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SPEED ENHANCEMENTS (MPI) FOR CAMx PROBING
TOOLS ON COMPUTER CLUSTERS
Project A-63
Leader:
A. M. Dunker
R. S. MacArthur
Scope and Objective
The objective of this project is to revise CAMx
so that multiple computer processors can be used to increase the speed of
simulations involving probing tools.
Current Status and Future Program
Currently, the CAMx and CMAQ regional
ozone/PM/visibility models are being applied to annual periods by states and
several Regional Planning Organizations to address the regional haze
requirements and PM2.5 and 8-hour ozone attainment issues. Although
there are some fundamental differences in their formulation, CMAQ and CAMx are
both considered state-of-the science models. CRC has funded the implementation
of several probing tools in CAMx that extract additional information from the
model to assist in understanding predictions and evaluating control strategies.
The three probing tools are the Decoupled Direct Method (DDM) for sensitivity
analysis, Process Analysis (PA), and Source Apportionment (SA).
With help from Sandia National Laboratory, EPA
implemented the Message Passing Interface (MPI) capability in CMAQ so that the
model could be run on computer clusters. As a consequence, despite the fact
that CAMx is more computationally efficient than CMAQ when run on a single
computer, CMAQ simulations now require less time because the model can be run on
multiple computer processors. Thus, implementing MPI capability in CAMx is
important to the continued use of the model. This is especially true when using
one or more probing tools for annual modeling, in which case a single simulation
can take several months without MPI.
The Midwest Ozone Group (MOG), a stakeholder
group that consists of utilities, other industries and local agencies, provided
a limited amount of initial funding to initiate the MPI implementation in CAMx.
The MOG seed funding has allowed the rewriting of the CAMx code into FORTRAN90,
conversion of model data arrays to use dynamic allocation, and other code
restructuring and modifications needed to allow the implementation of MPI. The
U.S. EPA Office of Air Quality Planning and Standards (OAQPS) provided
additional funding of a comparable amount to implement the multi-processor
capability into the core portion of CAMx that calculates pollutant
concentrations. However, this funding is insufficient to implement MPI for the
probing tools.
This project, built on the work funded by MOG
and EPA, extended the multi-processor capability in CAMx to the probing tools.
The modified code was tested for a regional simulation using each of the probing
tools. The reduction in simulation time for the concentrations and the probing
tools was determined, as compared to a simulation employing a single processor.
The advantages and disadvantages of using multi-processors was reported.
Guidance was developed on the optimal number of processors to employ in
simulations with probing tools. The instructions for using multi-processors
were documented in the User's Manual along with any required changes in input.
The committee
approved the project plan and ENVIRON was selected to conduct the project
beginning in June 2006. Deliverables from the project include the revised CAMx
code with multi-processor capability for the probing tools. The User's Manual
for CAMx will be updated to describe the new capability of the model and how
best to use it. The Final Report has been published and has been posted on the
CRC website.
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