United States Environmental Protection Agency Office of Research and Development
National Exposure Research Laboratory
Research Abstract
Government Performance Results Act Goal: Clean Air
Significant Research Findings:
Development and Evaluation of the Morphecule Approach
for Incorporating Complex Chemistry in Air Quality Models
Scientific Problem and Air quality models are critical tools used by the U.S. EPA and the
Policy Issues states in their efforts to ensure that the air we breathe is healthful.
These models, which describe both the atmospheric movement and the
chemical reactions of air pollutants, are used by the states to develop
their air pollution management strategies. The models are used to
develop control strategies for ozone, particulate matter (PM), and
hazardous air pollutants or air toxics. The atmospheric chemistry of
ozone involves the complex interactions of thousands of different
chemical reactions, and describing the chemistry of other important
pollutants, like secondary organic particulate matter and secondary
toxic chemicals, requires even more reactions.
Including this level of detailed chemistry in a current air quality model
would overwhelm even the most powerful computers available;
therefore, the chemistry in current models is always extremely
simplified. Air quality models represent the thousands of reactions
that actually occur in the atmosphere by only about 80-200 model
reactions. These simplifications allow the model to run efficiently, but
they sometimes lead to inaccuracies in the model predictions. Such
inaccuracies are especially important to the complex control strategy
choices facing EPA and the states today. To address this problem, the
U.S. EPA's National Exposure Research Laboratory has developed a
way to perform these calculations more efficiently, but without losing
accuracy in the predictions. This method, the Morphecules approach,
can efficiently and realistically describe the complex atmospheric
chemistry of ozone and other photochemical pollutants in regulatory
and research air quality models.
Research Approach The Morphecules approach continually assigns individual chemical
species into groups ("morphecules") in the air quality model. The
computer intensive parts of the air quality model are done with this
smaller set of groups, but the model remembers the individual
National Exposure Research Laboratory — October 2001
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chemical species within each group so that they can be recreated from
the morphecules at each time step. This allows the model to retain
detailed information about the atmospheric chemistry of ozone and
other photochemical oxidants, yet still efficiently use computer
resources.
The research involved developing the morphecule framework by which
chemical species can be aggregated and dis-aggregated as needed. The
framework was then implemented in computer code and thoroughly
tested - to ensure that it worked correctly computationally, and that it
represented an improvement to current approaches in representing
"real" chemical species accurately.
Results and
Implications
With the ability to perform detailed atmospheric photochemistry using
the Morphecules approach, researchers will no longer be dependant on
the limited number of existing mechanisms and their "tuned"
simplifications. For pollutants such as ozone and well known simple
secondary air toxics, this means that concentrations can be predicted
with greater certainty and that the resulting state implementation plans
and risk assessments will be more accurate. For pollutants which
cannot be represented by current mechanisms due to their complexity,
such as secondary organic particulate matter, researchers will finally
be able to develop chemical mechanisms and incorporate them in air
quality models. This approach allows for the development of a suite of
different chemical mechanisms that can be tailored to the particular
type of simulation that is required. State and federal governments can
more easily reconcile their need for chemical complexity with the
availability of computer resources. It will give academic researchers,
who may need an extreme degree of complexity, the means to
implement this chemistry in a 3-D model.
This research supports the Agency's Goal of Clean Air (Goal 01) and
achievement of Objective 1: "By 2010 improve the air quality for
Americans living in areas that do not meet the National Ambient Air
Quality Standards for ozone and particulate matter." It directly
supports Annual Performance Measure 91: "Complete development
and evaluation of the 'morphecule' approach; and complete analysis
for implementation and testing of the Morphecule mechanism in
Models-3/CMAQ."
Research
Collaboration and
Publications
The morphecules software was developed at the University of North
Carolina, Chapel Hill, and evaluated by Lockheed Martin Services, Inc.
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Examples of recent publications from this study include:
Atkinson, R., 1997. Gas-Phase Tropospheric Chemistry of Volatile Organic
Compounds: 1. Alkanes and Alkenes. Journal of Physical and Chemical
Reference Data, 26, 215-290.
Jeffries, H., and M. Kessler, 1999. A User's Guide to MComp Mechanism Compiler
Program for Morphecule Mechanisms, a Part of Morpho, Report to EPA from
the University of North Carolina, Chapel Hill, June 15, 1999.
Jeffries, H., and M. Kessler, 1999. A User's Guide to MEval Solver Program for
Morphecule Mechanisms, a Part of Morpho, Report to EPA from the University
of North Carolina, Chapel Hill, June 15, 1999.
Jeffries, H., andM. Kessler, 1999. Morphecule/Allomorph Reaction Mechanisms,
Report to EPA from the University of North Carolina, Chapel Hill, June 15,
1999.
Sexton, K. and H. Jeffries, 1999, UNC Chamber Data and Model Simulations Using
Morpho, Report to EPA from the University of North Carolina, Chapel Hill, July
20, 1999.
Gery, M., 1999, Designing Morphecule Mechanisms, Report to EPA from
Atmospheric Research Associates, Boston, MA, June 15, 1999.
Lockheed Martin, 200, Performance of Morphecules Software II: Test Results and
Recommendations, Report on Task Order 259, contract 68W70055 with
Lockheed Martin Services, Inc., November 30, 2000.
Future Research Once the libraries for interfacing this software with an air quality
model are completed, we will implement it fully into the Models-
3/Community Multiscale Air Quality (CMAQ) modeling system. We
will compare its predictions to those from simplified chemical
mechanisms across the full spectrum of conditions available using
Models3. Future plans include creating mechanisms using the
morphecule approach for complex secondary air toxics and complex
organic compounds that form particulates and to calculate atmospheric
reactivities of anthropogenic emissions.
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Information
Contacts for Questions and inquiries can be directed to:
Additional Deborah J. Luecken
US EPA, Office of Research and Development
National Exposure Research Laboratory
Research Triangle Park, NC 27711
Phone: 919/541-0244
E-mail: luecken.deborah@epamail.epa.gov
Federal funding for this research was administered under EPA
contracts 68D50129 with the University of North Carolina, Chapel
Hill, and 68W70055 with Lockheed Martin Services, Inc.
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