Proposed Replacement of CALINE3 

with AERMOD in Appendix W NPRM

11th Modeling Conference

Research Triangle Park, NC

August 12, 2015

Chris Owen

U.S. EPA/OAQPS/AQAD/AQMG

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CALINE3 workgroup

• Chris Owen (OAQPS)

• James Thurman (OAQPS)

• Laura Berry (OTAQ)

• David Heist (ORD)

• Mike Leslie (Region 5)

• Meg Patulski (OTAQ)

• Sue Kimbrough (ORD)

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Summary of EPA proposed actions for 

mobile source modeling

• Propose to replace CALINE3, CAL3QHC, and 

CAL3QHCR with AERMOD as the Appendix A preferred 

dispersion model for all mobile source modeling of inert 

pollutants 

• Proposal is based on the following:

– AERMOD has updated dispersion science relative to CALINE3

– Model intercomparisons show that AERMOD outperforms 

CALINE3

– Simplified implementation of mobile source modeling for CAA 

requirements 

• Updates to Sections 4.2.3 and 7.2.3 of the proposed 

Appendix W 

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CALINE3 Background/History

• CALINE3 developed by Benson (1979). 

– Dispersion theory based on “P-G stability classes”

– Single meteorological condition

• CAL3QHC developed from CALINE3 for screening 

– Adds queueing algorithm for emissions from intersections

• CAL3QHCR developed from CAL3QHC for refined 

analyses

– Adds the ability to use 1-year of meteorological data, hourly 

emissions variation, additional averaging periods

– Met preprocessor only available for very old met data

• CALINE3 replaced by CALINE4 (Benson, 1984)

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AERMOD Background/History

• Promulgated as the EPA’s preferred dispersion model for 

most applications in 2005 revisions to Appendix W

• Reflects state of the science dispersion model formulation, 

i.e., 

– Planetary boundary layer (PBL) scaling parameter to 

characterize stability and determine dispersion rates

– Monin-Obukhov (M-O) similarity profiling of winds near the 

surface

– In replacing ISC3 in 2005, one of the major technical 

advancements was to replace the P-G stability class dispersion 

estimates (same as CALINE3) with the turbulence-based 

dispersion rates consistent with PBL and M-O

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Model Performance Evaluations and 

Intercomparisons

• Result summaries in the following slides are 

based on Heist et al. (2013), Estimating near-road 

pollutant dispersion: A model inter-comparison, 

Trans. Res. D., 93-105

• Published findings from two field studies with 

emissions of SF6 tracer specifically designed for 

evaluation of mobile emission modeling

– CALTRANS99 tracer experiment

– Idaho Falls barrier tracer experiment

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CALTRANS Study: Model performance summary

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• Model statistics show that 

AERMOD/RLINE almost 

identical

• CALINE overpredicts

• Q-Q plot shows that 

AERMOD is best at highest 

CALINE3 concentrations

CALINE4 CALINE3

CALINE4
Idaho Falls Tracer Study: Model performance summary

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• Q-Q plot shows that 

AERMOD/RLINE is best at 

highest concentrations 

• Model statistics show that 

AERMOD/ADMS almost 

identical

• CALINE underpredicts

CALINE4

CALINE4
Streamlined implementation for mobile sources

• Appendix W NPRM will bring commonality and 

consistency in modeling analyses for EPA 

regulatory applications

– AERMOD already preferred for PM2.5, PM10

– One model for mobile sources rather than 4

– AERMOD has more options for source characterization 

and computation of design values

– FAA uses AERMOD in their EDMS/AEDT

• EPA fully supports AERMOD with continued 

development and updates to meet regulatory 

needs and issues 

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EPA Transition Plans Under Appendix W 

NPRM

• EPA is taking comment on transition period from 

CALINE3 to AERMOD in NPRM

– Proposing a 1 year transition period after final rule, i.e., 

slightly less than 2 years from now until formal transition 

to AERMOD 

• EPA plans to provide training 

– Training package with examples

– Webinars and trainings for stakeholders

– Air Pollution Training Institute course # 423, Air pollution 

dispersion models

– Project level training for Hot-spot analyses

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Relevant docket items

• Document Title: Technical Support Document (TSD) 

for Replacement of CALINE3 with AERMOD for 

Transportation Related Air Quality Analyses, EPA 

Document EPA-454/B-15-002

• http://www.epa.gov/ttn/scram/11thmodconf/CAL3_A

ERMOD_Replacement_TSD.pdf

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