proposed revisions to the guideline on air quality models dan jamieson air permits division texas...
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Proposed Revisions to the Guideline on Air Quality Models
Dan JamiesonAir Permits Division
Texas Commission on Environmental QualityAdvanced Air Permitting Seminar 2015
Guideline
• What is the Guideline?– EPA-preferred models–Recommended techniques
• Why have it?–Common basis and consistency
Guideline
• Where is the Guideline?–Published as Appendix W to 40 CFR Part 51–As a result, changes follow rulemaking
process• Timeline:–Comment period– Final rule package
Proposed Revisions
• Two basic types:
– Substantive changes to address various topics
– Editorial changes to update and reorganize information
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
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
Proposed Revisions
– Tier 2 (cont.) - • Sept. 2014 clarification memo includes
minimum ratio of 0.2• Guideline provides flexibility on minimum ratio• Impact??–Use of existing ARM–Equation coded in AERMOD
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
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
Proposed Revisions
– First tier: relationship between precursor emissions and source impact - • Peer-reviewed literature• Previous modeling results• Reduced-form model
Proposed Revisions
– Second tier: conduct photochemical grid modeling - • New draft guidance• Consult with us early
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
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
Proposed Revisions
–Proposed screening approach
–Near-field application of preferred model at 50 kilometers:• If results < SILs – done• If results > SILs – further analysis
Proposed Revisions
– For further analysis, no preferred model
– For single-source or cumulative modeling – consult with us and EPA early
Proposed Revisions
• EPA’s Model Clearinghouse:–Coordination between EPA/Regional Offices
–Helps resolve issues not in Guideline
–Helps with considerations of alternative models
Proposed Revisions
–Proposing that Regional Offices consult with Model Clearinghouse on use of alternative models:• Formal concurrence memo• Impact??–Permit review time
Proposed Revisions
• Procedures – cumulative analysis:–Proposed changes for model inputs and
background concentrations
–Based on clarification memos issued since 2010 (new standards)
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
Proposed Revisions
–Nearby source: in vicinity of source under consideration - • Explicitly model
–Other source: all other sources - • Accounted for by monitoring data
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
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
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
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
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
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
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?
Contact InformationDan Jamieson - –Air Dispersion Modeling Team– (512) 239-4342–[email protected]
Questions?