Highlights from the 2016 Guideline on Air Quality Models Conference

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Highlights from the 2016 Guideline
on Air Quality Models Conference
Rocky Mountain States Section of the Air & Waste
Management Association - Denver, CO
April 21, 2016
Sergio A. Guerra, Ph.D. – CPP Inc.

Outline
• Updates on AERMOD modeling system
• Building Downwash
• Prognostic meteorological data
• Ozone and Secondary PM2.5
• Long Range Transport
• What’s next?

Background
• Revisions to Appendix W were proposed by
EPA on July 29, 2015
• Public comment closed on October 27, 2015
• Final rulemaking by July 7 or 8th of 2016
• References:
– 11th Modeling Conference Presentations
https://www3.epa.gov/ttn/scram/11thmodconfpres.htm
– Guideline on AQ Models: The New Path, 6th
Specialty Conference
https://www3.epa.gov/ttn/scram/11thmodconfpres.htm

AERMOD Updates
EPA has proposed that the following options be incorporated
into the regulatory versions of AERMOD and AERMET:
• The ADJ_U* option in AERMET;
• The LOWWIND3 option in AERMOD;
• The BUOYLINE option in AERMOD for modeling buoyant line
sources; and
• The POINTCAP and POINTHOR source type options in
AERMOD to model capped and horizontal stacks.
• NOx-NO2 conversion
– ARM2
– PVMRM2

AERMET/AERMOD ADJ_U*
• The Beta ADJ_U* option in AERMET associated
with the Bulk Richardson Number (BULKRN)
option has been modified to include a more
refined method for calculating THSTAR and
extending its applicability for very stable/low
wind conditions, based on Luhar and Raynor
(BLM, v132, 2009);
• The updated ADJ_U* option with BULKRN also
includes modifications to subroutine TGINIT in
AERMOD to calculate THSTAR;
• EPA has proposed that the ADJ_U* option (with
or without BULKRN) be incorporated into the
regulatory version of AERMET.

AERMET/AERMOD ADJ_U*
• Friction velocity (u*) computed by
AERMET.
• u* used to calculate mixing height,
initial horizontal and vertical
dispersion (sigma-y and sigma-z)
• EPA noted in 2007 issues with high
concentrations due to treatment of
light winds.
• AERMOD users started to identify
highest impacts associated with low
wind speeds (i.e., <1 m/s) during
night hours.

AERMOD-Low Wind Options
AERMOD v15181 includes a new LOWWIND3 (LW3) non-DFAULT/BETA
option:
• LOWWIND3 increases minimum value of sigma-v from 0.2 to 0.3
m/s, consistent with the LOWWIND2 option, but eliminates upwind
dispersion, consistent with the LOWWIND1 option;
• The LOWWIND3 option uses an “effective” sigma-y value that
replicates the centerline concentration accounting for meander,
but sets concentrations to zero (0) for receptors more than
6*sigma-y off the plume centerline, similar to the FASTALL option;
• EPA has proposed in that the LOWWIND3 option be incorporated
into regulatory version, while the LOWWIND1 and LOWWIND2
options are still available for testing & evaluation purposes.

Capped and Horizontal Stacks
Draft/BETA options for capped & horizontal stacks have been
incorporated in AERMOD (beginning with v06341):
• Source types POINTCAP & POINTHOR used to trigger BETA options;
• User inputs actual stack exit velocity (Vs) and stack diameter (Ds);
• The Model Clearinghouse procedure is used for non-downwash
sources;
• For the POINTHOR option with downwash the exit velocity is
assigned as the initial horizontal velocity of the plume;
• For the POINTCAP option with downwash, the initial plume radius is
assigned as 2*Ds to account for initial plume spread from the cap,
and the initial horizontal velocity of the plume is assigned as the
initial exit velocity specified by the user divided by 4 to account for
suppressed momentum and buoyancy.

NOx to NO2 Conversion
• EPA has proposed that the ARM2 and
PVMRM2 options be incorporated as
regulatory options.
http://www.atmos.washington.edu/~lbaylon/research.html

Buoyant Line Sources
• Beginning with v15181, AERMOD includes an option to model
buoyant line sources, using the BUOYLINE source type;
• The BUOYLINE option in AERMOD model allows for modeling
of buoyant line sources using meteorological data processed
through the AERMET meteorological processor;
• The BUOYLINE option in AERMOD also allows use of the
processing options to support the form of the 1-hr NO2, 1-hr
SO2 and 24-hr PM2.5 NAAQS.

Mobile Source Modeling
• Proposal includes replacement of CALINE3,
CAL3QHC, and CAL3QHCR with AERMOD as
the Appendix A preferred dispersion model
for all mobile source modeling of inert
pollutants
• Technical Support Document (TSD) for
Replacement of CALINE3 with AERMOD for
Transportation Related Air Quality Analyses,
EPA Document EPA-454/B-15-002
http://www.epa.gov/ttn/scram/11thmodconf/CAL3_A ERMOD_Replacement_TSD.pdf

Model Clearinghouse Activity
• On use of ARM2
– July 16, 2015; Region 2
– December 22, 2015; Region 4
• On use of Adj-u* beta option and POINTHOR&POINTCAP
– February 10, 2016; Region 10
• Upcoming concurrence
– Definition of minimum ambient ratio in ARM2; Region 6
– Use of Adj-u* for tall stack in complex terrain; Region1
– Use of wind tunnel derived building dimensions; Region 4
– Informal memo on use of Adj-u* and LOWWWIND3 options

Use of Beta Options
• Clarification on the Approval Process for
Regulatory Application of the AERMOD
Modeling System Beta Options
• https://www3.epa.gov/ttn/scram/guidance/clarification/AERMOD_Beta_Options_Memo-20151210.pdf

Building Downwash
• Priority for EPA’s OAQPS and ORD
• Upcoming clearinghouse memo from Region 4
• PRIME2 Advisory Committee

PRIME
AERMOD’s Building Downwash Algorithm
• Used EPA wind tunnel data
base and past literature
• Developed analytical
equations for cavity height,
reattachment, streamline
angle, wind speed and
turbulence
• Developed for specific
building dimensions
• When buildings outside of
these dimensions, theory falls
apart

BPIP Diagnostic Tool
http://bit.do/cppwind-BPIPDiagnostic
Likely Overprediction Factor for each Flow Vector
Source 1

ComplianceCompliance
CPP’s EBDCPP’s EBD
BPIP Diagnostic
ToolBuilding Geometry
Meteorological Data
Terrain Data
AERMET
AERMAP
Operating Parameters
AERMOD
OtherInputs
Building
Inputs
BPIP Diagnostic Tool

Summary of Needed Updates to
PRIMEFlaws that may cause overpredictions:
1. Building wake growth starts at wrong location – leads overestimated wake
height and building downwash zone.
2. Start of building downwash occurs at the wrong location – leads to
overstated downwash.
3. Height of building downwash zone (high turbulence) is overestimated.
4. Reduced velocity calculation in wake needs improvement – leads to
incorrect plume rise calculation.
5. Streamlines for porous structures should be horizontal and wake velocity
and turbulence parameterization is not correct.
6. Streamlines and wakes velocity/turbulence parameterization incorrect for
streamlined structures.
7. Transition back to ambient turbulence is questionable.
More information is available in papers and presentations #34 and #25
(Petersen and Guerra, 2016)

AERMOD/PPRIME
Overestimates
Downwash
Reality
Summary of Needed Updates to
PRIME

Refinery Structures Upwind
Solid BPIP Structure Upwind
No Structures
Streamlines for Lattice Structures

PRIME2 Advisory Committee
Subcommittee of the Atmospheric Modeling and
Meteorology Committee (APM) of the Technical
Council of the Air and Waste Management Association
(AWMA).
The two purposes of this committee include to:
1. Provide a technical review forum to improve the
PRIME building downwash algorithms
2. Establish a mechanism to review, approve and
implement new science into the model for this and
future model improvements

PRIME2 Advisory Committee
– EPA mentioned that building downwash is a
priority
– Had about 40-50 people attend the initial meeting
– Got an update from ORD about some of their
work related to building downwash
– EPA is looking into publishing a technical paper
soon
– EPA’s ORD will be collaborating with this
committee

Meteorological Data
• Prognostic meteorological data
– No representative NWS station and infeasible to
collect site-specific data
– No fewer than 3-years of data
– Mesoscale Model Interface Program (MMIF)
developed to read prognostic data (i.e., WRF) to
create data for input into AERMET and AERMOD,
as well as other dispersion models
• Draft guidance and evaluation of MMIF
available
https://www3.epa.gov/ttn/scram/11thmodconf/Draft_MMIF_Guidance.pdf

Ozone and PM2.5 Formation
Included in Chapter 5 of proposed
Appendix W as a tiered approach:
• First Tier:
– Use of existing technical information
such as previous photochemical
modeling
– Model Emission Rates for Precursors
(MERPs) is a Tier 1 tool
– MERPS will not replace SERs
– Guidance will be forthcoming

Ozone and PM2.5 Formation
• Tier 2 relates to using models
to assess impacts from single
sources on ozone and PM2.5
formation
– Use of chemical models is
recommended including:
• Eulerian (e.g., CAMx, CMAQ)
• Lagrangian (e.g., CALPUFF,
SCICHEM)

Single Source Impacts
• Source impact estimation approaches
– Brute force approach
– Decoupled direct method (DDM) sensitivity
– Source apportionment

Source Impact Estimation
Approaches
Baker, K. Estimating Ozone and Secondary PM2.5 for Permit Related Programs, A&WMA’s 6th Specialty Conference -
Chapel Hill, NC, April 12, 2006

Long Range Transport
• EPA proposing that Appendix W no longer contain
language requiring use of CALPUFF or other
Lagrangian model for LRT assessments.
• For NAAQS demonstrations: Near-field modeling is
sufficient to address whether a source will cause
of contribute to a NAAQS violation so EPA does
not consider a LRT assessment beyond 50 km
necessary for inert pollutants.
• EPA recognizes that LRT assessments may be
necessary in limited situations for PSD increment
and proposes a screening approach where
CALPUFF or other appropriate model/tool may be
used.

IWAQM Update
• Interagency Workgroup on AQ Modeling
• FLAG Guidance is being updated
• Current guidance tied to Appendix W
• Plan is to have it be a stand alone document
• CALPUFF will likely continue to be used for the
next 3-5 years
• MMIF documentation will be emphasized

What's Coming?
The good
• Some beta options in AERMOD are
expected to become default
– Horizontal/capped stack
– Adjusted surface roughness in AERMET
– LOWWIND3 option
– ARM2 and PVMRM2 for NOx to NO2
conversion

What's Coming?
Ozone and PM2.5 formation
• Uncertainty
– For Tier 1 and Tier 2 ozone and PM2.5
evaluations
– Long Range Transport
• More time and expense
• Analyses more vulnerable to legal
challenge

Sergio A. Guerra, PhD
sguerra@cppwind.com
Mobile: + 612 584 9595
CPP, Inc.
2400 Midpoint Drive, Suite 190
Fort Collins, CO 80525
+ 970 221 3371
www.cppwind.com @CPPWindExperts
Thanks!

Highlights from the 2016 Guideline on Air Quality Models Conference

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