Documentation of the Evaluation of CALPUFF and Other Long ...

ecommendations for using the CALPUFF LRT dispersion model for addressing far‐field air
quality and AQRV issues at Class I areas. The IWAQM Phase II report did not recommend any
specific settings for running CALMET and noted that the required expert judgment to develop a
set of recommended CALMET settings would be developed over time.
In 2003, EPA issued revisions to the Guidelines on Air Quality Models (Appendix W) that
recommended using the CALPUFF LRT dispersion model to address far‐field (> 50 km) air quality
issues associated with chemically inert compounds. The EPA Air Quality Modeling Guidelines
were revised again in 2005 to include AERMOD as the EPA‐recommended dispersion model for
near‐source (< 50 km) air quality issues.
CALPUFF Modeling Guidance
EPA convened a CALPUFF workgroup starting in 2005 to help identify issues with the 1998
IWAQM Phase II recommendations. The CALPUFF workgroup began to revisit the evaluation of
CALPUFF against tracer test field experiments. In May 2009, EPA released a reassessment of
the IWAQM Phase II recommendations (EPA, 2009a) that raised issues with settings used in
recent CALMET model applications. CALMET is typically applied using prognostic
meteorological model (i.e., MM5 or WRF) three‐dimensional wind fields as an input first guess
and then applying diagnostic wind effects (e.g., blocking, deflection, channeling and slope
flows) to produce a STEP1 wind field. CALMET then blends in surface and upper‐air
meteorological observations into the STEP1 wind field using an objective analysis (OA)
procedure to produce the resultant STEP2 to wind field that is provided as input into CALPUFF.
CALMET also diagnoses several other meteorological variables (e.g., mixing heights). CALMET
contains numerous options that can significantly affect the resultant meteorological fields. The
EPA IWAQM reassessment report found that the CALMET STEP1 diagnostic effects and STEP2
OA procedures can degrade the MM5/WRF wind fields. Furthermore, the IWAQM
reassessment report noted that options used in some past CALMET applications were selected
based on obtaining a desired outcome rather than based on good science. Consequently, the
2009 IWAQM reassessment recommended CALMET settings that would “pass through”
MM5/WRF meteorological fields as much as possible for input into CALPUFF. However, further
testing of CALMET by the EPA CALPUFF workgroup found that the recommended CALMET
settings in the May 2009 IWAQM reassessment report did not achieve the intended desired
result to “pass through” as much as possible the MM5/WRF meteorological variables as
CALMET still re‐diagnosed some and modified other meteorological variables. Based in part on
testing by the CALPUFF workgroup using the tracer test field experiments, on August 31, 2009
EPA released a Clarification Memorandum (EPA, 2009b) that contained specific EPA‐FLM
recommended settings for operating CALMET for regulatory applications.
Mesoscale Model Interface (MMIF) Tool
In the meantime, EPA has developed the Mesoscale Model Interface (MMIF) tool that will “pass
through” as much as possible the MM5/WRF meteorological output to CALPUFF without
modifying the meteorological fields (Emery and Brashers, 2009; Brashers and Emery 2011;
2012). The CALPUFF Workgroup has been evaluating the CALPUFF model using the CALMET
and MMIF meteorological drivers for four tracer test field experiments. For some of the field
experiments, additional LRT dispersion models have also been evaluated. This report
documents the work performed by the CALPUFF workgroup over the 2009‐2011 time frame to
evaluate CALPUFF and other LRT dispersion models using four tracer test field experiment
databases.
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