UNITED STATES ENVIRONMENTAL PROTECTION AGENCY 

RESEARCH TRIANGLE PARK, NC 27711 

JUN 3 0 2015 

MEMORANDUM 

SUBJECT: 

FROM: 

TO: 

Summary of CALPUFF Ownership since 2003 Promulgation 

Tyler 

Air Quality 

J. Fox

Modeling 

, Group Leader

Group

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Office of Air Quality Planning and Standards 

Proposed Regulatory Docket No. EPA-HQ-OAR-20 15-0310 

Introduction 

OFFICE OF 

AIR QUALITY PLANNING 

AND STANDARDS 

The 2003 Guideline recommended the CALPUFF modeling system as the preferred 

model for long-range transport (i.e., source-receptor distances of 50 to several hundred 

kilometers) of emissions from point, volume, area, and line sources for primary criteria 

pollutants (e.g, PM and S02). EPA issued a number of communications in 2004 with the model 

developer, Earth Tech's Atmospheric Studies Group, to address the use of this modeling system 

for long range assessments consistent with the Guideline, to emphasize the need for modeling 

protocols, and to provide clarity on need for EPA approval to change the "EPA recommended" 

version of the model in the context of continual evolution of the modeling system (Fox, 2004; 

U.S. EPA, 2004). To facilitate the process of updating the system, EPA developed the CALPUFF 

Update Tool for use in the approval process that first presented at the gth Modeling Conference 

and has been applied for each model update since 2007. 

Over the past decade, we have experienced a number of complex applications of the 

CALPUFF modeling system that challenged its regulatory performance and required frequent 

interactions across the modeling community including those between EPA, the model developer 

and other stakeholders. During this same timeframe, there were a number of developments to the 

CALPUFF modeling system that necessitated additional interactions across EPA, the model 

developer and other stakeholders. These interactions have been complicated by the changes in 

ownership and the related uncertainties of the development process which was evident during the 

update to the VISTAS version of CALPUFF as summarized by EPA presentations at the 91

h 

Modeling Conference. 

Recycled/Recyclable • Printed wfth Vegetable Oil Based Inks on 100% Recycled Paper (40% Postconsumer) 
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This memorandum provides details on the frequent changes in ownership of this 

modeling system as support of the EPA’s concerns about the management and maintenance of 

the model code since its promulgation in the 2003 Guideline.

Chronology of Model Updates and Changes in Ownership

• April 2003: EPA promulgates the CALPUFF modeling system, version 5.7, as its preferred 

long-range transport model for regulatory applications under the 2003 revisions to the 

Guideline.

• May 2004: EPA formally arranges for Earth Tech’s Atmospheric Studies Group to openly 

distribute at no cost on their website (www.src.com) the CALPUFF modeling system code, 

processors, and documentation (Fox, 2004)

• April 2006: EPA learns that TRC Environmental Corporation has purchased the CALPUFF 

modeling system from Earth Tech Inc. with management and staff of the Atmospheric 

Studies Group joining TRC.

• April 2006: Model developer updates the CALPUFF modeling system with a new Version 6 

series in conjunction with MMS and updates to Version 5 series in conjunction with 

VISTAS.

• May 2006: EPA approves an update to the CALPUFF modeling system to version 5.711a to 

address various bug fixes (as described in Model Change Bulletin A).

• June 2007: EPA approves update to the CALPUFF modeling system to version 5.8 based on 

the VISTAS series of codes (as described in Model Change Bulletins B, C, and D).

• November 2010: Model developer updates the CALPUFF modeling system, version 6 series, 

with new chemistry options based on Karamchandani et al (2008). 

• May 2011: EPA learns of the departure of key management and staff of TRC’s Atmospheric 

Studies Group responsible for the CALPUFF modeling system to Exponent, Inc.

• December 2013: EPA approves updates to the CALPUFF modeling system to version 5.8.4 

to address various bug fixes (as described in Model Change Bulletins E, F, and G).

• June 2014: EPA is advised by TRC Environmental Corporation that is has assigned all rights 

to the CALPUFF Modeling System to Exponent, Inc (Dodd, 2015)

• June 2015: Model developer updates the CALPUFF modeling system with a new Version 7 

series and bug fixes to the EPA recommended version 5.8.4.
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Summary

To summarize, the EPA is providing this memorandum to the docket of the “Revision to 

the Guideline on Air Quality Models: Enhancements to the AERMOD Dispersion Modeling 

System and Incorporation of Approaches to Address Ozone and Fine Particulate Matter”

proposed rule as support of the EPA’s concerns about the management and maintenance of the 

CALPUFF modeling system since its promulgation in the 2003 Guideline. As shown above, 

there have been a number of updates to the CALPUFF modeling system both in the EPA 

approved series 5 versions and in the model developer’s series 6 versions with a lag in the ability 

for EPA to adequately understand, review and approve changes largely due to the lack of an 

open development process. In fact, just prior to release of this memorandum, EPA was informed 

by Exponent, Inc of updates to the CALPUFF modeling system with a new Version 7 release and 

bug fixes to the EPA recommended version 5.8.4 without any prior notice. Since the 

promulgation of the CALPUFF modeling system, the regulatory application of this modeling 

system has been unduly complicated by these changes in ownership and the related uncertainties 

of the development process for this modeling system.

If you have additional questions regarding this memorandum or the proposed rulemaking, 

please feel free to contact me, (919) 541-5562 or fox.tyler@epa.gov, or contact George Bridgers, 

(919) 541-5563 or bridgers.george@epa.gov.

References

Dodd, Martin H, 2015. “RE: CALPUFF”, Letter to Tyler Fox, U.S. EPA, June 17, 2014.

Fox, Tyler J, 2006. “EPA approval of CALPUFF v5.711a”, Letter to Joseph S. Scire, TRC, May 

26, 2006.

Fox, Tyler J, 2004. “EPA agreement with Earth Tech regarding distribution and updates to 

CAPUFF”, Letter to Joseph S. Scire, Earth Tech Inc, May 10, 2004.

Karamchandani, P., S Chen, and C Seigneur, 2008. “CALPUFF Chemistry Updates”, Report 

prepared for American Petroleum Institute. Atmospheric & Environmental Research Inc, San 

Ramon, CA. February 2008.

U.S. EPA, 2004. “Application of CALPUFF for Long-Range Transport”, Memorandum from 

Peter Tsirigotis, U.S. EPA/OAQPS, Research Triangle Park, NC. May 10, 2004.

cc: Richard Wayland, C304-02

Brian Doster, OGC

Melina Williams, OGC

George Bridgers, C439-01