PNNL-13501 - Pacific Northwest National Laboratory

This new aerosol module is called MOSAIC (Model for
Simulating Aerosol Interactions and Chemistry) (Zaveri
1997), and has recently been included in the PEGASUS
framework. MOSAIC is capable of simulating the multistage
(mixed-phase) growth features in multicomponent
aerosols consisting of various salts of sulfate, nitrate,
chloride, ammonium, and sodium. An example of twostage
deliquescence curve (increasing relative humidity)
is illustrated in Figure 2 for a sea-salt aerosol consisting
of equimolar mixture of Na2SO4 and NaCl. On the
efflorescence curve (decreasing relative humidity), the
particle is shown to remain supersaturated (liquid-phase)
all the way down to 50% relative humidity.
Particle Mass Change, W tot /W dry
5
4
3
2
1
Equimolar Mixture of Na 2 SO 4 and NaCl
Deliquescence Curve (Experimental, Tang, 1997)
Efflorescence Curve (Experimental, Tang, 1997)
Deliquescence Curve (MOSAIC)
Efflorescence Curve (MOSAIC)
50 60 70
Relative Humidity (%)
80 90
Figure 2. Particle mass change at 298 K of a mixed Na 2SO 4-
NaCl particle (equimolar mixture): model predictions and
experimental results
Summary and Conclusions
This project broadens the range of environmental media
being investigated at the Laboratory. It also greatly
increases the range of spatial and temporal scales and
processes that are being addressed. As part of the testing
of PEGASUS, we have evaluated the downward transport
of fine filaments of reactive gases from the stratosphere
that span geographical scales of thousands of kilometers.
We have also tested the new chemical mechanism against
observations made within air masses that started their
journey on the west coast of North America and have
been transported inland to Phoenix, Arizona. Molecularscale
homogeneous and heterogeneous reactions and mass
transfer processes occur within both processes. Because
of its performance, as measured by the proportionality
between speedup and the number of processors,
PEGASUS can include detailed information for processes
that would otherwise be too computationally expensive
for a standard air chemistry model. Access to this tool
will position scientists to perform research in atmospheric
chemistry that links the results obtained in laboratory
studies with large-scale air quality and climate change
models.
References
Ansari AS and SN Pandis. 1999. “Prediction of
multicomponent inorganic atmospheric aerosol behavior.”
Atmos. Environ. 33:745-757.
Berkowitz CM, X Bian, and RA Zaveri. 2000.
Development of a tool for investigating multiphase and
multiscale atmospheric chemical and physical processes.
PNNL-13203, Pacific Northwest National Laboratory,
Richland, Washington.
Lurmann FW, AC Lloyd, and R Atkinson. 1986. “A
chemical mechanism for use in long-range transport/acid
deposition computer modeling.” Journal of Geophysical
Research 90:10,905-10,936.
Tang IN. 1997. “Thermodynamic and optical properties
of mixed-salt aerosols of atmospheric importance.”
Journal of Geophysical Research 102:1883-1893.
Zaveri RA. 1997. Development and evaluation of a
comprehensive tropospheric chemistry model for regional
and global applications. Ph.D. dissertation, Virginia
Polytechnic Institute and State University, Blacksburg,
Virginia.
Zaveri RA and LK Peters. 1999. “A new lumped
structure photochemical mechanism for large-scale
applications.” Journal of Geophysical Research
104:30,387-30,415.
Publications and Presentations
Fast JD, X Bian, and CM Berkowitz. 1999. “Regionalscale
simulations of stratospheric intrusions of ozone over
Eastern North America during the summer of 1991.”
Preprints, Symposium on Interdisciplinary Issues in
Atmospheric Chemistry, January 10-15, 1999, Dallas,
Texas, pp. 16-23. American Meteorological Society,
Boston, Massachusetts.
Zaveri RA and LK Peters. 1999. “A new lumped
structure photochemical mechanism for large-scale
applications.” Journal of Geophysical Research
104:30,387-30,415.
Earth System Science 209