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Guidance on the Use of the Mesoscale Model
Interface Program (MMIF) for AERMOD
Applications

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EPA-454/B-23-006
October 2023

Guidance on the Use of the Mesoscale Model Interface Program (MMIF) for

AERMOD Applications

U.S. Environmental Protection Agency
Office of Air Quality Planning and Standards
Air Quality Assessment Division
Research Triangle Park, North Carolina

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Preface

This document provides guidance on the use of prognostic meteorological data and the
Mesoscale Model Interface Program (MMIF) in AERMOD. Included in this document are
descriptions of the inputs to MMIF and recommendations on using MMIF output in AERMOD.
This document is an update of the June 2022 MMIF guidance document (EPA-454/B-22-011)
and reflects changes to MMIF from MMIF version 4.0 to version 4.1 and the update from
AERMET 22112 to AERMET 23132 to support overwater MMIF applications with the addition
of the Coupled Ocean Atmosphere Response Experiment (COARE) algorithms to AERMET
proposed in the 2023 revision of the Guideline on Air Quality Models.

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Acknowledgements

MMIF was developed by Ramboll Environ International Corporation under EPA contract
number EP-D-07-102, work assignments 2-06, 4-06, 5-08, and 10-1 and EPA Contract No EP-D-
12-044, work assignment 4-07. The MMIF user's guide was developed by Bart Brashers, Chris
Emery, and Prakash Karamchandani of Ramboll Environ. This guidance document was
developed by the Air Quality Modeling Group of the Air Quality Assessment Division of the
Office of Air Quality Planning and Standards in collaboration with representatives of EPA
Regions 5, 7, and 8.

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Contents

Preface	ii

Acknowledgements	iii

Tables	v

1.	Introduction	1

2.	Guidance on using prognostic meteorological data for use in AERMOD	1

2.1	Number of years to model	2

2.2	Prognostic model options	2

2.2.1 Development of meteorological fields	2

2.3	Model output quality assurance	3

2.3.1 Operational evaluation	3

3.	Guidance on running MMIF for AERMOD	3

3.1	MMIF Input File	4

3.2	Recommended options for selected keywords	7

3.2.1	Outputs	7

3.2.1.1	AERMET	7

3.2.1.2	AERMOD	8

3.2.2	PBL calculations	8

3.2.3	Output layers and heights	9

3.2.4	Grid cells to process	9

3.3	Surface characteristics	10

3.4	Treatment of low winds	10

3.5	Minimum mixing height and absolute value of Monin-Obukhov length	10

3.6	Overland and overwater applications	11

3.7	Post-processing of outputs	12

4.	References	14

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Tables

Table 1. AERMET/AERMOD keywords in MMIF input file

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1. Introduction

The guidance discussed in this document are recommendations for running the Mesoscale Model
Interface (MMIF) program1 to generate inputs for AERMET and AERMOD. The guidance
discussed in this document is an update to the June 2022 MMIF guidance (EPA-454/B-22-011).
In this guidance document, when references are made to running MMIF for AERMOD, it should
be inferred that this refers to AERMET as well. For regulatory applications, MMIF should be
run to generate AERMET inputs as stated in section 8.4.2(a) and 8.4.5.1(b) of the final revisions
to EPA's Guideline on Air Quality Models (U.S. EPA, 2017)2 and the proposed 2023 revisions to
Appendix W. Regulatory applications that do not follow these sections of Appendix W will need
to consult with the appropriate reviewing authority and guidelines outlined in section 3.2 of
Appendix W. Given that Appendix W and specific EPA modeling guidance are often cited in
relation to other non-regulatory modeling applications, such as air quality analysis and disclosure
purposes under NEPA, the approach presented in this guidance document for regulatory
applications also has relevance to these non-regulatory applications. While MMIF can process
data for other air quality models (e.g., CALPUFF and SCICHEM), the emphasis in this guidance
is for AERMOD applications conducted for regulatory purposes.

This guidance document will summarize some of the inputs needed for AERMET and
AERMOD MMIF processing but will refer to the MMIF User's Guide (Ramboll Environ, 2023)
for more details. MMIF users are strongly encouraged to read this user's guide to obtain specific
details on running MMIF

2. Guidance on using prognostic meteorological data for use in AERMOD

In general, air quality modeling applications rely on the use of meteorological grid models.

These models are used to more accurately simulate atmospheric processes (e.g., temperature,
wind speed and direction, etc.) across a specific area. In retrospective simulations (i.e., modeling
past events), the blending of observed data with computed fields yields results that are bound by
ground truth.

There are several meteorological grid models that can be used to develop inputs for air quality
models. The most used by EPA and the modeling community is the Weather Research and
Forecasting (WRF) model (Skamarock et al., 2008)3, which is supported across a broad
community and provides state-of-the-science parameterizations of the atmosphere. Additionally,
the Fifth Generation Penn State/NCAR Mesoscale Model (MM5) (Grell et al., 1994) can

1	http://www.epa.gov/ttn/scram/dispersion_related.htm#mmif

2	Hereafter, the Guideline will be referred to as Appendix W.

3	http://www.wrf-model.org/index.php

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generate the necessary meteorological inputs to air quality models; however, its development and
maintenance is no longer supported.

2.1	Number of years to model

As discussed in Section 8.4.2(e) of Appendix W (both final 2017 and proposed 2023 revisions),
at least three years are required to be modeled in the prognostic model. The most recent three
years are preferred, and the prognostic model domain or selected grid cells should be
representative of the domain. See Section 8.4.b of Appendix W for more details about
representativeness of meteorological data.

2.2	Prognostic model options

2.2.1 Development of meteorological fields

For development of prognostic meteorological fields, a rigorous approach has been established
within the atmospheric chemistry community. In this section, a basic guideline for
recommendations on producing prognostic meteorological data will be provided. For more
details related to approaches on developing modeled meteorology, please see Section 2.6 of the
Modeling Guidance for Demonstrating Attainment of Air Quality Goals for Ozone, PM2.5, and
Regional Haze (U.S. EPA, 2014).

Dynamic meteorological models such as WRF and MM5, have myriad options available to solve
for various processes within the atmosphere. Specific model options will not be provided, given
that different areas of interest may respond differently under certain conditions. It is expected
that the physical options chosen will be thoroughly evaluated to support their use.

With regards to defining a meteorological modeling domain, it is recommended that the domain
be of sufficient size and resolution to adequately capture mesoscale characteristics that impact a
source location. As an example, in an area of complex, mountainous terrain, the nearest NWS
observation site may not be adequately representative. In this case, the scale of meteorological
model is recommended to be high enough to capture specific mountain/valley flows and be large
enough to represent the upstream and other mesoscale meteorological features. Conversely, in
areas where terrain and mesoscale characteristics may be more homogenous, a reasonably coarse
model resolution may be applied. In addition, to avoid issues with grid boundary effects, it is
recommended the modeling domains be centered over the source location. Specific case
examples are provided in U.S. EPA (2018).

It is also recommended that any meteorological modeling be performed using four-dimensional
data assimilation (FDDA) as outlined in U.S. EPA (2014). FDDA involves providing the model
with inputs related to observed and/or analyzed meteorological conditions. This technique is

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useful in improving atmospheric simulations and constraining the model from varying widely
from actual observations.

2.3 Model output quality assurance
2.3.1 Operational evaluation

Demonstration of the adequacy of prognostic meteorological fields can be established through
appropriate diagnostic and statistical performance evaluations consistent with recommendations
provided in the appropriate EPA guidance. A quantitative, statistical, and graphical analysis of
the prognostic data should be completed, comparing the data to available NWS automated
surface observation station (ASOS) data, as well as operational profiler data (if available),
pairing both in space and time. This analysis should be completed for all years (at least three) of
prognostic meteorological data to be used in the air quality simulations. Since the spatial scope
of each variable could be different, representativeness should be judged for each variable
separately as discussed in Section 8.4.2(b) of the final Appendix W (U.S. EPA, 2017). For
example, for a variable such as wind direction, the data should ideally be collected near plume
height to be adequately representative; especially for sources located in complex terrain,
whereas, for a variable such as temperature, data from a station several kilometers away from the
source may be adequately representative. The grid resolution of the prognostic meteorological
data should also be considered and evaluated appropriately, particularly for projects involving
complex terrain. Several software packages are available for use in completing this evaluation
(e.g., AMET (Appel et al., 2011) and METSTAT (http://www.camx.com/download/support-
software.aspx)). The adequacy of output from the meteorological models is contingent upon the
concurrence with the appropriate reviewing authorities as defined in section 8.4.5.2(a) of the
final Appendix W.

3. Guidance on running MMIF for AERMOD

Much of the guidance presented here follows the MMIF user's guide (Ramboll Environ, 2023).
Relevant information from the user's guide is summarized in this guidance for convenience but
the user is strongly encouraged to read the full MMIF user's guide before attempting to run
MMIF. Section 3.1 below discusses the inputs to MMIF, Section 3.2 discusses the relevant
options to AERMOD and grid cells to process. Section 3.3 discusses the use of surface
characteristics outside of MMIF, Sections 3.4 and 3.5 discuss the use of minimum wind speeds,
mixing height and Monin-Obukhov length, Section 3.6 discusses the new features for overland
and overwater processing, and Section 3.7 discusses post-processing the output from MMIF
needed for input into AERMOD.

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3.1 MMIF Input File

MMIF processing is done via a control file with keywords to denote inputs, processing options,
and outputs. Table 1 lists the keywords used to run MMIF for AERMET and AERMOD input
only. A sample control file that illustrates all the keywords can be generated for MMIF by
typing "mmif-sample" at the command prompt. See Section 4.2 of the User's Guide (Ramboll
Environ, 2023) for more information.

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Table 1. AERMET/AERMOD keywords in MMIF input file.

Keyword

Description

Syntax

Start

Date and time (Local Standard Time) to start
processing

Start YYYY MM DD HH
Or

Start YYYYMMDDHH
Or

Start YYYY-MM-
DD HH:mm:ss





Stop

Date and time (LST) to stop processing

Stop YYYY MM DD HH
Or

Stop YYYYMMDDHH
Or

Stop YYYY-MM-
DD HH:mm:ss









Timezone

The global time zone shift from Greenwich Mean
Time (GMT); Western

hemisphere time zones are denoted by negative
numbers

Timezone HH

Grid

Specifies the requested output sub-grid's lower left
(LL) and upper right (UR) corners; Grid corners can
be specified by grid cell I, j coordinates (IJ), latitude
and longitude (LL or LATLON) or MM5/WRF
projected coordinate system (KM)

GRID IJ iLL jLL iUR jUR
Or

GRID LL LatLL LonLL LatUR
LatRR
Or

GRID KM xLL yLL xUR yUR

Point

Output point for AERMET, AERMOD, or
AERCOARE processing. The point can be specified
by grid cell I, j coordinates (IJ), latitude and
longitude (LL or LATLON) or MM5/WRF projected
coordinate system (KM). An optional time zone
shift can also be listed1. The point keyword can be
repeated for each point to be outputted.

Point IJ IJ [Timezone]

Or

POINT LL Lat Lon [Timezone]
Or

POINT KM X Y [Timezone]

Layers

Specify the output layer structure. Layers can be
aggregated (K), interpolated using layer tops (TOP),
or interpolated using mid layer (MID).

Layers K Layeri
Layer2...LayerN
Or

Layers TOP Topi Top2...TopN
Or

Layers MID Midi Mid2.. .MidN





Origin

Over-ride the X,Y grid origin values found in the
MM5 or WRF output file. The user specifies a
latitude (LAT) and longitude (LON).

Origin LAT LON

C AL S CIMIXHT

A value of WRF causes MMIF to pass through the
PBL depth from the model with no changes. A value
of MMIF causes MMIF to re-calculate PBL depths
using a Bulk Richardson approach with 20 times the
vertical resolution of the model data.

WRF or MMIF

AERMIXHT

Option to specify what mixing heights to use for
MMIF to AERMET processing. Options are WRF
(no recalculation of mixing heights), MMIF (MMIF
recalculated mixing heights) or AER MIXHT (allow
AERMET to calculate mixing heights)

WRF, MMIF, or
AERMIXHTS

AERMINMIXHT

Specify the minimum allowed mixing height for
AERMOD SFC output. Default is 1 m as based on
AERMET

AER MIN MIXHT VALUE

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Table 1. Continued

Keyword

Description

Syntax

AERMINOBUK

Specify the minimum allowed absolute value of the
Monin-Obukhov length for AERMOD SFC output. The
default is 1 m as based on AERMET

AER MIN OBUK VALUE

AERMINSPEED

Specify the minimum wind speed in m/s (VALUE) for
AERMOD surface output file. This value should be set
to 0 for both MMIF to AERMET and MMIF to
AERMOD output.

AER MIN SPEED VALUE

FSLINTERVAL

Specify the number of hours (VALUE) to write for
each day to the upper air file for input into AERMET.
The default value is 12 representing the 00Z and 12Z
soundings. A value of 6 would write output for 00Z,
06Z, 12Z, and 18Z. A value of 1 would write output
for each model hour.

FSL INTERVAL VALUE

AERLAYERS

Specify the lowest and highest layer indices (two
integers) to write to the AERMET input site-specific
data and AERMOD profile file (PFL file). All layers
between the two indices will be written to the file.

AER LAYERS VALUE

OUTPUT

Specifies the outputs from MMIF for AERMET,
AERCOARE, and AERMOD (MODEL keyword) and
output files2.

OUTPUT MODEL FORMAT
FILENAME

INPUT

Input MM5 or WRF filename. This input is repeatable
for a MMIF run.

INPUT FILENAME

METFORM

Keyword to tell MMIF which model MM5 or WRF is
being accessed. MMIF can auto-detect the model type
so in general this is not needed.

METFORM MM5
Or

METFORM WRF

CLOUDCOVER

Specify the source of the cloud cover written by MMIF

CLOUDCOVER ANGEVINE
Or

CLOUDCOVER WRF
Or

CLOUDCOVER RANDALL









AERU SETSKC

Specify if cloud cover is required output for AERMET.
The default value if F and should be set to F for use
with AERMET version 21112 and earlier. The value
can be T for AERMET versions 22112 and later.

AERU SETSKC VALUE

AER_U SE_NEW

Specify if outputs are for versions of AERMET 21112
or earlier (set to F) or 22112 and later (set to T). The
default value is F

AER_U SE_NE W VALUE







1.	See Section 4.2 of the MMIF user's guide regarding the global time zone shift and point specific time zone
shifts.

2.	More information about the output options is discussed in Section 3.2 below.

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3.2 Recommended options for selected keywords

While most input options will be left to the discretion of the user, some recommendations on
inputs are made in this guidance. One such option is the output option of MMIF, keyword
OUTPUT. While MMIF can process data for input into AERMET, or AERMOD, the
requirement for regulatory applications is to process the prognostic meteorological data for input
into AERMET as discussed in Sections 8.4.2(a) and 8.4.5.1(b) of Appendix W, as AERMET is
the meteorological pre-processor for AERMOD as discussed in those sections. The data is then
processed in AERMET for input into AERMOD. Processing MMIF output through AERMET
also allows the user to take advantage of some of the options in AERMET, such as the u*
adjustment option. See the AERMET user's guide for details about options (U.S. EPA, 2022).
For non-regulatory applications, the user may choose AERMET or AERMOD and should
consult with and seek concurrence from collaborating agencies or parties involved in such
modeling applications.

3.2.1 Outputs

For any air quality model, the OUTPUT option is used to specify several files. While these are
discussed in the MMIF user's guide in detail, they are summarized below for AERMET and
subsequent input AERMOD and direct input into AERMOD as well (non-regulatory
applications).

3.2.1.1 AERMET

For AERMET, the first set of files is specified using the USEFUL keyword. This keyword
creates a DOS batch file or Linux shell script that is used to run AERMET and the appropriate
number of input files, depending on the AERMET version. For AERMET versions 21112 and
earlier (AERUSENEW = F), the DOS batch file or Linux shell script that is created runs all
three stages of AERMET in batch mode. It also creates the stage 1, stage 2, and stage 3 input
files with the appropriate values set for the AERMET keywords such as LOCATION, XDATES,
etc. For AERMET versions 22112 and later (AER USE NEW = T), the DOS batch file or
Linux shell script that is created runs stage 1 and 2 in a single combined run. It also creates the
combined stage 1 and 2 input file with the appropriate values set for the AERMET keywords
such as LOCATION, XDATES, etc. See the AERMET user's guide (U.S. EPA, 2023a) for
details on the combined stage 1 and 2 input file. Once the appropriate input stage files (stage 1,
2, and 3 for AERMET 21112 and earlier, combined stage 1 and 2 for AERMET 22112 and later)
have been created, the user should check those files to ensure the correct GMT offset is used.
For the upper air pathway of the stage 1 file, the LOCATION keyword should have a GMT
offset corresponding to the station's location. For example, if the processed grid cell is in the
Eastern time zone of the U.S. the GMT offset on the LOCATION keyword should be 5. For the
surface data, the offset should be zero as that has been formatted for local time.

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The second file that is generated is specified using the keyword ONSITE. This creates a site-
specific type of meteorological file that is processed via the ONSITE path in AERMET for
AERMET 21112 and earlier or the PROG keyword for AERMET 22112 and later (U.S. EPA,
2022). The PROG and ONSITE pathways are largely analogous to each other. The PROG
pathway was introduced with AERMET 21DRF and 22112 to allow AERMET to process MMIF
output for overwater locations. This file contains 2-meter and 10-meter data and upper air data
up to levels specified with the keywords MINLAYER, MAXLAYER, or LAYERS to control
the number of output layers. Other data included are precipitation, surface pressure and mixing
height (if requested). Beginning with MMIF version 4.0, the following are also output: cloud
cover, sensible heat flux, latent heat flux, surface friction velocity (u*), hourly surface roughness
(zo), potential temperature lapse rate above the mixing height, Monin-Obukhov length, and
convective velocity scale (w*). Beginning with version 4.1, three additional variables, sea-
surface temperature, downward longwave radiation, and sea surface temperature measurement
depth are also output for overwater cells only. These variables are output in support of the
overwater variable pass-through introduced with AERMET 22112 and capability in AERMET to
use the Coupled Ocean Atmosphere Response Experiment (COARE) algorithms (Fairall, et al,
2003) introduced in AERMET 23132. See Section 3.6 below for more information about the
overland and overwater data flag.

The third keyword, FSL creates a file that mimics an upper air data file in the Forecast Systems
Laboratory (FSL) format. The keyword UPPERAIR can also be used. See Section 2.2.1 of the
MMIF user's guide for more details.

The final keyword is AERSFC, which generates an AERSURFACE type output file with surface
characteristics (albedo, Bowen ratio, and surface roughness). Note, that these are monthly
surface characteristics for the period being processed. See Section 2.2.1 of the MMIF user's
guide for more details.

3.2.1.2 AERMOD

Three files are generated for AERMOD. The USEFUL file is a file containing the ME pathway
information of the AERMOD input file, i.e., ME STARTING, SURFFILE, PROFFILE,
SURFDATA, UADATA, etc. information. The SFC keyword generates the AERMOD ready
surface data file and the PFL keyword generates the profile data file for input into AERMOD.

3.2.2 PBL calculations

Three options are available for PBL or mixing height calculations when processing MMIF to
output files for AERMET inputs via the AER MIXHT option, 1) a pass through of the WRF
PBL heights (AER_MIXHT=WRF), 2) recalculation of the PBL heights using a Bulk
Richardson approach (AER_MIXHT=MMIF), based on Vogelezang and Holtslag (1996) and
Louis (1979) and, no PBL heights passed to the AERMET site-specific data file
(AER_MIXHT=AERMET). This option uses AERMET to use its own algorithms to calculate

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mixing heights. For MMIF inputs to AERMOD, there are still two options available via the
CALSCI MIXHT option (formerly the PBLrecalc option). The two options are passing the
WRF mixing heights (MIXHT=WRF) or recalculation by MMIF (MIXHT=MMIF). At this
time, the choice of which option to use is left to the discretion of the user as limited evaluations
(U.S. EPA, 2018) have shown little difference in the three methods. Note that if a user utilizes
the PBL pass through or recalculation method and wishes to use AERMET derived mixing
heights later, the user can rerun MMIF or just omit the MIXHT variable and modify the read
statement for the site-specific meteorological file.

3.2.3 Output layers and heights

An important keyword for output is the LAYERS keyword. As shown in Table 1, the user can
specify different options for the output layers from MMIF. While the choice of layers is case
specific and may be dependent on the prognostic model's layer structure, two possible defaults
should be adequate in most cases. The first is based on the FLM guidance and the second is a
default use of MID (interpolation using layer mid-point heights) and the specification of heights
corresponding to the AERMOD vertical grid. These heights are: 25, 50, 75, 100, 125, 150, 175,
200, 250, 300, 350, 400, 450, 500, 600, 700, 800, 900, 1000, 1500, 2000, 2500, 3000, 3500,
4000, 4500, and 5000. These values have been used in past MMIF evaluations (U.S. EPA,
2018). The LAYERS keyword controls the output of the FSL formatted upper air file used by
AERMET and the profile file used by AERMOD when processing MMIF to AERMOD. The
AER LAYERS keyword is used to control the output of the site-specific data file read by
AERMET. The AER LAYERS can be a subset of the LAYERS values.

3.2.4 Grid cells to process

An AERMOD run uses surface meteorological data from one point and upper air data from one
point. While MMIF can process multiple points, i.e., grid cells, the grid cell used in the
AERMOD simulation should be representative of the modeling domain, following the
recommendations of Section 8.4.5(b) of Appendix W. Depending on the size of the modeling
domain and the grid resolution of the prognostic meteorological data, most often the
representative grid cell will be the grid cell containing the facility of interest. This will often be
the case for NSR/PSD types of applications. When the AERMOD modeling domain overlaps
several grid cells of the prognostic meteorological data, such as for SIP demonstrations, the grid
cell that is most representative of the domain should be selected following guidance on
representativeness in Sections 8.4.1.b and 8.4.2.b of the final Appendix W, or it may be
necessary to conduct multiple AERMOD runs for different grid cells and post-process the results
to calculate the appropriate concentration metrics for the application (i.e. design values).

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3.3 Surface characteristics

MMIF will output surface characteristics, albedo, Bowen ratio, and surface roughness for input
into AERMET and in the AERMOD ready surface meteorological file. When outputting data for
AERMET, MMIF outputs surface characteristics for one 360° sector at monthly resolution.
Beginning with MMIF 4.0, MMIF also outputs hourly surface roughness. The hourly surface
roughness is used by AERMET 22112 and later for overwater applications, but the monthly
value is used for overland applications. The surface characteristics are based on the land use
data used by the prognostic meteorological model. These surface characteristics should be used
as they are representative of the processed grid cell as discussed in Section 8.4.2(b) of the final
Appendix W.

3.4 Treatment of low winds

When processing MMIF for input into AERMET or AERMOD, MMIF will use the
AERMINSPEED value as a wind speed threshold, for which winds below that threshold are
treated as calms. This is for winds at any vertical level in the input dataset. For input to
AERMET, MMIF will generate the onsite wind speed threshold option (THRESHOLD keyword)
with the user supplied value (AER MIN SPEED) for the stage 1 AERMET input file.

Normally, the purpose of the threshold in AERMET is to treat winds below the threshold as calm
and the threshold speed is a function of the starting threshold of a site-specific anemometer. See
the AERMET user's guide (U.S. EPA, 2023a) for details about this option in AERMET. When
generating MMIF output for direct AERMOD input, winds below the AER MIN SPEED value
will be treated as calms in the AERMOD surface file. For both MMIF to AERMET and MMIF
to AERMOD, the user should set the minimum wind speed, AER MIN SPEED, to zero, since
the input is prognostic data and does not have a functional minimum threshold as found in an
anemometer.

When processing MMIF output in AERMET, if the lowest level's wind speed is below the
AERMET allowable limit (21/2 x avmin, where avmin=0.2 m/s), AERMET will reset the wind
speed to the lower limit allowed in AERMET for output to the surface file. This adjustment does
not take place for other levels in the WRF output file. See the AERMET user's guide for more
details (U.S. EPA, 2023a). When processing MMIF output for direct input to AERMOD, no
such adjustment will occur in MMIF. The wind speed from WRF is output to the AERMOD
surface and profile files.

3.5 Minimum mixing height and absolute value of Monin-Obukhov length

New, beginning in MMIF 3.3, is the ability to specific a minimum mixing height and minimum
value of Monin-Obukov length when processing MMIF for AERMOD output. The default
minimum values for each option are 1 m, as defined in Table 1 and discussed in the MMIF
User's Guide (Ramboll Environ, 2023). Currently, the defaults are the recommended values for

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these options. Note, these values are not to be confused with the minimum mixing height and
Monin-Obukhov length that can be specified for COARE processing (U.S. EPA, 2023a).

3.6 Overland and overwater applications

Beginning with MMIF 4.0, for AERMET 22112 and later, MMIF creates a single combined
stage 1 and 2 input file to AERMET. A new pathway, PROG, was added to AERMET
beginning with version 22112 (U.S. EPA, 2023a). The PROG pathway is analogous to the
ONSITE pathway and allows AERMET to output the data such that AERMOD knows the data
are derived from MMIF. As part of the new PROG pathway, MMIF outputs an optional data
type flag with the DATA keyword for the PROG data in the AERMET input file, only when
processing MMIF for AERMET 22112 or later. The data file associated with the DATA
keyword is the ONSITE data file described in Section 3.2.1 above. The new data flag is either
"OL" for overland or "OW" for overwater. MMIF automatically determines if the requested
grid cell is land based or water based and sets the flag accordingly. AERMET uses the flag to
appropriately use the variables in the ONSITE (or PROG) data file. If the data are overland, then
AERMET will ignore the input u*, cloud cover, Monin-Obukhov length, w*, potential
temperature lapse rate, sensible and latent heat fluxes,4 and hourly z0. AERMET 22112 will
process the MMIF output as done in previous versions of AERMET.

Beginning with AERMET version 23132, the user has two choices in AERMET to process data
that are overwater. The first option is to use the AERMET control file as it is output from MMIF
and use all input variables when needed, including the hourly z0, and use the Monin-Obukhov
length to determine the stability for the hour. The second option, introduced with the 2023
revisions to Appendix W (Section 8.4.6) is to use the COARE algorithms in AERMET and allow
the COARE algorithms to calculate variables such as surface friction velocity and Monin-
Obukhov length, among others. For guidance on the processing of prognostic data for overwater
applications and COARE processing in AERMET, as well as more information about the data
flag, see the AERMET User's Guide (U.S. EPA, 2023a). For an evaluation of the two options
see U.S. EPA (2023b).

In some applications, depending on the location and horizontal grid resolution of the prognostic
data, MMIF may determine the data are overland or overwater, but the application may be best
suited by the opposite designation. For example, a coastal location or location near a large
inland body of water (such as the Great Lakes) may be designated as overwater when in fact, the
application is best suited as treated as overland, or vice-versa. In such cases, the user can modify
the AERMET input control file to change the data flag. The user should exercise best
professional judgment and consult with the appropriate reviewing authority in such situations.

4 Latent heat flux is currently not used by AERMET for either overland or overwater applications.

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If the data flag is changed from "OW" to "OL", then the user should make the following changes
to the AERMET input control file:

1.	Change the DATA flag from OW to OL to tell AERMET the data are overland

2.	In the METPREP pathway, add the keyword string METHOD STABLEBL BULKRN.
This is done because AERMET will ignore the input cloud cover, Monin-Obukhov
length, and u* and will use the Bulk Richardson number approach to calculate u* and
Monin-Obukhov length as done with previous versions of AERMET and MMIF output.
See Section 3.7.11.1 of the AERMET User's guide (U.S. EPA, 2023a) for information
on the Bulk Richardson Number syntax.

If the data flag is changed from "OL" to "OW", then the user only has to change the data flag
from "OL" to "OW" in the AERMET control file. The user can also comment out the METHOD
STABLEBL BULKRN line, but AERMET will not use the Bulk Richardson Number approach
anyway since u* and Monin-Obukhov length are used or calculated by the COARE algorithms if
COARE processing is invoked (see below).

If the user wishes to use the COARE algorithms in AERMET with overwater data, the user
should make the following changes to the AERMET input control file:

1.	Add the keyword string METHOD COARE RUN COARE in the METPREP pathway.

2.	For any COARE options, add the string METHOD COARE along with the options. See
the AERMET user's guide for keywords and syntax

3.7 Post-processing of outputs

When processing MMIF for AERMET files, a single MMIF run will produce an upper air file in
the FSL format, a surface data file that will be read into AERMET as site-specific data, and
surface characteristics (albedo, Bowen ratio, and surface roughness) at monthly resolution for
twelve sectors. These output files will cover the period processed in MMIF. In most situations,
a single MMIF run will not cover an entire three period or even a one-year period. If that is the
case, the ONSITE files generated by the MMIF can be simply concatenated into a single file for
the three-year period or individual yearly files before input into AERMET. The files must be
concatenated in temporal order. The same can be done for the FSL files. For the surface
characteristics files, when using AERMET version 22112 or later, the user can specify the
surface characteristics file and appropriate years to use in the AERMET control file. See the
AERMET user's guide for details. When using versions of AERMET earlier than 22112, the
AERSFC files cannot be simply concatenated. For a single MMIF run, the surface
characteristics are output for all twelve months and sectors. The months outside of the data
processing window set by START and STOP will have missing values, while the months inside
the window will have non-missing values. To create a valid AERSFC file covering the entire
three-year period or desired period, an AERSURFACE file must be created with non-missing
values for all months and sectors. This can be created by simply cutting and pasting the non-
missing values for each month/sector combination into a single file. When creating this file, the
user should make sure to incorporate the header line from one of the files into the concatenated
file. This line is "** Generated by MMIF..." This line indicates to AERMET that the

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meteorological data comes from MMIF and not an observed site-specific dataset. This
information is then passed to AERMOD via the surface meteorological file created by
AERMET. While this does not affect the data calculations in AERMET and AERMOD,
including the line ensures transparency when data files are reviewed.

An alternative approach to the file concatenation steps described above, is to run AERMET for
each period processed and concatenate AERMOD ready surface and profile files from the
multiple AERMET runs. For the profile files, the files can be simply concatenated together,
preserving the temporal order of the data (e.g., January 1, hour 1 of the first processed year is the
first line and December 31, hour 24 of the last processed year is the last record of the
concatenated file). For the surface files, AERMET generates a header record for each file (the
record that lists the location, station identifiers, and AERMET version). When concatenating the
surface files, the header record for the first concatenated file should be retained. Only the data
records from the remaining surface files are needed. If the header records are retained for all
files, AERMOD will not run correctly. Again, the files should be concatenated in temporal
order. These steps also apply for processing AERMOD ready files when post-processing MMIF
output for AERMOD.

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4. References

Appel, K.W., Gilliam, R.C., Davis, N., Zubrow, A., and Howard, S.C.: Overview of the

Atmospheric Model Evaluation Tool (AMET) vl.l for evaluating meteorological and air
quality models, Environ. Modell. Softw., 26, 4, 434-443, 2011.

Fairall, C.W., E.F. Bradley, J.E. Hare, A.A. Grachev, and J.B. Edson, 2003: "Bulk

Parameterization of Air-Sea Fluxes: Updates and Verification for the CO ARE
Algorithm." J. Climate, 16, 571-591.

Grell, G., J. Dudhia, and D.R. Stauffer: A description of the fifth-generation Penn State/NCAR
Mesoscale Model (MM5), NCAR Tech. Note NCAR/TN-398+STR, 122 pp.

Louis, J.F. 1979. "A Parametric Model of Vertical Eddy Fluxes in the Atmosphere." Journal of
Atmospheric Science, 35, 187-202.

Ramboll Environ, 2023: The Mesoscale Model Interface Program (MMIF) Version 4.1 User's
Manual.

Skamarock, W. C., Klemp, J. B., Dudhia J., Gill, D. O., Barker, D. M., Duda, M. G., Huang, X-
Y., Wang, W., and Powers, J. G.: A Description of the Advanced Research WRF
Version 3, National Centre of Atmospheric Research, Boulder, Colorado, 2008.

U.S. EPA, 2017. Guideline on Air Quality Models. 40 CFR Part 51 Appendix W.

U.S. EPA, 2018: Evaluation of Prognostic Meteorological Data in AERMOD Applications.

EPA-454/R-18-002. U.S. Environmental Protection Agency, Research Triangle Park, NC
27711.

U.S. EPA, 2023a: User's Guide for the AERMOD Meteorological Preprocessor (AERMET).
EPA-454/B-23-005. U.S. Environmental Protection Agency, Research Triangle Park,
NC 27711.

U.S. EPA, 2023b: Evaluation of Prognostic Meteorological Data in AERMOD Overwater

Applications. EPA-454/R-23-010. U.S. Environmental Protection Agency, Research
Triangle Park, NC 27711.

Vogelezang D. and A. Holtslag, 1996. "Evaluation and model impacts of alternative boundary-
layer height formulations." Boundary Layer Meteor., 81, 245-26.

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United States	Office of Air Quality Planning and Standards	Publication No. EPA-454/B-23-006

Environmental Protection	Air Quality Assessment Division	October 2023

Agency	Research Triangle Park, NC

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