EPA 910-R-15-001 d Alaska
United States Region 10 Idaho
Environmental Protection 1200 Sixth Avenue Oregon
Agency Seattle WA 98101 Washington
Office of Environmental Assessment September 2015
cvEPA Combined WRF/MMIF/
AERCOARE/AERMOD
Overwater Modeling
Approach for Offshore
Emission Sources
Technical Summary
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Combined WRF/MMIF/
AERCOARE/AERMOD Overwater
Modeling Approach for Offshore
Emission Sources
Technical Summary
EPA Contract No. EP-W-09-028
Work Assignment No. M12PG00033R
Prepared for:
U.S. Environmental Protection Agency
Region 10
1200 Sixth Avenue
Seattle, WA 98101
and
U.S. Department of the Interior
Bureau of Ocean Energy Management
45600 Woodland Road
Sterling, VA 20166
Prepared by:
Amec Foster Wheeler
Environmental & Infrastructure, Inc.
4021 Stirrup Creek Dr., Suite 100
Durham, NC 27703
and
RAMBOLL ENVIRON
773 San Marin Drive, Suite 2115
Novato, CA, 94998
September 2015
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Under Interagency Agreement (IA) number M12PGT00033R dated 9 August 20121 between the U.S.
Department of the Interior (DOI), Bureau of Safety and Environmental Enforcement (BSEE) on
behalf of the Bureau of Ocean Energy Management (BOEM) and the U.S. Environmental Protection
Agency (EPA), Region 10 (R10) established a collaboration in which the regulatory approved
AERMOD (AERMIC [AMS/EPA Regulatory Model Improvement Committee] Model) dispersion
program2 was evaluated for predicting near field concentration impacts (< 50 kilometers) from
emission sources located at overwater locations, e.g., outer continental shelf (OCS). The objectives
of the collaboration are to (1) replace the Offshore and Coastal Dispersion (OCD) dispersion model3
with AERMOD for sea surface based emission releases, and (2) assess the use of Weather
Research and Forecasting (WRF) model4 predicted meteorology in lieu of overwater meteorological
measurements from towers and/or buoys with AERMOD. The work plan consisted of six tasks to
address the objectives of the collaboration study5. The results and findings are presented in a three
volume report. Volume 1 is a project report that discusses Tasks 1, 4, 5 and 6 in detail and provides
only summaries of Tasks 2 and 3. Task 2 and Task 3 details are contained in Volume 2 and Volume
3, respectively. This report is a technical summary of the six tasks that comprised the collaboration
study.
A. Task 1. Evaluation of Two Outer Continental Shelf Weather Research and Forecasting
Model Simulations for the Arctic
Task 1 involved the review two existing WRF datasets for the Arctic Ocean that could be
used to provide the necessary meteorological variables for dispersion model simulations of
OCS sources within their domains. The objective of this task was to examine the differences
between the two datasets, analyze model performance with overwater measurements, apply
the Mesoscale Model Interface (MMIF)6 Program and AERMOD-COARE (Coupled Ocean-
Atmosphere Response Experiment) (AERCOARE)7'8 to the datasets using different options
to develop meteorological input files for AERMOD, and compare AERMOD model
predictions from the resulting datasets using simulations of typical OCS sources.
After the first MMIF runs were completed and reviewed, peculiar planetary boundary layer
(PEL) height and precipitation values were observed every three hours from one of the
datasets. The problem was traced to the version of WRF used to perform a reanalysis.
9Additionally, shortcomings were noted with the other dataset, namely: 1) the domain does
not extend far enough east to cover the Beaufort Sea where many potential lease blocks
1 Environmental Protection Agency. 2012. Interagency Agreement No. M12PG00033R with the Bureau of Safety
and Environmental Enforcement on behalf of Bureau of Ocean Energy Management, Herndon, VA. Region 10
Seattle, WA. Augusts.
2 Environmental Protection Agency. 2004. User's Guide for the AMS/EPA Regulatory Model-AERMOD. Publication
No. EPA-454/B-03-001. Office of Air Quality Planning and Standards, Research Triangle Park, NC. September.
3 DiCristofaro, D.C. and S.R. Hanna. 1989. OCD: The Offshore and Coastal Dispersion Model, Version 4. Volume I:
User's Guide and Volume II: Appendices. Sigma Research Corporation, Westford, MA
4 National Center for Atmospheric Research. 2014. Weather Research & Forecasting (WRF) ARW Version 3
Modeling System User's Guide. Mesoscale & Meteorology Division, Boulder, CO.
5 Environmental Protection Agency. 2012. Order for Supplies or Services, Contract No. EP-W-09-028.
Headquarters Procurement Operations, Ariel Rios Building, 1200 Pennsylvania Ave, NW, Washington DC.
September 6.
6 Brashers, B. and C. Emery. 2014. The Mesoscale Model Interface Program (MMIF), Draft User's Manual.
Prepared for the Air Quality Assessment Division, U.S. Environmental Protection Agency. ENVIRON International
Corporation, Air Sciences Group, Novato, CA.
7 Fairall, C and E.F. Bradley. 2003. The TOGA-COARE Bulk Air-Sea Flux Algorithm. NOAA/ERL/ETL, 325 Broadway,
Boulder, CO. September 2.
8 Richmond, K. and R. Morris. 2012. Evaluation of the Combined AERCOARE/AERMOD Modeling Approach for
Offshore Shores. Prepared for U.S. Environmental Protection Agency, Region 10. EPA-910-R-12-007. ENVIRON
International Corporation, Novato, CA.
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exist and several have already been leased, and 2) the dataset covers only the open-water
period and could not be used in dispersion modeling assessments of permanent sources.
The peculiar results and shortcomings of the datasets made both datasets unsuitable for the
needs of this collaboration study.
B. Task 2. Evaluation of Weather Research and Forecasting Model Simulations for Five Tracer
Gas Studies with AERMOD
Task 2 included the comparison of WRF-driven AERMOD results to the concentrations
measured during five offshore tracer gas studies (i.e., Cameron, LA; Carpinteria, CA; Pismo
Beach, CA; Ventura, CA, and Oresund, Denmark). Four of the five tracer gas studies,
involving experiments conducted over North American waters (coastal waters of California
and the Gulf of Mexico), were used previously to evaluate COARE and AERCOARE. The
fifth tracer gas study was the Oresund Nordic Dispersion Experiment conducted during 1984
in the strait that separates Denmark and Sweden and was also used to evaluate CALPUFF,
Version 69. Volume 2 provides details of the methodology and analyses used in this task.
The report also presented results of the AERMOD performance evaluations, and analyzed
how modeling options affect model performance.
The results of this task suggested small differences in the key meteorological variables can
cause large differences in predicted tracer gas concentrations for a given hour. Although
many of the WRF simulations perform reasonably well when compared to regional surface
observation of winds and temperatures, relatively small differences near the overwater point
of release can have a large effect on stability which is a function of the "sign" of air-sea
temperature difference. Spatial gradients of sea surface temperature (SST) near the coast
and wind direction play key roles in the simulation of the stability and PEL heights over the
water.
The model performance analysis of the field experiments examined in this study
demonstrated WRF based AERMOD simulations can result in estimates of concentration as
good as or better than AERMOD simulations using observations - but not in all cases - and
is dependent upon the reanalysis and PBL scheme.
C. Task 3. Analysis of AERMOD Performance using Weather Research and Forecasting Model
Predicted and Measured Meteorology in the Arctic
Task 3 analyzed alternative methods for supplying meteorological variables to AERMOD for
regulatory air quality modeling of sources located overwater. It is hypothesized, given an
appropriate overwater meteorological dataset, that AERMOD can be applied for New Source
Review (NSR) demonstrations following the same modeling procedures as used for sources
over land. That is, a combined modeling approach where the meteorological variables are
provided by WRF and processed by MMIF and optionally AERCOARE. In this task,
AERMOD is run using predicted meteorology and four observational datasets over the
Chukchi and Beaufort Seas along the Arctic coasts of AK with the same hypothetical
emission source scenarios for years 2010-2012 during the open water/ice free season. Year
2009 was excluded because of the lack of temperature profiler data. The modeling
methodologies and analyses conducted under this task are discussed in detail in Volume 3.
The analyses suggest WRF was able to produce hourly meteorological datasets that
compared favorably to over-water measurements. Most AERMOD concentration results
using WRF meteorology were adequate, falling within the fraction-factor-of-two lines and
producing robust highest concentration values that corresponded well with observation-
9 Earth Tech. 2006. Development of the Next Generation Air Quality Models for Outer Continental Shelf (DCS)
Application. Final Report: Volume 1. Prepared for the U.S. Department of the Interior, Minerals Management
Service, Office of International Activities and Marine Minerals. January.
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driven AERMOD results. Furthermore, the results suggest WRF extracted meteorology can
be used as an alternative to offshore observations for air permitting in such areas. However,
there was little discernable advantage in using AERCOARE to process meteorology
extracted from WRF using MMIF to develop the input meteorology for AERMOD. The results
also indicate that WRF extracted meteorology be filtered by limits on minimum wind speed,
mixing height, and Monin-Obukhov length to avoid extreme conditions not typically observed
over water.
D. Task 4. Evaluation of Predicted and Measured Mixing Heights
Task 4 provided a comparison of mixing heights derived from WRF to observations in the
Arctic. Available sources were surveyed for in-situ upper air observations in the Arctic
marine environment. These sources included Shell's Kipp & Zonen passive microwave
profiler installed at Endeavor Island in the Beaufort Sea, the radiosondes launched as part of
quality assurance procedures for the profiler, and radiosondes launched during Japanese
Agency for Marine-Earth Science and Technology (JAMSTEC) research cruises10, currently
only available for 2009 in the Chukchi Sea. Predicted heights from the WRF solutions were
compared to measured temperature profiles (i.e., profiler and radiosonde). The analyses
conducted under this task are discussed further in Volume 1.
Observed mixed layer heights were analyzed from the Kipp & Zonen profiler11, JAMSTEC,
and National Weather Service soundings from Barrow, AK by two methods: 1) subjective
hand analyses (i.e., a visual inspection of the plotted profiles by a trained meteorologist) and
2) objective analyses using a Critical Bulk Richardson Number (CBRN)12 approach. The
WRF mixing height output was analyzed twice using MMIF: 1) the 'pass-through' option and
2) the CBRN calculation. Comparisons of the WRF and MMIF mixing heights to the hand
analyses and CBRN approach, as well as mixing heights derived by AERMOD's
meteorological preprocessor (AERMET)13 at Endeavor Island generally showed little
correlation (r), with the best comparisons to the CBRN of r = 0.65 to 0.70.
Profiles generated by WRF captured the essence and variation of the structure of the
JAMSTEC soundings remarkably well. In comparing the mixing heights estimated using the
CBRN method for both the WRF/MMIF and JAMSTEC soundings, 75 percent of the
estimates fell within a fraction-factor-of-two with a correlation of about 0.6.
E. Task 5. Evaluation of AERSCREEN for Arctic OCS Application
The objective of Task 5 is to develop and evaluate a systematic approach for generating
screening meteorology representative of overwater conditions that can be incorporated into
AERSCREEN in lieu of MAKEMET14, the overland meteorological processor for
AERSCREEN, or used directly by AERMOD in place of observed data. Three exploratory
screening datasets were developed for input to AERCOARE to generate the input
meteorology for AERMOD by: 1) reviewing and analyzing meteorological data collected for
10 International Arctic Research Center (IARC) and Japan Agency for Marine-Earth Science Technology (JAMSTEC)
Annual Report. For the period April 1, 2009 to March 31, 2010. IARC, Fairbanks, AK
11 Hoefler Consulting Group. 2010. Quality Assurance Project Plan for the Endeavor Island (Endicott)
Meteorological Monitoring Program, Prudhoe Bay, AK. Prepared for Shell Offshore, Inc., Anchorage, AK. April.
12 Gryning and Batchvarova. 2003. Marine atmospheric boundary-layer height estimated from NWP model
output. International Journal of Environment and Pollution, 147-153.
13 Environmental Protection Agency. 2004. User's Guide for the AERMOD Meteorological Preprocessor (AERMET).
Publication No. EPA-454/B-03-002. Office of Air Quality Planning and Standards, Research Triangle Park, NC.
November.
14 Environmental Protection Agency. 2011. AERSCREEN User's Guide. EPA-454/B-11-001. Office of Air Quality
Planning and Standards, Research Triangle Park, NC. March.
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and developed in Task 3 to determine typical ranges of key meteorological parameters for
the open water ice-free Arctic (includes buoy data, WRF data); 2) using the information from
step 1 to develop an initial screening dataset from combinations of ranges of values of the
minimum set of meteorological parameters required by AERCOARE (wind speed, wind
direction, air-sea temperature difference, relative humidity, and mixing height) to calculate
meteorology needed by AERMOD; 3) refine the initial dataset to produce two additional
datasets. The derivation of the three exploratory datasets are explained in more detail in
Section 6 of Volume 1.
Hypothetical emission sources, as described in Volume 1, were modeled utilizing the three
exploratory screening meteorological datasets. The same sources were used for refined
modeling driven by 1) meteorological data extracted from WRF using MMIF and input to
AERCOARE or directly to AERMOD, 2) observations from buoy data input to AERCOARE,
and 3) AERMOD-ready datasets for the Beaufort and Chukchi Seas provided by EPA Region
10 to support permit applications for offshore exploratory drilling.
The one-hour high-first-highest (H1H) concentrations from each of the three screening
datasets were compared to concentration estimates from refined modeling. No screening
dataset yielded consistently conservative results across all emission sources. The
development of the screening data sets and analyses conducted under this task are
discussed in detail in Volume 1.
More detailed analyses of the screening and refined modeling results are needed such as
extracting, reviewing, and comparing the hourly meteorological data corresponding with the
one-hour H1H concentrations that could provide insights into possible refinements to the
screening datasets. An evaluation of scaling parameters for the 3-, 8-, and 24-hr averaging
periods is needed to make this a viable option for screening modeling in the Arctic.
F. Task 6. Collaboration Study Seminar
EPA Region 4 in Atlanta, GA hosted the DOI BOEM/EPA Region 10 Collaboration Study
Seminar and Demonstration on 16 and 17 September 2014. Details of the seminar are
presented in Volume 1.
The status and/or results of each of the above five tasks, including hands-on demonstrations,
were presented by EPA R10 and its contractor team of AMEC (Prime) and ENVIRON
(subcontractor). For the hands-on demonstrations, the attendees were provided personal
computers that allowed them to follow along as the presenter ran through the exercises.
After the seminar, each EPA and BOEM/BSEE regional office were provided a flash drive
that included all the PowerPoint presentations, exercises, agenda and attendance sheet.
There were twenty (20) attendees at the seminar and demonstration. The attendees included
two from BSEE, seven from BOEM, and eleven from EPA regional offices. In addition, a
conference call line was setup so that technical staff from the EPA's Office of Air Quality
Planning and Standards (OAQPS) could listen in and ask questions.
Volumes 2 and 3 will be used to support R10's recommendation that WRF predicted meteorology
preprocessed by MMIF and input into AERMOD satisfies the regulatory requirements as an
alternative model pursuant to Appendix W in 40 CFR 51 (Appendix W). However, subsequent
studies and experiments are needed to address peer review comments that were not fully addressed
in the three volumes. Of particular relevance for offshore emission sources is the need for a
shoreline fumigation algorithm and a platform downwash algorithm in AERMOD to replace OCD, and
updated tracer gas experiments to evaluate model performance. In addition, R10 suggested
changes to Appendix W that addresses the use of five (5) years WRF predicted meteorology and the
MMIF program with the AERMOD.
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