Use of CALPUFF for Regio

Oil and Gas Analyses

D.N. Blewitt, CCM

Comments on behalf of the 

American Petroleum Institute
Oil and Gas Use of CALPU

• CALPUFF is being used for analysis of future year 

regional air quality impacts under NEPA (Environm

Impact Statements) for oil and gas development in 

West

• A typical NEPA analysis includes up to 700 source

impacts are projected over a 20 year period

• Air quality modeling approach is: “Use the best av

science to support NEPA analyses, and give greaconsideration to peer-reviewed science and methodology over that which is not peer-reviewe(Bureau of Land Management (BLM) National 

Environmental Policy Act Handbook H-1790-1

)
Oil and Gas Use of CALPU

(continued)

• Visibility and deposition impacts from NOx 

emissions are the pollutants of concern 

• AQRV modeling approach is to develop a b

emission inventory of sources not included monitoring data which is then added to cumemissions from new sources 
Issues with the Use of CALPU

for Cumulative EIS Analys

• Formulation of CALPUFF chemistry• Lack of a robust model performance evalua

a full chemistry mode

• Indication of model bias for NO

3 impacts 

compared to monitored values

• Outdated and prescriptive IWAQM method

is required for model application
MESOPUFF II CALPUFF 

Chemistry

In the MESOPUFF II chemistry module used in CA

SO4 formation is described by 4 variables:

1) Solar Radiation;

2) Background Ozone (surface, user provided);3) Atmospheric Stability; and4) Relative Humidity (surrogate for aqueous-phase)

NO3 formation is described by 3 variables:

1) Background Ozone; 

2) Atmospheric Stability; and3) Plume NOx Concentration
CALPUFF MESOPUFF I

Chemistry Limitations

1) Aqueous-phase SO

4 formation is inaccura

because it is solely based on surface relative 

humidity (RH). In reality, aqueous-phase SO

formation is not at all affected by RH.

2 The MESOPUFF II transformation rates w

developed using temperatures of 86, 68 and 5A 50°F minimum temperature will overstate and NO

3 formation under cold conditions. – A 

major issue in the intermountain West 
Scatter plots of predicted and observed Nitrate (NO3) concent

by the CMAQ V4.4 (red) and CMAQ-MESOPUFF-II chemistry (left b

2002 at all IMPROVE (top), and CASTNet (right) sites in the Un

Source: Environ
Comparison of CALPUFF Chemistry Modules

Particulate nitrate concentrations as a function of downwind distance (relative humidity set to 95%)MCHEM=1 MESOPUFF II chemistry MCHEM=3 Original RIVAD treatmentMCHEM=5 refers to the new RIVAD treatment (ISORROPIA). 
Verification of the CALPUFF Mo

• There is very limited data regarding 

accuracy of the CALPUFF Model in tmode in which it is being applied

• The Southwest Wyoming Technical A

Forum (SWWYTAF) is one study thaexamined CALPUFF Model accuracy a full chemistry mode
SWWYTAF Results

• RIVAD chemistry was used• When boundary conditions were included, 

model agreement was very good

• Results were unpaired in time and space • Analysis indicated that NO

3 formation was 

limited by NH

3 concentrations

• This is not the way that agencies are requir

that the model should be used
Examples of CALPUFF Mon

Comparisons

The following examples present a strong 

indication that the as CALPUFF Mod

using the IWAQM protocol, has a substantial bias towards over predictin

NO

3 concentrations 
0 100 200 300 400 500

NO3 Concentration (ng/m3)

1

10

100

23456789

2030405060708090

0.90.80.70.60.5

Frequency (%)

05 Monitored05 Modeled

Figure 2. Cumulative Frequency Distribution for Bridger Class I Area NO3 Concentrations Modeled versus Monitored 1988-2005
0 100 200 300 400 500

NO3 Concentration (ng/m3)

1

10

100

23456789

2030405060708090

0.90.80.70.60.5

Fr e q

u

e

n

c

y

(

%)

888990919293949596979899000102030405

Figure 10.. Cumulative Frequency Distribution for Bridger Class I Area NO3 Concentrations1988-2005

NO3 Concentrations Have Not Changed Over Period of Record

Frequency Distribution of NO3 at Bridger IMPROV
0

10 0

20 030 040 050 060 070 080 090 0

88 89 9 0 91 9 2 9 3 94 95 96 9 7 9 8 9 9 0 

Y e a r

Maximum Measured NO3 Concentrations Measured at the Bridge
0 20 40 60 80

Relative Extinction Contribution (%)

8

12162024

Visual Range(dv)

SO4NO3

0 20 40 60 80

Relative Extinction Contribution (%)

8

12162024

Visural Range(dv)

OgranicsEC

0 10 20 30 40 50

Relative Extinction Contribution (%)

8

12162024

Visual Range(dv)

SoilCM

Relative Extinction Contribution for Various Specthe 100 Worst Days at Bridger (Raleigh Scatterinincluded)

X Axis = Relative Extinction Contribution (%)

Y Axis = Visual Range (dv)
1988 1992 1996 2000 2004

Year

0

102030

Visual range mm-1

Trends in Visual Range 1988 through 2004

N

ote: Straig

ht lin

e is le

a

st s

q

u

are fit

Bridger Visibility Monitoring 
CDPHE BART Hayden 

CALPUFF Analysis

Average 8.67 0.44 0.28

Ratio o

NO3/SO

Monitor

Period 

Recor

Ratio of 

NO3/SO4

Monitoring

2002

Ratio of NO3/SO4CALPUFF

Conclusion: CALPUFF does not replicate the actual monitored Nratio. 
88 89 90 91 92 93 94 95 96 97 98 99

Year

48

121620

Visual Range (dv)

-20,000020,00040,00060,00080,000

Change in NOx Emissions (t/yr)

80th percentile visural range (cleanest)20th percentile visual range (cleanest)Change in emissions

Figure 7. Estimated Change in NOx Emissions in the Southwestern Colorado and Northern New Mexico versus Measured Visual Range 

Estimated Change in NOx Emissions in Southwester

and Northern New Mexico 

Versus 

Measured Visual Range At Mesa Verde
Case Estimated 

Increase in NOx Emissions (t/yr)

Max Increase in Visibility (dv)

Number of 

Days with Projected Change in Visibility Greater than dv

Monitoring Data 80,000 Neg. 0CALPUFF Modeling for SUIT

7,482 0.8 0

Southwest Colorado Measured Changes in Visib

Compared to CALPUFF Modeled Visibility
Recommendations

EPA needs to revisit the use of CALPUFF in 

regional AQRV analyses

Long Term

– There is a strong need to perform a comprehens

model evaluation of CALPUFF using full chem

– Other candidate models should be included in su

analysis 

– Data bases are becoming available in Wyoming 

Colorado (NEPA and Four Corner analyses) tha

be used for such an analysis

– After a model evaluation is conducted, IWAQM 

revise the guidance on model application of CA(public process)
Recommendations (continu

Short TermUntil a comprehensive model evaluation is 

conducted, CALPUFF analyses should ina simulation of existing conditions that cacompared to monitoring data in order to 

provide an analysis of model performanc

– Future year CALPUFF analyses should b

in a relative mode for AQRV analyses