# Proposed changes in AERMOD for NO2 modeling in Appendix W NPRM 11 th 

## Modeling Conference Research Triangle Park, NC August 12, 2015 Chris Owen U.S . EPA/OAQPS/AQAD/AQMG 1

# NO2 workgroup • Chris Owen (OAQPS) • Roger Brode (OAQPS) • Tim Leon - Guerrero (Region 3) • Andy Hawkins (Region 5) • Erik Snyder (Region 6) • Rob Elleman (Region 10) • Sue Kimbrough (ORD) 2

# Summary of EPA proposed actions for changes in NO2 modeling in AERMOD: Section 4.2.3.4 of proposed Appendix W • Propose to make ARM2 the regulatory default option for Tier 2 screening • Propose to make OLM and PVMRM regulatory default options for Tier 3 screening • Propose to update PVMRM dispersion and plume calculations (PVMRM2) 3

# ARM2 Adoption and Implementation • Propose to make ARM2 the new Tier 2 NO2 regulatory screening option

– ARM2 Based on API study, Podrez, 2014 (Atm. Env ., 103, pp 163 – 170)

– Modify the default minimum ambient NO2/NOx ratio to 0.5

4 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100%

0 200 400 600 800 1000 1200NO2/NOX
NOX (PPB) ARM2 PVMRM, 0.5 ISR max PVMRM, 0.5 ISR DV PVMRM, 0.2 ISR max PVMRM, 0.2 ISR DV Comparison of ARM2 and PVMRM for various in - stack ratios

# OLM and PVMRM Adoption and Implementation

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## • Propose to make OLM and PVMRM Tier 3 NO2 regulatory screening option

– No default for background ozone

– Default maximum ambient NO2/NOx ratio of 0.9

– Default in - stack ratio of 0.5 for primary & nearby source

– Default in - stack ratio of 0.2 for distant sources

– PVMRM for relatively isolated, elevated point sources

– OLM for other sources

# Modifications of PVMRM • Updates to PVMRM with new PVMRM2 option

– Use “absolute” dispersion coefficients in stable conditions

– Several modification to the computation of the plume volume

– Additional miscellaneous bug fixes 

## • EPA proposes to replace PVMRM with PVMRM2, so both versions are provided in AERMOD 15181 to facilitate evaluations 6

# PVMRM2 Results for Empire Abo

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10 100 1000Predicted Conc (μg/m3)

Observed Conc (μg/m 3) AERMOD Model - NM N Monitor w/S-O3 - 1hr NO2 Q-Q Plot - PVMRM2 w/Adj &BulkRn

FULL PVMRM2 OLMGRP PVMRM1

10 100 1000

10 100 1000Predicted Conc (μg/m3)

Observed Conc (μg/m 3) AERMOD - NM S Monitor w/N -O3 - 1hr NO2 Q - Q Plot - PVMRM2 wAdj & BulkRn

FULL PVMRM2 OLMGRP PVMRM1 Empire Abo North Monitor Empire Abo South Monitor

# Regulatory Status of Tier 2 and 3 Methods • All NO2 options are defined as screening techniques

– If Appendix W promulgated as proposed, • NO2 options would no longer be alternative models, and would not need approval by Regional Office; however, their use would occur in agreement with the appropriate reviewing authority (Section 4.2.1b). • Because of the complexities of the Tier 3 options, applicants would need to consult the EPA Regional Office in addition to the reviewing authority (Section 4.2.3.4e).

– This goes into effect with final version of AERMOD (16XXX). Thus, at present: ARM2, OLM, and PVMRM are still beta in 15181 and require Regional Office approval • See Model Clearing House memo 15 - II - 01, “Use of beta ARM2 Technique as an Alternative Model”, Aug 8, 2015 8

# Relevant docket items • Document Title: Technical support document (TSD) for NO2 - related AERMOD Modifications, EPA document number EPA- 454/B - 15 - 004 • http:// www.epa.gov/ttn/scram/11thmodconf/AERMO D_NO2_changes_TSD.pdf

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