for Low Wind Conditions

Draft BETA test options are included in AERMOD (beginning with the version dated 

12345) for addressing concerns regarding model performance under low wind speed conditions, 

including the LOWWIND1, LOWWIND2, and LOWWIND3 options on the MODELOPT 

keyword. The LOWWIND1 BETA option increases the minimum value of sigma-v from 0.2 to 

0.5 m/s and "turns off" the horizontal meander component. The LOWWIND2 BETA option 

increases the minimum value of sigma-v from 0.2 to 0.3 m/s, but incorporates the meander 

component with some adjustments. Under the LOWWIND2 option an upper limit of 0.95 is 

applied to the meander factor (FRAN). The LOWWIND3 BETA option increases the minimum 

value of sigma-v from 0.2 to 0.3 m/s, uses the FASTALL approach to replicate the centerline 

concentration accounting for horizontal meander, but utilizes an effective sigma-y and eliminates 

upwind dispersion. The LOWWIND1, LOWWIND2, and LOWWIND2 BETA options are 

mutually exclusive and the model will issue a fatal warning message if more the one 

LOWWIND option is specified.

Although the LOWWIND1, LOWWIND2 and LOWWIND3 BETA options incorporate 

preset values for the minimum sigma-v, and in the case of LOWWIND2 and LOWWIND3 the 

maximum meander factor, consistent with the developmental nature and the BETA status of 
32

these options, a LOW_WIND keyword has been added to the CO pathway that allows users to 

adjust the minimum sigma-v value (SVmin) for both LowWind options (within a range of 0.01 to 

1.0 m/s), and the minimum wind speed value (WSmin), within a range from 0.01 to 1.0 m/s. 

Inclusion of the LOW_WIND keyword is intended to facilitate further testing and evaluation of 

the LowWind options. Absent user-specified values on the LOW_WIND keyword, a default 

value of 0.2828 m/s is used for WSmin, consistent with the default applied in previous versions 

of AERMOD based on SQRT(2*SVmin*SVmin) with SVmin=0.2. The LOW_WIND keyword 

also allows users to adjust the maximum value for the meander factor (FRANmax), within a 

range of 0.50 to 1.0, inclusive, when the LOWWIND2 option is used. The syntax and type of 

the LOW_WIND keyword are:

Syntax: CO LOW_WIND SVmin (WSmin) [for LOWWIND1]

CO LOW_WIND SVmin (WSmin (FRANmax)) [for LOWWIND2]

CO LOW_WIND SVmin (WSmin (FRANmax)) [for LOWWIND3]

Type: Optional, Non-repeatable

where SVmin is the minimum value of sigma-v, within a range of 0.01 to 1.0 m/s, WSmin is the 

minimum wind speed, within a range of 0.01 to 1.0 m/s, and FRANmax is the maximum 

meander factor under the LOWWIND2 option, within a range of 0.50 to 1.0, inclusive. The 

WSmin parameter on the LOW_WIND keyword is optional for both LowWind options, and the 

FRANmax parameter is also optional for the LOWWIND2 and LOWWIND3 options. However, 

a value for WSmin must also be included in order to specify a value for FRANmax. 

In addition to the adjustments to SVmin and meander described above, all of the 

LowWind BETA options also modify the adjustment of vector mean wind speeds (based on Eq. 

112, p. 79, of the AERMOD Model Formulation Document (Cimorelli, et al., 2004)) to use the 

original values of sigma-v based on Section 4.1.6 of the AERMOD MFD, before they are 

adjusted based on SVmin. 

In addition to the LowWind BETA options, an option has been incorporated in the 

AERMET meteorological processor (beginning with the version dated 12345) to address 

concerns regarding model performance under low wind conditions. The ADJ_U* option in 
33

AERMET, which adjusts the surface friction velocity (U*) under low-wind/stable conditions

based on Qian and Venkatram (2011), can be used with or without the LOWWIND1, 

LOWWIND2 or LOWWIND3 options. However, use of meteorological data based on the 

ADJ_U* option requires that the BETA option be specified on the MODELOPT keyword even if 

the BETA LowWind options are not used since the ADJ_U* option is also considered a nonDefault option. Beginning with version 13350 of AERMET, an adjustment to U* under the 

ADJ_U* option is also available as a BETA option for applications utilizing the Bulk Richardson 

Number (BULKRN) method, based on Luhar and Raynor (2009) (see also AECOM (2009)). 

See the AERMET Model Change Bulletin (MCB) #4 and AERMET User's Guide Addendum for 

additional details regarding the ADJ_U* option in AERMET. 

As noted above, the LowWind BETA options in AERMOD and the ADJ_U* option in 

AERMET are considered to be non-Default options and are therefore subject to the alternative 

model provisions in Section 3.2 of Appendix W (40 CFR Part 51). Users should coordinate with 

the appropriate reviewing authority regarding the procedures and requirements for approval of 

these BETA options for regulatory modeling applications. Appendix F provides a summary of 

evaluations of the LowWind BETA options in AERMOD in conjunction with the ADJ_U* 

option in AERMET.

2.2 DEPOSITION ALGORITHM INPUTS AND OPTIONS

The AERMOD model includes algorithms for both dry and wet deposition of both 

particulate and gaseous emissions. Based on the guidance provided for application of the 

AERMOD model in Appendix W, and based on the history of deposition algorithms in the 

AERMOD and ISC models, the particle deposition algorithms with a user-specified particle size 

distribution (referred to below as “Method 1”) can be applied under the regulatory default option. 

This option is comparable to the particle deposition algorithm in the ISCST3 model (EPA, 

1995a). The gas deposition algorithms and the “Method 2” option for particle deposition based 

on the ANL draft report (Wesely, et al, 2002) are considered to be non-DFAULT options in 

AERMOD, and the model will issue a fatal error message and abort processing if the DFAULT 

option is specified with the gas deposition or Method 2 particle deposition options. As discussed 
34

above in Section 1.2, the TOXICS option formerly associated with the options for gas deposition 

and Method 2 for particle deposition is no longer used in the AERMOD model. No additional 

option switches are required to allow use of these non-DFAULT options. Table 1-1 in Section 

1.2 summarizes the required keywords and regulatory status of various deposition options within 

AERMOD. The remainder of this section provides a detailed description of the model input 

parameters associated with the deposition algorithms.

2.2.1 Definition of Seasons for Gas Dry Deposition

The gas deposition algorithms in AERMOD include land use characteristics and some 

gas deposition resistance terms based on five seasonal categories, defined in Table 2 of the ANL 

report as:

Seasonal Category 1: Midsummer with lush vegetation

Seasonal Category 2: Autumn with unharvested cropland

Seasonal Category 3: Late autumn after frost and harvest, or winter with no snow

Seasonal Category 4: Winter with snow on ground (with generally continuous snow 

cover)

Seasonal Category 5: Transitional spring with partial green coverage or short annuals

The user correlates these seasonal definitions to calendar months through the GDSEASON 

keyword on the CO pathway. The syntax and type of the GDSEASON keyword are:

Syntax: CO GDSEASON Jan Feb Mar ... Dec

Type: Optional, Non-repeatable

where a numeric value from 1 to 5 is entered for each of the twelve calendar months to associate 

it with the seasonal definitions given above. This keyword is optional for the model, but 

mandatory when applying the gas deposition algorithms, unless the GASDEPVD option for userspecified dry deposition velocity on the CO pathway is used, described below in Section 2.2.5. 

Note that some of the seasonal categories defined above may not apply for certain regions, such 

as Category 4, winter with continuous snow cover, for moderate climates.
35

2.2.2 Definition of Land Use Categories for Gas Dry Deposition

The gas deposition algorithms include some gas deposition resistance terms based on five 

seasonal categories, defined above, and nine land use categories as follows (from Table 1 of the 

ANL report):

Land Use Category Description

1 Urban land, no vegetation

2 Agricultural land

3 Rangeland

4 Forest

5 Suburban areas, grassy

6 Suburban areas, forested

7 Bodies of water

8 Barren land, mostly desert

9 Non-forested wetlands

The user defines the land use categories by direction sector through the GDLANUSE keyword 

on the CO pathway. The syntax and type of the GDLANUSE keyword are:

Syntax: CO GDLANUSE Sec1 Sec2 Sec3 ... Sec36

Type: Optional, Non-repeatable

where a numeric value from 1 to 9 is entered for each of the 36 direction sectors (every 10 

degrees) to associate it with the land use definitions given above. This keyword is optional for 

the model, but mandatory when applying the gas deposition algorithms, unless the GASDEPVD 

option for user-specified deposition velocity is used. The first value, Sec1, corresponds with the 

land use category, downwind of the application site, for winds blowing toward 10 degrees, plus 

or minus 5 degrees. The downwind sectors are defined in clockwise order, with Sec36 

corresponding to winds blowing toward 360 degrees (North), and should generally reflect 

conditions downwind relative to the source location. The user can specify "repeat values" by 

entering a field such as "36*3" as a parameter for the GDLANUSE keyword. The model will 

interpret this as "36 separate entries, each with a value of 3." Since the model must identify this 
36

as a single parameter field, there must not be any spaces between the repeat-value and the value 

to be repeated.

2.2.3 Option for Overriding Default Parameters for Gas Dry Deposition

An optional keyword is available on the Control (CO) pathway to allow the user to 

override the default values of the reactivity factor (fo), and the fraction (F) of maximum green 

leaf area index (LAI) for seasonal categories 2 (autumn/unharvested cropland) and 5 (transitional 

spring), for use with the gas dry deposition algorithms.

The syntax and type of the GASDEPDF keyword are summarized below:

Syntax: CO GASDEPDF React F_Seas2 F_Seas5 (Refpoll)

Type: Optional, Non-repeatable

where the parameter React is the value for pollutant reactivity factor (fo), and F_Seas2 and 

F_Seas5 are the fractions (F) of maximum green LAI for seasonal categories 2 and 5, 

respectively. The parameter Refpoll is the optional name of the pollutant. If the optional 

GASDEPDF keyword is omitted, then the default value of 0 is used for React, and default values 

of 0.5 and 0.25 are used for F_Seas2 and F_Seas5, respectively. A value of F=1.0 is used for 

seasonal categories 1, 3, and 4. A reactivity factor value of 1 should be input for ozone (O3), 

titanium tetrachloride (TiCl4), and divalent mercury (Hg2+), and a value of 0.1 should be input 

for nitrogen dioxide (NO2). 

2.2.4 Specifying Source Parameters for Gas Deposition (Dry and/or Wet)

The input of source parameters for dry and wet deposition of gaseous pollutants is 

controlled by the GASDEPOS keyword on the SO pathway. The gas deposition variables may 

be input for a single source, or may be applied to a range of sources.

The syntax, type, and order for the GASDEPOS keyword are summarized below:
37

Syntax: SO GASDEPOS Srcid (or Srcrng) Da Dw rcl Henry

Type: Optional, Repeatable

Order: Must follow the LOCATION card for each source input

where the Srcid or Srcrng identify the source or sources for which the inputs apply, the 

parameter Da is the diffusivity in air for the pollutant being modeled (cm2

/s), Dw is the 

diffusivity in water for the pollutant being modeled (cm2/s), rcl is the cuticular resistance to 

uptake by lipids for individual leaves (s/cm), and Henry is the Henry's Law constant (Pa 

m3/mol). Values of the physical parameters for several common pollutants may be found in the 

appendices to the ANL report (Wesely, et. al, 2002). 

2.2.5 Option for Specifying the Deposition Velocity for Gas Dry Deposition

An optional keyword is available on the Control (CO) pathway to allow the user to 

specify the dry deposition velocity for gaseous emissions. A single dry deposition velocity can 

be input for a given model run, and is used for all sources of gaseous pollutants. Selection of this 

option will by-pass the algorithm for computing deposition velocities for gaseous pollutants, and 

should only be used when sufficient data to run the algorithm are not available. Results of the 

AERMOD model based on a user-specified deposition velocity should be used with extra 

caution. 

The syntax and type of the GASDEPVD keyword are summarized below:

Syntax: CO GASDEPVD Uservd

Type: Optional, Non-repeatable

where the parameter Uservd is the gaseous dry deposition velocity (m/s). A non-fatal warning 

message is generated by the model if a value of Uservd greater than 0.05 m/s (5 cm/s) is input by 

the user. When the GASDEPVD keyword is used, the GDSEASON, GDLANUSE, and 

GASDEPRF keywords for the CO pathway, and the GASDEPOS keyword for the SO pathway, 

are no longer applicable and cannot be used in the same model run. As a result, gas wet 
38

deposition processes (DEPOS, WDEP, and WETDPLT) cannot be simulated with the 

GASDEPVD option is used.

2.2.6 Specifying Source Parameters for Particle Deposition

The AERMOD model includes two methods for handling dry and/or wet deposition of 

particulate emissions. Method 1 is used when a significant fraction (greater than about 10 

percent) of the total particulate mass has a diameter of 10 μm or larger, or when the particle size 

distribution is known. The particle size distribution must be known reasonably well in order to 

use Method 1. Method 2 may be used when the particle size distribution is not well known and 

when a small fraction (less than 10 percent of the mass) is in particles with a diameter of 10 μm 

or larger. The deposition velocity for Method 2 is calculated as the weighted average of the 

deposition velocity for particles in the fine mode (i.e., less than 2.5 μm in diameter) and the 

deposition velocity for the coarse mode (i.e., greater than 2.5 μm but less than 10 μm in 

diameter). As described in Sections 1.2 and 2.2, use of the Method 2 option is considered nonDFAULT.

2.2.6.1 Specifying Particle Inputs for Method 1

The input of source variables for particle deposition using Method 1 is controlled by three 

keywords on the SO pathway, PARTDIAM, MASSFRAX, and PARTDENS. These inputs are 

comparable to the particulate inputs used in the ISCST3 model (EPA,1995a). The particle 

variables may be input for a single source, or may be applied to a range of sources.

The syntax, type and order for these three keywords are summarized below:

Syntax: SO PARTDIAM Srcid (or Srcrng) Pdiam(i), i=1,Npd

SO MASSFRAX Srcid (or Srcrng) Phi(i), i=1,Npd

SO PARTDENS Srcid (or Srcrng) Pdens(i), i=1,Npd

Type: Optional, Repeatable

Order: Must follow the LOCATION card for each source input
39

where the Srcid or Srcrng identify the source or sources for which the inputs apply, and where 

the Pdiam array consists of the mass-mean aerodynamic particle diameter (microns) for each of 

the particle size categories, the Phi array is the corresponding mass fractions (between 0 and 1) 

for each of the categories, and the Pdens array is the corresponding particle density (g/cm3

) for 

each of the categories.

The number of particle size categories for a particular source is Npd. The user does not 

explicitly tell the model the number of categories being input, but if continuation cards are used 

to specify particle size variables, all inputs of a keyword for a particular source or source range 

must be contiguous, and the number of categories must agree for each of the three keywords 

input for a particular source. As many continuation cards as needed may be used to define the 

inputs for a particular keyword. The model checks the inputs to ensure that the mass fractions 

sum to 1.0 (within 2 percent) for each source input, and issues a warning message if that range is 

exceeded. The model also ensures that mass fractions for each particle size category are within 

the proper range (between 0 and 1), and issues fatal error messages for any value exceeded that 

range.

2.2.6.2 Specifying Particle Inputs for Method 2

The Method 2 particle information is input through the METHOD_2 keyword on the SO 

pathway. The syntax, type, and order for the METHOD_2 keyword are summarized below:

Syntax: SO METHOD_2 Srcid (or Srcrng) FineMassFraction Dmm

Type: Optional, Repeatable

Order: Must follow the LOCATION card for each source input

where the Srcid or Srcrng identify the source or sources for which the inputs apply, the 

parameter FineMassFraction is the fraction (between 0 and 1) of particle mass emitted in the fine 

mode, less than 2.5 microns, and Dmm is the representative mass-mean aerodynamic particle 
40

diameter in microns. Estimated values of fine particle fractions and mass mean diameters for 

various pollutants are provided in Appendix B of the ANL report (Wesely, et al, 2002).

2.2.7 Specifying Emission and Output Units

Since the AERMOD model allows for both concentration and deposition to be output in 

the same model run, the EMISUNIT keyword (see Section 3.3.6 of the AERMOD User’s Guide 

(EPA, 2004a)) cannot be used to specify emission unit factors if more than one output type is 

being generated. The AERMOD model therefore allows for concentration and deposition units 

to be specified separately through the CONCUNIT and DEPOUNIT keywords, respectively. 

The syntax and type of the CONCUNIT keyword are summarized below:

Syntax: SO CONCUNIT Emifac Emilbl Conlbl

Type: Optional, Non-repeatable

where the parameter Emifac is the factor to convert emission rate input units to the desired 

output units, Emilbl is the label for the emission input units (up to 40 characters), and Conlbl is 

the output unit label (up to 40 characters) for concentration calculations. The syntax and type of 

the DEPOUNIT keyword are summarized below:

Syntax: SO DEPOUNIT Emifac Emilbl Deplbl

Type: Optional, Non-repeatable

where the parameter Emifac is the factor to convert emission rate input units to the desired 

output units, Emilbl is the label for the emission input units (up to 40 characters), and Deplbl is 

the output unit label (up to 40 characters) for deposition calculations. 

2.2.8 Deposition Velocity and Resistance Outputs

In order to facilitate review and testing of the deposition algorithms in the AERMOD 

model, the model includes an option to output the main resistance terms and deposition velocities 
41

for gaseous and particle sources. These optional outputs are generated if the user specifies the 

‘CO DEBUGOPT MODEL’ option described in Section 3.2.13 of the AERMOD User’s Guide 

(EPA, 2004a). The gas deposition data are written to a file called GDEP.DAT, which includes 

the values of Ra, Rb, Rc, and Vdg (see Wesely, et al, 2002, for definitions) for each source and for 

each hour modeled. A header record is included to identify the columns. The particle deposition 

data are written to a file called PDEP.DAT, which includes the values of Ra, Rp, Vg, and Vd for 

each source and for each hour modeled. The particle outputs are labeled as being based on either 

Method 1 or Method 2. For Method 1, results are output for each particle size category. The 

filename and file units for these data files are hardcoded in the model, and the files are 

overwritten each time the model is executed. Since these files include data for each source for 

each hour, file sizes may become large.

2.2.9 Meteorological Data for Deposition Algorithms

The AERMET meteorological processor was modified (beginning with the version dated 

04300) to output additional meteorological parameters needed for the deposition algorithms in 

AERMOD. The additional variables include the precipitation code, precipitation rate, relative 

humidity, surface pressure, and cloud cover. These additional variables are automatically 

included after the standard variables for each hour, and do not require any additional user input. 

The precipitation data needed for wet deposition calculations in AERMOD can be obtained from 

the SAMSON, HUSWO or ISHD (TD-3505) formats currently supported by AERMET (EPA, 

2004b). 

The input meteorological data file consists of a header record that includes the latitude 

and longitude, surface station ID (e.g., WBAN number), upper air station ID, the on-site station 

ID, and the AERMET version date (see Section D.1 of the AERMOD model user=s guide (EPA, 

2004a)). The meteorological data file for the deposition algorithms is read as a FREE format file, 

i.e., each field on a record is separated from adjacent fields by a comma or by one or more 

spaces. The subsequent data records contain the following variables in the order listed:
42

Variable Description Format

Year Integer

Month Integer

Day of Month Integer

Julian Day (Day of Year) Integer

Hour of Day Integer

Heat Flux (W/m2) Real

Surface Friction Velocity, u* (m/s) Real

Convective Velocity Scale, w* (m/s) Real

Lapse Rate above Mixing Height (K/m) Real

Convective Mixing Height (m) Real

Mechanical Mixing Height (m) Real

Monin-Obukhov Length, L (m) Real

Surface Roughness Length, zo (m) Real

Bowen Ratio Real

Albedo Real

Reference Wind Speed (m/s) Real

Reference Wind Direction (degrees) Real

Reference Height for Wind (m) Real

Ambient Temperature (K) Real

Reference Height for Temperature (m) Real

Precipitation Code (0-45) Integer

Precipitation Amount (mm) Real

Relative Humidity (%) Real

Surface Pressure (mb) Real

Cloud Cover (tenths) Integer

2.3 OPEN PIT SOURCE OPTION

The open pit source option is invoked by specifying a source type of OPENPIT on the 

source location (SO LOCATION) card. The OPENPIT source algorithm can be used to model 

particulate or gaseous emissions from open pits, such as surface coal mines and rock quarries. If 

particulate emissions are modeled, the user must specify the particle size information through the 

appropriate keywords described in Section 2.2. The OPENPIT algorithm uses an effective area 

for modeling pit emissions, based on meteorological conditions, and then utilizes the numerical 

integration area source algorithm to model the impact of emissions from the effective area 

sources. A complete technical description of the OPENPIT source algorithm is provided in the 

ISC3 Model User=s Guide - Volume II (EPA, 1995b). 
43

The AERMOD model accepts rectangular pits with an optional rotation angle specified 

relative to a north-south orientation. The rotation angle is specified relative to the vertex used to 

define the source location on the SO LOCATION card (e.g., the southwest corner). The syntax, 

type and order for the SRCPARAM card for OPENPIT sources are summarized below: 

Syntax: SO SRCPARAM Srcid Opemis Relhgt Xinit Yinit Pitvol (Angle)

Type: Optional, Repeatable

Order: Must follow the LOCATION card for each source input

where the Srcid parameter is the same source ID that was entered on the LOCATION card for a 

particular source, and the other parameters are as follows:

Opemis - open pit emission rate in g/(s-m2),

Relhgt - average release height above the base of the pit in meters, 

Xinit - length of X side of the open pit (in the east-west direction if Angle is 0 

degrees) in meters,

Yinit - length of Y side of the open pit (in the north-south direction if Angle is 0 

degrees) in meters,

Pitvol - volume of open pit in cubic meters, and

Angle - orientation angle for the rectangular open pit in degrees from North, measured 

positive in the clockwise direction (optional).

The same emission rate is used for both concentration and deposition calculations in the 

AERMOD model. It should also be noted that the emission rate for the open pit source is an 

emission rate per unit area, which is different from the point and volume source emission rates, 

which are total emissions for the source. The Relhgt parameter cannot exceed the effective depth 

of the pit, which is calculated by the model based on the length, width and volume of the pit. A 

Relhgt of 0.0 indicates emissions that are released from the base of the pit.

If the optional Angle parameter is input, and the value does not equal 0.0, then the model 

will rotate the open pit clockwise around the vertex defined on the SO LOCATION card for this 
44

source. The relationship between the Xinit, Yinit, and Angle parameters and the source location, 

(Xs,Ys), for a rotated pit is the same as for rectangular area sources. The Xinit dimension is 

measured from the side of the area that is counterclockwise along the perimeter from the vertex 

defined by (Xs,Ys), while the Yinit dimension is measured from the side of the open pit that is 

clockwise along the perimeter from (Xs,Ys). Unlike the area source inputs, the Yinit parameter 

is not optional for open pit sources. The Angle parameter is measured as the orientation relative 

to North of the side that is clockwise from (Xs,Ys), i.e. the side with length Yinit. The Angle 

parameter may be positive (for clockwise rotation) or negative (for counterclockwise rotation), 

and a warning message is generated if the absolute value of Angle is greater than 180 degrees. 

The selection of the vertex to use for the source location is not critical, as long as the relationship 

described above for the Xinit, Yinit, and Angle parameters is maintained.

The aspect ratio (i.e., length/width) of open pit sources should be less than 10 to 1. 

However, since the pit algorithm generates an effective area for modeling emissions from the pit, 

and the size, shape and location of the effective area is a function of wind direction, an open pit 

cannot be subdivided into a series of smaller sources. Aspect ratios of greater than 10 to 1 will 

be flagged by a warning message in the output file, and processing will continue. Since open pit 

sources cannot be subdivided, the user should characterize irregularly-shaped pit areas by a 

rectangular shape of equal area. Receptors should not be located within the boundaries of the 

pit; concentration and/or deposition at such receptors will be set to zero. Such receptors will be 

identified during model setup and will be flagged in the summary of inputs.

An example of a valid SRCPARAM input card for an open pit source is given below:

SO SRCPARAM NORTHPIT 1.15E-4 0.0 150.0 500.0 3.75E+6 30.0

where the source ID is NORTHPIT, the emission rate is 1.15E-4 g/(s-m2), the release height is 

0.0 m, the X-dimension is 150.0 m, the Y-dimension is 500.0 m, the pit volume is 3.75E+6 cubic 

meters (corresponding to an effective pit depth of about 50 meters) and the orientation angle is 

30.0 degrees clockwise from North.
45

2.4 LINE SOURCE OPTION

Beginning with version 12345, a LINE source type has been added to the SO pathway. 

The LINE source option is invoked by specifying a source type of LINE on the source location 

(SO LOCATION) card. The LINE source type option allows users to specify line-type sources 

based on a start-point and end-point of the line and the width of the line, as an alternative to the 

current AREA source type for rectangular sources. The LINE source type utilizes the same 

routines as the AREA source type, and will give identical results for equivalent source inputs. 

The LINE source type also includes an optional initial sigma-z parameter to account for initial

dilution of the emissions. As with the AREA source type, the LINE source type does not include 

the horizontal meander component in AERMOD. Since the LINE source type utilizes the AREA 

source algorithms, the runtime optimizations associated with the FASTAREA option will also 

apply to LINE sources if included.

The syntax, type and order for the LOCATION card for LINE sources are summarized 

below: 

Syntax: SO LOCATION Srcid LINE Xs1 Ys1 Xs2 Ys2 (Zs)

Type: Mandatory, Repeatable

Order: Must be the first card for each source input

where the Srcid parameter is the user-specified source ID, Xs1 and Ys1 are the x and y 

coordinates for the midpoint of one end of the LINE, Xs2 and Ys2 are the x and y coordinates for 

the midpoint of the other end of the LINE, and Zs is the optional elevation of the source above 

sea-level. 

The syntax, type and order for the SRCPARAM card for LINE sources are summarized 

below: 
46

Syntax: SO SRCPARAM Srcid Lnemis Relhgt Width (Szinit)

Type: Mandatory, Repeatable

Order: Must follow the LOCATION card for each source input

where the Srcid parameter is the same source ID that was entered on the LOCATION card for a 

particular source, and the other parameters are as follows:

Lnemis - line source emission rate in g/(s-m2),

Relhgt - average release height above ground in meters (unless ELEVUNIT keyword is 

used to specify elevations in feet), 

Width - width of the source in meters (with a minimum width of 1m),

Szinit - initial vertical dimension of the line source in meters (optional),

As noted above, the LINE source type option in AERMOD uses the same algorithms as used for 

the AREA source type for rectangular sources, and will give identical results for equivalent 

source definitions. The LINE source emission rate is in g/(s-m2) and the model assumes that 

emissions are uniformly distributed across the dimensions of the LINE source. As with the 

AREA source type, the LINE source type does not include the horizontal meander component 

that is incorporated for POINT and VOLUME sources. Also, as with the AREA source type, the 

LINE source type will estimate concentrations (and/or deposition) at receptors located within the 

dimensions of the source. 

2.5 SPECIFYING BACKGROUND CONCENTRATIONS

Beginning with version 11059, users can specify uniform or temporally varying background 

concentrations using the BACKGRND keyword on the SO pathway, and beginning with version 

13350 users can vary background concentrations by wind sector. Background concentrations 

can be included with any source group to estimate cumulative ambient impacts. Background 

concentrations can be specified using a range of options similar to those available with the 

EMISFACT keyword for source emissions, or on an hourly basis from a separate data file. For 
47

applications that include sector-varying background concentrations, the sectors are defined based 

on the SO BGSECTOR keyword, as follows:

Syntax: SO BGSECTOR StartSect1 StartSect2 . . . StartSectN, where N ≤ 6

Type: Optional, Non-Repeatable

For applications that include sector-varying background concentration the minimum sector width 

allowed is 30 degrees and warning messages will be issued for sector widths less than 60 

degrees. Sector-varying background concentrations will be selected based on the flow 

vector, i.e., the downwind direction, based on the wind direction specified in the surface 

meteorological data file. 

For applications that do not include sector-varying background concentrations, the syntax 

of the BACKGRND keyword is as follows:

Syntax: SO BACKGRND BGflag BGvalue(i), i=1,n

 and/or

SO BACKGRND HOURLY BGfilnam (BGformat)

Type: Optional, Repeatable

where the BGflag parameter is the variable background concentration flag, BGvalue is the array 

of background concentration values associated with BGflag, HOURLY indicates use of an 

hourly background file, BGfilnam is the filename for the hourly background data, and BGformat 

is the optional Fortran format of the hourly background file (‘free’ format is used by default). 

The BGfilnam can be up to 200 characters in length based on the default parameters in

AERMOD. Double quotes (“) at the beginning and end of the filename can also be used as field 

delimiters to allow filenames with embedded spaces. 

For applications that include sector-varying background concentrations, the syntax of the 

BACKGRND keyword is as follows:
48

Syntax: SO BACKGRND SECTn BGflag BGvalue(i), i=1,n

 and/or

SO BACKGRND SECTn HOURLY BGfilnam (BGformat)

Type: Optional, Repeatable

where the SECTn parameter identifies the applicable sector as defined on the SO BGSECTOR 

keyword, and the other parameters are as defined above.

The HOURLY background file must include the year, month, day, and hour, followed by 

the background concentration, in that order (unless specified differently through the BGformat

parameter). The year can be specified as either a 2-digit or 4-digit year. If an optional Fortran 

format is specified using the BGformat parameter, the year, month, day, and hour variables must 

be read as integers using the Fortran I format, and the background concentration must be read as 

a real variable, using the Fortran F, E, or D format, e.g., (4I2,F8.3). Note that background values 

that do not include decimal places can be read as Fx.0, where x is the length of the data field. 

The BGformat parameter must include the open and close parentheses as shown in the example, 

and may also include embedded spaces if double quotes (“) are used to delimit the field. A 

warning message will be generated if the specified format does not meet these requirements, and 

AERMOD may also issue a fatal error message when reading the file in cases where real 

variables are read with an integer format, or vice versa.

If the optional BGformat parameter is missing, then the model will read the background

data using a Fortran ‘free’ format, i.e., assuming that commas or spaces separate the data fields, 

and that the fields are in the order given above. The date sequence in the background data file 

must also match the date sequence in the hourly meteorological data files. 

Note that the HOURLY option and an option to specify values based on the BGflag 

parameter can both be specified in the same model run. This allows the user to specify 

background concentrations on a temporally-varying basis, such as SEASHR, that can be used to 

substitute for missing values in an hourly background file. NOTE: AERMOD will issue a 

fatal error message and abort processing if missing data are encountered in an HOURLY

background file unless the user provides other temporally-varying background 
49

concentrations (e.g., SEASHR, etc.) to substitute for missing data. Background 

concentration units can be specified using the BACKUNIT keyword, described below. If the 

BACKUNIT keyword is omitted, default units of PPB are assumed for background NO2 and 

SO2, PPM for CO, and UG/M3 for all other pollutants. Background concentrations specified in 

units of PPB or PPM are converted to UG/M3 based on reference temperature (25 C) and 

pressure (1013.25 mb).

To include background concentrations with a particular source group, the reserved 

“source ID” of BACKGROUND (or BACKGRND) can be included on the SRCGROUP 

keyword, including source group ALL. NOTE: AERMOD will NOT automatically include 

background concentrations in source group ALL, but the user can specify that background be 

included in results for group ALL by including the BACKGROUND (or BACKGRND) keyword 

after ‘ALL’ on the SRCGROUP keyword. Users can also include the NOBACKGROUND (or 

NOBACKGRND) keyword after ‘ALL’ on the SRCGROUP keyword to explicitly indicate that 

BACKGROUND is NOT included with group ‘ALL.’ The contribution of background 

concentrations can also be tracked separately by including a source group with BACKGROUND 

as the only “source ID.” NOTE: The source of background concentrations and the method 

used to incorporate background concentrations in a cumulative impact assessment involves 

several considerations and should be documented and justified on a case-by-case basis. 

Background concentrations specified with the BACKGRND keyword are combined with 

source impacts on a temporally-paired basis to estimate cumulative ambient impacts. However, 

since modeled concentrations are not calculated for hours with calm or missing meteorological 

data, background concentrations are also omitted for those hours. This may result in the 

background contribution being lower than expected for short-term averages of 3-hours up to 24-

hours for periods when the denominator used to calculate the multi-hour average is adjusted in 

accordance with EPA’s calms policy (see Section 8.3.4.2 of Appendix W), which is implemented 

within the AERMOD model. For example, if 12 hours out of a 24-hour period are calm or 

missing, the calms policy dictates that the 24-hour average concentration would be based on the 

sum of the 12 non-calm/non-missing hours divided by 18. The contribution from background 

concentrations would also be based on the sum of background values for the 12 non-calm/non-
50

missing hours, divided by 18. If background was specified as uniform during that 24-hour 

period, then the contribution from background would appear to be 33.3% lower than expected 

(i.e., 12/18). 

The BGflag parameter must be specified as one of the following secondary keywords (the 

number in parentheses indicates the number of values required for each option):

ANNUAL - annual background value (n=1),

SEASON - background values vary seasonally (n=4),

MONTH - background values vary monthly (n=12),

HROFDY - background values vary by hour-of-day (n=24),

WSPEED - background values vary by wind speed (n=6),

SEASHR - background values vary by season and hour-of-day (n=96),

HRDOW - background values vary by hour-of-day, and day-of-week [M-F, Sat, Sun] 

(n=72), 

HRDOW7 - background values vary by hour-of-day, and the seven days of the week 

[M, Tu, W, Th, F, Sat, Sun] (n=168),

SHRDOW - background values vary by season, hour-of-day, and day-of-week [M-F, 

Sat, Sun] (n=288), 

SHRDOW7 - background values vary by season, hour-of-day, and the seven days of the

week [M, Tu, W, Th, F, Sat, Sun] (n=672),

MHRDOW - background values vary by month, hour-of-day, and day-of-week [M-F, 

Sat, Sun] (n=864), and

MHRDOW7 - background values vary by month, hour-of-day, and the seven days of the

week [M, Tu, W, Th, F, Sat, Sun] (n=2,016).

The seasons are defined in the following order: Winter (Dec., Jan., Feb.), Spring (Mar., Apr., 

May), Summer (Jun., Jul., Aug.), and Fall (Sep., Oct., Nov.). The wind speed categories used 

with the WSPEED option may be defined using the ME WINDCATS keyword. If the

WINDCATS keyword is not used, the default wind speed categories are defined by the upper
51

bound of the first five categories as follows (the sixth category is assumed to have no upper

bound): 1.54, 3.09, 5.14, 8.23, and 10.8 m/s. The BACKGRND keyword may be repeated as 

many times as necessary to input all of the background values, and repeat values may be used for 

the numerical inputs, e.g., 12*25.6 can be used to specify a value of 25.6 for 12 adjacent “cells” 

within the array of values.

Background concentration units can be specified on the optional BACKUNIT keyword 

on the SO pathway. The syntax of the BACKUNIT keyword is as follows:

Syntax: SO BACKUNIT BGUnits

Type: Optional, Non-repeatable

where the BGUnits parameter specifies the units as parts-per-billion (PPB), parts-per-million 

(PPM), or micrograms/cubic-meter (UG/M3). Units specified on the BACKUNIT keyword are 

applied to HOURLY and temporally-varying background values if both are included in the same 

model run. If the BACKUNIT keyword is omitted, default units of PPB are assumed for 

background NO2 and SO2, PPM for CO, and UG/M3 for all other pollutants. Background 

concentrations specified in units of PPB or PPM are converted to UG/M3 based on reference 

temperature (25 C) and pressure (1013.25 mb).

2.6 OPTIONS FOR MODELING NO2

This section provides a description of the AERMOD inputs related to the non-Default 

PVMRM, PVMRM2, and OLM options for modeling the conversion of NO to NO2, and, 

beginning with version 13350, the Default Ambient Ratio Method (ARM) option and nonDefault/Beta Ambient Ratio Method – 2 (ARM2). A technical description of the PVMRM 

algorithm as incorporated within AERMOD is provided in an Addendum to the AERMOD 

Model Formulation Document (Cimorelli, et al., 2004). Additional information regarding 

options for NO2 modeling are provided in Technical Support Document (TSD) for NO2-related 

AERMOD Modifications (EPA, 2015). Background on the original development of the 

PVMRM option is provided by Hanrahan (1999a and 1999b). 
52

The ARM option is based on Tier 2 of the multi-tiered approach for modeling NO2

impacts discussed in Section 5.4.2 of Appendix W (EPA, 2005). Further guidance on the 

application of the ARM approach is provided in a clarification memo issued on March 1, 2011 

(EPA, 2011). The ARM2 option is based on work sponsored by API (API, 2013) to develop a 

method to adjust the modeled NOx concentrations based on an empirical relationship between 

ambient NOx and ambient NO2 concentrations. A key difference between the PVMRM, 

PVMRM2, and OLM methods, as compared to the ARM and ARM2 methods, is that ARM and 

ARM2 do not require the user to input background ozone (O3) concentrations. In addition, the 

ARM and ARM2 options do not require user-specified in-stack NO2/NOx ratios, as required by 

PVMRM, PVMRM2, and OLM; however, the default minimum ratio utilized in the ARM2 

method may not be appropriate in cases where the sources being modeled are known to have 

relatively high in-stack NO2/NOx ratios.

The PVMRM, PVMRM2, and OLM algorithms have been implemented as non-Default

options, which means that the PVMRM, PVMRM2, and OLM options cannot be used if the 

Default keyword is included on the CO MODELOPT card. As described in Section 2.1.1, a 

BETA-test draft model option, PSDCREDIT, has been added for use when an application is for 

increment consumption with PSD credits using PVMRM or PVMRM2. The special source 

grouping required for the PSDCREDIT option is described below in Section 2.6.6.1.

It is important to note that the OLM, PVMRM, PVMRM2, ARM, and ARM2 

options listed above for modeling the conversion of NO to NO2 are NOT applied to the 

background NO2 concentrations input through the SO BACKGRND option (described in 

Section 2.5). The background NO2 concentrations, if provided, will be added to the 

modeled NO2 concentrations after the NO-NO2 conversion has been calculated. For Tier 2 

applications involving temporally-varying background NO2 concentrations, the ARM or 

ARM2 option in AERMOD should be used to ensure that the ambient ratios are applied 

only to the modeled NO2 concentrations before adding the contribution from background 

NO2 concentrations. 
53

2.6.1 Specifying Ozone Concentrations for PVMRM, PVMRM2, and OLM Options

The background ozone concentrations for the PVMRM, PVMRM2, and OLM options 

can be input as a single value through the OZONEVAL keyword on the CO pathway, as 

temporally-varying values through the O3VALUES keyword on the CO pathway, or as hourly 

values from a separate data file specified through the OZONEFIL keyword on the CO pathway. 

The user must specify background ozone concentrations through the OZONEVAL, O3VALUES, 

or OZONEFIL keyword in order to use the PVMRM, PVMRM2, or OLM options. The 

OZONEVAL or O3VALUES keyword may also be specified with the OZONEFIL keyword, in 

which case the value(s) entered on the OZONEVAL or O3VALUES keyword will be used to 

substitute for hours with missing ozone data in the hourly ozone data file. Beginning with 

version 13350 users can vary background ozone concentrations by wind sector. For applications 

that include sector-varying background ozone concentrations, the sectors are defined based on 

the CO O3SECTOR keyword, as follows:

Syntax: CO O3SECTOR StartSect1 StartSect2 . . . StartSectN, where N ≤ 6

Type: Optional, Non-Repeatable

For applications that include sector-varying background concentration the minimum sector width 

allowed is 30 degrees and warning messages will be issued for sector widths less than 60 

degrees. Sector-varying background concentrations will be selected based on the flow 

vector, i.e., the downwind direction, based on the wind direction specified in the surface 

meteorological data file. 

The syntax of the OZONEVAL keyword is as follows:

Syntax: CO OZONEVAL O3Value (O3Units) (w/o sectors)

 or

CO OZONEVAL SECTn O3Value (O3Units) (w/ sectors)

Type: Optional, Non-repeatable
54

where the O3Value parameter is the background ozone concentration in the units specified by the 

optional O3Units parameter (PPM, PPB, or UG/M3), and SECTn refers to the user-specified 

sector defined on the optional O3SECTOR keyword for which the O3Value inputs are applied. 

If the optional O3Units parameter is missing, then the model will assume units of 

micrograms/cubic-meter (UG/M3) for the background ozone values. If units of PPM or PPB are 

used, then the model will convert the concentrations to micrograms/cubic-meter based on 

reference temperature (25 C) and pressure (1013.25 mb).

The syntax of the O3VALUES keyword is as follows, and is similar to the EMISFACT 

keyword on the SO pathway for specifying temporally-varying emission rates:

Syntax: CO O3VALUES O3Flag O3values(i), i=1,n (w/o sectors)

 or

CO O3VALUES SECTn O3Flag O3values(i), i=1,n (w/ sectors)

Type: Optional, Repeatable

where the SECTn parameter specifies the applicable sector as defined on the optional

O3SECTOR keyword, and where the parameter O3Flag is the variable ozone concentration flag, 

and must be specified as one of the following secondary keywords (the number in parentheses 

indicates the number of values required for each option):

ANNUAL - annual ozone value (n=1); equivalent to OZONEVAL keyword in PPB,

SEASON - ozone values vary seasonally (n=4),

MONTH - ozone values vary monthly (n=12),

HROFDY - ozone values vary by hour-of-day (n=24),

WSPEED - ozone values vary by wind speed (n=6),

SEASHR - ozone values vary by season and hour-of-day (n=96),

HRDOW - ozone values vary by hour-of-day, and day-of-week [M-F, Sat, Sun] 

(n=72), 
55

HRDOW7 - ozone values vary by hour-of-day, and the seven days of the week [M, Tu,

W, Th, F, Sat, Sun] (n=168),

SHRDOW - ozone values vary by season, hour-of-day, and day-of-week [M-F, Sat,

Sun] (n=288), 

SHRDOW7 - ozone values vary by season, hour-of-day, and the seven days of the week 

[M, Tu, W, Th, F, Sat, Sun] (n=672),

MHRDOW - ozone values vary by month, hour-of-day, and day-of-week [M-F, Sat,

Sun] (n=864), and

MHRDOW7 - ozone values vary by month, hour-of-day, and the seven days of the week 

[M, Tu, W, Th, F, Sat, Sun] (n=2,016).

The O3Values array is the array of ozone values, where the number of values is shown 

above for each O3Flag option. The seasons are defined in the following order: Winter (Dec., 

Jan., Feb.), Spring (Mar., Apr., May), Summer (Jun., Jul., Aug.), and Fall (Sep., Oct., Nov.). The 

wind speed categories used with the WSPEED option may be defined using the ME

WINDCATS keyword. If the WINDCATS keyword is not used, the default wind speed 

categories are defined by the upper bound of the first five categories as follows (the sixth 

category is assumed to have no upper bound): 1.54, 3.09, 5.14, 8.23, and 10.8 m/s. The 

O3VALUES keyword may be repeated as many times as necessary to input all of the ozone 

values, and repeat values may be used for the numerical inputs.

The order of inputs specified for the hour-of-day/day-of-week options (HRDOW, 

SHRDOW, SHRDOW7, etc.) are by hour-of-day, then season or month, if applicable, and then 

by day-of-week. For the HRDOW/SHRDOW/MHRDOW options, the days of the week are 

specified in the order of Weekdays (M-F), Saturdays, and Sundays. For the 

HRDOW7/SHRDOW7/ MHRDOW7 options, the days of the week are specified in the order of 

Mondays, Tuesdays, etc., through Sundays. Section 2.6.1 below includes an example illustrating 

the order of inputs for these options for the EMISFACT keyword.
56

Ozone concentrations specified on the O3VALUES keyword are assumed to be in units 

of PPB unless the OZONUNIT keyword is specified. The syntax of the OZONUNIT keyword is 

as follows:

Syntax: CO OZONUNIT OzoneUnits

Type: Optional, Non-repeatable

where the OzoneUnits parameter specifies the units as parts-per-billion (PPB), parts-per-million 

(PPM), or micrograms/cubic-meter (UG/M3). Units specified on the CONCUNIT keyword are 

only applied to ozone concentrations input thought O3VALUES keyword, which assumes 

default units of PPB if the OZONUNIT keyword is not specified. Ozone concentrations 

specified in units of PPB or PPM are converted to UG/M3 based on reference temperature (25 C) 

and pressure (1013.25 mb). 

Hourly ozone concentrations can be input through the optional OZONEFIL keyword. 

The syntax of the OZONEFIL keyword is as follows:

Syntax: CO OZONEFIL O3FileName (O3Units) (O3Format) (w/o sectors)

 or

CO OZONEFIL SECTn O3FileName (O3Units) (O3Format) (w/ sectors)

Type: Optional, Non-repeatable

where the O3FileName parameter is the filename for the hourly ozone concentration file, the 

optional O3Units parameter specifies the units of the ozone data (PPM, PPB, or UG/M3, with 

UG/M3 as the default), and the optional O3Format parameter specifies the Fortran format to read 

the ozone data. If sector-varying ozone concentrations are being used, based on the CO 

O3SECTOR keyword, then the applicable sector ID needs to specified, e.g., ‘SECT1’ indicates 

that values are specified for the first sector. The O3FileName can be up to 200 characters in 

length based on the default parameters in AERMOD. Double quotes (“) at the beginning and 

end of the filename can also be used as field delimiters to allow filenames with embedded 

spaces. 
57

The hourly ozone file must include the year, month, day, and hour, followed by the ozone 

concentration, in that order (unless specified differently through the O3Format parameter). The 

year can be specified as either 2-digit or 4-digit year. If an optional Fortran format is specified 

using the O3Format parameter, the year, month, day, and hour variables must be read as integers 

using the Fortran I format, and the ozone concentration must be read as a real variable, using the 

Fortran F, E, or D format, e.g., (4I2,F8.3). Note that ozone values that do not include decimal 

places can be read as Fx.0, where x is the length of the data field. However, ozone values that to 

not include decimal places may be read incorrectly if the O3Format specified for reading the data 

includes decimal places. For example, a value of ‘1234’ would be interpreted as ‘123.4’ if a 

format of F4.1 was used. The O3Format parameter must include the open and close parentheses 

as shown in the example, and may also include embedded spaces if double quotes (“) are used to 

delimit the field. A warning message will be generated if the specified format does not meet 

these requirements, and AERMOD may also issue a fatal error message when reading the file in 

cases where real variables are read with an integer format, or vice versa.

If the optional O3Format parameter is missing, then the model will read the ozone data 

using a Fortran ‘free’ format, i.e., assuming that commas or spaces separate the data fields, and 

that the fields are in the order given above. The date sequence in the ozone data file must match 

the date sequence in the hourly meteorological data files. As with the OZONEVAL keyword, if 

units of PPM or PPB are used, then the model will convert the concentrations to 

micrograms/cubic-meter based on reference temperature (25 C) and pressure (1013.25 mb).

Values of ozone concentrations in the ozone data file that are less than zero or greater 

than or equal to 900.0 will be regarded as missing. If background ozone values have been 

specified using the OZONEVAL and/or O3VALUES keyword, then the appropriate value will 

be used to substitute for missing ozone data from the ozone file. If no OZONEVAL or 

O3VALUES keywords are used, then the model will assume full conversion of NO to NO2 for 

hours with missing ozone data.
58

2.6.2 Specifying the Ambient Equilibrium NO2/NOx Ratio for PVMRM, PVMRM2, and OLM

The PVMRM and PVMRM2 options for modeling conversion of NO to NO2 incorporate

a default NO2/NOx ambient equilibrium ratio of 0.90. Beginning with version 11059 of 

AERMOD, a default equilibrium ratio of 0.90 has also been incorporated in the OLM option. A 

NO2/NOx equilibrium ratio other than 0.90 can be specified for either the PVMRM, PVMRM2,

or OLM option through the optional NO2EQUIL keyword on the CO pathway. The syntax of 

the NO2EQUIL keyword is as follows:

Syntax: CO NO2EQUIL NO2Equil

Type: Optional, Non-repeatable

where the NO2Equil parameter is the NO2/NOx equilibrium ratio and must be between 0.10 and 

1.0, inclusive. 

2.6.3 Specifying the Default In-stack NO2/NOx Ratio for PVMRM, PVMRM2, and OLM

The PVMRM, PVMRM2, and OLM options for modeling conversion of NO to NO2

require that an in-stack NO2/NOx ratio be specified. Based on guidance issued June 28, 2010, 

regarding the 1-hour NO2 NAAQS, AERMOD has been modified to require the user to specify 

in-stack NO2/NOx ratios for each source under the OLM, PVMRM, and PVMRM2 options, i.e., 

AERMOD no longer assumes a default in-stack ratio of 0.10 for the OLM, PVMRM, or 

PVMRM2 option. 

The in-stack NO2/NOx ratio can be specified for the PVMRM, PVMRM2, or OLM 

options by using either the CO NO2STACK card to specify a default value to be used for all 

sources, or by using the SO NO2RATIO card to specify a value on a source-by-source basis. 

The SO NO2RATIO card can also be used to override the default value for specific sources if the 

CO NO2STACK card has been specified. The syntax of the NO2STACK keyword is as follows:
59

Syntax: CO NO2STACK NO2Ratio

Type: Optional, Non-repeatable

where the NO2Ratio parameter is the default in-stack NO2/NOx ratio that will be used, unless 

overridden on a source-by-source basis by the SO NO2RATIO card (described below). The 

value of NO2Ratio must be between 0.0 and 1.0, inclusive. Users should note that while CO 

NO2STACK is an optional keyword, the OLM and PVMRM options require the user to specify 

an in-stack NO2/NOx ratio for each source, using either the CO NO2STACK or SO NO2RATIO 

cards (described in Section 2.6.4), or both.

2.6.4 Specifying In-stack NO2/NOx Ratios by Source for PVMRM, PVMRM2, and OLM

As noted above, the PVMRM, PVMRM2, and OLM options for modeling NO2

conversion require in-stack NO2/NOx ratios to be specified for each source, i.e., AERMOD no 

longer assumes a default in-stack ratio of 0.10 for the OLM option. The user can specify instack NO2/NOx ratios through the optional NO2RATIO keyword on the SO pathway. The 

syntax of the NO2RATIO keyword is as follows:

Syntax: SO NO2RATIO SrcID or SrcRange NO2Ratio

Type: Optional, Repeatable

Order: Must follow the LOCATION card for each source input

where the SrcID or SrcRange identify the source or sources for which the inputs apply, and 

where the NO2Ratio parameter specifies the in-stack ratio. In this way, the user can specify a 

single in-stack NO2/NOx ratio for a group of stacks. For example, the following input:

SO NO2RATIO STACK1-STACK10 0.15

will apply the in-stack ratio of 0.15 to sources with IDs falling within the range STACK1 to 

STACK10. Any value specified on the SO NO2RATIO card will override the default ratio, if 

any, specified on the CO NO2STACK card. Users should note that while SO NO2RATIO is an 
60

optional keyword, the PVMRM and PVMRM2 options require the user to specify an in-stack 

NO2/NOx ratio for each source, using either the CO NO2STACK (described in Section 2.6.3) or 

SO NO2RATIO cards, or both.

2.6.5 Specifying Combined Plumes for OLM

The OLM option for modeling NO2 conversion includes an option for specifying which 

sources are to be modeled as combined plumes, i.e., where the NOx within the plumes competes 

for the available ambient ozone. Sources which are not specified for modeling as combined 

plumes will be modeled as individual plumes, i.e., where all of the ambient ozone is available for 

conversion of NO to NO2. The selection of individual or combined plume option for OLM is 

specified through the OLMGROUP keyword on the SO pathway. The syntax of the 

OLMGROUP card is as follows:

Syntax: SO OLMGROUP OLMGrpID SrcID’s and/or SrcRange’s 

 or

SO OLMGROUP ALL

Type: Optional, Repeatable (except for OLMGROUP ALL)

Order: Must follow the LOCATION card for each source input;

OLMGROUP ALL must follow the LOCATION card for all sources

where OLMGrpID identifies a group to be treated as a combined plume with OLM, and the 

SrcID's and/or SrcRange's identify the sources to be included in the OLM group. As with the SO 

SRCGROUP card, individual source IDs and source ranges may be used on the same record, and 

if more than one input card is needed to define the sources for a particular OLM group, then 

additional records may be input by repeating the pathway, keyword and OLM group ID. A user 

can also specify an OLMGrpID of ALL, which means that OLM will be applied on a combined 

plume basis to all sources. However, unlike the SO SRCGROUP card, the results will not be 

output for a specific OLM group unless the same group of sources is also identified on a 

SRCGROUP card. Another constraint for the OLMGROUP keyword is that a source cannot be 

included in more than one OLM group.
61

If a source is not selected for an OLMGROUP card, then OLM will be applied to that 

source as an individual plume. Other than the similarity in syntax, there is no connection in the 

model between the groups defined on the OLMGROUP card and groups defined on the 

SRCGROUP card. The OLMGROUP card relates to how the results are processed within the 

model for the OLM option, and the SRCGROUP card simply controls how source impacts are 

grouped in the model outputs.

If the user identifies one or more groups of sources to apply OLM on a combined plume 

basis using the OLMGROUP card, the model will still need to calculate the concentration for 

individual plumes within the OLM group in order for the model to sum the results for the sources 

listed on the SRCGROUP card(s). The individual source concentrations are calculated by 

applying the ratio of the combined concentration for the OLM group with and without OLM to 

each source within the OLM group.

2.6.6 Specifying Ambient NO2/NOx Ratios for the ARM and ARM2 Options

The Default ARM and non-Default/BETA ARM2 options, incorporated in AERMOD 

beginning with version 13350, are both based on applying an ambient ratio of NO2/NOx to a 

modeled NOx concentration to estimate ambient NO2 concentrations. The ARM option utilizes 

separate ambient ratios for modeling 1-hr and annual NO2 impacts, whereas the ARM2 option 

applies an ambient ratio to the 1-hr modeled NOx concentrations based on a formula derived 

empirically from ambient monitored ratios of NO2/NOx. Default values based on EPA 

recommendations for the 1-hr and annual ambient ratios under the ARM option are 0.80 (EPA, 

2011) and 0.75 (EPA, 2005), respectively. The ARM2 option includes default upper and lower 

limits on the ambient ratio applied to the modeled NOx concentration of 0.9 and 0.2, 

respectively. The default ratios for the ARM and ARM2 options can be modified using the 

optional ARMRATIO on the CO pathway as follows:
62

Syntax: CO ARMRATIO ARM_1h (ARM_ann) For ARM Option

 or

CO ARMRATIO ARM2_Min ARM2_Max For ARM2 Option

Type: Optional, Non-Repeatable

2.6.7 Modeling NO2 Increment Credits with PVMRM or PVMRM2

Due to the ozone-limiting effects of the PVMRM and PVMRM2 options, the predicted 

concentrations of NO2 are not linearly proportional to the emission rate. Therefore, the approach 

of modeling NO2 increment consumption with PSD credits through the use of a negative 

emission rate for credit sources cannot be used with the PVMRM or PVMRM2 option. 

However, the draft PSDCREDIT option allows modeling PSD increment credits for NO2 when 

the PVMRM or PVMRM2 option is specified. The PSDCREDIT option is currently 

implemented as a BETA-test option, and requires that the PVMRM (or PVMRM2) and BETA 

options be specified. The PSDCREDIT option utilizes a new PSDGROUP keyword, described 

below, to identify which sources consume or expand increment. This option is not valid if the 

OLM option is specified, and no comparable option is available for modeling increment credits 

with the OLM option. The user should check with the appropriate reviewing authority for 

further guidance on modeling increment credits for NO2.

A general discussion of concepts related to modeling increment consumption is provided 

below, followed by a description of inputs required to use the BETA-test PSDCREDIT option 

for PVMRM and PVMRM2.

2.6.7.1 Increment Consuming and Baseline Sources

Increment is the maximum allowable increase in concentration of a pollutant above a

baseline concentration for an area defined under the Prevention of Significant Deterioration 

(PSD) regulations. The PSD baseline area can be an entire State or a subregion of a State such as 

a county or group of counties. Increment standards exist for three pollutants: SO2 (3-hr, 24-hr, 
63

and annual averages), NO2 (annual average), and PM-10 (24-hr and annual average). Increment 

consumption is the additional air quality impact above a baseline concentration.

The baseline concentration is the ambient concentration of the pollutant that existed in

the area at the time of the submittal of the first complete permit application by any source in that 

area subject to PSD regulations. A baseline source is any source that existed prior to that first 

application and the baseline date is the date of the PSD application. This baseline date is referred 

to as the minor source baseline date in PSD regulations. By definition, baseline sources do not 

consume increment. However, any baseline source that retires from service after the baseline 

date expands the increment available to new sources. Therefore, a PSD modeling analysis 

performed for a new source may need to account for this increment expansion. Such an analysis 

may therefore involve identification of three groups of sources: 1) increment-consuming sources; 

2) retired (increment-expanding) baseline sources; and 3) existing, non-retired, baseline sources.

2.6.7.2 Calculating Increment Consumption under the PSDCREDIT Option

Calculating increment consumption under the PSDCREDIT option in AERMOD is not a 

simple arithmetic exercise involving the three groups of sources defined above. Since the 

amount of ozone available in the atmosphere limits the conversion of NO to NO2, interactions of

plumes from the existing and retired baseline sources with those from the increment consuming 

sources must be considered as part of the calculation of net increment consumption. Without the 

PSDCREDIT option, properly accounting for the potential interaction of plumes among the 

different source categories would require post-processing of results from multiple model runs. 

Internal “post”-processing algorithms have been incorporated in AERMOD under the 

PSDCREDIT option to account for the apportioning of the three groups of sources to properly 

calculate increment consumption from a single model run.

Define the following three source groupings for the discussion that follows:
64

A = increment-consuming sources;

B = non-retired baseline sources; and

C = retired baseline, increment-expanding sources.

The calculation of the amount of increment consumption by the A sources cannot simply be 

estimated by modeling the A sources alone because of the possible interaction of those plumes 

with the plumes from B sources. The PVMRM algorithm is designed to account for such plume 

interactions and calculate the total NO to NO2 conversion in the combined plumes based on the 

amount of ozone available. Therefore, the total increment consumption by the A sources is 

given by the difference between (1) the total future impact of increment consuming sources and 

non-retired baseline sources (A+B) and (2) the total current impact (B), which can be expressed 

as (A+B) – (B). Here (A+B) represents the value that would be compared against the National 

Ambient Air Quality Standard (NAAQS) for NO2 during PSD review of the A sources. 

In a case where some of the baseline sources have been retired from service (C sources), 

the PSD regulations allow the consideration of increment expansion when assessing compliance 

with the PSD increment. However, the amount of increment expansion cannot be estimated by 

simply modeling the C sources alone because of the possible interaction of those plumes with the 

plumes from B sources. Therefore, the total increment expansion, i.e., PSD credit, is calculated 

as the difference between (1) the total impact prior to the retirement of C sources, i.e. (B+C), and 

(2) the total impact from existing (non-retired) baseline sources (B), which can be expressed as 

(B+C) – (B).

Finally, the net increment consumption is given by the difference between total increment 

consumption and the total increment expansion, or

[(A+B) – (B)] – [(B+C) – (B)] (1)

Note that in the absence of any increment expansion, the net increment consumption is equal to 

the total increment consumption [(A+B) – (B)], as described above.
65

These expressions of net increment consumption and expansion cannot be interpreted as 

algebraic equations. Instead, the terms within parentheses represent the results of separate model 

runs that account for the combined effects of NOx conversion chemistry on specific groups of 

sources. The expression shown in Equation 1 above represents four model simulations: (A+B), 

(B), (B+C), and (B) again. In this case, the two (B) terms do cancel each other and we are left 

with:

[(A+B)] – [(B+C)] (2)

The expression presented in Equation 2 summarizes how the net increment consumption 

calculation is performed under the PSDCREDIT option. Under this option, AERMOD first 

models the A and B groups together, then models the B and C groups together, and finally 

computes the difference to obtain the desired result, i.e., the value to compare to the PSD 

increment standard. In order for AERMOD to perform the special processing associated with 

this option, the user must define which sources belong to each of the groupings defined above. 

The next section describes how this is accomplished.

2.6.7.3 Specifying Source Groups under the PSDCREDIT Option

The PSDCREDIT option introduces limitations on grouping sources in order to calculate 

increment consumption as described in the previous section. A new keyword, PSDGROUP, is 

used to group the sources to correctly calculate the increment consumption. The syntax, type, 

and order are similar to the regular SRCGROUP keyword and are summarized below:

Syntax: SO PSDGROUP Grpid Srcid’s and/or Srcrng’s

Type: Mandatory for PSDCREDIT option, Repeatable

Order: Must follow the last keyword in the SO pathway before FINISHED

If the PSDCREDIT model option is specified, the PSDGROUP keyword must be used. The 

SRCGROUP keyword cannot be used under the PSDCREDIT option since results from other 

groupings beyond these three do not have any meaning when the PSDCREDIT option is invoked 
66

and sources are allocated to the calculation of increment consumption. Special source groups for 

outputting model results are defined within AERMOD for the PSDCREDIT option, as described 

in the next section.

Only the following special PSD group ID’s can be used. Failure to use these group ID’s 

will result in a fatal error message during setup processing by AERMOD. The group ID’s are:

INCRCONS – increment-consuming sources (group A above); these can be new 

sources or modifications to existing sources;

NONRBASE – existing, non-retired baseline sources (group B above); and

RETRBASE – retired (increment-expanding or PSD credit) baseline sources (group C

above).

It is important to note that the source emission inputs for sources included in the RETRBASE 

PSD group must be entered as positive numbers, unlike other types of PSD credit modeling 

where negative emissions are input to simulate the impact of the credit sources on the increment 

calculation. The increment-expanding contribution from RETRBASE sources is accounted for 

within the AERMOD model under the PSDCREDIT option.

The group ID’s can appear in any order, but these are the only three that can be specified. 

If there are no retired baseline sources (i.e., no baseline sources are retired), the keyword 

RETRBASE can be omitted. Likewise, if there are no non-retired baseline sources (i.e., all 

baseline sources have been retired), the NONRBASE keyword can be omitted. The special 

group ID ‘ALL’ that can be used with the SRCGROUP keyword cannot be used with the 

PSDGROUP keyword. As with the SRCGROUP keyword for non-PSDCREDIT applications, 

the group ID’s are repeatable and they must be the last keyword before FINISHED on the SO 

pathway when the PSDCREDIT option is specified.

Source ranges, which are described in more detail in Section 3.3.3 of the AERMOD 

User’s Guide (EPA, 2004a), are input as two source IDs separated by a dash, e.g., STACK1-

STACK10. Individual source IDs and source ranges may be used on the same card. If more 

than one input card is needed to define the sources for a particular group, then additional cards 
67

may be input, repeating the pathway, keyword and group ID. A source can appear in only one of 

these source groups, and must be assigned to one of the groups. 

The requirements for specifying sources and source groups under the PSDCREDIT 

option are summarized below:

• The SRCGROUP keyword cannot be used with the PSDCREDIT option;

• Special PSD group ID’s must be used with the PSDGROUP keyword;

• The group ID ALL is not allowed when the PSDCREDIT option is specified;

• A source must appear in one, and only one, of the PSDGROUPs; and

• Emission rates for increment-expanding (RETRBASE) sources must be entered as 

positive values.

2.6.7.4 Model Outputs under the PSDCREDIT Option

Unlike the regular SRCGROUP keyword, the PSDGROUP keyword does not define how 

the source impacts are grouped for model output. As described in the previous sections, the 

PSDGROUP keyword defines the different categories of sources needed in order to properly 

account for NOx conversion chemistry under the PVMRM option. 

The model outputs under the PSDCREDIT option in AERMOD are based on 

demonstrating compliance with the air quality standards, i.e., the NAAQS and PSD increment 

for NO2. As a result, AERMOD uses hardcoded “SRCGROUP” names of ‘NAAQS’ and 

‘PSDINC’ to label these two types of outputs. The results output under the ‘NAAQS’ source 

group label are based on the calculation of (A+B) as described above in Section 2.6.6.2. The 

results reported under the ‘PSDINC’ source group label are based on the expression presented 

above in Equation 2.

2.7 VARIABLE EMISSION RATES

2.7.1 Specifying Variable Emission Factors (EMISFACT)
68

The AERMOD model provides the option of specifying variable emission rate factors for

individual sources or for groups of sources. The syntax, type and order of the EMISFACT 

keyword are summarized below:

Syntax: SO EMISFACT SrcID or SrcRange Qflag Qfact(i), i=1,n

Type: Optional, Repeatable

Order: Must follow the LOCATION card for each source input

where the SrcID parameter is the same source ID that was entered on the LOCATION card for a

particular source. The user also has the option of using the SrcRange parameter for specifying a

range of sources for which the emission rate factors apply, instead of identifying a single source. 

This is accomplished by two source ID character strings separated by a dash, e.g., STACK1-

STACK10. The use of the SrcRange parameter is explained in more detail in the description of 

the BUILDHGT keyword (see Section 3.3.3 of the AERMOD User’s Guide).

The parameter Qflag is the variable emission rate flag, and must be specified as one of 

the following secondary keywords (the number in parentheses indicates the number of values 

required for each option):

SEASON - emission rates vary seasonally (n=4),

MONTH - emission rates vary monthly (n=12),

HROFDY - emission rates vary by hour-of-day (n=24),

WSPEED - emission rates vary by wind speed (n=6),

SEASHR - emission rates vary by season and hour-of-day (n=96),

HRDOW - emission rates vary by hour-of-day, and day-of-week [M-F, Sat, Sun] 

(n=72), 

HRDOW7 - emission rates vary by hour-of-day, and the seven days of the week [M,

Tu, W, Th, F, Sat, Sun] (n=168),

SHRDOW - emission rates vary by season, hour-of-day, and day-of-week [M-F, Sat,

Sun] (n=288), 
69

SHRDOW7 - emission rates vary by season, hour-of-day, and the seven days of the

week [M, Tu, W, Th, F, Sat, Sun] (n=672),

MHRDOW - emission rates vary by month, hour-of-day, and day-of-week [M-F, Sat,

Sun] (n=864), and

MHRDOW7 - emission rates vary by month, hour-of-day, and the seven days of the week 

[M, Tu, W, Th, F, Sat, Sun] (n=2,016).

The Qfact array is the array of factors, where the number of factors is shown above for 

each Qflag option. The seasons are defined in the following order: Winter (Dec., Jan., Feb.), 

Spring (Mar., Apr., May), Summer (Jun., Jul., Aug.), and Fall (Sep., Oct., Nov.). The wind speed 

categories used with the WSPEED option may be defined using the ME WINDCATS keyword. 

If the WINDCATS keyword is not used, the default wind speed categories are defined by the 

upper bound of the first five categories as follows (the sixth category is assumed to have no 

upper bound): 1.54, 3.09, 5.14, 8.23, and 10.8 m/s. The EMISFACT card may be repeated as 

many times as necessary to input all of the factors, and repeat values may be used for the 

numerical inputs. Examples for the more recent HRDOW and MHRDOW options are presented 

below, with column headers to indicate the order in which values are to be to input:
70

SO EMISFACT STK1 HRDOW enter 24 hourly scalars for each of the “days”, first for Weekdays

 (Monday-Friday), then for Saturdays, and finally for Sundays, e.g.,

** Weekdays: Hrs: 1-5 6 7-17 18 19-24

SO EMISFACT STK1 HRDOW 5*0.3 0.5 11*1.0 0.5 6*0.3

** Saturdays: Hrs: 1-5 6 7-17 18 19-24

SO EMISFACT STK1 HRDOW 5*0.3 0.5 11*1.0 0.5 6*0.3

** Sundays: Hrs: 1-5 6 7-17 18 19-24

SO EMISFACT STK1 HRDOW 5*0.3 0.5 11*1.0 0.5 6*0.3

SO EMISFACT STK1 HRDOW7 enter 24 hourly scalars for each of the “days”,

 first for Mondays, then for Tuesdays, ..., then for Saturdays,

and finally for Sundays, e.g.,

** Mondays: Hrs: 1-5 6 7-17 18 19-24

SO EMISFACT STK1 HRDOW7 5*0.3 0.5 11*1.0 0.5 6*0.3

** Tuesdays: Hrs: 1-5 6 7-17 18 19-24

SO EMISFACT STK1 HRDOW7 5*0.3 0.5 11*1.0 0.5 6*0.3

 .

 .

 .

** Saturdays: Hrs: 1-5 6 7-17 18 19-24

SO EMISFACT STK1 HRDOW7 5*0.3 0.5 11*1.0 0.5 6*0.3

** Sundays: Hrs: 1-5 6 7-17 18 19-24

SO EMISFACT STK1 HRDOW7 5*0.3 0.5 11*1.0 0.5 6*0.3

SO EMISFACT STK1 MHRDOW enter 24 hourly scalars for each of the twelve months, first for 

Weekdays

 (Monday-Friday), then for Saturdays, and finally for Sundays, e.g.,

** Weekdays JAN FEB MAR APR MAY JUN . . . NOV DEC

SO EMISFACT STK1 MHRDOW 24*1.0 24*0.8 24*0.6 24*0.8 24*1.0 24*0.8 24*0.6 24*0.8

** Saturdays:

SO EMISFACT STK1 MHRDOW 24*1.0 24*0.8 24*0.6 24*0.8 24*1.0 24*0.8 24*0.6 24*0.8

** Sundays:

SO EMISFACT STK1 MHRDOW 24*1.0 24*0.8 24*0.6 24*0.8 24*1.0 24*0.8 24*0.6 24*0.8

SO EMISFACT STK1 MHRDOW7 enter 24 hourly scalars for each of the twelve months,

 first for Mondays, then for Tuesdays, ..., then for Saturdays,

and finally for Sundays, e.g.,

** Mondays JAN FEB MAR APR MAY JUN . . . NOV DEC

SO EMISFACT STK1 MHRDOW7 24*1.0 24*0.8 24*0.6 24*0.8 24*1.0 24*0.8 24*0.6 24*0.8

** Tuesdays JAN FEB MAR APR MAY JUN . . . NOV DEC

SO EMISFACT STK1 MHRDOW7 24*1.0 24*0.8 24*0.6 24*0.8 24*1.0 24*0.8 24*0.6 24*0.8

 .

 .

 .

** Saturdays:

SO EMISFACT STK1 MHRDOW7 24*1.0 24*0.8 24*0.6 24*0.8 24*1.0 24*0.8 24*0.6 24*0.8

** Sundays:

SO EMISFACT STK1 MHRDOW7 24*1.0 24*0.8 24*0.6 24*0.8 24*1.0 24*0.8 24*0.6 24*0.8
71

2.7.2 Specifying an Hourly Emission Rate File (HOUREMIS)

The source (SO) pathway includes an option for inputting hourly emission rates for the

AERMOD model, controlled by the HOUREMIS keyword. AERMOD currently allows for a

single hourly emission file to be used with each model run. The syntax, type and order for this

keyword are summarized below:

Syntax: SO HOUREMIS Emifil Srcid's (and/or Srcrng's)

Type: Optional, Repeatable

Order: Must follow the LOCATION card for each source input

where the Emifil parameter specifies the filename for the hourly emission file, and Srcid or 

Srcrng identify the source or sources for which hourly emission rates are included. The Emifil 

filename can be up to 200 characters in length based on the default parameters in AERMOD. 

Double quotes (“) at the beginning and end of the filename can also be used as field delimiters to 

allow filenames with embedded spaces. Source ranges, which are described in more detail in 

Section 3.3.3 of the AERMOD User’s Guide (EPA, 2004a), are input as two source IDs 

separated by a dash, e.g., STACK1-STACK10. The user may include more than one 

HOUREMIS card in a runstream file, if needed to specify additional sources, but there can be 

only one hourly emissions file, and therefore the filename must be the same on all HOUREMIS 

cards.

The format of each record of the hourly emissions file includes a pathway and keyword

(SO HOUREMIS), followed by the Year, Month, Day, Hour, Source ID, and emission rate (in 

the appropriate units). For POINT sources, the stack gas exit temperature (K), and stack gas exit

velocity (m/s) are also specified. Beginning with version 09292, the release heights and initial 

dispersion coefficients can also be varied on an hourly basis for AREA, AREAPOLY, 

AREACIRC, and VOLUME sources using the HOUREMIS option. The user selects this 

enhanced option by including the additional source parameters in the hourly emissions file. 

AERMOD determines whether hourly release heights and initial dispersion coefficients are being 

used based on the first HOUREMIS record for each source, and these additional parameters must 
72

be included on all HOUREMIS records unless the emissions are missing, which is indicated by 

leaving the emission rate and all fields beyond the source ID blank. 

The hourly emissions file is processed using the same routines used to process the 

runstream input file, therefore each of the parameters must be separated by at least one space, but 

otherwise the format is flexible. It is also not necessary to include the SO HOUREMIS on each 

line, as long as the parameters (Year, Month, etc.) do not begin before column 13. The data in 

the hourly emission file must also include the exact same dates as are included in the 

meteorological input files, and the source IDs must correspond to the source IDs defined on the 

SO LOCATION cards and be in the same order as defined in the ‘aermod.inp’ file. 

The model will check for a date mismatch between the hourly emissions file and the 

meteorological data, and also for a source ID mismatch. However, it is not necessary to process 

the entire hourly emissions file on each model run, i.e., the correct emissions data will be read if 

the ME DAYRANGE or the ME STARTEND cards (see Section 3.5.4 of the AERMOD User’s 

Guide) are used, as long as all the dates (including those that are processed and those that are 

skipped) match the meteorological data files. 

An example of several lines from an hourly emissions file for two point sources is 

provided below:

The use of hourly varying release heights and initial dispersion coefficients for VOLUME and 

AREA sources is illustrated in the following example:

SO HOUREMIS 88 8 16 1 STACK1 52.5 382.60 12.27

SO HOUREMIS 88 8 16 1 STACK2 44.3 432.33 22.17

SO HOUREMIS 88 8 16 2 STACK1 22.3 377.88 9.27

SO HOUREMIS 88 8 16 2 STACK2 42.2 437.68 19.67

SO HOUREMIS 88 8 16 3 STACK1 51.5 373.72 11.87

SO HOUREMIS 88 8 16 3 STACK2 41.3 437.28 18.77

SO HOUREMIS 88 8 16 4 STACK1 36.0 374.83 9.63

SO HOUREMIS 88 8 16 4 STACK2 43.7 437.68 18.23
73

For POINT sources, the model will use the stack release height and stack inside diameter defined 

on the SO SRCPARAM card, but will use the emission rate, exit temperature and exit velocity 

from the hourly emission file. As noted above regarding VOLUME and AREA sources, if the 

emission rate, exit temperature and exit velocity are not included for a particular hour, i.e, any or 

all of those fields are blank, the model will interpret emissions data for that hour as missing and 

will set the parameters to zero. Since the emission rate will be zero, there will be no calculations 

made for that hour and that source.

2.8 OUTPUT OPTIONS

A number of enhancements have been incorporated in AERMOD, beginning with version 

11059, to more fully support the form of the new 1-hour NO2 and SO2 standards, as well as the 

24-hour PM2.5 standard. The form of these NAAQS are similar in that they are based on a 

ranked percentile value averaged over the number of years processed. In order to support 

implementation of recent guidance regarding modeling to demonstrate compliance with these 

NAAQS, the RECTABLE keyword had been modified to allow user-specified ranks of shortterm averages (for all pollutants) up to the 999th highest value. The previous version of 

AERMOD was limited to the 10th-highest value and also restricted the rank for the 24-hour 

PM2.5 NAAQS to the 8th highest value (corresponding to the 98th percentile of daily values 

during a year).

2.8.1 Output Options for 24-hour PM2.5 and 1-hour NO2 and SO2 Standards

Beginning with version 11059, three output options have been incorporated on the OU 

pathway to support the 1-hour NO2 and SO2 standards, especially the analyses that may be 

required to determine a source’s (or group of sources) contributions to modeled violations of the 

SO HOUREMIS 88 3 1 1 VOL1 500.0 2.0 2.0 2.0

SO HOUREMIS 88 3 1 1 AREA1 5.000 2.0 2.0

SO HOUREMIS 88 3 1 2 VOL1 500.0 2.0 2.0 3.0

SO HOUREMIS 88 3 1 2 AREA1 5.000 2.0 3.0

SO HOUREMIS 88 3 1 3 VOL1 500.0 2.0 2.0 4.0

SO HOUREMIS 88 3 1 3 AREA1 5.000 2.0 4.0
74

NAAQS for comparison to the Significant Impact Level (SIL). The form of the standards, based 

on averages of ranked values across years, complicates this analysis, especially for the 1-hour 

NO2 and SO2 standards which are based on ranked values from the distribution of daily 

maximum 1-hour averages. One of the options (MAXDCONT) can also be used for the 24-hour 

PM2.5 NAAQS.

The MAXDCONT option, applicable to 24-hour PM2.5, 1-hour NO2 and 1-hour SO2

standards, can be used to determine the contribution of each user-defined source group to the 

high ranked values for a target source group, paired in time and space. This is accomplished as 

an internal post-processing routine after the main model run is completed. The user can specify 

the range of ranks to analyze, or can specify an upper bound rank, e.g., 8th-highest for 1-hour 

NO2 (note that “upper bound” rank implies a higher concentration, while “lower bound” rank 

implies a lower concentration), and a threshold value, such as the NAAQS, for the target source 

group. The model will process each rank within the range specified, but will stop after the first 

rank (in descending order of concentration) that is below the threshold. 

The syntax, type and order of the optional MAXDCONT keyword are summarized 

below:

Syntax: OU MAXDCONT GrpID UpperRank LowerRank FileName (FileUnit)

 or

OU MAXDCONT GrpID UpperRank THRESH ThreshValue FileName (FileUnit)

Type: Optional, Repeatable

where GrpID is the target or reference source group toward which contributions are being 

determined, UpperRank and LowerRank are the upper bound and lower bound ranks (where 

upper bound rank implies higher concentrations and lower bound rank implies lower 

concentrations), THRESH indicates that the lower bound rank is determined based on a lower 

concentration threshold, ThreshValue is the user-specified concentration threshold for GrpID 

impacts which serves as a lower bound on the range of ranks analyzed, FileName is the output 

file name, and (FileUnit) is the optional file unit. The filename can be up to 200 characters in 

length based on the default parameters in AERMOD. Double quotes (“) at the beginning and 
75

end of the filename can also be used as field delimiters to allow filenames with embedded 

spaces. When the THRESH option is selected AERMOD will skip the contribution analysis for 

any receptor where the target GrpID impact is less than the threshold, and will stop processing 

completely after the first rank where the target GrpID values are below the threshold for all 

receptors. NOTE: It is important note that the range of ranks that can be analyzed under 

the MAXDCONT option is limited to the range of ranks (not the individual ranks) 

specified on the OU RECTABLE keyword, even when the THRESH option is used in lieu 

of specifying a LowerRank value. AERMOD will issue a fatal error if the THRESH option 

is used and the range of ranks is less than or equal to 8 for the 1-hr SO2 NAAQS, or less 

than or equal to 12 for the 1-hr NO2 and 24-hr PM2.5 NAAQS. Non-fatal warning 

messages will be generated if the THRESH option is used and the range of ranks is less 

than or equal to 24 for the 1-hr SO2 NAAQS, or less than or equal to 28 for the 1-hr NO2 

and 24-hr PM2.5 NAAQS. 

When the MAXDCONT option is specified, AERMOD stores all meteorological 

variables in memory for each hour during the initial stage of processing in order to optimize the 

model runtime during the post-processing stage. Any temporally-varying emissions and

background concentrations, including background ozone concentrations for the OLM and 

PVMRM options, are also stored in memory for each hour. While optimizing runtime for the 

post-processing, this approach may also significantly increase the memory storage requirements 

of the model. In addition, since the MAXDCONT option extracts meteorological variables and 

other temporally-varying data stored in memory to optimize runtime, the MAXDCONT option 

cannot be used with the model “re-start” option using the INITFILE and SAVEFILE keywords 

on the CO pathway, or with the MULTYEAR option on the CO pathway. 

The MAXDAILY option, introduced with version 11059, is applicable to 1-hour NO2 and 

1-hour SO2 NAAQS and generates a file of daily maximum 1-hour concentrations for a specified 

source group, for each day in the data period processed. The MAXDAILY file provides an 

interim output that may be useful for analyzing the 1-hour NO2 and SO2 NAAQS. The syntax, 

type and order of the optional MAXDAILY keyword are summarized below:
76

Syntax: OU MAXDAILY GrpID FileName (FileUnit)

Type: Optional, Non-repeatable

where GrpID is the source group selected for daily maximum 1-hour values, FileName is the 

name of the MAXDAILY output file, and FileUnit is the optional file unit. The filename can be 

up to 200 characters in length based on the default parameters in AERMOD. Double quotes (“) 

at the beginning and end of the filename can also be used as field delimiters to allow filenames 

with embedded spaces. 

Another option applicable to 1-hour NO2 and 1-hour SO2 NAAQS introduced with 

version 11059, the MXDYBYYR keyword, generates a summary of daily maximum 1-hour 

concentrations by year for each rank specified on the RECTABLE keyword. The data periods 

included in the MXDYBYYR file are the periods used in the MAXDCONT postprocessing 

option. The syntax, type and order of the optional MXDYBYYR keyword are summarized 

below:

Syntax: OU MXDYBYYR GrpID FileName (FileUnit)

Type: Optional, Non-repeatable

where GrpID is the source group selected for daily maximum 1-hour values summarized by year, 

FileName is the name of the MXDYBYYR output file, and FileUnit is the optional file unit. The 

filename can be up to 200 characters in length based on the default parameters in AERMOD. 

Double quotes (“) at the beginning and end of the filename can also be used as field delimiters to 

allow filenames with embedded spaces. 

2.8.2 Miscellaneous Output Options

The optional SUMMFILE keyword can be used to generate a separate formatted output 

file containing the summary of high ranked values included at the end of the standard 

‘aermod.out’ file. The optional FILEFORM keyword can be used to specify the use of 

exponential notation, rather than fixed format as currently used, for results that are output to 
77

separate result files. The optional NOHEADER keyword can be used to suppress file headers in 

formatted output file options. These new options are described below.

The syntax, type and order of the optional SUMMFILE keyword are summarized below:

Syntax: OU SUMMFILE SummFileName

Type: Optional, Non-repeatable

where the SummFileName is the name of the external file containing the summary of high 

ranked values. The SUMMFILE filename can be up to 200 characters in length based on the 

default parameters in AERMOD. Double quotes (“) at the beginning and end of the filename can 

also be used as field delimiters to allow filenames with embedded spaces. In addition to the 

summary of high ranked values, the SUMMFILE also includes the “MODEL SETUP OPTIONS 

SUMMARY” page from the main ‘aermod.out’ file.

The syntax, type and order of the optional FILEFORM keyword are summarized below:

Syntax: OU FILEFORM EXP or FIX

Type: Optional, Non-repeatable

where the EXP parameter specifies that output results files will use exponential-formatted 

values, and the FIX parameter specifies that the output results files will use fixed-formatted 

values. The default option is to use fixed-formatted results, so use of FILEFORM = ‘FIX’ is 

extraneous. Note that AERMOD only examines the first three characters of the input field, so 

that the full terms of ‘EXPONENTIAL’ or ‘FIXED’ can also be used. The format specified on 

this optional keyword is applicable to PLOTFILEs, plot-formatted POSTFILEs, MAXIFILEs, 

RANKFILEs, and SEASONHR files, but will not affect the format of results in the standard 

‘aermod.out’ file or the optional SUMMFILE. The FILEFORM optional may be useful to 

preserve precision in applications with relatively small impacts, especially for the purpose of 

post-processing hourly concentrations using the POSTFILE option. The option may also be 

useful for applications with relatively large impacts that may overflow the Fortran format 
78

specifier of F13.5 used for fixed-formatted outputs. AERMOD will issue a warning message if 

values that exceed the range allowed for fixed-format are detected unless the FILEFORM EXP 

option has been selected.

The syntax, type and order of the optional NOHEADER keyword are summarized below:

Syntax: OU NOHEADER FileType1 FileType2 FileType3 ... FileTypeN

 or

OU NOHEADER ALL

Type: Optional, Non-repeatable

where FileTypeN identifies the keywords for formatted output files for which the file headers 

will be suppressed, which may include the includes the following file types: POSTFILE, 

PLOTFILE, MAXIFILE, RANKFILE, SEASONHR, MAXDAILY, MXDYBYYR, and 

MAXDCONT. The keyword ALL may be used to specify that header records will be suppressed 

for ALL applicable output file types.

2.9 MODEL STORAGE LIMITS

The AERMOD model has been designed using a dynamic storage allocation approach,

where the model allocates data storage as needed based on the number of sources, receptors,

source groups, and input requirements, up to the maximum amount of memory available on the 

computer being used. The AERMOD model uses dynamic arrays to allocate data storage at 

model runtime rather than at compile time. The AERMOD model preprocesses the model 

runstream input file to determine the data storage requirements for a particular model run, and 

then allocates the input data arrays before processing the setup data. Once the setup processing is 

completed, the model allocates storage for the result arrays. When allocating data storage, the 

AERMOD model traps for errors, e.g., not enough memory available to allocate. If the allocation 

is unsuccessful, then an error message is generated by the model and further processing is 

prevented. If the CO RUNORNOT NOT option is selected, the model will still go through all 

array allocations so that the user can determine if sufficient memory is available to complete the 
79

run. Also, an estimate of the total amount of memory needed for a particular run is printed out as 

part of the first page of printed output.

The storage parameters that are established at model runtime are as follows:

NSRC = Number of Sources

NREC = Number of Receptors

NGRP = Number of Source Groups

NOLM = Number of OLM Groups (OLMGROUP Keyword)

NAVE = Number of Short Term Averaging Periods

NVAL = Number of High Values by Receptor (RECTABLE Keyword)

NTYP = Number of Output Types (CONC currently is the only output type)

NMAX = Number of Overall Maximum Values (MAXTABLE Keyword)

NQF = Number of Variable Emission Rate Factors per Source

NPDMAX = Number of Particle Diameter Categories per Source

NVMAX = Number of Vertices for Area Sources (including AREA, AREACIRC, and 

AREAPOLY source types) and/or OPENPIT Sources

NSEC = Number of Sectors for Building Downwash Parameters (set to 36 if 

downwash sources are included)

NURB = Number of Urban Areas (URBANOPT Keyword)

NNET = Number of Cartesian and/or Polar Receptor Networks

IXM = Number of X-coord (Distance) Values per Receptor Network

IYM = Number of Y-coord (Direction) Values per Receptor Network

NARC = Number of Receptor Arcs Used with EVALCART Keyword

NEVE = Number of Events for EVENT processing

The MAXDCONT option on the OU pathway introduced with version 11059 to 

determine source group contributions to modeled values under the 24-hr PM2.5 and 1-hr SO2 

and NO2 NAAQS can significantly increase the memory requirements of AERMOD due to the 

fact that all meteorological and other variables needed to perform the MAXDCONT processing 

are stored in memory in order to optimize model runtime. The memory requirements for the 
80

MAXDCONT have been optimized with version 12060, and a new option on the ME pathway 

was also introduced with version 12060 to further reduce memory requirements for applications 

involving less than five (5) years of meteorological data, e.g., if one or more years of sitespecific meteorological data area being used. The NUMYEARS keyword on the ME pathway 

allows the user to specify the number of years of data being processed for purposes of allocating 

array storage for the MAXDCONT option, with a default value of five (5) years being assumed 

if the optional NUMYEARS keyword is omitted. The syntax of the optional NUMYEARS 

keyword is summarized below:

Syntax: ME NUMYEARS NumYrs

Type: Optional, Non-repeatable

where NumYrs specifies the number of (full) years of meteorological data being processed.
81

3.0 REFERENCES

AECOM, 2010: AERMOD Low Wind Speed Evaluation Study Results, AECOM Environment, 

Westford, MA.

API, 2013: Ambient Ratio Method Version 2 (ARM2) for use with AERMOD for 1-hr NO2 

Modeling: Development and Evaluation Report. American Petroleum Institute, Washington, DC.

http://www.epa.gov/ttn/scram/models/aermod/ARM2_Development_and_Evaluation_ReportSeptember_20_2013.pdf

Cimorelli, A. J., S. G. Perry, A. Venkatram, J. C. Weil, R. J. Paine, R. B. Wilson, R. F. Lee, W. 

D. Peters, R. W. Brode, and J. O. Paumier, 2004: AERMOD: Description of Model 

Formulation. EPA 454/R-03-004. U. S. Environmental Protection Agency, Research Triangle 

Park, North Carolina 27711.

EPA, 1995a: User=s Guide for the Industrial Source Complex (ISC3) Dispersion Models, 

Volume I - User Instructions. EPA-454/B-95-003a. U.S. Environmental Protection Agency, 

Research Triangle Park, North Carolina 27711.

EPA, 1995b: User=s Guide for the Industrial Source Complex (ISC3) Dispersion Models, 

Volume II - Description of Model Algorithms. EPA-454/B-95-003b. U.S. Environmental 

Protection Agency, Research Triangle Park, North Carolina 27711.

EPA, 2000. Meteorological Monitoring Guidance for Regulatory Modeling Applications. EPA454/R-99-005. Office of Air Quality Planning & Standards, Research Triangle Park, NC. (PB 

2001-103606)

EPA, 2003: AERMOD Deposition Algorithms - Science Document (Revised Draft). U.S. 

Environmental Protection Agency, Research Triangle Park, North Carolina 27711.

EPA, 2004a: User=s Guide for the AMS/EPA Regulatory Model - AERMOD. EPA454/B-03-001. U.S. Environmental Protection Agency, Research Triangle Park, North Carolina 

27711.

EPA, 2004b: User=s Guide for the AERMOD Meteorological Processor (AERMET). EPA454/B-03-002. U.S. Environmental Protection Agency, Research Triangle Park, North Carolina 

27711. 

EPA, 2005: Guideline on Air Quality Models, Appendix W to 40 CFR Part 51. U.S. 

Environmental Protection Agency, Research Triangle Park, North Carolina 27711.

http://www.epa.gov/ttn/scram/guidance/guide/appw_05.pdf

EPA, 2007: AERMOD Modeling System Update. Presented at EPA R/S/L Modelers 

Workshop, Virginia Beach, VA

http://www.cleanairinfo.com/regionalstatelocalmodelingworkshop/archive/2007/presentations/T

uesday%20-%20May%2015%202007/AERMOD_Modeling_System_Update.pdf
82

EPA, 2009: AERMOD Implementation Guide (Revised March 19, 2009), U.S. Environmental 

Protection Agency, Research Triangle Park, North Carolina 27711.

http://www.epa.gov/ttn/scram/7thconf/aermod/aermod_implmtn_guide_19March2009.pdf

EPA, 2008: Risk and Exposure Assessment to Support the Review of the NO2 Primary National 

Ambient Air Quality Standard. EPA-452/R-08-008a. U.S. Environmental Protection Agency, 

Research Triangle Park, North Carolina 27711.

EPA, 2010a: Modeling Procedures for Demonstrating Compliance with PM2.5 NAAQS. 

Stephen D. Page Memorandum, dated March 23, 2010. U.S. Environmental Protection Agency, 

Research Triangle Park, North Carolina 27711.

EPA, 2010b: Applicability of Appendix W Modeling Guidance for the 1-hour NO2 National 

Ambient Air Quality Standard. Tyler Fox Memorandum, dated June 28, 2010. U.S. 

Environmental Protection Agency, Research Triangle Park, North Carolina 27711.

EPA, 2010c: Applicability of Appendix W Modeling Guidance for the 1-hour SO2 National 

Ambient Air Quality Standard. Tyler Fox Memorandum, dated August 23, 2010. U.S. 

Environmental Protection Agency, Research Triangle Park, North Carolina 27711.

EPA, 2011: Additional Clarification Regarding Application of Appendix W Modeling Guidance 

for the 1-hour NO2 National Ambient Air Quality Standard. Tyler Fox Memorandum, dated 

March 1, 2011. U.S. Environmental Protection Agency, Research Triangle Park, North Carolina 

27711.

EPA, 2014: Guidance for PM2.5 Modeling. May 20, 2014, Publication No. EPA-454/B-14-001. 

Office of Air Quality Planning & Standards, Research Triangle Park, NC. 

http://www.epa.gov/ttn/scram/guidance/guide/Guidance_for_PM25_Permit_Modeling.pdf.

EPA, 2015: Technical support document (TSD) for NO2-related AERMOD modifications. July

2015, Publication No. EPA-454/B-15-004. Office of Air Quality Planning & Standards, 

Research Triangle Park, NC.

Hanrahan, P.L., 1999a. "The plume volume molar ratio method for determining NO2/NOx ratios 

in modeling. Part I: Methodology," J. Air & Waste Manage. Assoc., 49, 1324-1331.

Hanrahan, P.L., 1999b. "The plume volume molar ratio method for determining NO2/NOx ratios 

in modeling. Part II: Evaluation Studies," J. Air & Waste Manage. Assoc., 49, 1332-1338.

Luhar, A.K., and K. N. Rayner, 2009: “Methods to Estimate Surface Fluxes of Momentum and 

Heat from Routine Weather Observations for Dispersion Applications under Stable 

Stratification”, Boundary-Layer Meteorology, 132, 437–454.

Qian, W., and A. Venkatram, 2011: "Performance of Steady-State Dispersion Models Under 

Low Wind-Speed Conditions", Boundary Layer Meteorology, 138, 475-491. 
83

Walcek, C., G. Stensland, L. Zhang, H. Huang, J. Hales, C. Sweet, W. Massman, A. Williams, J, 

Dicke, 2001: Scientific Peer-Review of the Report "Deposition Parameterization for the 

Industrial Source Complex (ISC3) Model." The KEVRIC Company, Durham, North Carolina.

Wesely, M.L, P.V. Doskey, and J.D. Shannon, 2002: Deposition Parameterizations for the 

Industrial Source Complex (ISC3) Model. Draft ANL report ANL/ER/TRB01/003, DOE/xxnnnn, Argonne National Laboratory, Argonne, Illinois 60439.

Note: All references listed here, with the exception of AECOM (2010), Hanrahan (1999a and 

1999b), Qian and Venkatram (2011), Luhar and Rayner (2009) and EPA (2008), can be found 

on the U.S. EPA SCRAM website at the following url: http://www.epa.gov/ttn/scram/
A-1

APPENDIX A. ALPHABETICAL KEYWORD REFERENCE

This appendix provides an alphabetical listing of all of the keywords used by the 

AERMOD model. Each keyword is identified as to the pathway for which it applies, the

keyword type (either mandatory or optional, and either repeatable or non-repeatable), and with a 

brief description of the function of the keyword. For a more complete description of the 

keywords, including a list of associated parameters, refer to Section 2.0 of this Addendum, the 

Functional Keyword/Parameter Reference in Appendix B of this Addendum, and/or the Detailed 

Keyword Reference in Section 3 of the AERMOD User’s Guide (EPA, 2004a).
A-2

Keyword Path Type Keyword Description

AREAVERT SO M – R Specifies location of vertices for an AREAPOLY source type 

(mandatory if AREAPOLY source is used)

ARMRATIO CO O - N Option to override default minimum and maximum (equilibrium)

ratios for the ARM or ARM2 options

AVERTIME CO M – N Averaging time(s) to process 

BACKGRND SO O – R Option to specify temporally varying background concentrations

BACKUNIT SO O – N Option to specify units for background concentrations

BGSECTOR SO O – N Option to specify wind sectors for use in varying background 

concentrations of the pollutant being modeled by wind direction.

BUILDHGT SO O – R Building height values for each wind sector

BUILDLEN SO O – R Building projected length values for each wind sector

BUILDWID SO O – R Building projected width values for each wind sector

CONCUNIT CO O – N Optional conversion factors for emission input units and 

concentration output units

DAYRANGE ME O – R Specifies days or ranges of days to process (default is to process all 

data)

DAYTABLE OU O – N Option to provide summaries for each averaging period for each 

day processed.

DCAYCOEF CO O – N Optional decay coefficient for exponential decay

DEBUGOPT CO O – N Option to generate detailed result and meteorology files for 

debugging purposes

DEPOUNIT SO O – N Optional conversion factors for emission input units and deposition 

output units

DISCCART RE O – R Defines discretely placed receptors referenced to a Cartesian 

system

DISCPOLR RE O – R Defines discretely placed receptors referenced to a polar system

ELEVUNIT SO

RE

O – N

O – N

Defines input units for receptor elevations (RE path), or source 

elevations (SO path) (defaults to meters)

EMISFACT SO O – R Optional input for variable emission rate factors

EMISUNIT SO O – N Optional conversion factors for emission units and concentration 

units

ERRORFIL CO O – N Option to generate detailed error listing file (error file is mandatory 

for CO RUNORNOT NOT case)

EVALCART RE O – R Defines discretely placed receptor locations referenced to a 

Cartesian system, grouped by arc for use with the EVALFILE 

output option

EVALFILE OU O – R Option to output file of normalized arc maxima for model 

evaluation studies
A-3

Keyword Path Type Keyword Description

EVENTFIL CO O – N Specifies whether to generate an input file for EVENT model

EVENTLOC EV M – R Describes receptor location for an event

EVENTOUT OU M – N Specifies level of output information provided by the EVENT 

model

EVENTPER EV M – R Describes data and averaging period for an event

FILEFORM OU O – N Specify fixed or exponential format for output results files

FINISHED ALL M – N Identifies the end of inputs for a particular pathway

FLAGPOLE CO O – N Specifies whether to accept receptor heights above local terrain (m) 

for use with flagpole receptors, and allows for a default flagpole 

height to be specified

GASDEPDF CO O – N Option to override default parameters for gas dry deposition

GASDEPOS SO O – R Specify source parameters for gas deposition algorithms

GASDEPVD CO O – N Option to specify deposition velocity for gas dry deposition

GDLANUSE CO O – N Specify land use categories by sector for gas dry deposition

GDSEASON CO O – N Specify seasonal definitions for gas dry deposition

GRIDCART RE O – R Defines a Cartesian grid receptor network

GRIDPOLR RE O – R Defines a polar receptor network

HALFLIFE CO O – N Optional half-life for exponential decay

HOUREMIS SO O – R Option for specifying hourly emission rates in a separate file

INCLUDED SO, 

RE, EV 

O – R Option to include input data from a separate file in the runstream 

for the SO and/or RE pathways, or for the EV pathway for 

EVENTs

INITFILE CO O – N Option to initialize model from file of intermediate results 

generated by SAVEFILE option

LOCATION SO M – R Identifies coordinates for particular source location

LOW_WIND CO O – N Option for user-specified parameters for the LOWWIND1 and 

LOWWIND2 BETA options

MASSFRAX SO O – R Optional input of mass fraction for each particle size category

MAXDAILY OU O – R Option to output file of daily maximum 1-hour values for each day 

processed; only applicable for 1-hour NO2 and 1-hour SO2 NAAQS

MAXDCONT OU O – R Option to output contributions of each source group to ranked 

values averaged across years for a reference source group, paired in 

time and space; only applicable for 24-hour PM2.5, 1-hour NO2, 

and 1-hour SO2 NAAQS

MAXIFILE OU O – R Option to list events exceeding a threshold value to file (if CO 

EVENTFIL option is used, these events are included in the input

file generated for the EVENT model)

MAXTABLE OU O – R Option to summarize the overall maximum values
A-4

Keyword Path Type Keyword Description

METHOD_2 SO O – R Specify optional source parameters for METHOD_2 option for 

particle deposition

MODELOPT CO M – N Job control and dispersion options

MULTYEAR CO O – N Specifies that run is part of a multi-year run, e.g., for PM-10 H6H 

in five years

MXDYBYYR OU O – R Option to output file of daily maximum 1-hour values by year, for 

each year processed; only applicable for 1-hour NO2 and 1-hour 

SO2 NAAQS

NOHEADER OU O – N Option to suppress file headers for output file options, e.g., 

POSTFILE, PLOTFILE, MAXDCONT, etc

NO2EQUIL CO O – N Option to override default NO2/NOx equilibrium ratio for PVMRM

or OLM

NO2RATIO SO O – R Option to specify in-stack NO2/NOx equilibrium ratio for OLM and 

PVMRM options by source

NO2STACK CO O – N Option to specify default in-stack NO2/NOx equilibrium ratio for 

OLM and PVMRM options; may be overridden by NO2RATIO

NUMYEARS ME O – N Option to specify the number of years of meteorological data being 

processed for purposes of allocating array storage for the OU 

MAXDCONT option

OLMGROUP SO O – R Specifies sources to combine for OLM option for merging plumes

OZONEFIL CO O – N Specifies hourly ozone file for OLM and PVMRM options

OZONEVAL CO O – N Specifies background value of ozone for OLM and PVMRM 

options

OZONUNIT CO O – N Option to specify units for temporally-varying ozone 

concentrations for the O3VALUES keyword.

O3SECTOR CO O – N Option to specify wind sectors for use in varying background ozone 

(O3) concentrations by wind direction for use with OLM and 

PVMRM options.

O3VALUES CO O – R Option to specify temporally varying ozone concentrations for use 

with OLM and PVMRM options for estimating NO2

PARTDENS SO O – R Specifies particle density by size category for particle deposition

PARTDIAM SO O – R Specifies particle diameters by size category for particle deposition

PLOTFILE OU O – R Option to write certain results to a storage file suitable for input to 

plotting routines

POLLUTID CO M – N Identifies pollutant being modeled

POSTFILE OU O – R Option to write results to a mass storage file for postprocessing

PROFBASE ME M – N Specifies the base elevation for the potential temperature profile

PROFFILE ME M – N Describes input profile meteorological data file
A-5

Keyword Path Type Keyword Description

PSDGROUP SO O – R Specifies source groups for PSDCREDIT option with PVMRM

RANKFILE OU O – R Option to produce output file of ranked values for Q-Q plots

RECTABLE OU O – R Option to output high ranked value(s) by receptor

RUNORNOT CO M – N Identifies whether to run model or process setup information only

SAVEFILE CO O – N Option to store intermediate results for later restart of the model 

after user or system interrupt

SCIMBYHR ME O – N Specifies sampling parameters for the SCIM option

SEASONHR OU O – R Option to output values by season and hour-of-day 

SITEDATA ME O – N Describes on-site meteorological station

SRCGROUP SO M – R Identification of source groups

SRCPARAM SO M – R Identifies source parameters for a particular source

STARTEND ME O – N Specifies start and end dates to be read from input meteorological 

data file (default is to read entire file)

STARTING ALL M – N Identifies the start of inputs for a particular pathway

SUMMFILE OU O – N Option to output summary of high ranked values to separate file

SURFDATA ME M – N Surface meteorological station

SURFFILE ME M – N Describes input surface meteorological data file

TITLEONE CO M – N First line of title for output

TITLETWO CO O – N Optional second line of output title

TOXXFILE OU O – R Creates output file for use with TOXX model component of 

TOXST

UAIRDATA ME M – N Upper air meteorological station

URBANOPT CO O – R Option to specify population for urban option

URBANSRC SO O – R Option to specify use of urban option by source

WDROTATE ME O – N Wind direction rotation adjustment

WINDCATS ME O – N Upper bound of wind speed categories

XBADJ SO O – R Along-flow distances from the stack to the center of the upwind 

face of the projected building

YBADJ SO O – R Across-flow distances from the stack to the center of the upwind 

face of the projected building
B-1

APPENDIX B. FUNCTIONAL KEYWORD/PARAMETER REFERENCE

This appendix provides a functional reference for the keywords and parameters used by 

the input runstream files for the AERMOD model. The keywords are organized by functional 

pathway, and within each pathway the order of the keywords is based on the function of the 

keyword within the preprocessor. The pathways used by the preprocessor are as follows, in the 

order in which they appear in the runstream file and in the tables that follow:

CO - for specifying overall job COntrol options; and

SO - for specifying SOurce location information (optional);

RE - for specifying REceptor information; and

ME - for specifying MEteorology information and options;

EV - for specifying EVent information and options;

OU - for specifying OUtput file information.

The pathways and keywords are presented in the same order as in the Detailed Keyword 

Reference in Section 3 of the AERMOD User’s Guide (EPA, 2004a), and in the Quick Reference 

at the end of the manual, with the exception of new keywords that are not reflected in the 

original user’s guide.

Two types of tables are provided for each pathway. The first table lists all of the 

keywords for that pathway, identifies each keyword as to its type (either mandatory or optional 

and either repeatable or non-repeatable), and provides a brief description of the function of the 

keyword. The second type of table presents the parameters for each keyword, in the order in 

which they should appear in the runstream file where order is important, and describes each 

parameter in detail.

The following convention is used for identifying the different types of input parameters. 

Parameters corresponding to secondary keywords which should be input "as is" are listed on the 

tables with all capital letters and are underlined, although none of the inputs to AERMOD are 

treated as case-sensitive. Other parameter names are given with an initial capital letter and are 

not input "as is." In all cases, the parameter names are intended to be descriptive of the input 

variable being represented, and they often correspond to the Fortran variable names used in the 
B-2

AERMOD code. Parentheses around a parameter indicate that the parameter is optional for that 

keyword. The default that is taken when an optional parameter is left blank is explained in the 

discussion for that parameter.
B-3

TABLE B-1

DESCRIPTION OF CONTROL PATHWAY KEYWORDS

CO Keywords Type Keyword Description

STARTING M – N Identifies the start of CONTROL pathway inputs

TITLEONE M – N First line of title for output

TITLETWO O – N Optional second line of title for output

MODELOPT M – N Job control and dispersion options

AVERTIME M – N Averaging time(s) to process

URBANOPT O – R Specifies parameters for urban dispersion option

POLLUTID M – N Identifies type of pollutant being modeled

HALFLIFE1 O – N Optional half life used for exponential decay

DCAYCOEF1 O – N Optional decay coefficient

GASDEPDF O – N Option to override default parameters for gas dry deposition

GASDEPVD O – N Option to specify deposition velocity for gas dry deposition

GDLANUSE O – N Specify land use categories by sector for gas dry deposition

GDSEASON O – N Specify seasonal definitions for gas dry deposition

LOW_WIND O – N Option for user-specified parameters for the LOWWIND1 and LOWWIND2 BETA 

options

NO2EQUIL O – N Option to override default NO2/NOx equilibrium ratio for PVMRM or OLM

NO2STACK O – N Option to specify default in-stack NO2/NOx equilibrium ratio for OLM and 

PVMRM options; may be overridden by NO2RATIO option on SO pathway

ARMRATIO O – N Option to override default minimum and maximum (equilibrium) ratios for the 

ARM or ARM2 options

O3SECTOR O – N Specifies optional wind sectors for use in varying background ozone (O3) 

concentrations by wind direction for use with OLM and PVMRM options; can be 

used with the OZONEFIL, OZONEVAL, and O3VALUES options.

OZONEFIL O – R Specifies filename for hourly ozone file for use with OLM and PVMRM options

OZONEVAL O – R Specifies background value of ozone for use with OLM and PVMRM options

O3VALUES O – R Option to specify temporally varying ozone concentrations for use with OLM and 

PVMRM options for estimating NO2

OZONUNIT O – N Option to specify units for temporally-varying ozone concentrations for the 

O3VALUES keyword

FLAGPOLE O – N Specifies whether to accept receptor heights above local terrain (m) for use with 

flagpole receptors, and allows for default flagpole height to be specified

RUNORNOT M – N Identifies whether to run model or process setup information only
B-4

EVENTFIL2 O – N Specifies whether to generate an input file for EVENT model

SAVEFILE3 O – N Option to store intermediate results for restart of model after user or system interrupt

INITFILE3 O – N Option to initialize model from intermediate results generated by SAVEFILE option

MULTYEAR3 O – N Option to process multiple years of meteorological data (one year per run) and 

accumulate high short term values across years

DEBUGOPT O – N Option to generate detailed result and meteorology files for debugging purposes

ERRORFIL O – N Option to generate detailed error listing file

FINISHED M – N Identifies the end of CONTROL pathway inputs

Type: M – Mandatory N – Non-Repeatable

O – Optional R – Repeatable

1) Either HALFLIFE or DCAYCOEF may be specified. If both cards appear a warning message 

will be issued and the first value entered will be used in calculations. The DFAULT 

option assumes a half life of 4 hours for SO2 modeled in urban mode.

2) The EVENTFIL keyword controls whether or not to generate an input file for EVENT 

processing. The primary difference between AERMOD “regular” processing and EVENT 

processing by AERMOD is in the treatment of source group contributions. The AERMOD 

model treats the source groups independently, whereas EVENT processing determines 

individual source contributions to particular events, such as the design concentrations 

determined from AERMOD, or user-specified events. By specifying the EVENTFIL keyword, 

an input runstream file will be generated that can be used directly for EVENT 

processing. The events included in the generated EVENT processing input file are 

defined by the RECTABLE and MAXIFILE keywords on the OU pathway, and are placed in the 

EVent pathway.

3) The SAVEFILE and INITFILE keywords work together to implement the model's re-start 

capabilities. Since the MULTYEAR option utilizes the re-start features in a special 

way to accumulate high short term values from year to year, it cannot be used together 

with the SAVEFILE or INITFILE keyword in the same model run.
B-5

TABLE B-2

DESCRIPTION OF CONTROL PATHWAY KEYWORDS AND PARAMETERS

Keyword Parameters

TITLEONE Title1

 where: Title1 First line of title for output, character string of up to 68 characters 

(additional characters can be included on the TITLEONE keyword, 

but only the first 68 characters are printed in the output files).

TITLETWO Title2

 where: Title2 Optional second line of title for output, character string of up to 68 

characters (any additional characters are not printed)

MODELOPT DFAULT BETA CONC AREADPLT FLAT NOSTD NOCHKD NOWARN SCREEN SCIM PVMRM PSDCREDIT

 DEPOS and/or or or PVMRM2 

 DDEP ELEV WARNCHKD or OLM 

 and/or or ARM

 WDEP or ARM2

FASTALL DRYDPLT WETDPLT NOURBTRAN LOWWIND1 VECTORWS

 or or or or

FASTAREA NODRYDPLT NOWETDPLT LOWWIND2

 or

 LOWWIND3

 where: DFAULT

BETA

CONC

DEPOS

DDEP

WDEP

AREADPLT

FLAT

ELEV

NOSTD

NOCHKD

WARNCHKD

Specifies that regulatory default options will be used; specification of 

DFAULT option will override non-DFAULT options that may be 

specified

Non-DFAULT option that allows for draft, “Beta” test options to be 

used; includes PSDCREDIT option and capped and horizontal 

stack releases

Specifies that concentration values will be calculated

Specifies that total deposition flux values will be calculated

Specifies that dry deposition flux values will be calculated

Specifies that wet deposition flux values will be calculated

Specifies use of non-DFAULT method for optimized plume 

depletion due to dry removal mechanisms for area sources

Non-DFAULT option of assuming flat terrain will be used

Default option of assuming elevated terrain will be used;

Note: Both FLAT and ELEV may be specified in the same model 

run to allow specifying the non-DFAULT FLAT terrain option on 

a source-by-source basis (see the SO LOCATION keyword for 

specifying FLAT sources)

Non-DFAULT option of no stack-tip downwash will be used

Non-DFAULT option of suspending date checking will be used for 

non-sequential meteorological data files, also implemented when 

SCREEN option is specified

Specifies option for issuing warning messages rather than fatal errors 

for non-sequential meteorological data files 
B-6

Keyword Parameters

NOWARN

SCREEN

SCIM

PVMRM

PVMRM2

OLM

ARM

ARM2

PSDCREDIT

FASTALL

FASTAREA

DRYDPLT

NODRYDPLT

WETDPLT

NOWETDPLT

NOURBTRAN

LOWWIND1

LOWWIND2

LOWWIND3

VECTORWS

Option to suppress detailed listing of warning messages in the main 

output file will be used

Non-DFAULT option for running AERMOD in a screening mode 

for AERSCREEN will be used

Non-DFAULT Sampled Chronological Input Model (SCIM) option; 

applies to ANNUAL averages only; SCIM sampling parameters 

must be specified on the ME pathway

Non-DFAULT Plume Volume Molar Ratio Method (PVMRM) for 

NO2 conversion will be used 

Non-DFAULT Plume Volume Molar Ratio Method – 2 (PVMRM2) 

for NO2 conversion will be used 

Non-DFAULT Ozone Limiting Method (OLM) for NO2 conversion 

will be used 

DFAULT Ambient Ratio Method (ARM) for NO2 conversion will be 

used

Non- DFAULT Ambient Ratio Method – 2 (ARM2) for NO2

conversion will be used

Non-DFAULT BETA test option to calculate the increment 

consumption with PSD credits using the PVMRM option 

Non-DFAULT option to optimize model runtime for POINT, 

VOLUME and AREA sources (AREA optimizations formerly 

associated with TOXICS option) 

Non-DFAULT option to optimize model runtime for AREA sources 

(formerly associated with TOXICS option) 

Option to incorporate dry depletion (removal) processes associated 

with dry deposition algorithms; dry depletion will be used by 

default if dry deposition algorithms are invoked 

Option to disable dry depletion (removal) processes 

Option to incorporate wet depletion (removal) processes associated 

with wet deposition algorithms; wet depletion will be used by 

default if wet deposition algorithms are invoked

Option to disable wet depletion (removal) processes.

Non-DFAULT option to revert to the urban option as implemented

prior to version 11059 (see Section 2.1.1).

Non-DFAULT BETA option to address concerns regarding model 

performance under low wind speed conditions (see Section 

2.1.10). Cannot be used with LOWWIND2 or LOWWIND3

option.

Non-DFAULT BETA option to address concerns regarding model 

performance under low wind speed conditions (see Section 

2.1.10). Cannot be used with LOWWIND1 or LOWWIND3 

option.

Non-DFAULT BETA option to address concerns regarding model 

performance under low wind speed conditions (See Section 

2.1.10). Cannot be used with LOWWIND1 or LOWWIND2 

option.

Option to specify that input wind speeds are vector mean (or 
B-7

Keyword Parameters

resultant) wind speeds, rather than scalar means (see Section 

2.1.2). The VECTORWS option is not linked with the DFAULT 

option.

AVERTIME Time1 Time2 . . . TimeN MONTH PERIOD

 or

 ANNUAL

 where: TimeN

MONTH

PERIOD

ANNUAL

Nth optional averaging time (1, 2, 3, 4, 6, 8, 12, or 24-hr)

Option to calculate MONTHly averages 

Option to calculate averages for the entire data PERIOD; for the 

MULTYEAR option, the summary of highest PERIOD averages is 

based on the highest PERIOD average across the individual years 

processed with MULTYEAR

Option to calculate ANNUAL averages (assumes complete years); 

for multi-year meteorological data files, with and without the 

MULTYEAR option, the multi-year average of the ANNUAL 

values is reported

URBANOPT For multiple urban areas:

UrbanID Urbpop (Urbname) (UrbRoughness)

For single urban area:

Urbpop (Urbname) (UrbRoughness)

 where: UrbanID

UrbPop

(UrbName)

(UrbRoughness)

Specifies the alphanumeric urban ID (up to eight characters)

Specifies the population of the urban area

Specifies the name of the urban area (optional)

Specifies the urban surface roughness length, meters (optional, 

defaults to 1.0m; value other than 1.0m treated as non-DFAULT)

POLLUTID Pollut (H1H or H2H or INC)

 where: Pollut Identifies type of pollutant being modeled. Any name of up to eight 

characters may be used, e.g., SO2, NOX, CO, PM25, PM-2.5, 

PM10, PM-10, TSP or OTHER. 

NOTE: Some processing options are pollutant-specific, and 

require the user to specify the appropriate pollutant ID. For 

example, use of PM10, PM-10, PM25, PM2.5, PM-2.5, PM-25, 

LEAD, NO2, SO2, or OTHER allows for the use of the 

MULTYEAR option.

Use of PM25, PM2.5, PM-2.5, or PM-25, triggers special 

processing for the PM-2.5 NAAQS, based on values averaged 

across the number of years processed (see Section 2.1.5.1).

Use of NO2 or SO2 triggers special processing for their respective 

1-hr NAAQS based on daily maximum 1-hr concentrations, 

averaged across the number of years modeled if the CO 
B-8

Keyword Parameters

H1H or

H2H or

INC

AVERTIME keyword includes 1-hr averages (see Section 2.1.7).

Use of NO2 is required in order to use the OLM and PVMRM 

options for simulating conversion of NO to NO2.

Use of SO2 also triggers the use of a 4-hour half-life for SO2 decay 

for urban applications under the regulatory default option.

Use of the H1H or H2H or INC keyword (not case-specific) disables 

the special processing requirements associated the 1-hr NO2 and 

SO2 NAAQS and the 24-hr PM2.5 NAAQS. Specifying one of 

these keywords would allow for modeling PM2.5 24-hr 

increments which are based on the H2H value, and also allow 

evaluating NO2 options in AERMOD based on incomplete years

of field measurements.

HALFLIFE Haflif

 where: Haflif Half life used for exponential decay (s)

DCAYCOEF Decay

 where: Decay Decay coefficient for exponential decay (s-1) = 0.693/HAFLIF

GASDEPDF React F_Seas2 F_Seas5 (Refpoll)

 where: React

F_Seas2

F_Seas5

(Refpoll)

Value for pollutant reactivity factor (fo)

Fraction (F) of maximum green LAI for seasonal category 2

Fraction (F) of maximum green LAI for seasonal category 5

Optional name of reference pollutant

GASDEPVD Uservd

 where: Uservd User-specified dry deposition velocity (m/s) for gaseous pollutants

GDLANUSE Sec1 Sec2 ... Sec36

 where: Sec1

Sec2

.

.

Sec36

Land use category for winds blowing toward sector 1 (10 degrees)

Land use category for winds blowing toward sector 2 (20 degrees)

Land use category for winds blowing toward sector 36 (360 degrees)

GDSEASON Jan Feb ... Dec

 where: Jan

.

.

.

.

Dec

Seasonal category for January:

1 = Midsummer/Lush vegetation; 

2 = Autumn/Unharvested cropland; 

3 = Late autumn after harvest or Winter with no snow; 

4 = Winter with continuous snow cover; or

5 = Transitional spring/partial green coverage/short annuals)

Seasonal category for December
B-9

Keyword Parameters

LOW_WIND SVmin (WSmin) [for LOWWIND1]

SVmin (WSmin (FRANmax)) [for LOWWIND2]

SVmin (WSmin (FRANmax)) [for LOWWIND3]

 where: SVmin

(WSmin)

(FRANmax)

Minimum value of sigma-v, within a range of 0.01 to 1.0 m/s

Minimum value of wind speed, within a range of 0.01 to 1.0 m/s

Maximum value meander factor, within a range of 0.50 to 1.0 

inclusive

NO2EQUIL NO2Equil

 where: NO2Equil Equilibrium ratio of NO2/NOx for the PVMRM, PVMRM2, and 

OLM options; between 0.1 and 1.0, inclusive (default is 0.9)

NO2STACK NO2Ratio

 where: NO2Ratio Default in-stack ratio of NO2/NOx for PVMRM, PVMRM2, and 

OLM options, which may be overridden by NO2RATIO keyword 

on SO pathway. 

NOTE: Beginning with version 11059, AERMOD no longer 

assumes a default in-stack ratio of 0.1 for the OLM option.

ARMRATIO ARM_1hr (ARM_Ann) For ARM Option

 or

ARM2_Min ARM2_Max For ARM2 Option

 where: ARM_1hr

ARM_Ann

ARM2_Min

ARM2_Max

ARM ambient ratio for NO2/NOx applied for 1hr NO2 

concentrations, with a default value of 0.80

ARM ambient ratio for NO2/NOx applied for Annual NO2 

concentrations, with a default value of 0.75

Minimum ARM2 ambient ratio, with a default value of 0.20

Maximum ARM2 ambient ratio, with a default value of 0.90

O3SECTOR StartSect1 StartSect2 . . . StartSectN, where N is ≤ 6

 where: StartSect1 

StartSect2

.

.

StartSectN

Starting direction for the first sector

Starting direction for the second sector

.

.

Starting direction for the last sector

NOTE: The minimum sector width allowed is 30 degrees, and 

warning messages will be issued for sector widths less than 60 

degrees. Sector-varying O3 concentrations will be selected based 

on the flow vector, i.e., the downwind direction based on the 

wind direction specified in the surface meteorological data file.

OZONEFIL O3FileName (O3Units) (O3Format) (without O3SECTORs)

 or

SECTn O3FileName (O3Units) (O3Format) (with O3SECTORs)
B-10

Keyword Parameters

 where: SECTn

O3FileName

(O3Units)

(O3Format)

Applicable sector (n = 1 to 6) defined on the CO O3SECTOR 

keyword, if specified

Filename for hourly ozone data file (YR, MN, DY, HR, O3Value)

Units of ozone data (PPM, PPB, or UG/M3); default is UG/M3

Fortran format statement to read ozone file; default is FREE-format, 

i.e., comma or space-delimited data fields (Yr Mn Dy Hr 

O3Value). The O3Format parameter must include open and close 

parentheses, the date variables must be read as integers (Fortran I 

format), and the O3Value must be read as real (Fortran F, E, or D 

format), e.g., ‘(4I2,F8.3)’. The year may be specified as a 2-digit 

or 4-digit year, and the data period in the OZONEFIL must match 

the data period in the meteorological data files.

OZONEVAL O3Value (O3Units ) (without O3SECTORs)

 or

SECTn O3Value (O3Units) (with O3SECTOR)

 where: SECTn

O3Value

(O3Units)

Applicable sector (n = 1 to 6) defined on the CO O3SECTOR 

keyword, if specified

Background ozone concentration; also used to substitute for missing 

data in OZONEFIL

Units of ozone value (PPM, PPB, or UG/M3); default is UG/M3

O3VALUES O3Flag O3values(i), i=1,n) (without O3SECTORs)

 or

SECTn O3Flag O3values(i), i=1,n) (with O3SECTORs)

 where: SECTn

O3Flag 

O3values

Applicable sector (n = 1 to 6) defined on the CO O3SECTOR 

keyword, if specified

Background ozone values flag:

ANNUAL for annual; SEASON for seasonal; MONTH for 

monthly; HROFDY for hour-of-day; WSPEED for wind speed 

category; SEASHR for season-by-hour; HRDOW for emission 

rates vary by hour-of-day, and day-of-week [M-F, Sat, Sun]; 

HRDOW7 for emission rates vary by hour-of-day, and the seven 

days of the week [M, Tu, W, Th, F, Sat, Sun]; SHRDOW for 

season by hour-of-day by day-of-week (M-F,Sat,Sun); 

SHRDOW7 for season by hour-of-day by day-of-week 

(M,Tu,W,Th,F,Sat,Sun); MHRDOW for month by hour-of-day by 

day-of-week (M-F,Sat,Sun); MHRDOW7 for month by hour-ofday by day-of-week (M,Tu,W,Th,F,Sat,Sun)

Array of background concentrations, for: ANNUAL, n=1;

 SEASON, n=4; MONTH, n=12; HROFDY, n=24; 

 WSPEED, n=6; SEASHR, n=96; HRDOW, n=72; 

 HRDOW7, n=168; SHRDOW, n=288; SHRDOW7, n=672;

 MHRDOW, n=864; MHRDOW7, n=2016

NOTE: Background ozone values input through the O3VALUES 

keyword are assumed to be in units of PPB, unless modified by the 
B-11

Keyword Parameters

OZONUNIT keyword.

OZONUNIT OzoneUnits

 where: OzoneUnits Ozone concentration units for O3VALUES, specified as PPB for 

parts-per-billion, PPM for parts-per-million, or UG/M3 for 

micrograms/cubic-meter.

FLAGPOLE (Flagdf)

 where: (Flagdf) Default value for height of (flagpole) receptors above local ground, a 

default value of 0.0 m is used if this optional parameter is omitted

RUNORNOT RUN or NOT

 where: RUN

NOT

Indicates to run full model calculations

Indicates to process setup data and report errors, but to not run full 

model calculations

EVENTFIL (Evfile) (Evopt)

 where: (Evfile)

(Evopt)

Identifies the filename to be used to generate a file for input to 

EVENT model (Default=EVENTFIL.INP)

Optional parameter to specify the level of output detail selected for 

the EVENT model: either SOCONT or DETAIL (default is 

DETAIL if this parameter is omitted)

SAVEFILE (Savfil) (Dayinc) (Savfl2)

 where: (Savfil)

(Dayinc)

(Savfl2)

Specifies name of disk file to be used for storing intermediate results 

(default = SAVE.FIL); file is overwritten after each dump

Number of days between dumps (optional: default is 1)

Optional second disk filename to be used on alternate 

dumps - eliminates risk of system crash during the dump. If blank, 

file is overwritten each time.

INITFILE (Inifil)

 where: (Inifil) Specifies name of disk file of intermediate results to be used for 

initializing run (default = SAVE.FIL)

MULTYEAR (H6H) Savfil (Inifil)

 where: (H6H)

Savfil

(Inifil)

Optional field formerly used to specify that High-Sixth-High is being 

calculated for use in PM10 processing; no longer required

Specifies name of file to be used for storing results at the end of the 

year

Optional name of file used for initializing the results arrays from 

previous year(s). The Inifil parameter is not used for the first year 

in the multi-year run.

DEBUGOPT MODEL (Dbgfil) and/or METEOR (Dbmfil) and/or PRIME (Prmfil) and/or DEPOS

 and/or

[AREA (AreaDbFil) or LINE (LineDbFil)]
B-12

Keyword Parameters

 and/or

[PVMRM (Dbpvfil) or OLM (OLMfil) or ARM (ARMfil) or ARM2 (ARM2fil)]

 where: MODEL

(Dbgfil)

METEOR

(Dbmfil)

PRIME

(Prmfil)

DEPOS

AREA or

LINE

(AreaDbfil)

PVMRM

(Dbpvfil)

PVMRM2

(Dbpvfil)

OLM

(OLMfil)

ARM

(ARMfil)

ARM2

(ARM2fil)

Specifies that MODEL debugging output will be generated

Optional filename for the model calculation debug file (a default 

filename of ‘MODEL.DBG’ will be used if omitted)

Specifies that METEORological profile data file will be generated

Optional filename for the meteorological profile data file (a default 

filename of ‘METEOR.DBG’ will be used if omitted)

Specifies that PRIME debugging output will be generated

Optional filename for PRIME debug file (a default filename of 

‘PRIME.DBG’ will be used if omitted)

Specifies that DEPOSition debugging output will be generated, using 

default filenames of ‘GDEP.DAT’ for gas deposition and 

‘PDEP.DAT’ for particle deposition.

Specifies that AREA or LINE debugging output will be generated, 

including debugging outputs for OPENPIT sources, if included in 

the modeling.

Optional filename for AREA debug file (a default filename of 

‘AREA.DBG’ will be used if omitted)

Specifies that PVMRM debugging output will be generated

Optional filename for PVMRM debug file (a default filename of 

‘PVMRM.DBG’ will be used if omitted)

Specifies that PVMRM2 debugging output will be generated

Optional filename for PVMRM2 debug file (a default filename of 

‘PVMRM2.DBG’ will be used if omitted)

Specifies that OLM debugging output will be generated

Optional filename for OLM debug file (a default filename of 

‘OLM.DBG’ will be used if omitted)

Specifies that ARM debugging output will be generated

Optional filename for ARM debug file (a default filename of 

‘ARM.DBG’ will be used if omitted)

Specifies that ARM2 debugging output will be generated

Optional filename for ARM2 debug file (a default filename of 

‘ARM2.DBG’ will be used if omitted)

Note: The user can specify any of the applicable debug options 

for a particular model run, and the options can be specified in 

any order. However, the optional filenames must be specified 

immediately after the keyword option associated with the 

filename. Also note that debugging information that was 

written to the main ‘aermod.out’ file for the MODEL debug 

option prior to version 13350 is now written to the applicable 

debug file (either MODEL or PRIME), and beginning with 

version 14134 debug information for AREA/LINE/OPENPIT 

sources is written to the AREA debug file.

ERRORFIL (Errfil)

 where: (Errfil) Specifies name of detailed error listing file (default = ERRORS.LST)
B-13

TABLE B-3

DESCRIPTION OF SOURCE PATHWAY KEYWORDS

SO Keywords Type Keyword Description

STARTING M – N Identifies the start of SOURCE pathway inputs

ELEVUNIT O – N Defines input units for source elevations (defaults to meters), must be first 

keyword after SO STARTING if used.

LOCATION M – R Identifies coordinates for particular source

SRCPARAM M – R Identifies source parameters for a particular source

BUILDHGT O – R Building height values for each wind sector

BUILDLEN O – R Building projected length values for each wind sector

BUILDWID O – R Building projected width values for each wind sector

XBADJ O – R Along-flow distances from the stack to the center of the upwind face of the 

projected building

YBADJ O – R Across-flow distances from the stack to the center of the upwind face of the 

projected building

AREAVERT M – R Specifies location of vertices for an AREAPOLY source type (mandatory if 

AREAPOLY source is used)

URBANSRC O – R Identifies which sources to model with urban effects

EMISFACT O – R Optional input for variable emission rate factors

EMISUNIT O – N Optional unit conversion factors for emissions, concentrations

CONCUNIT O – N Optional conversion factors for emissions and concentrations

DEPOUNIT O – N Optional conversion factors for emissions and depositions

PARTDIAM O – R Input variables for optional input of particle size (microns)

MASSFRAX O – R Optional input of mass fraction for each particle size category

PARTDENS O – R Optional input of particle density (g/cm3) for each size category

METHOD_2 O – R Optional input of parameters for METHOD_2 particle deposition

GASDEPOS O – R Optional input of gas deposition parameters

NO2RATIO O – R Option to specify in-stack NO2/NOx equilibrium ratio for OLM and 

PVMRM options by source

HOUREMIS O – R Option for specifying hourly emission rates in a separate file

BGSECTOR O – N Specifies optional wind sectors for use in varying background 

concentrations by wind direction for the pollutant being modeled, as 

specified on the BACKGRND keyword 
B-14

SO Keywords Type Keyword Description

BACKGRND O – R Option to specify temporally varying background concentrations

BACKUNIT O – N Option to specify units for background concentrations

INCLUDED O – R Option to include data from a separate file in the runstream

OLMGROUP O – R Specifies sources to combine for OLM option to account for merging 

plumes

PSDGROUP1 O – R Specifies source groups for PSDCREDIT option with PVMRM

SRCGROUP1 M – R Identification of source groups

FINISHED M – N Identifies the end of SOURCE pathway inputs

1) The PSDGROUP or SRCGROUP keywords must be the last keyword within the SO pathway 

before the FINISHED keyword. The SRCGROUP keyword is mandatory, unless the 

PSDCREDIT option is used, which requires the PSDGROUP option instead.
B-15

TABLE B-4

DESCRIPTION OF SOURCE PATHWAY KEYWORDS AND PARAMETERS

Keyword Parameters

ELEVUNIT METERS or FEET

 where: METERS

FEET

Specifies input units for source base elevations of meters (default if 

ELEVUNIT is omitted)

Specifies input units for source elevations of feet

 Note: This keyword applies to source base elevations only.

LOCATION SrcID Srctyp Xs Ys (Zs) [for all Srctyp’s except LINE]

 or

 (FLAT) [for ‘FLAT & ELEV’ option]

 or

SrcID Srctyp Xs1 Ys1 Xs2 Ys2 (Zs) [for LINE Srctyp]

 or

 (FLAT) [for ‘FLAT & ELEV’ option]

 where: SrcID

Srctyp

Xs

Ys

Xs1, Xs2

Ys1, Ys2

(Zs)

(FLAT)

Source identification code (unique alphanumeric string of up to 12 

characters)

Source type: POINT, POINTCAP, POINTHOR, VOLUME, 

AREA, AREAPOLY, AREACIRC, OPENPIT, LINE, or

BUOYLINE *

x-coord of source location, corner for AREA, AREAPOLY, and 

OPENPIT, center for AREACIRC (m)

y-coord of source location, corner for AREA, AREAPOLY, and 

OPENPIT, center for AREACIRC (m)

x-coords of midpoint for start and end of LINE source (m)

y-coords of midpoint for start and end of LINE source (m)

Optional z-coord of source location (elevation above mean sea 

level, defaults to 0.0 if omitted)

Optional keyword to indicate non-DFAULT option for identifying 

sources to model as FLAT terrain 

 * Refer to Appendix G for details regarding inputs for 

BUOYLINE sources. 

SRCPARAM SrcID Ptemis Stkhgt Stktmp Stkvel Stkdia (POINT, POINTCAP,

 POINTHOR source)

 Vlemis Relhgt Syinit Szinit (VOLUME source)

 Aremis Relhgt Xinit (Yinit) (Angle) (Szinit) (AREA source)

 Aremis Relhgt Nverts (Szinit) (AREAPOLY source)

 Aremis Relhgt Radius (Nverts) (Szinit) (AREACIRC source)

 Lnemis Relhgt Width (Szinit) (LINE source)

 Opemis Relhgt Xinit Yinit Pitvol (Angle) (OPENPIT source)
B-16

Keyword Parameters

 where: SrcID

__Emis

___Hgt

Stktmp

Stkvel

Stkdia

Syinit

Szinit

Xinit

Yinit

Angle

Nverts

Radius

Width

Pitvol

Source identification code

Source emission rate: in g/s for Ptemis and Vlemis; g/(s-m2) for 

Aremis, Lnemis, and Opemis

Source physical release height above ground (center of height for 

VOLUME, height above base of pit for OPENPIT)

Stack gas exit temperature (K)

Stack gas exit velocity (m/s)

Stack inside diameter (m)

Initial lateral dimension of VOLUME source (m)

Initial vertical dimension of VOLUME, AREA, LINE source (m)

Length of side of AREA source in X-direction (m)

Length of side of AREA source in Y-direction (m) (optional 

parameter, assumed to be equal to Xinit if omitted)

Orientation angle (deg) of AREA or OPENPIT source relative to N 

measured positive clockwise, rotated around the source location, 

(Xs,Ys) (optional parameter, assumed to be 0.0 if omitted)

Number of vertices used for AREAPOLY or AREACIRC source 

(optional for AREACIRC sources)

Radius of circular area for AREACIRC source (m)

Width of LINE source (m)

Volume of OPENPIT source (m3)

BUILDHGT SrcID (or SrcRange) Dsbh(i), i=1,36

 where: SrcID

SrcRange 

Dsbh

Source identification code

Range of sources (inclusive) for which building dimensions apply, 

entered as two alphanumeric strings separated by a '-'

Array of direction-specific building heights (m) beginning with 10 

degree flow vector and incrementing by 10 degrees clockwise

BUILDLEN SrcID (or SrcRange) Dsbl(i), i=1,36

 where: SrcID

SrcRange 

Dsbl

Source identification code

Range of sources (inclusive) for which building dimensions apply

Array of direction-specific building lengths (m) beginning with 10 

degree flow vector and incrementing by 10 degrees clockwise

BUILDWID SrcID (or SrcRange) Dsbw(i), i=1,36

 where: SrcID

SrcRange 

Dsbw

Source identification code

Range of sources (inclusive) for which building dimensions apply

Array of direction-specific building widths (m) beginning with 10 

degree flow vector and incrementing by 10 degrees clockwise

XBADJ SrcID (or SrcRange) Xbadj(i), i=1,36

 where: SrcID

SrcRange 

Xbadj(i)

Source identification code

Range of sources (inclusive) for which XBADJ distances apply

Array of direction-specific along-wind distances beginning with 10 

degree flow vector and incrementing by 10 degrees clockwise

YBADJ SrcID (or SrcRange) Ybadj(i), i=1,36
B-17

Keyword Parameters

 where: SrcID

SrcRange 

Ybadj(i)

Source identification code

Range of sources (inclusive) for which YBADJ distances apply

Array of direction-specific across-wind distances beginning with 10 

degree flow vector and incrementing by 10 degrees clockwise

AREAVERT SrcID Xv(1) Yv(1) Xv(2) Yv(2) ... Xv(i) Yv(i)

 where: SrcID

Xv(1)

Yv(1)

Xv(i)

Yv(i)

Source identification code

X-coordinate of the first vertex of an AREAPOLY source (must be 

the same as the value of Xs for that source defined on the SO 

LOCATION card)

Y-coordinate of the first vertex of an AREAPOLY source (must be 

the same as the value of Ys for that source defined on the SO 

LOCATION card)

X-coordinate for the ith vertex of an AREAPOLY source

Y-coordinate for the ith vertex of an AREAPOLY source

URBANSRC For multiple urban areas:

UrbanID SrcID’s and/or SrcRng’s

For single urban areas:

SrcID’s and/or SrcRng’s

User may also specify ‘ALL’ for SrcID’s to assign all sources as urban.

 where: UrbanID

SrcID

SrcRange 

Specifies the alphanumeric urban ID (up to eight characters)

Specifies which source(s) will be modeled with urban effects

Specifies a range of sources that will be modeled with urban effects

EMISFACT SrcID (or SrcRange) Qflag Qfact(i), i=1,n

 where: SrcID

SrcRange 

Qflag

Qfact

Source identification code

Range of sources (inclusive) for which emission rate factors apply

Variable emission rate flag:

SEASON for seasonal; MONTH for monthly; HROFDY for 

hour-of-day; WSPEED for wind speed category; SEASHR for 

season-by-hour; HRDOW for emission rates vary by hour-ofday, and day-of-week [M-F, Sat, Sun]; HRDOW7 for emission 

rates vary by hour-of-day, and the seven days of the week [M, Tu, 

W, Th, F, Sat, Sun]; SHRDOW for season by hour-of-day by 

day-of-week (M-F,Sat,Sun); SHRDOW7 for season by hour-ofday by day-of-week (M,Tu,W,Th,F,Sat,Sun); MHRDOW for 

month by hour-of-day by day-of-week (M-F,Sat,Sun); 

MHRDOW7 for month by hour-of-day by day-of-week 

(M,Tu,W,Th,F,Sat,Sun)

Array of scalar emission rate factors, for:

 SEASON, n=4; MONTH, n=12; HROFDY, n=24; 

 WSPEED, n=6; SEASHR, n=96; HRDOW, n=72; 

 HRDOW7, n=168; SHRDOW, n=288; SHRDOW7, n=672;

 MHRDOW, n=864; MHRDOW7, n=2016
B-18

Keyword Parameters

EMISUNIT Emifac Emilbl Outlbl

 where: Emifac

Emilbl

Outlbl

Emission rate factor used to adjust units of output (default value is 

1.0E06 for CONC for grams to micrograms; default value is 3600 

for grams/sec to grams/m2/hr for deposition)

Label to use for emission units (default is grams/sec)

Label to use for output units; applies to first output type if more 

than one output type is generated (default is micrograms/m**3 

for concentration and grams/m**2 for deposition)

CONCUNIT Emifac Emilbl Conlbl

 where: Emifac

Emilbl

Conlbl

Emission rate factor used to adjust units of output (default value is 

1.0E06 for concentration for grams to micrograms)

Label to use for emission units (default is grams/sec)

Label to use for concentrations (default is micrograms/m3)

DEPOUNIT Emifac Emilbl Deplbl

 where: Emifac

Emilbl

Deplbl

Emission rate factor used to adjust units of output for deposition 

(default value is 3600 for grams/sec to grams/m2/hr) 

Label to use for emission units (default is grams/sec)

Label to use for deposition (default is grams/m2)

PARTDIAM SrcID (or SrcRange) Pdiam(i), i=1,Npd

 where: SrcID

SrcRange 

Pdiam

Source identification code

Range of sources (inclusive) for which size categories apply

Array of particle diameters (microns)

MASSFRAX SrcID (or SrcRange) Phi(i), i=1,Npd

 where: SrcID

SrcRange 

Phi

Source identification code

Range of sources (inclusive) for which mass fractions apply

Array of mass fractions for each particle size category

PARTDENS SrcID (or SrcRange) Pdens(i), i=1,Npd

 where: SrcID

SrcRange 

Pdens

Source identification code

Range of sources (inclusive) for which particle densities apply

Array of particle densities (g/cm3) for each size category

METHOD_2 SrcID (or SrcRange) FineMassFraction Dmm

 where: SrcID

FineMassFraction

Dmm

Source identification code

Fraction (between 0 and 1) of particle mass emitted in fine mode, 

less than 2.5 microns

Representative mass mean particle diameter in microns

GASDEPOS SrcID (or SrcRange) Da Dw rcl Henry

 where: SrcID

Da 

Dw 

Source identification code

Diffusivity in air for the pollutant being modeled (cm2/s)

Diffusivity in water for the pollutant being modeled (cm2/s)
B-19

Keyword Parameters

rcl 

Henry

Cuticular resistance to uptake by lipids for individual leaves (s/cm)

Henry's Law constant (Pa m3/mol)

NO2RATIO SrcID (or SrcRange) NO2Ratio

 where: SrcID

SrcRange 

NO2Ratio

Source identification code

Source ID range for specified ratio

In-stack ratio of NO2/NOx

HOUREMIS Emifil SrcID's SrcRange's

 where: Emifil

SrcID's

SrcRange's

Specifies name of the hourly emission rate file

Discrete source IDs that are included in the hourly emission file

Source ID ranges that are included in the hourly emission file

BGSECTOR StartSect1 StartSect2 . . . StartSectN, where N is ≤ 6

 where: StartSect1 

StartSect2

.

.

StartSectN

Starting direction for the first sector

Starting direction for the second sector

.

.

Starting direction for the last sector

NOTE: The minimum sector width allowed is 30 degrees, and 

warning messages will be issued for sector widths less than 60 

degrees. Sector-varying background concentrations will be 

selected based on the flow vector, i.e., the downwind direction, 

based on the wind direction specified in the surface 

meteorological data file.

BACKGRND BGflag BGvalue(i), i=1,n

 and/or (without BGSECTORs)

HOURLY BGfilnam (BGformat)

 or

SECTn BGflag BGvalue(i), i=1,n

 and/or (with BGSECTORs)

SECTn HOURLY BGfilnam (BGformat)

 where: SECTn

BGflag

Applicable sector (n = 1 to 6) defined on the SO BGSECTOR 

keyword, if specified

Variable background concentration flag:

ANNUAL for annual; SEASON for seasonal; MONTH for 

monthly; HROFDY for hour-of-day; WSPEED for wind speed 

category; SEASHR for season-by-hour; HRDOW for emission 

rates vary by hour-of-day, and day-of-week [M-F, Sat, Sun]; 

HRDOW7 for emission rates vary by hour-of-day, and the seven 

days of the week [M, Tu, W, Th, F, Sat, Sun]; SHRDOW for 

season by hour-of-day by day-of-week (M-F,Sat,Sun); 
B-20

Keyword Parameters

BGvalue

HOURLY

BGfilnam

(BGformat)

SHRDOW7 for season by hour-of-day by day-of-week 

(M,Tu,W,Th,F,Sat,Sun); MHRDOW for month by hour-of-day 

by day-of-week (M-F,Sat,Sun); MHRDOW7 for month by hourof-day by day-of-week (M,Tu,W,Th,F,Sat,Sun)

Array of background concentrations; for:

ANNUAL, n=1; SEASON, n=4; MONTH, n=12; 

HROFDY, n=24; WSPEED, n=6; SEASHR, n=96; 

HRDOW, n=72; HRDOW7, n=168; SHRDOW, n=288; 

SHRDOW7, n=672; MHRDOW, n=864; 

MHRDOW7, n=2016

Flag indicating that hourly background concentrations are specified 

in a separate data file; data period must match the meteorological 

data period being processed; no missing values are allowed in the 

hourly file, unless temporally-varying background concentrations 

are also specified through the BGflag parameter, which are used 

to substitute for missing hourly values.

Filename for hourly background concentrations

Optional Fortran format of hourly background concentration file; 

the default format is FREE format, i.e., comma or spacedelimited data fields (Yr Mn Dy Hr BGvalue). The BGformat

parameter must include open and close parentheses, the date 

variables must be read as integers (Fortran I format), and the 

BGvalue must be read as real (Fortran F, E, or D format), e.g., 

‘(4I2,F8.3)’. The year may be specified as a 2-digit or 4-digit 

year, and the data period in the HOURLY background file must 

match the data period in the meteorological data files. The 

BGformat parameter cannot include any blank spaces, unless the 

field in enclosed by double quotes.

NOTE: Background concentrations specified on the 

BACKGRND keyword are currently assumed to be in units of 

PPB for NO2 and SO2, PPM for CO, and UG/M3 for all other 

pollutants, unless otherwise specified on the SO BACKUNIT 

keyword. 

Background concentrations can be included with any source 

group, including group ‘ALL’, by including a “SrcID” of 

‘BACKGROUND’ on the SRCGROUP keyword. Note that 

background concentrations are automatically included 

with group ALL by default; however, background 

concentrations can be excluded from group ALL by 

including NOBACKGROUND (or NOBACKGRND) on 

the SRCGROUP ALL keyword.

BACKUNIT BGunits

 where: BGunits Background concentration units, specified as PPB for parts-per-
B-21

Keyword Parameters

billion, PPM for parts-per-million, or UG/M3 for 

micrograms/cubic-meter. Background concentrations input in 

units of PPB or PPM are converted to micrograms/cubic-meter 

based on reference temperature (25 C) and pressure (1013.25 

mb).

INCLUDED Incfil

 where: SrcIncFile Filename for the included source file, up to 200 characters in length; 

double quotes (“) may be used as delimiters for the filename to 

allow for embedded spaces; and quotes don’t count toward the 

limit of 200

OLMGROUP OLMGrpID SrcID's SrcRange's

 or

ALL

 where: OLMGrpID 

SrcID's 

SrcRange's

Group ID (Grpid = ALL specifies group including all sources)

Discrete source IDs to be included in group

Source ID ranges to be included in group

Note: Card may be repeated with same Grpid if more space is 

needed to specify sources

PSDGROUP PSDGrpID SrcID's SrcRange's

 where: PSDGrpID 

SrcID's 

SrcRange's

PSD GrpID for PSDCREDIT option, must be one of the following:

INCRCONS – increment-consuming sources,

NONRBASE – non-retired baseline sources, or

RETRBASE – retired (increment-expanding) baseline sources.

Discrete source IDs to be included in group

Source ID ranges to be included in group

Note: Card may be repeated with same PSDGrpID if more 

space is needed to specify sources

SRCGROUP SrcGrpID SrcID's SrcRange's

 where: SrcGrpID 

SrcID's 

SrcRange's

Group ID (Grpid = ALL specifies group including all sources)

Discrete source IDs to be included in group; a “SrcID” of 

‘BACKGROUND’ (or ‘BACKGRND’) can be used to include 

background concentrations, based on the BACKGRND keyword.

Also note that background concentrations are automatically 

included with group ALL; however, background concentrations 

can be excluded from group ALL by specifying 

‘NOBACKGROUND’ on the SRCGROUP ALL keyword. 

Source ID ranges to be included in group

Note: Card may be repeated with same Grpid if more space is 

needed to specify sources
B-22

TABLE B-5

DESCRIPTION OF RECEPTOR PATHWAY KEYWORDS

RE Keywords Type Keyword Description

STARTING M – N Identifies the start of RECEPTOR pathway inputs

ELEVUNIT O – N Defines input units for receptor elevations (defaults to meters), must be first 

keyword after RE STARTING if used.

GRIDCART O1 – R Defines a Cartesian grid receptor network

GRIDPOLR O1 – R Defines a polar receptor network

DISCCART O1 – R Defines the discretely placed receptor locations referenced to a Cartesian 

system

DISCPOLR O1 – R Defines the discretely placed receptor locations referenced to a polar system

EVALCART O1 – R Defines discrete Cartesian receptor locations for use with EVALFILE output 

option 

INCLUDED O – R Identifies an external file containing receptor locations to be included in the 

inputs 

FINISHED M - N Identifies the end of RECEPTOR pathway inputs

1) At least one of the following must be present: GRIDCART, GRIDPOLR, DISCCART, 

DISCPOLR, or EVALCART, unless the INCLUDED keyword is used to include receptor 

inputs from an external file. Multiple receptor networks can be specified in a single run, 

including both Cartesian and polar.
B-23

TABLE B-6

DESCRIPTION OF RECEPTOR PATHWAY KEYWORDS AND PARAMETERS

Keyword Parameters

ELEVUNIT METERS or FEET

 where: METERS

FEET

Specifies input units for receptor elevations of meters

Specifies input units for receptor elevations of feet

 Note: This keyword applies to receptor elevations only.

GRIDCART Netid STA

 XYINC Xinit Xnum Xdelta Yinit Ynum Ydelta

 or XPNTS Gridx1 Gridx2 Gridx3 .... GridxN, and

 YPNTS Gridy1 Gridy2 Gridy3 .... GridyN

 ELEV Row Zelev1 Zelev2 Zelev3 ... ZelevN

 HILL Row Zhill1 Zhill2 Zhill3 ... ZhillN

 FLAG Row Zflag1 Zflag2 Zflag3 ... ZflagN

 END

 where: Netid

STA

XYINC

Xinit

Xnum

Xdelta

Yinit

Ynum

Ydelta

XPNTS

Gridx1

GridxN

YPNTS

Gridy1

GridyN

ELEV

Row

Zelev

HILL

Row

Zhill

FLAG

Row

Zflag

END

Receptor network identification code (up to eight alphanumeric 

characters)

Indicates STArt of GRIDCART subpathway, repeat for each new Netid

Keyword identifying grid network generated from x and y increments

Starting local x-axis grid location in meters

Number of x-axis receptors

Spacing in meters between x-axis receptors

Starting local y-axis grid location in meters

Number of y-axis receptors

Spacing in meters between y-axis receptors

Keyword identifying grid network defined by series of x and y 

coordinates

Value of first x-coordinate for Cartesian grid

Value of 'nth' x-coordinate for Cartesian grid

Keyword identifying grid network defined by series of x and y 

coordinates

Value of first y-coordinate for Cartesian grid

Value of 'nth' y-coordinate for Cartesian grid

Keyword to specify that receptor elevations follow

Indicates which row (y-coordinate fixed) is being input

An array of receptor terrain elevations for a particular Row

Keyword to specify that hill height scales follow

Indicates which row (y-coordinate fixed) is being input

An array of hill height scales for a particular Row

Keyword to specify that flagpole receptor heights follow

Indicates which row (y-coordinate fixed) is being input

An array of receptor heights above local terrain elevation for a particular 

Row (flagpole receptors)

Indicates END of GRIDCART subpathway, repeat for each new Netid
B-24

Keyword Parameters

GRIDPOLR Netid STA

 ORIG Xinit Yinit,

 or ORIG Srcid

 DIST Ring1 Ring2 Ring3 ... RingN

 DDIR Dir1 Dir2 Dir3 ... DirN,

 or GDIR Dirnum Dirini Dirinc

 ELEV Dir Zelev1 Zelev2 Zelev3 ... ZelevN

 HILL Dir Zhill1 Zhill2 Zhill3 ... ZhillN

 FLAG Dir Zflag1 Zflag2 Zflag3 ... ZflagN

 END

 where: Netid

STA

ORIG

Xinit

Yinit

Srcid

DIST

Ring1

RingN

DDIR

Dir1

DirN

GDIR

Dirnum

Dirini

Dirinc

ELEV

Dir

Zelev

HILL

Row

Zhill

FLAG

Dir

Zflag

END

Receptor network identification code (up to eight alphanumeric 

characters)

Indicates STArt of GRIDPOLR subpathway, repeat for each new Netid

Optional keyword to specify the origin of the polar network (assumed to 

be at x=0, y=0 if omitted)

local x-coordinate for origin of polar network (m)

local y-coordinate for origin of polar network (m)

Source ID of source used as origin of polar network

Keyword to specify distances for the polar network

Distance to the first ring of polar coordinates (m)

Distance to the 'nth' ring of polar coordinates (m)

Keyword to specify discrete direction radials for the polar network

First direction radial in degrees (1 to 360)

The 'nth' direction radial in degrees (1 to 360)

Keyword to specify generated direction radials for the polar network

Number of directions used to define the polar system

Starting direction of the polar system

Increment (in degrees) for defining directions

Keyword to specify that receptor elevations follow

Indicates which direction is being input

An array of receptor terrain elevations for a particular direction radial

Keyword to specify that hill height scales follow

Indicates which row (y-coordinate fixed) is being input

An array of hill height scales for a particular Row Keyword to specify that 

flagpole receptor heights follow

Keyword to specify that flagpole receptor heights follow

Indicates which direction is being input

An array of receptor heights above local terrain elevation for a particular 

direction (flagpole receptors)

Indicates END of GRIDPOLR subpathway, repeat for each new Netid

DISCCART Xcoord Ycoord (Zelev Zhill) (Zflag)

 where: Xcoord

Ycoord

(Zelev)

(Zhill)

local x-coordinate for discrete receptor location (m)

local y-coordinate for discrete receptor location (m)

Elevation above sea level for discrete receptor location (optional), used 

only for ELEV terrain

Hill height scale (optional)
B-25

Keyword Parameters

(Zflag) Receptor height (flagpole) above local terrain (optional), used only with 

FLAGPOLE keyword

DISCPOLR Srcid Dist Direct (Zelev Zhill) (Zflag)

 where: Srcid

Dist

Direct

(Zelev)

(Zhill)

(Zflag)

Specifies source identification for which discrete polar receptor locations 

apply (used to define the origin for the discrete polar receptor)

Downwind distance to receptor location (m)

Direction to receptor location, in degrees clockwise from North

Elevation above sea level for receptor location (optional), used only for 

ELEV terrain

Hill height scale (optional)

Receptor height (flagpole) above local terrain (optional), used only with 

FLAGPOLE keyword

EVALCART Xcoord Ycoord Zelev Zhill Zflag Arcid (Name)

 where: Xcoord

Ycoord

Zelev

Zhill

Zflag

Arcid

(Name)

Local x-coordinate for discrete receptor location (m)

Local y-coordinate for discrete receptor location (m)

Elevation above sea level for discrete receptor location (optional), used 

only for ELEV terrain

Hill height scale (m) 

Receptor height (flagpole) above local terrain (optional), used only with 

FLAGPOLE keyword

Receptor arc ID used to group receptors along an arc or other grouping 

(up to eight characters)

Optional name for receptor (up to eight characters)

INCLUDED RecIncFile

 where: RecIncFile Identifies the filename for the included receptor file, up to 200 characters 

in length; double quotes (“) may be used as delimiters for the filename 

to allow for embedded spaces; quotes don’t count toward the limit of 

200
B-26

TABLE B-7

DESCRIPTION OF METEOROLOGY PATHWAY KEYWORDS

ME Keywords Type Keyword Description

STARTING M – N Identifies the start of METEOROLOGY pathway inputs

SURFFILE M – N Describes input meteorological surface data file

PROFFILE M – N Describes input meteorological profile data file

SURFDATA M – N Describes surface meteorological station

UAIRDATA M – N Describes upper air meteorological station

SITEDATA O – N Describes on-site meteorological station

PROFBASE M – N Specifies the base elevation for the potential temperature profile

STARTEND O – N Specifies start and end dates to be read from input meteorological data file 

(default is to read entire file)

DAYRANGE O – R Specifies days or ranges of days to process (default is to process all data)

SCIMBYHR O – N Specifies the parameters for the SCIM (Sampled Chronological Input 

Model) option (see CO MODELOPT)

WDROTATE O – N May be used to correct for alignment problems of wind direction 

measurements, or to convert wind direction from to flow vector

WINDCATS O – N Input upper bounds of wind speed categories, five values input - sixth 

category is assumed to have no upper bound (used for WSPEED option on 

the EMISFACT keyword)

FINISHED M – N Identifies the end of METEOROLOGY pathway inputs
B-27

TABLE B-8

DESCRIPTION OF METEOROLOGY PATHWAY KEYWORDS AND PARAMETERS

Keyword Parameters

SURFFILE Sfcfil

 where: Sfcfil Specify filename for surface meteorological input file

Note: FREE format is used for all SURFFILE reads beginning 

with version 09292.

PROFFILE Profil

 where: Profil Specify filename for profile meteorological input file

Note: FREE format is used for all PROFFILE reads beginning 

with version 09292.

SURFDATA Stanum Year (Name) (Xcoord Ycoord)

 where: Stanum

Year

(Name)

(Xcoord)

(Ycoord)

Station number, e.g. 5-digit WBAN number for NWS station

Year of data being processed (four digits)

Station name (optional)

x-coordinate of station location (m) (optional)

y-coordinate of station location (m) (optional)

UAIRDATA Stanum Year (Name) (Xcoord Ycoord)

 where: Stanum

Year

(Name)

(Xcoord)

(Ycoord)

Station number, e.g. 5-digit WBAN number for NWS station

Year of data being processed (four digits)

Station name (optional)

x-coordinate of station location (m) (optional)

y-coordinate of station location (m) (optional)

SITEDATA Stanum Year (Name) (Xcoord Ycoord)

 where: Stanum

Year

(Name)

(Xcoord)

(Ycoord)

Station number for on-site meteorological data station

Year of data being processed (four digits)

Station name (optional)

x-coordinate of station location (m) (optional)

y-coordinate of station location (m) (optional)

PROFBASE BaseElev (Units)

 where: BaseElev

(Units)

Base elevation (above MSL) for the potential temperature profile

Units of BaseElev: METERS or FEET (default is METERS)

STARTEND Strtyr Strtmn Strtdy (Strthr) Endyr Endmn Enddy (Endhr)

 where: Strtyr

Strtmn

Strtdy

(Strthr)

Endyr

Year of first record to be read

Month of first record to be read

Day of first record to be read

Hour of first record to be read (optional)

Year of last record to be read
B-28

Keyword Parameters

Endmn

Enddy

(Endhr)

Month of last record to be read

Day of last record to be read

Hour of last record to be read (optional)

Note: File read begins with hour 1 of the start date and ends with 

hour 24 of the end date if Stahr and Endhr are omitted.

DAYRANGE Range1 Range2 Range3 ... RangeN

 where: Range1

RangeN

First range of days to process, either as individual day (XXX) or as 

range (XXX-YYY); days may be input as Julian dates (XXX) or 

as month and day (XX/YY)

The 'N-th' range of days to process

NUMYEARS NumYrs

 where: NumYrs Specifies the number of years of meteorological data being 

processed for purposes of allocating array storage for the OU 

MAXDCONT option. A default value of 5 years is assumed if the 

optional NUMYEARS keyword is omitted.

SCIMBYHR NRegStart NRegInt (SfcFilnam PflFilnam)

 where: NRegStart

NRegInt

(SfcFilnam)

(PflFilnam)

Specifies the first hour to be sampled with the SCIM option; 

required to have a value from 1 to 24

Specifies the sampling interval, in hours

Optional output file name to list the surface meteorological data for 

the sampled hours

Optional output file name to list the profile meteorological data for 

the sampled hours

WDROTATE Rotang

 where: Rotang Specifies angle (in degrees) to rotate wind direction measurements 

to correct for alignment problems; value of Rotang is subtracted 

from WD measurements, i.e., rotation is counterclockwise

WINDCATS Ws1 Ws2 Ws3 Ws4 Ws5 

 where: Ws1

Ws2

Ws3

Ws4

Ws5

Upper bound of first wind speed category (m/s)

Upper bound of second wind speed category (m/s)

Upper bound of third wind speed category (m/s)

Upper bound of fourth wind speed category (m/s)

Upper bound of fifth wind speed category (m/s)

(sixth category is assumed to have no upper bound)
B-29

TABLE B-9

DESCRIPTION OF EVENT PATHWAY KEYWORDS

EV Keywords Type Keyword Description

STARTING M – N Identifies the start of EVENT pathway inputs

EVENTPER M – R Describes data and averaging period for an event

EVENTLOC M – R Describes receptor location for an event

INCLUDED O – R Identifies an external file containing EVENT data to be included in the 

inputs

FINISHED M – N Identifies the end of EVENT pathway inputs
B-30

TABLE B-10

DESCRIPTION OF EVENT PATHWAY KEYWORDS AND PARAMETERS

Keyword Parameters

EVENTPER Evname Aveper Grpid Date Conc

 where: Name

Grpid

Aveper

Date

Conc

Specify name of event to be processed (e.g. H002H24ALL), (up to 

ten alphanumeric characters)

Specify source group ID for event

Specify averaging period for event

Specify data period for event (ending YYMMDDHH for averaging 

period)

Specifies the concentration value generated during the initial nonEVENT processing

EVENTLOC Evname XR= Xr YR= Yr (Zelev Zhill) (Zflag)

 or

 RNG= Rng DIR= Dir (Zelev Zhill) (Zflag)

 where: Evname

XR=

YR=

RNG=

DIR=

(Zelev)

(Zhill)

(Zflag)

Specify name of event to be processed (e.g. H002H24ALL), (up to 

ten alphanumeric characters)

X-coordinate for event (discrete Cartesian receptor)

Y-coordinate for event (discrete Cartesian receptor)

Distance range for event (discrete polar receptor)

Radial direction for event (discrete polar receptor)

Terrain elevation for event (optional)

Hill height scale (optional)

Receptor height above ground for event (optional)

INCLUDED EventIncFile

 where: EventIncFile Identifies the filename for the included EVENT file, up to 200 

characters in length; double quotes (“) may be used as delimiters for 

the filename to allow for embedded spaces; and quotes don’t count 

toward the limit of 200

Note: EVENT locations can be input as either discrete Cartesian receptors (XR=, 

YR=) or as discrete polar receptors (RNG=, DIR=). Events that are specified 

in the file generated by the AERMOD model (CO EVENTFIL card) are always given 

as discrete Cartesian coordinates. Discrete polar receptors are assumed to 

be relative to an origin of (0,0).
B-31

TABLE B-11

DESCRIPTION OF OUTPUT PATHWAY KEYWORDS

OU Keywords Type Keyword Description

STARTING M – N Identifies the start of OUTPUT pathway inputs

RECTABLE O – R Option to specify value(s) by receptor for output

MAXTABLE O – R Option to summarize the overall maximum values

DAYTABLE O – N Option to print summaries for each averaging period for each day 

processed.

MAXIFILE O – R Option to list events exceeding a threshold value to file (if CO 

EVENTFIL option is used, these events are included in the input file 

generated for the EVENT model).

POSTFILE1 O – R Option to write results to a mass storage file for postprocessing.

PLOTFILE1 O – R Option to write certain results to a storage file suitable for 

input to plotting routines

TOXXFILE O – R Option to write results to a storage file suitable for input to the 

TOXX model component of TOXST or the RISK

RANKFILE O – R Option to output file of ranked values for Q-Q plots (must be used 

with the MAXTABLE keyword)

EVALFILE O – R Option to output file of normalized arc maxima from EVALCART 

receptors for model evaluation studies 

SEASONHR O – R Option to output results by season and hour-of-day

MAXDAILY O – R Option to output file of daily maximum 1-hour values for each day 

processed; only applicable for 1-hour NO2 and 1-hour SO2 NAAQS

MXDYBYYR O – R Option to output file of daily maximum 1-hour values by year, for each 

year processed; only applicable for 1-hour NO2 and 1-hour SO2 NAAQS

MAXDCONT O – R Option to output contributions of each source group to ranked values 

averaged across years for a reference source group, paired in time and 

space; only applicable for 24-hour PM2.5, 1-hour NO2, and 1-hour SO2

NAAQS 

SUMMFILE O – N Option to output summary of high ranked values to separate file

FILEFORM O – N Specify fixed or exponential format for output results files

NOHEADER O – N Option to suppress file headers for output file options, e.g., POSTFILE, 

PLOTFILE, MAXDCONT, etc.

EVENTOUT M – N Specifies the level of output information provided for EVENT 

Processing [EVENT Only]

FINISHED M – N Identifies the end of OUTPUT pathway inputs
B-32

1) POSTFILE is used to output concurrent concentration values for particular source 

groups and averaging times across the receptor network suitable for postprocessing. 

PLOTFILE is used to output specific design values, such as second high 

concentrations, across the receptor network, suitable for plotting concentration 

contours.
B-33

TABLE B-12

DESCRIPTION OF OUTPUT PATHWAY KEYWORDS AND PARAMETERS

Keyword Parameters

RECTABLE Aveper FIRST SECOND . . . SIXTH . . . TENTH and/or

Aveper 1ST 2ND . . . 6TH . . . 10TH and/or

Aveper 1 2 . . . 6 . . . 10 . . . N . . . 999

 where: Aveper

FIRST

SECOND

SIXTH

1ST

2ND

6TH

N

Averaging period to summarize with high values (keyword 

ALLAVE specifies all short-term averaging periods)

Select summaries of FIRST highest values by receptor

Select summaries of SECOND highest values by receptor

Select summaries of SIXTH highest values by receptor

Select summaries of 1ST highest values by receptor

Select summaries of 2ND highest values by receptor

Select summaries of 6TH highest values by receptor

Select summaries of N-th highest values by receptor (up to 999-th 

highest values)

Note:

If two parameters are input separated by a dash (e.g.

FIRST-THIRD or 4-12), then summaries of all high

ranked values within that range (inclusive) are provided.

If the CO EVENTFIL keyword is exercised, then the

events generated by the RECTABLE keyword are included

in the input file for EVENT model.

The range of ranks specified on the RECTABLE keyword

(but not the individual ranks specified) also determines

the range of ranks that may be considered with the 

MAXDCONT option.

MAXTABLE Aveper Maxnum

 where: Aveper

Maxnum

Averaging period to summarize with overall maximum values 

(keyword ALLAVE specifies all averaging periods)

Specifies number of overall maximum values to summarize 

DAYTABLE Avper1 Avper2 Avper3 . . .

 where: Avper1 Averaging period, e.g., 24 for 24-hr averages, to summarize with 

values by receptor for each day of data processed (keyword 

ALLAVE for first parameter specifies all averaging periods)

MAXIFILE Aveper GrpID Thresh Filnam (Funit)

 where: Aveper Specifies averaging period for list of values equal to or exceeding a 

threshold value
B-34

Keyword Parameters

GrpID

Thresh

Filnam

Funit

Specifies source group to be output to file

Threshold value (e.g. NAAQS) for list of exceedances

Name of disk file to store maximum values

Optional parameter to specify the file unit

Note:

If the CO EVENTFIL keyword is exercised, then the events 

generated by the MAXIFILE keyword are included in the input 

file for EVENT processing.

POSTFILE Aveper GrpID Format Filnam (Funit)

 where: Aveper

GrpID

Format

Filnam

Funit

Specifies averaging period to be output to file, e.g., 24 for 24-hr 

averages, PERIOD for period averages

Specifies source group to be output to file

Specifies format of file, either UNFORM for unformatted files or 

PLOT for formatted files for plotting

Specifies filename for output file

Optional parameter to specify the file unit

PLOTFILE Aveper GrpID Hivalu Filnam (Funit) (Short Term values)

Aveper GrpID Filnam (Funit) (PERIOD or ANNUAL averages)

 where: Aveper

GrpID

Hivalu

Filnam

Funit

Specifies averaging period to be output to file, e.g., 24 for 24-hr 

averages, PERIOD for period averages, etc.

Specifies source group to be output to file

Specifies rank to be included in high value summary (e.g. FIRST, 

SECOND, 1ST, 2ND, etc.) to be output to file (the rank must be 

included on the RECTABLE card)

Specifies filename for output file

Optional parameter to specify the file unit

TOXXFILE Aveper Cutoff Filnam (Funit)

 where: Aveper

Cutoff

Filnam

Funit

Specifies averaging period to be output to file, e.g., 1 for 1-hr 

averages.

Specifies cutoff (threshold) value in g/m3 for outputting results for 

AERMOD model

Specifies filename for output file

Optional parameter to specify the file unit

RANKFILE Aveper Hinum Filnam (Funit)

 where: Aveper

Hinum

Filnam

Funit

Specifies averaging period to be output to file, e.g., 24 for 24-hr 

averages

Specifies the number of high values to be ranked

Specifies filename for output file

Optional parameter to specify the file unit

EVALFILE SrcID Filnam (Funit)
B-35

Keyword Parameters

 where: SrcID

Filnam

Funit

Specifies the source ID to be output to file

Specifies filename for output file

Optional parameter to specify the file unit

SEASONHR GrpID FileName (FileUnit)

 where: GrpID

FileName

(FileUnit)

Specifies the source group ID to be output to file

Specifies filename for output file

Optional parameter to specify file unit

MAXDAILY GrpID FileName (FileUnit)

 where: GrpID

FileName

(FileUnit)

Specifies the source group ID to be output to file

Specifies filename for output file

Optional parameter to specify file unit

MXDYBYYR GrpID FileName (FileUnit)

 where: GrpID

FileName

(FileUnit)

Specifies the source group ID to be output to file

Specifies filename for output file

Optional parameter to specify file unit

MAXDCONT GrpID UpperRank LowerRank FileName (FileUnit)

 or

GrpID UpperRank THRESH ThreshValue FileName (FileUnit)

 where: GrpID

UpperRank

LowerRank

THRESH

ThreshValue

FileName

(FileUnit)

Specifies the source group ID to be output to file

Upper bound of ranks to evaluate for contributions

Lower bound of ranks to evaluate for contributions (note that lower 

rank refers to lower concentrations and higher rank refers to 

higher concentrations)

NOTE: The UpperRank and LowerRank values must be within 

the range of ranks specified on the RECTABLE keyword. 

AERMOD will analyze each rank within the range, regardless 

of whether the rank is specified explicitly on the RECTABLE 

keyword. 

Indicates that a threshold concentration (ThreshValue) will be 

specified as a limit on the lower bound rank to process

Lower threshold value for evaluating contributions; processing will 

stop after the first ranked value that is below ThreshValue

NOTE: The ThreshValue analysis will be limited to the range 

of ranks specified on the RECTABLE keyword (but not the 

individual ranks that are specified). A warning message is 

generated if the ThreshValue is not reached within the range of 

ranks analyzed.

Specifies filename for output file

Optional parameter to specify file unit

Note:

The range of ranks specified on the RECTABLE keyword

(but not the individual ranks specified) also determines
B-36

Keyword Parameters

the range of ranks that may be considered with the 

MAXDCONT option, even with the THRESH option.

SUMMFILE SummFileName

 where: SummFileName Specifies filename of output summary file

FILEFORM EXP or FIX

 where: EXP

FIX

Specifies that the output results files will use EXPonentialformatted values

Specifies that the output results files will use FIXed-formatted 

values (fixed-formatted values will be used if FILEFORM is 

omitted)

NOHEADER FileType1 FileType2 FileType3 . . . FileTypeN

 or

ALL

 where: FileTypeN 

ALL

Specifies the output file type(s) for which header records will be 

suppressed; includes the following file types:

POSTFILE, PLOTFILE, MAXIFILE, RANKFILE, 

SEASONHR, MAXDAILY, MXDYBYYR, and MAXDCONT

Specifies that header records will be suppressed for ALL applicable 

output file types

EVENTOUT SOCONT or DETAIL [EVENT Only]

 where: SOCONT

DETAIL

Provide source contribution information only in the event output

Include hourly concentrations for each source and hourly 

meteorological data in the event output
C-1

APPENDIX C. LIST OF ERROR/WARNING MESSAGES

This appendix provides a list of error, warning and informational messages used in the 

current version of the AERMOD model. Three types of messages can be produced by the model 

during processing of model inputs and during model calculations. These are described below:

• Fatal Errors that will halt any further processing, except to identify additional error

conditions (type E);

• Warnings that do not halt processing but indicate possible errors or suspect

conditions (type W); and

• Informational messages that may be of interest to the user but have no direct bearing 

on the validity of the results (type I). 

A more detailed explanation of the error handling and reporting procedures used in AERMOD is 

provided in Appendix C of the AERMOD User’s Guide (EPA, 2004a). The three message types 

are identified with the letters E (errors), W (warnings), and I (informational messages). The 

3-digit message numbers are generally grouped into categories corresponding to the different 

stages of the processing, although these distinctions may not always be obvious. These

categories are:

100 - 199 Input Runstream Image Structure Processing

200 - 299 Parameter Setup Processing

300 - 399 Data and Quality Assurance Processing

400 - 499 Run Time Message Processing

500 - 599 Input/Output Message Processing

The list provided below includes the message number, the main message text, and the “hint” 

field that may include additional details regarding the message. Note that the listing of 

messages in the AERMOD User’s Guide (EPA, 2004a) is not up-to-date. Several additional 

messages have been added to AERMOD since that time, and the numbering of some 

messages may have changed.
C-2

Message 

Number Error/Warning Message

Hint

(not updated)

100 Invalid Pathway Specified. The Troubled Pathway is

105 Invalid Keyword Specified. The Troubled Keyword is

109 Too many fields specified on runstream image; MAX=

110 Keyword is Not Valid for This Pathway. Keyword is

111 LOW_WIND Keyword specified without LOWWIND Options

112 User-specified minimum Sigma-V on LOW_WIND Keyword

113 User-specified minimum WindSpeed on LOW_WIND Keywd

114 User-specified maximum FRAN on the LOW_WIND Keywrd

115 STARTING or FINISHED Out of Sequence: Pathway = 

116 Vector Wind Speeds specified on MODELOPT Keyword 

120 Pathway is Out of Sequence: Pathway = 

121 LowWind1 Beta Option specified on MODELOPT Keyword

122 LowWind2 Beta Option specified on MODELOPT Keyword

125 Missing FINISHED-Runstream File Incomplete: ISTAT=

130 Missing Mandatory Keyword. The Missing Keyword is

131 Minimum sigmav value (SVmin) for LowWind1 Beta Opt

132 Minimum sigmav value (SVmin) for LowWind2 Beta Opt

133 Maximum FRAN value (FRANmax) for LowWind2 Beta Opt

135 Nonrepeatable Keyword or Recursed INCLUDED: Keywrd

136 Conflicting Beta Option - LowWind1 and LowWind2 

140 Invalid Order of Keyword. The Troubled Keyword is

141 Conflicting Options for NO2 conversion specified: 

142 Following Keyword Invalid Without PVMRM or OLM: 

143 Following Keyword Invalid Without PVMRM Option: 

144 Following Keyword Invalid Without OLM Option: 

145 Following Keyword Invalid Without ARM or ARM2: 

146 PSDGROUP Keyword Specified without PSDCREDIT Opt. 

147 Following Option is Invalid with PSDCREDIT Option:

148 Both OZONEVAL and O3VALUES keywords are specified 

149 Conflicting options specified on MODELOPT keyword:

150 Conflicting Options: MULTYEAR Option with 

151 Non-DFAULT NoUrbTran option selected on MODELOPT 
C-3

Message 

Number Error/Warning Message

Hint

(not updated)

152 ELEVUNIT card must be first for this Pathway: 

153 Conflicting Opts: MAXDCONT with Re-Start or MULTYR

154 Conflicting options: SCIM cannot be used with 

155 Conflicting Decay Keyword. Inputs Ignored for 

156 Option ignored - not valid with SCIM. Option = 

157 Wet SCIM Not Supported - Wet SCIM Inputs Ignored 

158 EMISUNIT Keyword Used With More Than 1 Output Type

159 EMISUNIT Keyword Used With the Following Keyword: 

160 Duplicate ORIG Secondary Keyword for GRIDPOLR: 

161 MAXDCONT option already defined for source group: 

162 Option only applies to 1-hr NO2 or 1-hr SO2 NAAQS:

163 Option only applies to 24h PM25, 1h NO2 or 1h SO2:

164 NOHEADER selected for non-specified output option:

165 Inconsistent temporally-varying BACKGRND options: 

166 BGSECTOR/O3SECTOR option invalid w/o BG/O3 Inputs:

167 Inconsistent temporally-varying O3VALUES options: 

168 Hourly BACKGRND already specified for this sector:

170 Invalid Secondary Keyword for Receptor Grid: 

171 Sector ID specified without Sector-varying Option:

175 Missing Secondary Keyword END for Receptor Grid: 

180 Conflicting Secondary Keyword for Receptor Grid: 

181 BULKRN Delta-T & SolarRad option for SBL was used 

182 MMIF-generated meteorological inputs were used 

183 Non-DFAULT option for MMIF-generated data without 

184 PROFFILE heights > 999m; inputs could be from MMIF

185 Either No Sources or No Receptors are specified!!!

186 THRESH_1MIN 1-min ASOS wind speed threshold used 

187 ADJ_U* Beta Option for Low Winds used in AERMET 

188 Non-Default ADJ_U* Option used in AERMET without 

189 No Keywords for OU Path and No PERIOD/ANNUAL Aves.

190 Incompatible Option Used With SAVEFILE or INITFILE

191 PM25, 1h NO2 or SO2 w/o MAXIFILE incompatible with
C-4

Message 

Number Error/Warning Message

Hint

(not updated)

192 FASTALL option also implies use of FASTAREA option

193 Units keyword specified without appropriate option

194 DEBUGOPT input option is invalid or not applicable

195 Incompatible Keyword used with GASDEPVD option 

196 Gas deposition algorithms are non-DFAULT options 

197 METHOD_2 for particulates is a non-DFAULT option 

198 TOXICS Option obsolete; see Users Guide Addendum 

199 Non-DFAULT BETA Option Required for 

200 Missing Parameter(s). No Options Specified For 

201 Not Enough Parameters Specified For the Keyword of

202 Too Many Parameters Specified For the Keyword of 

203 Invalid Parameter Specified. Troubled Parameter: 

204 Regulatory DFAULT Conflicts with Non-DFAULT Option

205 No Option Parameter Setting. Forced by Default to

206 Regulatory DFAULT Overrides Non-DFAULT Option For 

207 No Parameters Specified. Default Values Will Used.

208 Illegal Numerical Field Encountered in 

209 Negative Value Appears For Non-negative Variable. 

211 Duplicate Averaging Period Specified for Keyword 

212 END Encountered Without (X,Y) Points Properly Set 

213 ELEV Input Inconsistent With Option: Input Ignored

214 ELEV Input Inconsistent With Option: Defaults Used

215 FLAG Input Inconsistent With Option: Input Ignored

216 FLAG Input Inconsistent With Option: Defaults Used

217 More Than One Delimiter In A Field for Keyword 

218 Number of (X,Y) Points Does Not Match Number of 

219 Urban ID field is too long (>8); first 12 char: 

220 Missing Origin (Use Default = 0,0) In GRIDPOLR 

221 Missing Dist or Direction Setting In Polar Network

222 O3SECTOR or BGSECTOR Value is out of order: 

223 Missing Distance or Degree Field in 

224 SrcID specified on SRCGROUP keyword not defined: 
C-5

Message 

Number Error/Warning Message

Hint

(not updated)

225 SrcID specified on OLMGROUP keyword not defined: 

226 SrcID specified on PSDGROUP keyword not defined: 

227 O3SECTOR or BGSECTOR Width is out of range: 

228 Default(s) Used for Missing Parameters on Keyword 

229 Too Many Parameters - Inputs Ignored on Keyword 

230 Source ID field is too long (>12); first 12 chars:

231 Too Many Numerical Values Specified for 

232 OLMGroup ID field is too long (>8); first 12 char:

233 Building Dimensions Specified for Non-POINT Source

234 Too Many Sectors Input for 

235 Num of SRCGRPs exceeds limit for EVT name; Set=999

236 Not Enough BUILDHGTs Specified for SourceID 

237 Not Enough BUILDWIDs Specified for SourceID 

238 Not Enough BACKGRND Concentration Values Specified

239 Not Enough QFACTs Specified for SourceID 

240 Inconsistent Number of Particle Categories for 

241 Not Enough BUILDLENs Specified for SourceID 

242 No Particle Cat. or Gas Depos. Specified for SRCID

243 Wet depos (DEPOS, WDEP, WETDPLT) incompatible with

244 Source parameters are missing or incomplete for 

245 SrcGroup ID field is too long (>8); first 12 char:

246 Not Enough XBADJs Specified for SourceID 

247 Not Enough YBADJs Specified for SourceID 

248 Either BGVALs or BGFILE missing for this sector: 

249 Source elevation is missing (-9999.0); SRCID = 

250 Duplicate XPNT/DIST or YPNT/DIR Specified for GRID

252 Duplicate Receptor Network ID Specified. NETID = 

253 PSDGROUP ID field is too long (>8); first 12 char:

256 EVALFILE Option Used Without EVALCART Receptors 

259 Receptor elevation is missing (-9999.0); IREC = 

260 Number of EMISFACT/O3VALUES/BACKGRND values > max:

261 Not Enough O3VALUES Ozone Concentrations Specified
C-6

Message 

Number Error/Warning Message

Hint

(not updated)

262 First Vertex Does Not Match LOCATION for AREAPOLY 

264 Too Many Vertices Specified for AREAPOLY Source 

265 Not Enough Vertices Specified for AREAPOLY Source 

266 Invalid shape defined (area=0) for AREAPOLY source

271 O3FILE w/o O3VALs; full conv for hrs with miss O3 

272 Upper bound rank > Lower bound rank for MAXDCONT: 

273 Range of ranks for MAXDCONT THRESH Opt is limited:

276 Special proc for 1h-NO2/SO2 24hPM25 NAAQS disabled

277 Specified option not applicable for this pollutant

279 Multiple URBANOPT/URBANSRC inputs not allowed for:

280 Number of Output Types Specified Exceeds Max:NTYP=

282 Following SRCID Included in Multiple OLMGROUPs: 

283 OZONEVAL, O3VALUES or OZONEFIL Keyword Needed for 

284 Invalid POLLUTID Specified for PVMRM/OLM; Must Use

285 BACKGROUND and BACKGRND are invalid as Source IDs 

286 Following SRCID Included in Multiple PSDGROUPs: 

287 PSDGROUP ID Must be INCRCONS, RETRBASE or NONRBASE

288 Use of "*" for repeated values not meaningful for 

289 Source defined as both particulate and gaseous 

290 This array limit exceeded; possible coding error: 

291 Filename specified is too long. Maximum length = 

292 Potential problem with Fortran format specifier: 

293 User-specified met data format not used; use FREE

294 PERIOD and ANNUAL averages are both selected for 

295 Invalid Averaging Period Specified for SCREEN Mode

296 Averaging Period .NE. 1-Hr for TOXXFILE Option 

297 Aver. Period must be .LE. 24 for EVENT Processing 

298 Results reported for source group ALL include 

299 SRCGROUP ALL is missing, but is NOT required for 

300 Specified SRCID Has Not Been Defined Yet: KEYWORD=

301 Urban Area ID Has Not Been Defined. URBID = 

302 Following SRCID Included in Multiple Urban Areas: 
C-7

Message 

Number Error/Warning Message

Hint

(not updated)

303 Urban ID has already been defined. URBID = 

305 Stack height > or = EPA formula height for SRCID: 

310 Attempt to Define Duplicate LOCATION Card for SRC:

313 Attempt to Define Duplicate EVENTPER card for 

315 Attempt to Define Duplicate SRCPARAM Card for SRC:

317 Specified SRCID not included in any PSD/SRCGROUP: 

318 No Sources Defined for Urban Area. URBID = 

319 No Sources Included in Specified Source Group: 

320 Input Parameter May Be Out-of-Range for Parameter 

321 BACKGROUND concs are NOT included in any SRCGROUP!

322 Release Height Exceeds Effective Depth for OPENPIT

323 BACKGRND included w/o BACKGRND keyword for SrcGrp:

324 Release Height Exceeds 3000 Meters for SRCID: 

325 Negative Exit Velocity (Set=1.0E-5) for SRCID: 

330 Mass Fraction Parameters Do Not Sum to 1. for Src 

332 Mass Fraction Parameter Out-of-Range for Source 

334 Particle Density Out-of-Range for Source 

335 Particle Diameter Out-of-Range for Source 

336 NO2RATIO Missing or Invalid for OLM/PVMRM - SrcID:

338 Neg Emis Rate Cannot be Used with OLM/PVMRM. Src: 

340 Possible Error in PROFBASE Input: Value is < 0 

341 Emissions in HOUREMIS file < -90; set to 0.0 for 

342 Src ID Mismatch in Hourly Emissions File for ID = 

344 Missing HOUREMIS fields; EmisRate set = 0. KURDAT=

345 Problem processing the HOUREMIS file. KURDAT = 

346 Too many fields for HOUREMIS file. KURDAT = 

350 Julian Day Out Of Range at 

352 The "H6H" field is no longer required for MULTYEAR

353 Urban Roughness Length (m) May Be Out-of-Range: 

360 2-Digit Year Specified: Valid for Range 1950-2049 

361 Multiyear PERIOD/ANNUAL values for NO2/SO2 require

362 Multiyear 1h NO2/SO2 processing not applicable for
C-8

Message 

Number Error/Warning Message

Hint

(not updated)

363 Multiyr 24h/Ann PM25 processing not applicable for

365 Year Input is Greater Than 2147 

370 Invalid Date: 2/29 In a Non-leap Year. 

380 This Input Variable is Out-of-Range: 

381 Latitude in Surface File Is Not Valid: 

382 Error Decoding Latitude: 

384 Not enough fields specified for HOUREMIS; KURDAT =

386 PARTDIAM and METHOD_2 specified for same SRCID: 

387 METHOD_2 option already specified for this SRCID: 

389 Rotated buoyant line sources not in correct order:

390 Aspect ratio (L/W) of LINE source greater than 100

391 Aspect ratio (L/W) of AREA source greater than 100

392 Aspect ratio (L/W) of OPENPIT is greater than 10 

394 Met data may be from outdated version of AERMET: 

395 Met. Data Error; Incompatible Version of AERMET: 

396 Met data from outdated version of AERMET, version:

397 SCREEN option used without use of SCREEN Met Data 

398 SCREEN met used without specifying SCREEN option 

399 EXP format specified with no applicable file types

400 Output values exceed format limit; use OU FILEFORM

405 Value of PHEE Exceeds 1.0 on KURDAT = 

406 Number of Vertices Exceeds Max (NVMAX) for SRCID: 

409 Error Allocating Storage for Setup/Result Arrays! 

410 Wind Direction Out-of-Range. KURDAT = 

413 Number of Threshold Events > 999999 for Ave Period

415 MAXDCONT THRESH not reached within range of ranks 

420 Wind Speed Out-of-Range. KURDAT = 

430 Ambient Temperature Data Out-of-Range. KURDAT = 

432 Friction Velocity Out-of-Range. KURDAT = 

435 Surface Roughness Length Out-of-Range. KURDAT = 

438 Convective Velocity Data Out-of-Range. KURDAT = 

439 Monin-Obukhov Length Out-of-Range. KURDAT = 
C-9

Message 

Number Error/Warning Message

Hint

(not updated)

440 Calm Hour Identified in Meteorology Data File at 

441 Vert Pot Temp Grad abv ZI set to min .005, KURDAT=

442 Vert Pot Temp Grad abv ZI exceeds 0.1 K/m, KURDAT=

450 Record Out of Sequence in Meteorological File at: 

452 Missing hourly BACKGRND w/o BGSUB, KURDAT/Sector =

453 BGSUB for missing hourly BACKGRND, KURDAT/Sector =

454 Date/time Mismatch: BACKGRND File, KURDAT/Sector =

455 Date/time Mismatch: Hourly Emission File, KURDAT =

456 Date/time Mismatch on Surface & Profile. KURDAT =

457 Date/time Mismatch: OZONEFIL File, KURDAT/Sector =

458 O3SUB for missing hourly O3 value, KURDAT/Sector =

459 No Hrly O3 & No Sub; Use Full Conversion, KURDAT =

460 Missing Hour Identified in Meteor. Data File at 

465 Number of Profile Levels Exceeds Max: MXPLVL = 

470 Mixing Height Value is < or = 0.0. KURDAT = 

474 WS RefHt invalid (<0.001); Not msg or clm: KURDAT=

475 WS reference height is higher than 100m. KURDAT =

480 Less than 1yr for MULTYEAR, MAXDCONT or ANNUAL Ave

481 Data Remaining After End of Year. Number of Hours=

482 Too many years modeled for 24h-PM25 1h-NO2 1h-SO2:

483 User Start Date is Earlier Than Start of Met File 

484 Restart Date < STARTEND date or start of Met File 

485 MULTYR DataGap; Restart Date < STARTEND or MetFile

486 MULTYR Date Overlap; STARTEND Date < Restart Date 

487 MULTYR Date Overlap; MetFile Start < Restart Date 

488 First met HR.ne.1; ST results may not be valid 

489 First met HR.ne.1; EV results may not be valid for

490 Problem reading SURFFILE date for EVENTS; MNDYHR =

491 MAXDCONT option requires 1st Hr of met data = 01; 

492 SURFDATA YR .NE. 1st YR of file, adj to match file

493 SURFDATA YR must match 1st YR of file for DAYRANGE

495 Surface met file does not include enough variables
C-10

Message 

Number Error/Warning Message

Hint

(not updated)

496 Total precipitation in SURFFILE is zero (0.0) with

497 Possible code ERROR!!! EVENT mismatch for EVENTID:

498 Possible code ERROR! MAXDCONT mismatch GRP/RNK/REC

499 PRIME plume rise error; check stack parameters for

500 Fatal Error Occurs Opening the Data File of 

501 Dup Filename! Fatal Error Opening the Data File of

510 Fatal Error Occurs During Reading of the File of 

520 Fatal Error Occurs During Writing to the File of 

530 CAUTION! Met Station ID Mismatch with SURFFILE for

531 CAUTION! Met Station ID Missing from SURFFILE for 

540 No RECTABLE/MAXTABLE/DAYTABLE for Average Period 

550 File Unit/Name Conflict for the Output Option: 

555 File Unit/Name conflict across options: GRP# AVE 

560 User Specified File Unit .LE. 30 for OU Keyword: 

565 Possible Conflict With Dynamically Allocated FUNIT

570 Problem Reading Temporary Event File for Event: 

580 End of File Reached Trying to Read the File of 

585 Output data file for INITFILE option was not found

590 The INITFILE filename matches a SAVEFILE filename 

592 MAXIFILE includes data past start of MULTYEAR run 

593 POSTFILE includes data past start of MULTYEAR run 
D-1

APPENDIX D

EPA MODEL CLEARINGHOUSE MEMORANDUM

DATED JULY 9, 1993
D-2

 July 9, 1993

MEMORANDUM

SUBJECT: Proposal for Calculating Plume Rise for Stacks with Horizontal

 Releases or Rain Caps for Cookson Pigment, Newark, New Jersey

FROM: Joseph A. Tikvart, Chief

 Source Receptor Analysis Branch, TSD (MD-14)

TO: Ken Eng, Chief

 Air Compliance Branch, Region II

 In response to your request, the Model Clearinghouse has reviewed your

proposal for treating horizontal and capped stacks at Cookson Pigment so

that the model (SCREEN or ISC2) will properly treat plume rise from the

Cookson Pigment stacks. We concur in principle with the approach, with

some relatively minor changes.

 First, the analysis provided by New Jersey Department of Environmental

Protection is technically correct. We suggest, however, that the exit

velocity for horizontal and capped stacks be set to a lower figure than 0.1

m/s. A 0.1 m/s exit velocity may still result in significant momentum

plume rise being calculated, even though these kinds of sources should have

zero momentum rise. We therefore suggest setting the stack exit velocity

to a lower value, such as .001. 

 For horizontal stacks that are not capped, we suggest turning stack

tip downwash off, whether there are buildings or not. Stack tip downwash

calculations are inappropriate for horizontal stacks. 

 For vertical stacks that are capped, turn stack tip downwash off and

reduce the stack height by three times the actual stack diameter. The cap

will probably force stack tip downwash most of the time. The maximum

amount of the stack tip downwash (as calculated in ISC2) is three times the

stack diameter. Reducing the stack height by this amount, while turning

off the stack tip downwash option, causes the maximum stack tip downwash

effect. The resulting concentrations may err slightly on the high side.

For stacks with small diameters, such as those at Cookson Pigment, the

error should be quite small. Note, however, that this approach may not be

valid for large diameter stacks (say, several meters).

cc: A. Colecchia

 D. Wilson
E-1

APPENDIX E. EVALUATION OF MODIFIED URBAN OPTION

The urban option in AERMOD was modified, beginning with version 11059, to address 

potential issues associated with the transition from the nighttime urban boundary layer to the 

daytime convective boundary layer. Prior to version 11059, the enhanced dispersion associated 

with the urban nighttime heat island effect was ignored once the boundary layer turned 

convective. This could result in an unrealistic drop in the mixed layer height during early 

morning hours for urban applications, which could contribute to unrealistically high 

concentrations for low-level plumes. This effect was observed in the application of AERMOD 

for the Risk and Exposure Assessment (REA) in support of the NO2 NAAQS review in 

association with mobile source emissions (EPA, 2008). Beginning with version 11059 the urban 

option in AERMOD continues application of the urban boundary layer approach for urban 

sources until the daytime convective mixing height exceeds the urban nighttime mixing height, 

based on the user-specified population (Cimorelli, et al., 2004). This revision to AERMOD will 

generally reduce concentrations during the early morning transition to convective conditions for 

low-level urban sources, but may increase daytime concentrations for elevated urban sources. 

The modified implementation of the urban option was evaluated using data from the 1985 

Indianapolis SF6 urban field study (Perry, et al, 2005), and model-to-monitor comparisons at four 

ambient monitors for 2002 from the Atlanta NO2 REA (EPA, 2008). The Indianapolis study 

involved an elevated buoyant release and the Atlanta REA study involved mostly low-level 

mobile source emissions. Results from the Indianapolis study are presented in the form of Q-Q 

plots of ranked 1-hour modeled vs. observed concentrations, unpaired in time and space. Figure 

E-1 shows model performance for all stabilities and Figure E-2 shows model performance for 

convective conditions only. The revised urban option does not affect results under stable 

conditions. Results from the Atlanta NO2 REA are also presented in the form of Q-Q plots of 

1-hour ranked modeled vs. observed concentrations, unpaired in time, for each of the four 

ambient NO2 monitors, shown in Figures E-3 through E-6. Both of these evaluations show 

improved model performance with the modified urban option in AERMOD.
E-2

Figure E-1. 1-hour Q-Q Plot for Indianapolis SF6 Study for All Stabilities

Figure E-2. 1-hour Q-Q Plot for Indianapolis SF6 Study for Convective Conditions

0.01

0.1

1

10

0.01 0.1 1 10

PREDICTED

OBSERVED

INDIANAPOLIS SF6 1-HR Q-Q PLOT (CONC) - All Stabilities

AERMOD v09292

AERMOD v11059
E-3

Figure E-3. 1-hour Q-Q Plot for Atlanta NO2 Study for Monitor 0002

Figure E-4. 1-hour Q-Q Plot for Atlanta NO2 Study for Monitor 3001

Atlanta NO2 Study - 1-hr QQ Plot for Monitor 0002 - Urban Transition Adjustment

0

50

100

150

200

0 50 100 150 200

Observed Conc (ppb)

Predicted Conc (ppb)

0002 - New

0002 - Old

Atlanta NO2 Study - 1-hr QQ Plot for Monitor 3001 - Urban Transition Adjustment

0

50

100

150

200

0 50 100 150 200

Observed Conc (ppb)

Predicted Conc (ppb)

3001 - New

3001 - Old
E-4

Figure E-5. 1-hour Q-Q Plot for Atlanta NO2 Study for Monitor 0048

Figure E-6. 1-hour Q-Q Plot for Atlanta NO2 Study for Monitor JST

Atlanta NO2 Study - 1-hr QQ Plot for Monitor 0048 - Urban Transition Adjustment

0

50

100

150

200

0 50 100 150 200

Observed Conc (ppb)

Predicted Conc (ppb)

0048 - New 

0048 - Old

Atlanta NO2 Study - 1-hr QQ Plot for Monitor JST - Urban Transition Adjustment

0

50

100

150

200

0 50 100 150 200

Observed Conc (ppb)

Predicted Conc (ppb)

JST - New

JST - Old
F-1

APPENDIX F. EVALUATION OF LOW WIND BETA OPTIONS

Beginning with version 12345, AERMOD includes non-default BETA options to address 

concerns regarding model performance under low wind speed conditions. This included the 

LOWWIND1 and LOWWIND2 BETA options on the MODELOPT keyword in AERMOD, and 

the ADJ_U* option included in Stage 3 of the AERMET meteorological processor. Beginning 

with version 15181 a new LOWWIND3 BETA option was incorporated into AERMOD. The 

LOWWIND3 option increases the minimum value of sigma-v from 0.2 to 0.3 m/s, consistent 

with the LowWind2 option, but eliminates upwind dispersion, consistent with the LowWind1 

option. The LowWind3 option uses an “effective” sigma-y value that replicates the centerline 

concentration accounting for meander, but sets concentrations to zero (0) for receptors that are 

more than 6*sigma-y off the plume centerline, similar to the FASTALL option.

Updated evaluation results for these BETA options based on version 15181 of AERMOD are 

presented below for two field studies conducted in 1974 by the Air Resources Laboratory of the 

National Oceanic and Atmospheric Administration (NOAA) to investigate diffusion under low 

wind speed conditions at Idaho Falls (NOAA, 1974) and Oak Ridge (NOAA, 1976). These two 

field studies were used in the API-sponsored evaluations of AERMOD conducted by AECOM 

(AECOM, 2009), that were subsequently submitted as part of API’s public comments on EPA’s 

10th Conference on Air Quality Models held in March 2012. Each of these studies used tracer 

releases with three arcs of samplers located at 100m, 200m, and 400m from the release point.

Diagrams for each of the study areas are presented below.

In addition, since the ADJ_U* option in AERMET and the LowWind option in AERMOD are 

focused on improving model performance during periods of stable/low-wind conditions, 

additional evaluations are presented below for the Lovett evaluation database, a tall stack located 

in complex terrain where stable/low-wind conditions can also be important. 

The evaluation results presented here for the Idaho Falls and Oak Ridge studies were based in 

part on the information included in the AECOMs 2009 report and data files subsequently 

provided by AECOM. However, some adjustments to inputs were made based on an 

independent assessment of the surface roughness for each of the study locations, an adjustment 

to the effective tracer release height at Idaho Falls from 1.5 to 3m based on information provided 

on page 24 of the NOAA Technical Memorandum for Idaho Falls (NOAA, 1974), and 

adjustments to the wind measurement height for Oak Ridge based on the discussion in Section 

2.2 and information provided in Table 1 of the NOAA Technical Memorandum for Oak Ridge 

(NOAA, 1976). 

The AECOM evaluation for Oak Ridge assumed a 2m wind measurement height, whereas page 8 

of the NOAA report for Oak Ridge indicated that the wind measurements were “accomplished 

by laser anemometry” because wind speeds were “below the threshold of standard cup 

anemometers.” Footnotes in Table 1 also confirm that wind speeds were “measured by laser 

anemometers” for all tests, except for Test 11 where the wind speed was measured at the 30.5m 

level on one of meteorological towers included in the study. Given that the transmitters and 

receivers for the laser anemometer were located on the hills on either side of the valley where the 

tracer was released, at elevations between 50 to 100 feet higher than the elevation at the release 

point (based on Figure 2b of the NOAA report), a 2m wind measurement height may not be 
F-2

appropriate. However, the NOAA report does not indicate an “effective” measurement height 

above ground for the wind speeds measured by the laser anemometers. Another aspect of the use 

of laser anemometry that complicates the determination of an appropriate measurement height is 

that the “measured” wind speeds may represent more of a volume average than a point 

measurement. Since the wind speeds estimated by laser anemometry are likely to be more 

representative of vector averaged wind speeds than scalar averages the VECTORWS option in 

AERMOD was used for the Oak Ridge evaluations.

Based on these considerations, the evaluation results presented here were based on an “effective” 

wind measurement height of 10m, and the winds were also assumed to represent vector mean 

wind speeds. In addition to the different assumptions regarding the appropriate measurement 

height to assign to the observed wind speeds at Oak Ridge, the results presented below are based 

on a surface roughness length of 0.6m, consistent with the forest covering most of the study area 

at the time. The AECOM study assumed a much smaller roughness length of 0.2m.

A series of figures is provided below for each site, starting with the Oak Ridge study followed by 

the Idaho Falls study. For each site a series of Q-Q plots (results paired by rank), plots of 

concentrations paired in time, and residual plots showing the distribution of predicted/observed 

concentration ratios versus downwind distance are provided. Results are shown for the 

following scenarios:

• Current regulatory default options, i.e., no adjustments (No ADJ_U*/No LowWind)

• U* adjustment with no low wind options (ADJ_U*/No_LowWind)

• U* adjustment with LOWWIND1 (ADJ_U*/LowWind1)

• U* adjustment with LOWWIND2 (ADJ_U*/LowWind2)

• U* adjustment with LOWWIND3 (ADJ_U*/LowWind3)

Based on the limited meteorological data available for the Oak Ridge study, a single set of model 

comparisons is presented. Given the more robust meteorological data available from the Idaho 

Falls study, including multiple levels of wind speed, direction, temperature, and sigma-theta, 

several sets of meteorological inputs are evaluated, including the use of delta-T data with the 

Bulk Richardson Number (BULKRN) option available in AERMET.

Another important difference between these two field studies is that the Oak Ridge site was 

located in a hilly area on the Oak Ridge peninsula, with terrain elevations varying about 40m 

across the study area, with the tracer release point located near the center of the valley that cuts 

across the peninsula. Given the very low wind speeds during the study period, drainage flows 

and valley channeling may have influenced plume dispersion. The influence of terrain on lowlevel non-buoyant releases in AERMOD has not been assessed, and neither the AECOM nor 

EPA results for Oak Ridge have incorporated terrain elevations in their respective evaluations. 

As a result, the evaluations based on the Idaho Falls are likely to be more robust than the 

evaluations based on Oak Ridge.

As noted above, the Oak Ridge evaluations are based on a single set of meteorological inputs, 

whereas the Idaho Falls evaluation are based on a range of options given the more robust data 

available. These various sets of meteorological inputs for Idaho Falls are referred to in the figure 

captions as follows:

1. Base 1-level: no delta-T or turbulence (i.e., sigma-theta) data included;
F-3

2. Full 1-level: no delta-T data with sigma-theta data;

3. Base 2-level: delta-T data used with BULKRN option without sigma-theta;

4. Full 2-level: delta-T data used with BULKRN option with sigma-theta

Each of these data sets were used with and without the ADJ_U* option in AERMET and also 

with and without the LowWind options. For purposes of assessing the proposed BETA options, 

including the ADJ_U* option in AERMET and the LowWind options in AERMOD, the 

comparisons below are limited to the current default options, i.e., without ADJ_U* and without 

the LowWind option (labeled as NoADJ and NoLW), and the proposed options of ADJ_U* and 

LowWind3 (labeled as ADJ and LW3). 
F-4
F-5

A series of figures is provided below for each site, starting with the Oak Ridge study followed by 

the Idaho Falls study. For each site, a series of Q-Q plots (i.e., results paired by rank and arc 

distance), paired plots (i.e., results paired in time and arc distance), and residual plots (showing 

the distribution of Pred/Obs ratios by distance) are shown in the following order:

No ADJ_U* / No LowWind Option;

No ADJ_U* / LowWind1 Option; 

No ADJ_U* / LowWind2 Option;

No ADJ_U* / LowWind3 Option;

ADJ_U* / No LowWind Option;

ADJ_U* / LowWind1 Option; 

ADJ_U* / LowWind2 Option; and

ADJ_U* / LowWind3 Option. 
F-6

0

500

1000

1500

0 500 1000 1500

Predicted (μg/m3)

Observed (μg/m3)

Oak Ridge: Q-Q Plot - w/o ADJ_U* - NoLW Option - v15181

Obs vs AERMOD (Base 1-Layer, Vector WS, 10m-Zref, 0.6m-Zo) Predicted Arc-Max @ 3 DW Arcs

100-m Arc

200-m Arc

400-m Arc

0

400

800

1200

1600

0 400 800 1200 1600

Predicted (μg/m3)

Observed (μg/m3)

Oak Ridge: Q-Q Plot - w/o ADJ_U* - LowWind1 Option - v15181

Obs vs AERMOD (Base 1-Layer, Vector WS, 10m-Zref, 0.6m-Zo) Predicted Arc-Max @ 3 DW Arcs

100-m Arc

200-m Arc

400-m Arc
F-7

0

100

200

300

400

0 100 200 300 400

Predicted (μg/m3)

Observed (μg/m3)

Oak Ridge: Q-Q Plot - w/o ADJ_U* - LowWind2 Option - v15181

Obs vs AERMOD (Base 1-Layer, Vector WS, 10m-Zref, 0.6m-Zo) Predicted Arc-Max @ 3 DW Arcs

100-m Arc

200-m Arc

400-m Arc

0

50

100

150

200

0 50 100 150 200

Predicted (μg/m3)

Observed (μg/m3)

Oak Ridge: Q-Q Plot - w/o ADJ_U* - LowWind3 Option - v15181

Obs vs AERMOD (Base 1-Layer, Vector WS, 10m-Zref, 0.6m-Zo) Predicted Arc-Max @ 3 DW Arcs

100-m Arc

200-m Arc

400-m Arc
F-8

0

50

100

150

200

0 50 100 150 200

Predicted (μg/m3)

Observed (μg/m3)

Oak Ridge: Q-Q Plot - With ADJ_U* - NoLW Option - v15181

Obs vs AERMOD (Base 1-Layer, Vector WS, 10m-Zref, 0.6m-Zo) Predicted Arc-Max @ 3 DW Arcs

100-m Arc

200-m Arc

400-m Arc

0

100

200

300

400

0 100 200 300 400

Predicted (μg/m3)

Observed (μg/m3)

Oak Ridge: Q-Q Plot - With ADJ_U* - LowWind1 Option - v15181

Obs vs AERMOD (Base 1-Layer, Vector WS, 10m-Zref, 0.6m-Zo) Predicted Arc-Max @ 3 DW Arcs

100-m Arc

200-m Arc

400-m Arc
F-9

0

25

50

75

100

0 25 50 75 100

Predicted (μg/m3)

Observed (μg/m3)

Oak Ridge: Q-Q Plot - With ADJ_U* - LowWind2 Option - v15181

Obs vs AERMOD (Base 1-Layer, Vector WS, 10m-Zref, 0.6m-Zo) Predicted Arc-Max @ 3 DW Arcs

100-m Arc

200-m Arc

400-m Arc

0

25

50

75

100

0 25 50 75 100

Predicted (μg/m3)

Observed (μg/m3)

Oak Ridge: Q-Q Plot - With ADJ_U* - LowWind3 Opt - v15181

Obs vs AERMOD (Base 1-Layer, Vector WS, 10m-Zref, 0.6m-Zo) Predicted Arc-Max @ 3 DW Arcs

100-m Arc

200-m Arc

400-m Arc
F-10

0

50

100

150

200

0 50 100 150 200

Predicted (μg/m3)

Observed (μg/m3)

Oak Ridge: Paired Plot - With ADJ_U* - NoLW Option - v15181

Obs vs AERMOD (Base 1-Layer, Vector WS, 10m-Zref, 0.6m-Zo) Pred Arc-Max @ 3 DW Arcs

100-m Arc

200-m Arc

400-m Arc

0

100

200

300

400

0 100 200 300 400

Predicted (μg/m3)

Observed (μg/m3)

Oak Ridge: Paired Plot - With ADJ_U* - LowWind1 Option - v15181

Obs vs AERMOD (Base 1-Layer, Vector WS, 10m-Zref, 0.6m-Zo) Pred Arc-Max @ 3 DW Arcs

100-m Arc

200-m Arc

400-m Arc
F-11

0

25

50

75

100

0 25 50 75 100

Predicted (μg/m3)

Observed (μg/m3)

Oak Ridge: Paired Plot - With ADJ_U* - LowWind2 Option - v15181

Obs vs AERMOD (Base 1-Layer, Vector WS, 10m-Zref, 0.6m-Zo) Pred Arc-Max @ 3 DW Arcs

100-m Arc

200-m Arc

400-m Arc

0

25

50

75

100

0 25 50 75 100

Predicted (μg/m3)

Observed (μg/m3)

Oak Ridge: Paired Plot - With ADJ_U* - LowWind3 Opt - v15181

Obs vs AERMOD (Base 1-Layer, Vector WS, 10m-Zref, 0.6m-Zo) Pred Arc-Max @ 3 DW Arcs

100-m Arc

200-m Arc

400-m Arc
F-12

0.01

0.10

1.00

10.00

100.00

100 - ns=11 200 - ns=11 400 - ns=10

Predicted / Observed

Receptor Arcs

Oak Ridge: Residual Plot vs. DW Dist - w/o ADJ_U* - NoLW Option - v15181

Pred (AERMOD Base 1-Layer, Vector WS, 10m-Zref, 0.6m-Zo) vs Obs

0.01

0.10

1.00

10.00

100.00

100 - ns=11 200 - ns=11 400 - ns=10

Predicted / Observed

Receptor Arcs

Oak Ridge: Residual Plot vs. DW Dist - w/o ADJ_U* - LW1 Option - v15181

Pred (AERMOD Base 1-Layer, Vector WS, 10m-Zref, 0.6m-Zo) vs Obs
F-13

0.01

0.10

1.00

10.00

100.00

100 - ns=11 200 - ns=11 400 - ns=10

Predicted / Observed

Receptor Arcs

Oak Ridge: Residual Plot vs. DW Dist - w/o ADJ_U* - LW2 Option - v15181

Pred (AERMOD Base 1-Layer, Vector WS, 10m-Zref, 0.6m-Zo) vs Obs

0.01

0.10

1.00

10.00

100.00

100 - ns=11 200 - ns=11 400 - ns=10

Predicted / Observed

Receptor Arcs

Oak Ridge: Residual Plot vs. DW Dist - w/o ADJ_U* - LW3 Option - v15181

Pred (AERMOD Base 1-Layer, Vector WS, 10m-Zref, 0.6m-Zo) vs Obs
F-14

0.01

0.10

1.00

10.00

100.00

100 - ns=11 200 - ns=11 400 - ns=10

Predicted / Observed

Receptor Arcs

Oak Ridge: Residual Plot vs. DW Dist - With ADJ_U* - NoLW Option - v15181

Pred (AERMOD Base 1-Layer, Vector WS, 10m-Zref, 0.6m-Zo) vs Obs

0.01

0.10

1.00

10.00

100.00

100 - ns=11 200 - ns=11 400 - ns=10

Predicted / Observed

Receptor Arcs

Oak Ridge: Residual Plot vs. DW Dist - With ADJ_U* - LW1 Option - v15181

Pred (AERMOD Base 1-Layer, Vector WS, 10m-Zref, 0.6m-Zo) vs Obs
F-15

0.01

0.10

1.00

10.00

100.00

100 - ns=11 200 - ns=11 400 - ns=10

Predicted / Observed

Receptor Arcs

Oak Ridge: Residual Plot vs. DW Dist - With ADJ_U* - LW2 Option - v15181

Pred (AERMOD Base 1-Layer, Vector WS, 10m-Zref, 0.6m-Zo) vs Obs

0.01

0.10

1.00

10.00

100.00

100 - ns=11 200 - ns=11 400 - ns=10

Predicted / Observed

Receptor Arcs

Oak Ridge: Residual Plot vs. DW Dist - With ADJ_U* - LowWind3 Opt - v15181

Pred (AERMOD Base 1-Layer, Vector WS, 10m-Zref, 0.6m-Zo) vs Obs
F-16

The figures shown above for the Oak Ridge field study show significant overprediction with the 

current default options in AERMET and AERMOD. The LowWind2 and LowWind3 options 

without the ADJ_U* option exhibit much better performance, with LowWind3 showing the best 

results, but both options still show significant overpredictions. The LowWind1 option actually 

degrades model performance relative to the default options. These figures also show significant 

improvement in model performance with the ADJ_U* option in AERMET with and without the 

LowWind options. The LowWind2 option with ADJ_U* appears to show the best overall 

performance, with the LownWind3/ADJ_U* option showing some bias toward underprediction. 

However, as noted above, the evaluation results presented here do not account for the potential 

influence of terrain on modeled concentrations. Given the potential for valley channeling and 

drainage flows one might expect modeling results based on an assumption of flat terrain to 

underestimate concentrations for this study. Figure 7 from the NOAA Technical Memorandum 

shows horizontal isopleths of concentrations for Test #6 which appears to be stretched along the 

axis of the valley where the tracer was released. A similar pattern shows up with other tests.

The next series of figures shows evaluation results for Idaho Falls based on the degraded 1-layer 

meteorological data (i.e., no delta-T data for the BULKRN option and no sigma-theta data, 

starting with the DFAULT option (without ADJ_U* and NoLW), followed by the LowWind1, 

LowWind2, and LowWind3 option, followed by the results with the ADJ_U* option.
F-17

0

50

100

150

200

0 50 100 150 200

Predicted (μg/m3)

Observed (μg/m3)

Idaho Falls: Q-Q Plot - He=3m - 0.08m Zo - w/o ADJ_U* - NoLW Option - v15181

Obs (unfitted) vs AERMOD (Degraded 1-Layer, Scalar WS) Predicted Arc-Max @ 3 DW Arcs

100-m Arc

200-m Arc

400-m Arc

0

50

100

150

200

0 50 100 150 200

Predicted (μg/m3)

Observed (μg/m3)

Idaho Falls: Paired Plot - He=3m - 0.08m Zo - w/o ADJ_U* - NoLW Option - v15181

Obs (unfitted) vs AERMOD (Degraded 1-Layer, Scalar WS) Pred Arc-Max @ 3 DW Arcs

100-m Arc

200-m Arc

400-m Arc
F-18

The results for Idaho Falls based on the default options in AERMET and AERMOD exhibit 

overprediction of the observed concentrations of approximately a factor of 2, with is a much 

smaller bias than for the Oak Ridge study. As shown below, the bias toward overprediction is 

largely eliminated with the LowWind options in AERMOD, without the ADJ_U* option in 

AERMET. The average Pred/Obs concentration ratios are also generally consistent with 

downwind distance.

The results for Idaho Falls with the ADJ_U* option in AERMET also show generally good 

performance at the first arc of receptors at 100m downwind, with some tendency toward 

underprediction further downwind, especially when the LowWind options are also used. For this 

type of source, i.e., a non-buoyant, ground-level or low-level source (e.g., fugitive emission), the 

maximum ambient impacts are likely to occur at the fenceline.

0.01

0.10

1.00

10.00

100.00

100 - ns=11 200 - ns=11 400 - ns=11

Predicted / Observed

Receptor Arcs

Idaho Falls: Resid Plot vs. DW Dist - He=3m - 0.08m Zo - w/o ADJ_U* - NoLW Option - v15181

Pred (AERMOD Degraded 1-Layer, Scalar WS) vs Obs (unfitted)
F-19

0

50

100

150

200

0 50 100 150 200

Predicted (μg/m3)

Observed (μg/m3)

Idaho Falls: Q-Q Plot - He=3m - 0.08m Zo - w/o ADJ_U* - LW1 Option - v15181

Obs (unfitted) vs AERMOD (Degraded 1-Layer, Scalar WS) Predicted Arc-Max @ 3 DW Arcs

100-m Arc

200-m Arc

400-m Arc

0

50

100

150

200

0 50 100 150 200

Predicted (μg/m3)

Observed (μg/m3)

Idaho Falls: Paired Plot - He=3m - 0.08m Zo - w/o ADJ_U* - LW1 Option - v15181

Obs (unfitted) vs AERMOD (Degraded 1-Layer, Scalar WS) Pred Arc-Max @ 3 DW Arcs

100-m Arc

200-m Arc

400-m Arc
F-20

0.01

0.10

1.00

10.00

100.00

100 - ns=11 200 - ns=11 400 - ns=11

Predicted / Observed

Receptor Arcs

Idaho Falls: Resid Plot vs. DW Dist - He=3m - 0.08m Zo - w/o ADJ_U* - LW1 Option - v15181

Pred (AERMOD Degraded 1-Layer, Scalar WS) vs Obs (unfitted)
F-21

0

50

100

150

200

0 50 100 150 200

Predicted (μg/m3)

Observed (μg/m3)

Idaho Falls: Q-Q Plot - He=3m - 0.08m Zo - w/o ADJ_U* - LowWind2 Option - v15181

Obs (unfitted) vs AERMOD (Degraded 1-Layer, Scalar WS) Predicted Arc-Max @ 3 DW Arcs

100-m Arc

200-m Arc

400-m Arc

0

50

100

150

200

0 50 100 150 200

Predicted (μg/m3)

Observed (μg/m3)

Idaho Falls: Paired Plot - He=3m - 0.08m Zo - w/o ADJ_U* - LowWind2 Option - v15181

Obs (unfitted) vs AERMOD (Degraded 1-Layer, Scalar WS) Pred Arc-Max @ 3 DW Arcs

100-m Arc

200-m Arc

400-m Arc
F-22

0.01

0.10

1.00

10.00

100.00

100 - ns=11 200 - ns=11 400 - ns=11

Predicted / Observed

Receptor Arcs

Idaho Falls: Resid Plot vs. DW Dist - He=3m - 0.08m Zo - w/o ADJ_U* - LW2 Option - v15181

Pred (AERMOD Degraded 1-Layer, Scalar WS) vs Obs (unfitted)
F-23

0

50

100

150

200

0 50 100 150 200

Predicted (μg/m3)

Observed (μg/m3)

Idaho Falls: Q-Q Plot - He=3m - 0.08m Zo - w/o ADJ_U* - LowWind3 Option - v15181

Obs (unfitted) vs AERMOD (Degraded 1-Layer, Scalar WS) Predicted Arc-Max @ 3 DW Arcs

100-m Arc

200-m Arc

400-m Arc

0

50

100

150

200

0 50 100 150 200

Predicted (μg/m3)

Observed (μg/m3)

Idaho Falls: Paired Plot - He=3m - 0.08m Zo - w/o ADJ_U* - LowWind3 Option - v15181

Obs (unfitted) vs AERMOD (Degraded 1-Layer, Scalar WS) Pred Arc-Max @ 3 DW Arcs

100-m Arc

200-m Arc

400-m Arc
F-24

0.01

0.10

1.00

10.00

100.00

100 - ns=11 200 - ns=11 400 - ns=11

Predicted / Observed

Receptor Arcs

Idaho Falls: Resid Plot vs. DW Dist - He=3m - 0.08m Zo - w/o ADJ_U* - LW3 Option - v15181

Pred (AERMOD Degraded 1-Layer, Scalar WS) vs Obs (unfitted)
F-25

0

50

100

150

200

0 50 100 150 200

Predicted (μg/m3)

Observed (μg/m3)

Idaho Falls: Q-Q Plot - He=3m - 0.08m Zo - With ADJ_U* - NoLW Option - v15181

Obs (unfitted) vs AERMOD (Degraded 1-Layer, Scalar WS) Predicted Arc-Max @ 3 DW Arcs

100-m Arc

200-m Arc

400-m Arc

0

50

100

150

200

0 50 100 150 200

Predicted (μg/m3)

Observed (μg/m3)

Idaho Falls: Paired Plot - He=3m - 0.08m Zo - With ADJ_U* - NoLW Option - v15181

Obs (unfitted) vs AERMOD (Degraded 1-Layer, Scalar WS) Pred Arc-Max @ 3 DW Arcs

100-m Arc

200-m Arc

400-m Arc
F-26

0.01

0.10

1.00

10.00

100.00

100 - ns=11 200 - ns=11 400 - ns=11

Predicted / Observed

Receptor Arcs

Idaho Falls: Resid Plot vs. DW Dist - He=3m - 0.08m Zo - With ADJ_U* - NoLW Option - v15181

Pred (AERMOD Degraded 1-Layer, Scalar WS) vs Obs (unfitted)
F-27

0

50

100

150

200

0 50 100 150 200

Predicted (μg/m3)

Observed (μg/m3)

Idaho Falls: Q-Q Plot - He=3m - 0.08m Zo - With ADJ_U* - LowWind1 Option - v15181

Obs (unfitted) vs AERMOD (Degraded 1-Layer, Scalar WS) Predicted Arc-Max @ 3 DW Arcs

100-m Arc

200-m Arc

400-m Arc

0

50

100

150

200

0 50 100 150 200

Predicted (μg/m3)

Observed (μg/m3)

Idaho Falls: Paired Plot - He=3m - 0.08m Zo - With ADJ_U* - LowWind1 Option - v15181

Obs (unfitted) vs AERMOD (Degraded 1-Layer, Scalar WS) Pred Arc-Max @ 3 DW Arcs

100-m Arc

200-m Arc

400-m Arc
F-28

0.01

0.10

1.00

10.00

100.00

100 - ns=11 200 - ns=11 400 - ns=11

Predicted / Observed

Receptor Arcs

Idaho Falls: Resid Plot vs. DW Dist - He=3m - 0.08m Zo - With ADJ_U* - LW1 Option - v15181

Pred (AERMOD Degraded 1-Layer, Scalar WS) vs Obs (unfitted)
F-29

0

50

100

150

200

0 50 100 150 200

Predicted (μg/m3)

Observed (μg/m3)

Idaho Falls: Q-Q Plot - He=3m - 0.08m Zo - With ADJ_U* - LowWind2 Option - v15181

Obs (unfitted) vs AERMOD (Degraded 1-Layer, Scalar WS) Predicted Arc-Max @ 3 DW Arcs

100-m Arc

200-m Arc

400-m Arc

0

50

100

150

200

0 50 100 150 200

Predicted (μg/m3)

Observed (μg/m3)

Idaho Falls: Paired Plot - He=3m - 0.08m Zo - With ADJ_U* - LowWind2 Option - v15181

Obs (unfitted) vs AERMOD (Base 1-Layer, Scalar WS) Pred Arc-Max @ 3 DW Arcs

100-m Arc

200-m Arc

400-m Arc
F-30

0.01

0.10

1.00

10.00

100.00

100 - ns=11 200 - ns=11 400 - ns=11

Predicted / Observed

Receptor Arcs

Idaho Falls: Resid Plot vs. DW Dist - He=3m - 0.08m Zo - With ADJ_U* - LW2 Option - v15181

Pred (AERMOD Degraded 1-Layer, Scalar WS) vs Obs (unfitted)
F-31

0

50

100

150

200

0 50 100 150 200

Predicted (μg/m3)

Observed (μg/m3)

Idaho Falls: Q-Q Plot - He=3m - 0.08m Zo - With ADJ_U* - LowWind3 Option - v15181

Obs (unfitted) vs AERMOD (Degraded 1-Layer, Scalar WS) Predicted Arc-Max @ 3 DW Arcs

100-m Arc

200-m Arc

400-m Arc

0

50

100

150

200

0 50 100 150 200

Predicted (μg/m3)

Observed (μg/m3)

Idaho Falls: Paired Plot - He=3m - 0.08m Zo - With ADJ_U* - LowWind3 Option - v15181

Obs (unfitted) vs AERMOD (Degraded 1-Layer, Scalar WS) Pred Arc-Max @ 3 DW Arcs

100-m Arc

200-m Arc

400-m Arc
F-32

0.01

0.10

1.00

10.00

100.00

100 - ns=11 200 - ns=11 400 - ns=11

Predicted / Observed

Receptor Arcs

Idaho Falls: Resid Plot vs. DW Dist - He=3m - 0.08m Zo - With ADJ_U* - LW3 Option - v15181

Pred (AERMOD Degraded 1-Layer, Scalar WS) vs Obs (unfitted)
F-33

The Lovett data base includes a single 145m stack located within a few kilometers of complex 

terrain. The site area is shown below:

The Lovett data base includes a 100m meteorological tower with wind speed, wind direction, 

sigma-theta and temperature collected at the 10m, 50m, and 100m levels. In addition, sigma-w 

was also collected at the 10m and 100m levels. Past evaluations of AERMOD have shown good 

performance. Updated 1-hour results are presented below comparing model performance with 

full onsite meteorological data with and without the ADJ_U* and LowWind options, followed by 
F-34

comparisons with and without the ADJ_U* and LowWind options using degraded 

meteorological data inputs. Including the ADJ_U* option with full onsite meteorological data 

shows a slight improvement in model performance without the LowWind options, and little 

difference in performance for the LowWind2 compared to LowWind3 (the LowWind1 option 

was not included in this study.

The next set of comparisons are based on no temperature profile in the Lovett site-specific 

meteorological data. The model shows some overprediction without the temperature profile and 

without the ADJ_U* option, especially without the LowWind options. The model overprediction 

without the temperature profile is noticeably reduced when the ADJ_U* option is used. The 

modeled results shows more significant overprediction when the meteorological data is further 

degraded by eliminating the turbulence data (i.e., sigma-theta and sigma-w), with the 

overprediction bias exceeding a factor of 2. The overprediction without the temperature profile 

and turbulence data is significantly reduced when the ADJ_U* and LowWind options are used.

It’s also worth noting that results for the LowWind2 (LW2) and LowWind3 (LW3) options are 

nearly indistinguishable in this case.
F-35

10

100

1,000

10 100 1,000

MODELED

OBSERVED

LOVETT SO2 COMPLEX TERRAIN EVALUATION

Q-Q Plot of 1-Hr Conc. - v15181 - Full OS Met NoAdj

AERMOD_NoAdj_NoLW

AERMOD_NoAdj_LW2

AERMOD_NoAdj_LW3

10

100

1,000

10 100 1,000

MODELED

OBSERVED

LOVETT SO2 COMPLEX TERRAIN EVALUATION

Q-Q Plot of 1-Hr Conc. - v15181 - Full OS Met w/Adj

AERMOD_Adj_NoLW

AERMOD_Adj_LW2

AERMOD_Adj_LW3
F-36

10

100

1,000

10 100 1,000

MODELED

OBSERVED

LOVETT SO2 COMPLEX TERRAIN EVALUATION

Q-Q Plot of 1-Hr Conc. - v15181 - NoTempProf NoAdj

AERMOD_NoAdj_NoLW

AERMOD_NoAdj_LW2

AERMOD_NoAdj_LW3

10

100

1,000

10 100 1,000

MODELED

OBSERVED

LOVETT SO2 COMPLEX TERRAIN EVALUATION

Q-Q Plot of 1-Hr Conc - v15181 - NoTempProf - w/Adj

AERMOD_Adj_NoLW

AERMOD_Adj_LW2

AERMOD_Adj_LW3
F-37

10

100

1,000

10,000

10 100 1,000 10,000

MODELED

OBSERVED

LOVETT SO2 COMPLEX TERRAIN EVALUATION

Q-Q Plot of 1-Hr Conc - v15181 - NoTempProf - NoTurb NoAdj

AERMOD_NoAdj_NoLW

AERMOD_NoAdj_LW2

AERMOD_NoAdj_LW3

10

100

1,000

10,000

10 100 1,000 10,000

MODELED

OBSERVED

LOVETT SO2 COMPLEX TERRAIN EVALUATION

Q-Q Plot of 1-Hr Conc - v15181 - NoTempProf - NoTurb w/Adj

AERMOD_Adj_NoLW

AERMOD_Adj_LW2

AERMOD_Adj_LW3
G-1

APPENDIX G. USER INSTRUCTIONS FOR THE BUOYANT LINE 

SOURCE OPTION IN AERMOD
G-2

AERMOD Keywords for Buoyant Line Sources

One LOCATION record for each line that comprises the buoyant line source.

SO LOCATION sourceID BUOYLINE Xb Yb Xe Ye (Zs)

Xb, Yb = coordinate of the beginning of the line source (m)

Xe, Ye = coordinate of the end of the line source (m)

Zs = line elevation (m) - optional; defaults to 0.0 if omitted

One SRCPARAM record for each line that comprises the buoyant line source.

SO SRCPARAM sourceID blemis relhgt

Blemis = emission rate (g/s/m2)

Relhgt = release height (m)

The BLPINPUT keyword defines the average values for the buoyant line (as a whole 

and not as the individual lines that comprise the buoyant line source). The order shown 

is the same as the input in BLP (in the namelist RISE), with the variable name used in 

BLP shown in parentheses. This keyword can only appear once.

SO BLPINPUT blavgblen blavgbhgt blavgbwid blavglwid blavgbsep blavgfprm

blavgblen (L) = average building length (m)

blavgbhgt (HB) = average building height (m)

blavgbwid (WB) = average building width (m)

blavglwid (WM) = average line source width (m) (of the individual lines)

blavgbsep (DX) = average building separation (m) (between the individual lines)

blavgfprm (FPRIME) = average buoyancy parameter (m4/s3)

The BLPGROUP keyword identifies the buoyant lines that comprise the single buoyant 

line source. For the initial release, the BLPGROUP will not affect how AERMOD/BLP 

groups and processes the individual lines, i.e., AERMOD/BLP will process all lines as a 

single buoyant line source. This keyword will be useful when AERMOD is updated to 

process multiple buoyant line sources.

SO BLPGROUP BLPGrpID BuoyantLine SrcID’s and/or SrcRange’s

 or

SO BLPGROUP ALL