CALPUFF Regulatory Update 

Roger W. Brode

U.S. EPA/OAQPS

Air Quality Modeling Group

EPA R/S/L Modelers Workshop

June 10-12, 2008

Denver, CO
Outline

• Recap of where we were last year

• What we’ve accomplished since last year

• Unresolved technical issues with v5.8

• Other CALPUFF implementation issues

• Near-field Clarification Memo
CALPUFF Update Process

• Incumbent upon EPA to perform an 

independent assessment of CALPUFF 

when updating to new versions

• CALPUFF requires extensive assessment 

and understanding of changes made; 

approvals made by EPA, not developer 

• CALPUFF Update Tool – Introduced at 8th

Modeling Conference in Sept 2005
CALPUFF Update Tool

• Compares 2 CALPUFF versions; 

proposed (beta) vs. current version (base)

• Determines code changes and differences 

in results across 10 scenarios

• Provides a standardized methodology for 

evaluating changes in model codes
Analysis

Tool

Sources

Meteorology

Terrain

Differences

?

Resolve Document

BETA

BASE

CALPUFF Update Tool
CALPUFF Update Process:

Additional Assessments of v5.756

Table 1: Range of Maximum Absolute Percent 

Differences by Scenario for Initial Application of 

Assessment Tool

Scenario 1 -22.0 to +23.3

Scenario 2 -0.2 to +83.4

Scenario 3 -17.7 to +60.8

Scenario 4 -13.6 to +28.1

Scenario 5 -46.0 to +21.1

Scenario 6 -10.3 to +6.3

Scenario 7 -1.7 to +1.0

Scenario 8 -10.0 to +5.4

Scenario 9 -1.2 to +1.0

Scenario 10 No differences
CALPUFF Update Process:

Additional Assessments of v5.756

• TRC provided the following interim 

versions, to facilitate isolating impacts due to 

(1) bug fixes and (2) non-optional technical 

enhancements:

– CALMET v5.53c = CALMET v5.53a + bug fixes

– CALMET v5.53c2 = CALMET v5.53c + non-optional 

technical enhancements

– CALPUFF v5.711c = CALPUFF v5.711a + bug fixes
CALPUFF Update Process:

Additional Assessments of v5.756

• EPA conducted several tests in order to 

compare and isolate affects of the following 

categories of changes:

– Bug fixes

– Non-optional technical enhancements

– New default parameters for optional technical 

enhancements
CALPUFF Update Process:

Summary of Significant Findings

• Significant differences attributed to each of the 

three known factors: 

– Bug Fixes

– Non-optional Technical Enhancements

– New Default Parameters for Optional Technical 

Enhancements

• Of the three known factors, the New Default 

Parameters for Optional Technical Enhancements 

caused the largest differences overall

• Differences varied significantly across different 

scenarios and source types, with no significant 

overall bias evident
Table 6. CALPUFF Comparison Results for Scenarios 1 - 5 for Base v5.711a vs. Beta v5.8

Scenario

5

-0.88 -32.43

65 m Point Source

3

4 8.40 -4.55 -4.95

.

 No differences in highest ranked (design) values

0.68

99 m Point Source Buoyant Area Source

Source Type

Area Source Volume Source 30 m Point Source

-5.10 -7.36

1

2

-21.78 -6.71

0.02 -0.30

0.32 0.12

-18.37 -13.02

 Differences in one or more design values 

-0.02 0.00 -0.05 7.26 -3.98

2.35 0.58 25.24

-2.84 29.24

0.48

0.28

7.59

22.63

0.12

0.41

0.20

1.07

Scenario 2 - 65m Point Source, Salem Location

Percent Difference - 1st Highest, 1-Hour Averages

-400 -300 -200 -100 0 100 200 300 400

-400

-300

-200

-100

0

100

200

300

400
Figure 1: Contour Plot of Percent Differences for Scenario 2

Jordan Valley 65m Point Source; 4th-Highest 24-Hour Averages

Test 4 - CALPUFF (5.711c) and CALMET (5.53c2) vs. VISTAS (5.756/5.726) 

(with modified inputs to override new default parameter)

0 100 200 300

-200

-100

0

100

200
CALPUFF Update Process:

Additional Assessments of v5.756

• EPA has serious unresolved technical concerns 

regarding how the optional technical enhancements 

for mixing height have been implemented in 

CALMET

• These concerns are related to the new default 

parameters THRESHL and THRESHW for the 

threshold buoyancy energy flux over land and 

water, respectively

• These new thresholds were implemented as part of 

the MMS-sponsored enhancements, to prevent 

unlimited growth of the convective boundary layer 

over water
CALPUFF Update Process:

Additional Assessments of v5.756

• These new thresholds are defined (in the limited 

documentation available) as the “threshold 

buoyancy flux required to sustain convective mixing 

height growth” 

• However, the code indicates that when the sensible 

heat flux falls below the threshold, the convective 

mixing height is immediately assigned to 0m for 

that grid cell, eliminating convective turbulence

• A new convective boundary layer may form on 

subsequent hours
CALPUFF Update Process:

Additional Assessments of v5.756

• This behavior is masked somewhat by other 

defaults within CALMET, including the default 

minimum mixing height of 50m, the use of the 

maximum of convective and mechanical mixing 

heights as the overall mixing height, and the default 

option for upwind averaging of mixing heights 

• The default threshold is 0.05 W/m2/m.

– For example, if Zic = 3000m at 2pm, and H = 149 W/m2

at 3pm, then Zic = 0m at 3pm. A new CBL will likely form 

at 4pm.

• The following figures from Scenario 4 illustrate this 

behavior
Contour plot of convective mixing heights (m) with default THRESHL for 

Scenario 4, 10/19/92, 15:00 LST
Contour plot of convective mixing heights (m) with default THRESHL for 

Scenario 4, 10/19/92, 16:00 LST
Contour plot of convective mixing heights (m) with default THRESHL for 

Scenario 4, 10/19/92, 17:00 LST
Time series of convective mixing 

height from CALMET 
CALPUFF Update Process:

Resolution of Issues (Partial)

• TRC agreed to implement the following changes 

in the CALPUFF modeling system code, allowing 

EPA to approve v5.8:

– Incorporate the non-optional technical enhancements under the 

optional technical enhancements, removing non-optional technical 

enhancements as a potential source of differences;

– Incorporate a new regulatory default switch (MREG=1) in CALMET 

to allow the optional technical enhancements to be included in the 

model, but to require the user to override the default options to 

exercise these optional technical enhancements; and

– Modify the CALPUFF model code to include the minimum sigma-v 

of 0.5 m/s over water as part of the regulatory default setting.
CALPUFF Update Process:

Summary of Differences - Final

Range of Maximum Absolute Percent Differences by Scenario

Test 5 – Bug Fixes

Test 6 – Non-Optional

Technical Enhancements

Test 7 – New Default

Parameters

Test 8 – Base 5.711a vs.

Beta 5.8 (Final Test)1

Scenario 1 -1.0 to +22.6 -18.6 to +1.9 -22.0 to +24.4 -1.1 to +22.6

Scenario 2 -15.4 to +27.8 -30.5 to +0.7 -21.8 to +118.3 -21.8 to +29.2

Scenario 3 -5.1 to +6.0 -0.8 to +1.7 -19.3 to +60.8 -4.0 to +7.3

Scenario 4 -18.4 to +8.4 -0.7 to +4.2 -3.2 to +30.5 -18.4 to +8.4

Scenario 5 -32.4 to +9.5 -9.2 to +0.6 -41.8 to +20.9 -32.4 to +9.5

Scenario 6 -1.4 to +0.6 -2.0 to +6.3 -12.6 to +5.5 -1.4 to +0.6

Scenario 7 No differences > |0.01| -1.7 to +1.0 0.0 to +0.4 No differences > |0.01|

Scenario 8 -1.4 to +0.6 -2.0 to +3.1 -12.1 to +5.5 -1.4 to +0.6

Scenario 9 No differences > |0.01| -1.2 to +1.0 No differences > |0.01| No differences > |0.01|

Scenario 10 No differences No differences No differences No differences

1Test 8 differences are due to bug fixes, but include some additional bug fixes compared to Test 5. 
CALPUFF Implementation Issues

• Lack of adequate documentation

– New MREG option in CALMET not well-documented; CALMET.INP sample 

input file indicates “no default” and assigns value of MREG = 0, i.e., don’t 

enforce regulatory defaults!

– User’s guide last updated in 2000

– Many important technical details are not documented, except in the code

• Version control and overall management of CALPUFF 

modeling system

• PG vs. turbulence dispersion

– Addressed in March 2006 Model Clearinghouse Memo: not an automatic 

switch with promulgation of AERMOD, requires separate assessment

– Assessment is underway, but has uncovered other PG-class dependencies 

with turbulence option (see previous point)

• Pending assessment of v5.8’n’ and v6 updates

– Currently “on hold” due to broader issues

• CALPUFF near-field Clarification Memo
CALPUFF Near-field

Clarification Memorandum

• Status, plans, and caveats

– Draft memo undergoing internal OAQPS 

review, including AQPD and OGC

– Supplemental documentation also in draft status

 Documentation of v5.8 update

 Technical issues and concerns

 Reassessment of CALPUFF model performance

– Plan to release final clarification memo as soon 

as possible under signature of Chet 

Wayland, AQAD Director

– Information presented here is subject to change 

pending completion of reviews and draft 

documentation
CALPUFF Near-field

Clarification Memorandum

• Summary of Key Points:

– The EPA-preferred model for near-field regulatory applications (less than 50 

kilometers) for simple and complex terrain is AERMOD. The AERMOD model should 

be used for all near-field regulatory applications, unless an adequate determination is 

made that AERMOD is not appropriate for that application or is clearly less appropriate 

than an alternative model. [See paragraph 4.2.2(b) of Appendix W – “For a wide range of 

regulatory applications in all types of terrain, the recommended model is AERMOD.”]

– CALPUFF is not the EPA-preferred model for near-field applications, but may be 

considered as an alternative model on a case-by-case basis for near-field 

applications involving “complex winds,” subject to approval by the reviewing 

authority. The approval of CALPUFF for near-field regulatory applications should be 

based on case-specific justification, including necessary documentation and an adequate 

determination that AERMOD is not appropriate or clearly less appropriate than 

CALPUFF. Generalized approval of CALPUFF for near-field applications based on 

reference to other cases where CALPUFF has been approved for near-field use is not 

acceptable, unless such cases are similar enough to the application under review to be 

applicable, and are adequately documented to support that determination. [See 

paragraph 7.2.8(a) of Appendix W – “the CALPUFF modeling system (described in 

Appendix A) may be applied on a case-by-case basis for air quality estimates in such 

complex non-steady-state meteorological conditions.”]
CALPUFF Near-field

Clarification Memorandum

• From Preamble to April 2003 FR Notice 

promulgating CALPUFF:

– “We will require approval to be obtained prior to 

accepting CALPUFF for complex wind situations, as this 

will ensure that a protocol is agreed to between the 

parties involved, and that all are willing to accept the 

results as binding. As experience is gained in using 

CALPUFF for complex wind situations, acceptance will 

become clear and those cases that are problematic will 

be better identified.” (pp. 18441-2)
CALPUFF Near-field

Clarification Memorandum

• From Section 7.2.8 of Appendix W:

– “The setup and application of the model should be 

determined in consultation with the appropriate reviewing 

authority (paragraph 3.0(b)) consistent with limitations of 

paragraph 3.2.2(e).”

– Reference to paragraph 3.2.2(e) places CALPUFF in the 

status of an alternative model.
CALPUFF Near-field

Clarification Memorandum

• Paragraph 3.2.2(e) of Appendix W:

“e. Finally, for condition (3) in paragraph (b) of this subsection 

[preferred model is less appropriate for the specific application, or 

there is no preferred model], an alternative refined model may be 

used provided that:

i. The model has received a scientific peer review;

ii. The model can be demonstrated to be applicable to the problem on a 

theoretical basis;

iii. The data bases which are necessary to perform the analysis are 

available and adequate;

iv. Appropriate performance evaluations of the model have shown that 

the model is not biased toward underestimates; and 

v. A protocol on methods and procedures to be followed has been 

established.”
CALPUFF Near-field

Clarification Memorandum

• Summary of main steps:

1) a determination that treatment of complex winds is critical to 

estimating design concentrations;

2) a determination that the preferred model is not appropriate or less 

appropriate than CALPUFF; and 

3) a demonstration that the five criteria listed in paragraph 3.2.2(e) 

for use of an alternative model are adequately addressed. 

• Each of these steps involves case-specific 

considerations
CALPUFF Near-field

Clarification Memorandum

• Importance of consistency, spelled out in 

paragraph 1(b) of the Guideline:

“The model that most accurately estimates concentrations in the area of interest is 

always sought. However, it is clear from the needs expressed by the States and 

EPA Regional Offices, by many industries and trade associations, and also by the 

deliberations of Congress, that consistency in the selection and application of 

models and data bases should also be sought, even in case-by-case 

analyses. Consistency ensures that air quality control agencies and the general 

public have a common basis for estimating pollutant concentrations, assessing 

control strategies and specifying emission limits. Such consistency is not, however, 

promoted at the expense of model and data base accuracy. The Guideline

provides a consistent basis for selection of the most accurate models and data 

bases for use in air quality assessments.” 
Questions?