PNNL-13501 - Pacific Northwest National Laboratory

Development of a Tool for Investigating Multiphase and Multiscale Atmospheric Chemical and
Physical Processes
Study Control Number: PN99015/1343
Carl M. Berkowitz, Xindi Bian, Rahul Zaveri, Jerome D. Fast
A high performance reactive transport code was designed to simulate atmospheric processes that control tropospheric
oxidants and aerosols. Simulations can be produced at high spatial and temporal resolutions while also incorporating
detailed numerical representations of chemical and physical processes. State-of-the-art process modules, numerical
methods, and computational techniques are being incorporated in the model. This research will help us address key issues
on the formation and distribution of fine aerosols and tropospheric oxidants.
Project Description
The Department of Energy has a strong interest in air
quality and climate change. New national ambient air
quality standards for tropospheric ozone and particles less
than 2.5 micron diameter (PM2.5) are of special concern
to DOE. DOE is interested in developing a clearer
understanding of how emissions from energy production
lead to oxidant and aerosols, and under what conditions
emission controls will be effective. Complicating this
task is a lack of understanding of the basic mechanisms
by which fine particles are formed, how they interact with
atmospheric oxidants and ozone, and the mechanisms by
which they affect human health. As a result, the scientific
community recognizes that improved modeling
capabilities are needed to address the key issues facing
policymakers regarding ozone and particulate matter
smaller than 2.5 microns in diameter.
Introduction
Our objective has been to develop a computational tool
for analysis of multiphase atmospheric processes, which
occur over multi-decadal scales in space and time. The
modules have been built into a highly flexible and
portable framework and are capable of simulating
chemical reactions in the gas phase, in the aqueous phase,
and in and upon solid and mixed-phase particles.
Additional modules will treat the dispersion, transport,
scavenging, and deposition of trace materials in the
gaseous phase and in aerosols, cloud drops, and
precipitation. We have also begun using this model to
investigate the interaction of processes acting on different
scales. This tool now appears to be capable of performing
research in atmospheric chemistry linking results obtained
in laboratory studies with large-scale air quality and
climate change models.
Approach
The code we have developed is called PEGASUS, taken
from the winged horse of Greek mythology. The
acronym also identifies our Laboratory for developing the
code (PNNL), the mathematical framework (Eulerian),
the multiple chemical phase capability (gas and aerosols),
its scalability on high-performance computers, and that it
brings together, or creates a unified system, to describe
both chemical and meteorological processes. Modules are
being added to this basic gas-phase-only code that allow
the code to simulate the following processes:
• heterogeneous reactions on the surface and in the
interior of aerosols and cloud drops
• formation of new particles through multi-species gasto-particle
nucleation
• detailed treatment of the microphysical dynamics of
aerosol and droplet growth
• scavenging of gases and aerosols by clouds and
precipitation.
Whereas the formulations for simulating many of these
processes are available in the open literature, a substantial
effort has gone into integrating the various algorithms into
a computational architecture that enables them to easily
interact with existing and future modules. Along with the
addition of advanced process modules, we have
maintained the computational efficiency and accuracy by
Earth System Science 207