1. Proposed Revisions to the Guideline on Air Quality Models
Dan Jamieson
Air Permits Division
Texas Commission on Environmental Quality
Advanced Air Permitting Seminar 2015

2. Guideline What is the Guideline? Why have it? EPA-preferred models
Recommended techniques
Why have it?
Common basis and consistency
EPA – Environmental Protection Agency

3. Guideline Where is the Guideline? Timeline:
Published as Appendix W to 40 CFR Part 51
As a result, changes follow rulemaking process
Timeline:
Comment period
Final rule package
CFR – Title 40 Code of Federal Regulations
Appendix W can be found at

4. Proposed Revisions Two basic types:
Substantive changes to address various topics
Editorial changes to update and reorganize information

5. Proposed Revisions NO2 and tiered approach: Tiered approach is not new
Current Guideline addresses annual standard
Clarification memos and 1-hour standard
Proposed Guideline addresses both standards
NO2 – nitrogen dioxide

6. Proposed Revisions Tier 1: 100 percent conversion
Tier 2: replace existing ARM with ARM2 -
Based on hourly data of NO2 to NOx ratios
Empirically derived equation in AERMOD
Default minimum ratio of 0.5 and maximum ratio of 0.9
ARM – Ambient Ratio Method
NOX – oxides of nitrogen
AERMOD – American Meteorological Society/EPA Regulatory Model

7. Proposed Revisions Tier 2 (cont.) -
Sept clarification memo includes minimum ratio of 0.2
Guideline provides flexibility on minimum ratio
Impact??
Use of existing ARM
Equation coded in AERMOD
The September 2014 clarification memo can be found at

8. Proposed Revisions
Tier 3: OLM and PVMRM included in regulatory default version of AERMOD -
No longer alternative models
Still need to coordinate with us on model inputs
Revised PVMRM – PVMRM2
OLM – Ozone Limiting Method
PVMRM – Plume Volume Molar Ratio Method

9. Proposed Revisions Ozone and secondary PM2.5: Difficult to do
Currently, no preferred model for single- source assessment
Still no preferred model proposed, but EPA is recommending two-tier approach
PM2.5 – particulate matter with a diameter of 2.5 microns or less
O3 – ozone
Photo located at
Photo by Ulrich Thumult.
License can be found at
Bottom of photo cropped to show portion of skyline and focus on smog.

10. Proposed Revisions
First tier: relationship between precursor emissions and source impact -
Peer-reviewed literature
Previous modeling results
Reduced-form model

11. Proposed Revisions Second tier: conduct photochemical grid modeling -
New draft guidance
Consult with us early

12. Proposed Revisions
EPA to pursue rulemaking to establish SILs for PM2.5 and ozone
Also to introduce new tool – MERP:
If emissions < MERP – not expected to contribute significantly
SILs – Significant Impact Levels
MERP – Modeled Emissions Rates for Precursors

13. Proposed Revisions CALPUFF and Class I Increment:
CALPUFF preferred for long-range transport
Proposal to no longer have preferred model:
More flexibility
Available tools
Management of code
CALPUFF – California Puff model

14. Proposed Revisions Proposed screening approach
Near-field application of preferred model at 50 kilometers:
If results < SILs – done
If results > SILs – further analysis

15. Proposed Revisions For further analysis, no preferred model
For single-source or cumulative modeling – consult with us and EPA early

16. Proposed Revisions EPA’s Model Clearinghouse:
Coordination between EPA/Regional Offices
Helps resolve issues not in Guideline
Helps with considerations of alternative models

17. Proposed Revisions
Proposing that Regional Offices consult with Model Clearinghouse on use of alternative models:
Formal concurrence memo
Impact??
Permit review time

18. Proposed Revisions Procedures – cumulative analysis:
Proposed changes for model inputs and background concentrations
Based on clarification memos issued since 2010 (new standards)
Photo located at
Photo by Roy Luck.
License can be found at
Bottom and top of photo cropped slightly.

19. Proposed Revisions Emissions input data (Table 8-2):
New/modified source – allowable emissions
Nearby source – can use actual emissions data
Other source – represented by monitoring data

20. Proposed Revisions
Nearby source: in vicinity of source under consideration -
Explicitly model
Other source: all other sources -
Accounted for by monitoring data

21. Proposed Revisions
Identifying sources – isolated single-source vs. multi-source area:
Isolated: focus on other sources and use of background monitoring data
Multi-source: focus on determining nearby sources and background monitoring data for other sources

22. Proposed Revisions Proposing definition of modeling domain:
Geographic area for analysis
Includes all location of significant impacts
Area extending to most distant significant impact or 50 kilometers

23. Proposed Revisions Meteorological input data:
Recommending use of AERMINUTE:
Processor for 1-minute ASOS wind data
Reduces calm and missing hours
We use it in our processing
AERMINUTE – a meteorological pre-processor used to process 1-minute wind data for use with AERMET, the meteorological pre-processor for the AERMOD modeling system
ASOS – Automated Surface Observing Stations

24. Proposed Revisions
Proposing option to use prognostic meteorological data:
No NWS station or collecting on-site data is prohibitive/infeasible
MMIF – tool to convert data for use in AERMET
Coordinate with us early in the process
NWS – National Weather Service
MMIF – Mesoscale Model Interface program
AERMET – the meteorological pre-processor for the AERMOD modeling system

25. Proposed Revisions AERMOD modeling system:
New version (15181) as part of proposal
Updates subject to public review and comment
Current non-default/beta options proposed to be part of regulatory default option

26. Proposed Revisions Proposed updates: U-star in AERMET
LOWWIND3 in AERMOD
Horizontal/capped stacks
Buoyant line source option
Code for proposed NO2
Other enhancements/bug fixes
U-star – represents the surface friction velocity
LOWWIND3 – represents a proposed model keyword for use with AERMOD

27. Summary EPA proposing a number of revisions to the Guideline
We are looking at how they could affect us:
Revisions to our modeling guidance?
Pre-processed meteorological data sets?

28. Contact Information
Dan Jamieson -
Air Dispersion Modeling Team
(512)

29. Questions?