US EPA Releases AERMOD and AERMET Version 22112 and MMIF 4.0

AERMOD is the preferred air quality dispersion model of US-EPA and it is used all over the world as reference model for regulatory purposes.

On June 27, 2022, the U.S. EPA announced an upgrade to version 22112 of AERMOD and its meteorological data processor AERMET

The meteorological data processor MMIF has been updated, as well.

AERMOD 22112, AERMET 22112 and MMIF 4.0 include various bug fixes and some enhacements. The modifications are listed here.

Main updates and new options in AERMOD 22112 are:

  • Correction to calculation of plume penetration factor for tall stacks in an urban environment.
  • Correction to double counting the NO2 background concentrations when the PVMRM NOX-to-NO2 Tier 3 method is applied when modeling NO2.
  • Correction to number of BUOYLINE sources. Originally limited to 10, corrected to have no limit.
  • Correction to urban option for all source types and source-specific corrections BUOYLINE and RLINE/RLINEXT source types.
  • Debug files added for BUOYLINE and RLINE/RLINEXT source types and urban option.
  • Added meander to RLINE/RLINEXT source types.
  • General speed improvements for RLINE/RLINEXT source types.
  • Added RLINE/RLINEXT to FASTALL option.
  • Removed ALPHA requirement for using the urban option with RLINE/RLINEXT and source types. Note the use of the RLINE source type requires the BETA keyword and RLINEXT requires the ALPHA keyword.
  • NOMINO3 option has been added that removes the nighttime, stable, minimum ozone restriction of 40 ppb (78 ug/m3) for NO2 conversion.
  • The GRSM NO2 conversion method has been changed from ALPHA to BETA status.
  • The TTRM2 NO2 conversion method has been added as a new ALPHA NO2 conversion technique. TTRM2 applies the existing TTRM method with one of ARM2, OLM, or PVMRM and will select the lowest NO2 concentration from TTRM and the other selected NO2 technique.
  • Added platform downwash algorithm from the OCD model for offshore platforms as an ALPHA option. Platform downwash is enabled using the new keyword PLATFORM on SO pathway to input overwater platform dimensions. Platform downwash has been implemented for POINT, POINTHOR, and POINTCAP source types. Platform downwash does not utilize the PRIME downwash algorithm.
  • Added experimental source type SWPOINT as an ALPHA option to facilitate further research of sidewash phenomena caused by building downwash. Sidewash occurs when wind is at an oblique angle to the long side of an elongated building. In this circumstance, there is a lateral shift of the cavity that forms on the lee side of the building. This a point type source with limited input and no buoyancy and does not utilize the PRIME building downwash algorithm.
  • Added two ALPHA low wind options (FRANmin and PBAL) to the LOW_WIND keyword in the CO pathway. FRANmin is a user-specified minimum value for the meander factor within a range of 0.0 - 1.0 which overrides the default value of 0.0. PBAL is a secondary keyword to replace the default energy balance approach to determining plume meander with a momentum balance approach.

Main updates and new options in AERMET 22112 are:

  • AERMET now is composed of two stages instead of three stages. The first stage is unchanged, data ingestion and QA of NWS upper air data, NWS surface data, site- specific, or prognostic data. The merge stage, stage 2, has been eliminated. The old stage 3, the boundary layer calculations, is now stage 2. Throughout the rest of this memorandum, stage 2 refers to the boundary layer calculations stage.
  • AERMET 22112 can now run both stage 1 and stage 2 in a single AERMET run.
  • A new pathway, PROG for prognostic meteorological data, has been created. This pathway is analogous to the ONSITE pathway and allows AERMET to recognize the data is prognostic in nature. This pathway also allows for the special processing of overwater prognostic data. Prognostic data can be designated as overland or overwater with the PROG data keyword. This designation aids AERMET in determining which prognostic variables to process from the MMIF generated data file.
  • When inputting the processing dates via the XDATES keyword, the user must now input the years as 4-digit years.
  • AERMET retains the original case of input and output filenames from the control file. This makes the code more portable across operating systems.
  • The EXTRACT and QAOUT files have different formats than previous versions of AERMET. The ONSITE and PROG QAOUT file now has a consistent format regardless of the input data. Previously, the ONSITE QAOUT file followed the format of the raw input data file.
  • A new upper air data source, the Integrated Global Radiosonde Archive (IGRA) has been added in addition to the 6201 and FSL formats.
  • > AERMET now allows for the specification of year specific surface characteristics via the FREQ_SECT, FREQ_SECT2, AERSURF, and AERSURF2 keywords. This allows for a multi-year AERMET run for stage 2 in one AERMET run instead of separate annual AERMET runs when surface characteristics change on an annual basis.
  • For seasonal surface characteristics only, AERMET uses the primary and secondary station coordinates to determine the hemisphere of the respective station. This is used to allocate the seasonal characteristics to the appropriate months based on the hemisphere. For example, for winter characteristics, if the station is in the northern hemisphere, the winter characteristics are assigned to January, February, and December. If the station is in the southern hemisphere, then the winter characteristics are assigned to June-August. This feature allows the user to enter seasonal characteristics that represent the season for the hemisphere. That is, for applications in the southern hemisphere, the user does not need to assign representative summer surface characteristics to winter so that AERMET will assign the characteristics to the correct months.
  • For applications involving site-specific or prognostic mixing heights, AERMET 22112 smooths the mixing height based on the previous hour's mixing height in similar fashion as when AERMET calculates mechanical mixing heights. Previous versions of AERMET did not smooth the mechanical mixing heights read from the site-specific or prognostic data.
  • The variables that are type real in FORTRAN are now double precision in AERMET.


    • AERMET 22112 requires some fixes to compile with gfortran under Linux. You can read more here.

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