Use of CALPUFF for RegionalOil and Gas AnalysesD.N. Blewitt, CCMComments on behalf of theAmerican Petroleum InstituteOil and Gas Use of CALPUFF• CALPUFF is being used for analysis of future yearregional air quality impacts under NEPA (EnvironmentalImpact Statements) for oil and gas development in theWest• A typical NEPA analysis includes up to 700 sourcesandimpacts are projected over a 20 year period• Air quality modeling approach is: “Use the best availablescience to support NEPA analyses, and give greaterconsideration to peer-reviewed science andmethodology over that which is not peer-reviewed.”(Bureau of Land Management (BLM)NationalEnvironmental Policy Act Handbook H-1790-1)Oil and Gas Use of CALPUFF(continued)• Visibility and deposition impacts from NOxemissions are the pollutants of concern• AQRV modeling approach is to develop a baselineemission inventory of sources not included in themonitoring data which is then added to cumulativeemissions from new sourcesIssues with the Use of CALPUFFfor Cumulative EIS Analyses• Formulation of CALPUFF chemistry• Lack of a robust model performance evaluation ina full chemistry mode• Indication of model bias for NO3impactscompared to monitored values• Outdated and prescriptive IWAQM methodologyis required for model applicationMESOPUFF II CALPUFFChemistryIn the MESOPUFF II chemistry module used in CALPUFF,SO4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 ConcentrationCALPUFF MESOPUFF IIChemistry Limitations1) Aqueous-phase SO4formation is inaccuratebecause it is solely based on surface relativehumidity (RH). In reality, aqueous-phase SO4formation is not at all affected by RH.2 The MESOPUFF II transformation rates weredeveloped using temperatures of 86, 68 and 50°F.A 50°F minimum temperature will overstate SO4and NO3formation under cold conditions. –Amajor issue in the intermountain WestScatter plots of predicted and observed Nitrate (NO3) concentrationsby the CMAQ V4.4 (red) and CMAQ-MESOPUFF-II chemistry (left blue) for January2002 at all IMPROVE (top), and CASTNet (right) sitesin the United StatesSource: EnvironComparison of CALPUFF Chemistry ModulesParticulate nitrate concentrations as a function ofdownwind distance(relative humidity set to 95%)MCHEM=1 MESOPUFF II chemistryMCHEM=3 Original RIVAD treatmentMCHEM=5 refers to the new RIVAD treatment (ISORROPIA).Verification of the CALPUFF Model•There is very limited data regardingaccuracy of the CALPUFF Model in themode in which it is being applied•The Southwest Wyoming Technical AirForum (SWWYTAF) is one study thatexamined CALPUFF Model accuracy ina full chemistry modeSWWYTAF 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 NO3formation waslimited by NH3concentrations•This is not the way that agencies are requiringthat the model should be usedExamples of CALPUFF MonitorComparisonsThe following examples present a strongindicationthat the as CALPUFF Modelusing the IWAQM protocol, has asubstantial bias towards over predictingNO3concentrations0 100 200 300 400 500NO3 Concentration (ng/m3)1101002345678920304050607080900.90.80.70.60.5

Frequency (%)05 Monitored05 ModeledFigure 2. Cumulative Frequency Distribution for Bridger Class I Area NO3 ConcentrationsModeled versus Monitored 1988-20050 100 200 300 400 500NO3 Concentration (ng/m3)1101002345678920304050607080900.90.80.70.60.5

F r e q u e n c y ( % )888990919293949596979899000102030405Figure 10.. Cumulative Frequency Distribution for BridgerClass I Area NO3 Concentrations1988-2005NO3 Concentrations Have Not Changed Over Period ofRecordFrequency Distribution of NO3 at Bridger IMPROVE Monitor010 020 030 040 050 060 070 080 090 088 89 9 0 91 9 2 9 3 94 95 96 9 7 9 8 9 9 0 1 2 3Y e a rMaximum Measured NO3Concentrations Measured at the Bridger Class I Area0 20 40 60 80Relative Extinction Contribution (%)812162024

V i s u a l R a n g e ( d v )SO4NO30 20 40 60 80Relative Extinction Contribution (%)812162024

V i s u r a l R a n g e ( d v )OgranicsEC0 10 20 30 40 50Relative Extinction Contribution (%)812162024

V i s u a l R a n g e ( d v )SoilCMRelative Extinction Contribution for Various Species forthe 100 Worst Days at Bridger (Raleigh Scattering is notincluded)X Axis = Relative Extinction Contribution (%)Y Axis = Visual Range(dv)1988 1992 1996 2000 2004Year0102030

V i s u a l r a n g e m m -1Best 20 %Mid 20 %Worst 20 %Trends in Visual Range 1988 through 2004Note:StraightlineisleastsquarefitBridger Visibility MonitoringCDPHE BART HaydenCALPUFF Analysis0.280.448.67AverageRatio ofNO3/SO4MonitoringPeriod ofRecordRatio ofNO3/SO4Monitoring2002Ratio ofNO3/SO4CALPUFFConclusion: CALPUFF does not replicate the actual monitored NO3/SO4ratio.88 89 90 91 92 93 94 95 96 97 98 99Year48121620

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 emissionsFigure 7. Estimated Change in NOx Emissions in theSouthwestern Colorado andNorthern New Mexico versus Measured Visual RangeEstimated Change in NOx Emissions in Southwestern Coloradoand Northern New MexicoVersusMeasured Visual Range At Mesa VerdeCaseEstimatedIncrease in NOxEmissions (t/yr)Max Increasein Visibility(dv)Number ofDays withProjectedChange inVisibilityGreater than 1dvMonitoring Data80,000Neg.0CALPUFFModeling for SUIT7,4820.80Southwest Colorado Measured Changes in VisibilityCompared to CALPUFF Modeled VisibilityRecommendationsEPA needs to revisit the use of CALPUFF inregional AQRV analysesLong Term– There is a strong need to perform a comprehensivemodel evaluation of CALPUFF using full chemistry– Other candidate models should be included in suchananalysis– Data bases are becoming available in Wyoming andColorado (NEPA and Four Corner analyses) that couldbe used for such an analysis– After a model evaluation is conducted, IWAQM shouldrevise the guidance on model application of CALPUFF(public process)Recommendations (continued)Short TermUntil a comprehensive model evaluation isconducted, CALPUFF analyses should includea simulation of existing conditions that can becompared to monitoring data in order toprovide an analysis of model performance– Future year CALPUFF analyses should be usedin a relative mode for AQRV analyses