Proposed changes in AERMOD for 

NO2 modeling in Appendix W NPRM

11th Modeling Conference

Research Triangle Park, NC

August 12, 2015

Chris Owen

U.S. EPA/OAQPS/AQAD/AQMG

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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)

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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)

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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

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0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

0 200 400 600 800 1000 1200

NO2/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

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PVMRM2 Results for Empire Abo

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10

100

1000

10 100 1000

Predicted Conc (μg/m3)

Observed Conc (μg/m3)

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 1000

Predicted Conc (μg/m3)

Observed Conc (μg/m3)

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

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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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