EPA PM2.5 Modeling Guidance for Attainment Demonstrations

1. EPA PM2.5 Modeling Guidance for Attainment Demonstrations Brian Timin EPA/OAQPS Timin.brian@epa.gov February 20, 2007

2. Outline • Attainment demonstrations for PM2.5 • Modeled attainment test • Analyses related to local primary PM2.5 sources

3. Attainment Demonstrations • CAA Section 172(c) requires States with a nonattainment area to submit an attainment demonstration • All States must submit attainment demonstrations which include modeling (§51.1007) • Emissions inventories (base and future years) • Adopted control measures

4. Ozone/PM2.5/Regional Haze Modeling Guidance • “Guidance on the use of Models and Other Analyses for Demonstrating Attainment of Air Quality Goals for Ozone, PM2.5, and Regional Haze” http://www.epa.gov/scram001/guidance/guide/final-03-pm-rh-guidance.pdf • Original draft- January 2001 • Draft final- September 2006 • Final version- April 2007

5. What’s in the Guidance? • Part I- Using Model Results • Modeled Attainment tests • 8-hour ozone NAAQS • Unmonitored area analysis • Annual and 24-hour PM2.5 NAAQS • Unmonitored area analysis • Local area analysis (high primary PM2.5 areas) • Regional Haze reasonable progress • Supplemental analyses/weight of evidence • Activities to support Mid-Course review and future modeling • Required documentation

6. What’s in the Guidance? • Part II- Generating Model Results • Conceptual description • Modeling protocol • Selecting a model(s) • Choosing days/episodes • Selecting domain & spatial resolution • Developing met inputs • Developing emissions inputs • Evaluating model performance/diagnostic analyses

7. Modeled Attainment Tests • All O3/PM2.5/RH modeled attainment tests use model estimates in a “relative” sense • Premise: models are better at predicting relative changes in concentrations than absolute concentrations • Relative Response Factors (RRF) are calculated by taking the ratio of the model’s future to current predictions of PM2.5 or ozone • RRFs are calculated for ozone and for each component of PM2.5 and regional haze

8. Unmonitored Area Analysis (UAA) • The attainment test is a monitor based test • Future year design values should also be examined in unmonitored areas • Unmonitored Area Analysis (UAA) is recommended • Uses interpolated ambient design values and model output • Interpolated spatial fields (design values) are adjusted up or down based on modeled concentration gradients • Similar tests for ozone and PM2.5 • UAA not designed to look for unmonitored PM micro-scale hot-spot issues • 12 km resolution should be sufficient for annual NAAQS • Finer resolution may be needed to address 24-hr. NAAQS • UAA is a supplemental analysis • If a problem area is identified, guidance recommends implementing emissions controls or placing new monitor(s) in the area

9. Local Area Analysis (LAA) • Analysis to improve the accuracy of modeled emissions changes of local primary PM2.5 • Local primary PM2.5 gradients cannot be accurately modeled with a relatively coarse grid model • LAA provides a more accurate assessment of the change in air quality at monitors, due to changes in local primary emissions • Local area analysis can use either dispersion model or fine grid Eulerian model (1km?)

10. Local Area Analysis • Analysis is applied by quarter • For dispersion modeling analysis: • Identify local sources • Quantify local source contribution at monitor • Run dispersion model • Use relative change in concentration to adjust future year annual or 24-hour design values

11. Summary • All nonattainment areas must submit an attainment demonstration which includes future year modeling • All O3/PM2.5/RH modeled attainment tests use model estimates in a “relative” sense. • Local primary PM2.5 sources are addressed as part of the “unmonitored area analysis” and “local area analysis” • UAA is intended to examine PM2.5 gradients in unmonitored areas at 12km or finer resolution • LAA is intended to examine local PM2.5 contributions to existing FRM monitors

12. Appendix Select Language from: “Guidance on the use of Models and Other Analyses for Demonstrating Attainment of Air Quality Goals for Ozone, PM2.5, and Regional Haze”.

13. Unmonitored Area Analysis: Guidance Language(sections 3.4, 3.4.3, and 5.3) • Modeling Guidance section 3.4.3 • “It should be stressed that due to the lack of measured data, the examination of ozone and PM2.5 concentrations as part of the unmonitored area analysis is more uncertain than the monitor based attainment test. As a result, the unmonitored area analysis should be treated as a separate test from the monitor based attainment test. The results from the unmonitored area analysis should, at a minimum, be included as a supplemental analysis. While it is expected that additional emissions controls are needed to eliminate predicted violations of the monitor based test, the same requirements may not be appropriate in unmonitored areas.” • “It is recommended that predicted violations of the unmonitored area analysis are carefully scrutinized to determine whether they are likely to exist in the ambient air or whether they may be caused by an error or uncertainty in the modeling system. At a minimum, it may be appropriate to commit to additional deployment of ambient monitors in areas where the unmonitored area analysis predicts future violations [footnote: It would also be appropriate to commit to additional emissions controls in lieu of additional monitoring in unmonitored areas]. This monitoring would allow a better assessment in the future of whether the NAAQS is being met at currently unmonitored locations.”

14. Unmonitored Area Analysis: Guidance Language • Additional language (section 5.3) • “High primary PM concentrations can occur at (or near) existing monitors or in unmonitored areas. The modeled attainment test is primarily a monitor based test. As such, the focus of the attainment test is whether attainment can be reached at existing monitors. To address the issue of PM2.5 concentrations in unmonitored areas, we have recommended an “unmonitored area analysis” (see section 3.4). The unmonitored area analysis is intended to be the primary means for identifying high PM2.5 concentrations outside of traditionally monitored locations. The spatial resolution of the modeling that is the underlying basis of the unmonitored area analysis will determine how well it addresses primary PM hotspot issues. The finer the resolution of the grid model, the more likely that primary PM hotspots will be recognized. Based on the monitoring guidance, we believe that an unmonitored area analysis conducted at 12km or finer resolution is sufficient to address unmonitored PM2.5 for the annual NAAQS. Conducting the unmonitored analysis at 4km or finer resolution will provide an even more detailed analysis of the spatial gradients of primary PM2.5, especially when evaluating violations of the 24-hr. NAAQS.”

15. Local Area Analysis: Guidance Language(sections 5.3 and 5.3.1) • Modeling Guidance section 5.3.1 • “…., if a designated nonattainment area contains a few (as opposed to many which are spread out) concentrated sources of primary particulate matter, we would expect there to be some substantial spatial gradients in the primary portion of the organic carbon component and in the inorganic particulate matter (OPP) and elemental carbon (EC) components of ambient PM2.5 (these are often called “hotspots”). Substantial gradients are most likely to be a potential problem in addressing whether a proposed control strategy is sufficient to attain the 24-hour NAAQS for PM2.5.” • “It may be necessary to evaluate the impact of local primary PM sources for contributions to both the 24-hour and annual NAAQS. As stated earlier, it may not be appropriate to compare population oriented FRM sites that are dominated by point sources, to the annual NAAQS. But there are numerous cases where the impact from local sources is not dominant, but a sizable contributor to total PM2.5 (~10-30% of total annual average PM2.5). In these cases, a more refined analysis of the contribution of local primary PM2.5 sources to PM2.5 at the monitor(s) will help explain the causes of nonattainment at the monitor and may lead to the more efficient ways to attain the standard by controlling emissions from local sources.”