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Weight of Evidence Procedures and Their Potential for Corroborating Baton Rouge Five Parish 8-hr Ozone SIP Modeling. Prepared by T. W. Tesche Alpine Geophysics, LLC 27 July 2006. Baton Rouge 5-Parish 8-hr Ozone Modeling Study Technical Review Meeting -27 Jul ‘06. Goals of Collaborative WOE.

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Prepared by T. W. Tesche Alpine Geophysics, LLC 27 July 2006

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Prepared by t w tesche alpine geophysics llc 27 july 2006

Weight of Evidence Procedures and Their Potential for Corroborating Baton Rouge Five Parish 8-hr Ozone SIP Modeling

Prepared by

T. W. Tesche

Alpine Geophysics, LLC

27 July 2006

Baton Rouge 5-Parish 8-hr Ozone Modeling Study Technical Review Meeting -27 Jul ‘06

Goals of collaborative woe

Goals of Collaborative WOE

  • Provide independent confirmation that:

    • LDEQ modeling system is operating well

    • Final proposed control strategy(s) are sufficient to meet NAAQS within required time frame

Elements of woe analyses epa 2005 pg 32

Elements of WOE Analyses (EPA, 2005, pg 32)

  • A fully-evaluated, high-quality modeling analysis that projects future values that are very close to the NAAQS (e.g., 82 to 87 ppb).

  • Multiple supplemental analyses in three categories:

    • modeling

    • ozone/emissions trends

    • observational models

Elements of woe analyses epa 2005 pg 321

Elements of WOE Analyses (EPA, 2005, pg 32)

  • Weighting of individual analysis based on its ability to quantitatively assess the likelihood proposed control measures to yield attainment

  • Analyses using well-established analytical procedures, supported by sufficient data

  • Written technical description why aggregate analyses lead to a conclusive determination regarding the future attainment status of the area that differs from the modeled attainment test.

Benefits of collaborative woe

Benefits of Collaborative WOE

  • Draws upon stakeholder insight and resources

  • Increases opportunity for best modeling practice being brought to bear on ozone SIP

  • Allows introduction of information into the process that might not otherwise be available as the result of LDEQ and contractor resources, schedules, or capabilities

Woe benefits concluded

WOE Benefits (concluded)

  • Ensures that thoughtful, thorough weight of evidence analyses are performed for each non-attainment monitor to ensure that targeted, cost effective controls are identified and evaluated

  • Technical information produced will allow LDEQ air quality decision-makers and EPA to understand the effects of local controls in the broader context of the substantial ozone benefits expected to accrue in the ‘mid teens’ time frame as integrated ‘on the books control programs’ come to fruition.

Weight of evidence methods

Weight of Evidence Methods

  • Extended Use of PAQSM Results

  • Trends-Based Assessments

  • Observation-Based Methods

  • Alternative Application of Attainment Test

  • Corroboration of Source-Receptor Relationships

  • Alternative Base Cases

  • Comparison with egional Studies

  • Corroborating Efficacy of Controls

Extended use of model results

Extended Use of Model Results

  • When the PAQSM is shown to perform well, there is increased confidence using it to judge the adequacy of a control strategy

  • WOE metrics that a well-performing model can generate include:

    • Relative change in total amount of ozone > 85 ppb within the nonattainment area;

    • Relative change in grid cells > 85 ppb within the nonattainment area;

    • Relative change in grid cell-hours > 85 ppb within the nonattainment area;

    • Relative change in maximum modeled 8-hour ozone within the nonattainment area

  • These metrics can also be used to explore whether individual subregions are relatively unresponsive to emissions controls (“stiff”) while other parts of the domain are more response.

  • A well-performing model can be used to examine attainment in unmonitored areas in the domain, adding to the WOE determination.

Trends based assessments

Trends-Based Assessments

  • Independent of the PAQSM, it is possible -- within limits -- to extrapolate future year air quality in a nonattainment area through analysis of historical measured emissions and aerometric trends.

Trends based assessments ambient data

Trends-Based Assessments: Ambient Data

Trends based assessments emissions

Trends-Based Assessments: Emissions

Observation based methods

Observation-Based Methods

  • Observation-based methods can help:

    • Corroborate the reasonableness of PAQSM base case predictions (e.g., Blanchard, 2000; Sillman, 1995, 1998);

    • Confirm model sensitivity to emissions input changes, and

    • Assess the directionality of modeled emissions control strategies for

      • photochemical oxidants (Trainer et al., 1993; Blanchard et al., 1999; 2003; Koerber and Kenski, 2005) and

      • secondary aerosols (Blanchard et al., 2000).

Observation based methods1

Observation-Based Methods

  • Indicator species ratios -- ‘diagnostic probes’ -- are helpful in quantifying model’s response to emissions changes:

    • The ozone response surface probe [O3/NOx];

    • The chemical aging probe [NOz/NOy]; and

    • The ozone production efficiency probe [O3/NOz].

Alternative attainment test methods

Alternative Attainment Test Methods

  • 8-hr ozone Attainment Test methods reflect considerable research by EPA and the science community.

  • The procedures recommended in the final ozone guidance explicitly defined.

  • But, there remains room for alternative methods for conducting the Attainment Test.

  • The main requirement is that full technical justification of the alternative method(s) is provided and successfully negotiated with the EPA regional offices.

Alternative attainment test methods1

Alternative Attainment Test Methods

  • Alternate procedures for calculating the base year (current) 8-hr ozone DV;

  • Different thresholds in selecting days for RRF calculation

  • Elimination of some ‘RRF days’ due to model performance considerations

  • Use of a more recent base year

Effect of array size on attaindemo

Effect of Array Size on AttainDemo

Effect of imposing mpe criterion

Effect of Imposing MPE Criterion

Array size vs no of rrf days

Array Size vs. No. of RRF Days

More recent base case year

More Recent Base Case Year

Use of finer modeling grid size

Use of Finer Modeling Grid Size

Corroboration of s r relationships

Corroboration of S-R Relationships

  • Other tools, potentially more powerful than OBMs, can be used to determine whether ozone concentrations are sensitive to certain precursors (i.e., VOC, NOx) or source sectors (e.g., industrial, power generation, traffic).

  • Assuming reliable PAQSM base case MPE, ‘probing tools’ can be used to help explain why attainment is (or is not) demonstrate. Examples are:

    • Source apportionment analyses (OSAT/APCA)

    • Trajectory-based analyses

    • Process Analysis (PA)

Alternative base cases

Alternative Base Cases

  • Use of ‘alternative base cases’ is potentially helpful in

    • Elucidating model performance of a PAQSM,

    • Providing insight into the range of control strategy outcomes that can be expected as the result of uncertainties in or alternate methods for preparing model inputs.

  • Method demonstrated in various regions of U.S. (Reynolds, et al., 1996; Roth et al., 2005).

  • Method entails use of multiple, corroborative air quality models and associated input data sets (e.g., multiple meteorological data sets, alternative chemical mechanisms or emissions inventories)

  • For the 8-hr ozone Attainment Test and control strategy design, alternative base cases help reveal the sensitivity of estimated RRFs and DVs to the variations in inputs or model formulations.

  • In this way, decision-makers are supplied with additional information to help inform their choices.

Comparison with other studies

Comparison with Other Studies

  • Results from nearby attainment demonstration or overlapping large regional scale studies may provide useful information complementing the LDEQ’s 8-hr ozone modeling.

  • Results of ongoing attainment demonstrations in one part of a state or subregion may provide corroborating information for another nonattainment area.

  • Two immediately relevant examples include the ozone SIPS for the DFW and HGB areas.

  • While the Texas SIP modeling focuses on different episodes, they entail many other similarities and offer the potential for useful synergism.

  • There are also several recent EAC modeling studies in the Texas, Oklahoma, Florida, and the Gulf Coast region.

  • At the larger regional scale, the modeling being performed by the CENRAP, WRAP, VISTAS and MRPO each cover the Gulf Coast Region in their domains using the 2002 annual episode. MPRO has developed annual data bases for 2001 and 2003 as well.

Hgb model results compared with vistas 2009 2018 projections

HGB Model Results Compared with VISTAS 2009/2018 Projections

  • Extended

Hgb model results compared with vistas 2009 2018 projections1

HGB Model Results Compared with VISTAS 2009/2018 Projections

Comparison with other studies1

Comparison with Other Studies

  • Use of the VISTAS modeling in a Weight of Evidence’ mode for Houston revealed:

    • The 2000 monitored design values lead to significantly higher 2009 DVs in the HGB region when compared to use of the more recent 2002-2004 measured DVs (the red vs. blue bars);

    • Compared with the VISTAS 36 km results (light yellow bars), the DVs from the 4 km grid modeling with the post-2000 episodes (blue bars) are generally 2-4 ppb higher.

      • This result is directionally consistent with the North Carolina modeling (Arunanchalam et al., 2006) where moving from the 36 km to 4 km grid increased the DVs in many cases by 1-3 ppb.

      • This result is opposite the trend seen in the Upper Midwest modeling (Tesche et al., 2006d); and

    • At all monitors, the calculated DVs in 2018 are all well below the NAAQS.

Corroborating efficacy of emissions controls

Corroborating Efficacy of Emissions Controls

  • Various methods have been postulated for assessing a model’s reliability in predicting air quality response to changes in emissions.

  • EPA suggests

    • examination of conditions for which substantial changes in (accurately estimated) emissions occur;

    • ‘retrospective modeling’, that is, modeling before and after historical significant changes in emissions to assess whether the observed air pollution changes are adequately simulated; and

    • use of predicted and observed ratios of ‘chemical indicator species’.

    • In some urban-scale analyses, the use of weekday/weekend information has been helpful in assessing the model’s response to emissions changes.

Corroborating efficacy of emissions controls1

Corroborating Efficacy of Emissions Controls

  • Innovative statistical methods are available for estimating the reasonableness of modeled ozone control programs

  • Hogrefe and Rao, (2001) developed a probabilistic framework that enables decision makers to assess the chances that a given emissions control program will achieve the 8-hr NAAQS when the controls are applied.

  • Hogrefe et al., (2000) used the observed ozone time series power spectrum to corroborate that the model is responding consistent with ozone observations.

Corroborating efficacy of emissions controls2

Corroborating Efficacy of Emissions Controls

  • Hogrefe et al., (2000) examined underlying forcing mechanisms distinguishing days with high ozone vs. average or non episodic days (by spectral decomposition of a 3-month episode). They found that:

    • Ozone power spectrums represent sum of four temporal components: intraday timescale to the multi week timescale.

    • Form of the 8-h ozone NAAQS emphasizes the importance of longer-term fluctuations embedded in ozone time series data

    • Use of ozone time series power spectrum corroborated the MPE and provided additional information about efficacy of modeled control programs.

    • To adequately account for the interplay between the diurnal, synoptic, and baseline components influencing 8-hr ozone levels, it may be necessary to model domains of spatial extend 2000 to 2500 km and at least four synoptic cycles.

    • Modeling studies confined to small local grids and short episode durations may restrict the analysis to the intraday component, and thereby lose the ability to assess the efficacy of emissions control strategies needed to meet and maintain the 8-hr ozone NAAQS and to improve long-term trends in ozone air quality.



  • Encourage stakeholder technical support to LDEQ and contractors

  • Share emergent data bases and modeling findings to:

    • Encourage independent corroboration of technical work within meaningful timeframe

    • Facilitate development of technically sound, cost-effective emissions controls

  • Collaborate on performance of Weight of Evidence analyses to enable best decisions made with current and new modeling science and policy guidelines

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