# AERMOD Modeling System: v15181 Regulatory Update
Roger W. Brode U.S. EPA/OAQPS/AQAD/AQMG
11 th 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. 8/12/2015 U.S. Environmental Protection Agency 38/12/2015 U.S. Environmental Protection Agency 4 0 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000

C o n c( u g / m 3) urban rural RIVER ROUGE - URBAN (55,000) vs. RURAL

Meters 0 100 200 300 400 500 600 700

C o n c( u g / m 3) urban rural RIVER ROUGE - URBAN (55,000) vs. RURAL - New

Meters 

### 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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