# 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 8 th 

# 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 codesAnalysis Tool Sources Meteorology Terrain

Differences 

### ?

Resolve Document

BETA BASE 

# CALPUFF Update Tool

# CALPUFF Update Process: Additional Assessments of v5.756

# 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

# 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/m 2

## /m.

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

### at 3pm, then Zic = 0m at 3pm. A new CBL will likely form at 4pm. 

## • The following figures from Scenario 4 illustrate this behaviorContour plot of convective mixing heights (m) with default THRESHL for

Scenario 4 , 10/19/

92 , 15 : 00 LSTContour plot of convective mixing heights (m) with default THRESHL for

Scenario 4, 10/19/92, 16:00 LSTContour 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

1 Test 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?