AERMOD Modeling System:

v15181 Regulatory Update

Roger W. Brode

U.S. EPA/OAQPS/AQAD/AQMG

11th Modeling Conference

Research Triangle Park, NC

August 12, 2015

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Introduction

• The regulatory versions of the AERMOD dispersion 

model and AERMET meteorological processor were 

recently updated to version 15181 (June 30, 2015);

– The updates to v15181 of AERMOD and AERMET include 

several bug fixes, which are discussed below;

– Version 15181 of AERMOD & AERMET also incorporate 

proposed enhancements to the non-Default/BETA options 

which are discussed in the next presentation;

– The v15181 updates are documented in AERMOD Model 

Change Bulletin (MCB) 11 and AERMET MCB6.

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AERMOD Bug Fixes

• Incorporated a formulation bug fix to address issues 

with relatively tall stacks in relatively small urban 

areas:

– Previous versions may have applied an unrealistic limit on 

plume rise, resulting in anomalously high concentrations;

– Issue has been addressed in the AERMOD Implementation 

Guide, which recommended treating such sources as rural, 

with adequate justification;

– New version emulates approach used for penetrated 

sources during convective conditions;

– Example for tall stack with 55,000 population shown in next 

slide.

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RIVER ROUGE urban rural - URBAN (55,000) vs. RURAL

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RIVER ROUGE urban rural - URBAN (55,000) vs. RURAL -New

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Urban vs. Rural Concentrations Before and After Bug Fix 

Before After
AERMOD Bug Fixes (cont.)

• Corrected an issue with use of the NOSTD option 

with the POINTCAP option for capped stacks;

• Corrected an issue with the emission rate being 

modified for AREA, LINE and OPENPIT sources if 

the point source approximation was used under the 

FASTAREA or FASTALL option;

• Modified the tolerance parameter for AREA and LINE 

sources to address issues with winds blowing nearly 

perpendicular to the source.

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AERMOD Bug Fixes (cont.)

• Modified several subroutines to address issues 

associated with the PVMRM option:

– Included a more explicitly treatment of the vertical and 

horizontal dimensions of contributing sources for the 

penetrated plume contribution for unstable conditions;

– Modified the determination of NOx emissions from major 

contributing sources to account separately for the horizontal 

plume component and the terrain-responding plume 

component.

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AERMOD Bug Fixes (cont.)

• Modified subroutines HRLOOP, SET_METDATA and 

DAYRNG to address issues associated with the 

DAYRANGE keyword for leap years vs. non-leap 

years:

– DAYRANGE keyword allows user to specify days to process 

or a range of days;

– Days can be specified as Month/Day or as Julian day

– Month/Day inputs are unambiguous regarding leap year 

status;

– Julian day inputs are interpreted as leap year or non-leap 

year based on the first year in the data file.

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AERMET Bug Fixes

• Modified subroutines UCALST and MPPBL for the 

ADJ_U* option to improve consistency with Qian and 

Venkatram (BLM, v138, 2011):

– Use a constant value of 0.08 for theta-star (THSTAR);

– Full inclusion of the displacement height;

• Modified subroutine BULKRI to correct the calculation 

of CDN to use ZREF(IHR)/Z0(IHR) instead of 

Z2/Z0(IHR), and to use BETAM = 4.7 for the ADJ_U* 

option instead of 5.0.

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