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– Second tier: conduct photochemical grid modeling - • New draft guidance• Consult with us early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–daniel.jamieson@tceq.texas.gov

Questions?