PM2.5 Model Performance Evaluation- Purpose and Goals

PM2.5 Model Performance Evaluation- Purpose and Goals PM Model Evaluation Workshop February 10, 2004 Chapel Hill, NC Brian Timin EPA/OAQPS

Purpose • To discuss PM2.5 and Regional Haze model performance issues that are relevant to SIP modeling. • The discussions and information will be used to enhance the model performance evaluation section of the PM2.5 and Regional Haze modeling guidance.

Goals • For everyone in the community to learn more about the latest work on PM model performance evaluations • To gather enough information to be able to revise the guidance • To listen to opinions and recommendations

PM2.5 Model Performance Evaluation- What’s in the Modeling Guidance? PM Model Evaluation Workshop February 10, 2004 Chapel Hill, NC Brian Timin EPA/OAQPS

Contents • Status of guidance • What’s in the guidance • Review of Chapter 16- Model performance

Status of DRAFT Guidance • Draft “Guidance for Demonstrating Attainment of Air Quality Goals for PM2.5 and Regional Haze”, January 2001 • Living document - may be revised as needed and posted on EPA’s website http://www.epa.gov/scram001/guidance/guide/draft_pm.pdf • Will finalize guidance as part of PM2.5 implementation rule- 2004

What’s in the Guidance • Part I- Using Model Results • Attainment test • Annual PM2.5 NAAQS • 24 hr. PM2.5 NAAQS • Regional haze reasonable progress test • “Hot spot” modeling • Using weight of evidence • Data gathering needs • Required documentation

What’s in the Guidance- con’t • Part II- Generating Model Results • Conceptual description • Modeling protocol • Selecting a model(s) • Choosing days • Selecting domain & spatial resolution • Developing met inputs • Developing emissions inputs • Evaluating model performance (chapter 16) • Evaluating control strategies

Overview of Chapter 16 How Do I Assess Model Performance and Make Use of Diagnostic Analyses?

Model Performance- Introduction • How well is the model able to replicate observed concentrations of PM mass and its components (and precursors)? • How accurately does the model characterize sensitivity of changes in component concentrations to changes in emissions?

Types of Analyses • Operational • Statistics • Scatter plots • Time series plots • Diagnostic • Ratios of indicator species • Process analysis • Sensitivity tests

“Big Picture” Operational Evaluation • Graphical displays • PM2.5 and PM components • Time series plots • Scatter plots • Tile plots • Q-Q plots • Temporal resolution • Episodes, seasonal, annual

Operational Evaluation- Species • PM Species • PM2.5 mass • Sulfate • Nitrate • Mass associated with sulfate • Mass associated with nitrate • Elemental carbon • Organic carbon (organic mass) • Inorganic primary PM2.5 (IP) • Mass of individual constituents of IP

Operational Evaluation- Species • Gaseous Species • Ozone • SO2 • CO • NO2 • NOy • PAN • Nitric acid • Ammonia • Hydrogen peroxide

Evaluation- Statistical Metrics • Key question- How well does the model predict spatially averaged concentrations near a monitor which are averaged over the modeled days with corresponding monitored observations? • Basic metric- Normalized gross error • Averaged over monitor days • Greatest concern for good model performance at monitors that are exceeding the standards

Statistics In the Current Guidance • Normalized gross error • Normalized bias • Fractional error (means and standard deviation) • Fractional bias (means and standard deviation) • Aggregated statistics • Averaged over multiple sites

Calculation of Statistics- Issues • Many ways to calculate statistics • Averaging across days • Averaging across sites • Similar, but different metrics • Normalized mean error vs. mean normalized error • Low concentrations • Certain metrics are not appropriate when concentrations are very low

Performance Goals • “It is difficult to establish generally applicable numerical performance goals” • Model performance is not particularly important for components with small observed concentrations relative to other components • In a relative attainment test, a small observed component cannot have a large influence • “How good should a State expect performance of a model to be? Frankly, there is little basis for making recommendations at present (2001).”

Performance Goals • Expect performance for PM components to be worse than ozone • Ozone goals not appropriate • Numbers listed in guidance as example aggregated normalized gross error • Statistics averaged from several limited PM applications at the time (before 2001) • PM2.5 ~30-50% • Sulfate ~30-50% • Nitrate ~20-70% • EC ~15-60% • OC ~40-50%

Performance Goals • Relative proportions • Major components (> 30% of PM2.5) • Agree within +- 10% of relative portion • If sulfate is 50% of mass, then goal would be to predict sulfate that is 40-60% of total mass • Minor components • Agree within +- 5% of relative portion • Difficult to assess proportions if one component is way off (too high or too low)

Other Analyses • Analyses to address model response to emissions changes • Weekend/weekday emissions • Not sure if this is appropriate for PM • Ratios of indicator species • Many ratios developed for ozone chemistry • Several ratios exist for PM • NH4+NH3/HNO3+NO3+SO4 • Most PM ratio techniques require difficult to find trace gas measurements (e.g. NH3 and HNO3) • Retrospective analyses

Diagnostic Tests • Sensitivity analyses • Is model especially sensitive to an input or combination of inputs? • Initial and boundary conditions • Emissions inputs • Grid size and number of layers • Alternative met fields • Prioritize future data gathering • Assess robustness of a strategy • Prioritizing control efforts • Process analysis

Next Steps • Update modeling guidance • Metric definitions and calculations • Statistical benchmarks • Diagnostic analyses • Other analyses to test model’s relative response to emissions changes • Use workshop materials and discussion to help inform decisions • Looking for recommendations and opinions

PM2.5 Model Performance Evaluation- Purpose and Goals