United States
Environmental Protection
Agency
Atmospheric Sciences
Research Laboratory
Research Triangle Park NC 27711
Research and Development
EPA/600/S8-85/005 Apr. 1985
v>EPA Project Summary
An Interim User's Manual for
the Advanced Scavenging
Module: Version 1.2
J. M. Hales
This report provides a user's manual
for Version 1.2 of the Advanced
Scavenging Module (ASM). It is an in-
terim code and is intended primarily
for coordinating development of the
module with that of the evolving
NCAR Regional Acid Deposition
Model (RADM).
The ASM is currently in evolu-
tionary stages; the general framework
provided by Version 1.2 is sufficiently
well-established to provide the basis
for future versions. The code supplied
with this manual is a complete, opera-
tional system, and was tested.
The ASM is activated by two types
of subroutine calls from the host
code. Upon advancing to some
ground-level position (x,y) on the
host's numerical computation grid,
the ASM is interrogated (using the
first subroutine call) to produce the
vertical distributions of storm features
above that point. Following this,
scavenging computations are per-
formed repeatedly for each vertical
grid position, using the second
subroutine call. The primary outputs
from these secondary ASM interroga-
tions are the transformation rates
associated with the physical and
chemical components of the scaveng-
ing process. These rates are returned
to the host code and incorporated
with its normal numerical integration
procedure.
This Project Summary was
developed by EPA's Atmospheric
Sciences Research Laboratory,
Research Triangle Park, NC, to an-
nounce key findings of the research
project that fs fully documented in a
separate report of the same title (see
Project Report ordering information at
back).
Introduction
The Advanced Scavenging Module
(ASM) is a conceptual framework and
computer code for calculating the
precipitation scavenging of reactive and
nonreactive air pollutants. The module is
intended to be used in conjunction with a
regional, Eulerian "host" code, which ap-
proximates numerically the appropriate
equations of conservation and inter-
rogates the ASM for needed input regard-
ing wet-chemistry and scavenging proc-
esses. The ASM can be considered an ad-
vancement over its regional predecessors
at this point in time, because it is struc-
tured to allow a comparatively versatile
depiction of individual physicochemical
processes within the composite scaveng-
ing sequence. This in turn presents the
possibility of more accurate source-
receptor analysis, and the fruitful in-
vestigation of individual chemical con-
tributions, nonlinear effects, and
associated control strategies. The ASM is
being prepared primarily for the National
Center for Atmospheric Research (NCAR)
Regional Acid Deposition Model (RADM)
and an enhanced version of the existing
STEM II code, but is sufficiently versatile
to be incorporated with a number of addi-
tional Eulerian models as well.
This version of the module is not sub-
mitted as a product that is ready for
routine incorporation in a finalized
regional model. It is intended, rather, to
provide a systematic definition of
information-exchange requirements, for
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the purpose of helping to coordinate
development in the overall regional model-
ing effort. The Version 1.2 Scavenging
Module described in this report takes the
form of an executable system of
subroutines, which may be interrogated
by host codes for development and
shake-down purposes.
Major Features
The two coordination points are par-
ticularly important in this regard. The first
of these is the development of the host-
codes themselves, which must have a
number of interactive linkages with the
Scavenging Module. The second co-
ordination point is with those individuals
who are creating the wet-chemical con-
version parameterizations for the RADM.
In its present state the Scavenging
Module provides a convenient substrate
for interweaving these parameterizations
with cloud-physics processes and
gaseous-phase chemistry. Individuals
working on both of these efforts should
be totally aware of the protocols
established in the Scavenging Module, so
that a smooth coordination of these
linkages will occur. In this context it
should be noted that while many internal
features of the Scavenging Module are
not complete, the framework and
information-exchange scheme is in a
rather high state of development. Because
of this, coordination with other modules
and with the host codes can occur at this
point with minimum fear of future back-
tracking.
The Advanced Scavenging Module
bears a direct relationship with the evolv-
ing reactive storm models in the PLUVIUS
series, and many of the procedures and
parameterizations employed by the
Module are directly traceable to those
used in the PLUVIUS codes. Two primary
differences exist. The first of these is that
the Module is subservient to the host
code and is designed to work interactively
with a number of outside modules,
whereas the PLUVIUS models deal with
the total system of conservation equa-
tions. The second difference is that
PLUVIUS codes generate storm systems
on the basis of first principles, whereas
the Scavenging Module synthesizes the
storms on the basis of empirical formulae
and look-up tables. This feature is ap-
propriate to the Module for two major
reasons: first, it allows a very rapid and
computationally efficient generation of
essential properties; and second, it pro-
vides a convenient means for creating
spatially- and temporally-averaged storm
features. This is particularly important for
the target models, because of temporal
and spatial grid-mesh properties.
Module Operation
The ASM operates in two distinct
modes, which may be termed the "storm-
generation" and "scavenging" modes.
Activation of these modes is controlled
via a subroutine argument (MFUNCT),
and a number of internal bypass options
are available, depending on specific com-
putations required by the particular host
code in use.
In storm-generation mode, the ASM
creates vertical profiles of key storm
parameters above some chosen position
x,y at the surface. These parameters in-
clude quantities of the condensed-water
media and their associated interconversion
rates, as well as a number of auxiliary
variables (such as actinic flux) required for
reactive scavenging calculations.
Condensed-water media for this particular
version of the ASM have been lumped in-
to the three following categories:
• cloud water,
• rain,
• snow.
Vertical profiles of these condensed-
water classes are estimated using em-
pirical relationships. ASM Version 1.2
employs polynomial fitting functions for
this purpose, in conjunction with the
following "predictor variables," which
must be supplied by the host code: sur-
face precipitation rate, surface elevation,
surface temperature, storm-type index,
cloud-cover index, and cloud base eleva-
tion.
Cloud interconversion processes of
potential importance to the scavenging
process include:
• cloud autoconversion to rain,
• accretion of cloud water by rain,
• riming of cloud water by snow,
• deposition of water vapor to snow
surfaces,
• freezing of liquid water,
• melting of snow, and
• evaporation of condensed water.
Transport processes included by the
storm environment include:
• vertical fall velocities of snow and
rain, and
• dispersion of snow and rain arising
from differential settling of different
sizes of hydrometeors.
All of these properties are computed by
ASM in storm-generation mode. The code
is modularized to accommodate pro-
gressive improvements in characteriza-
tions of these features, and the present
Version 1.2 employs the rather simple ex-
pressions utilized by the PLUVIUS MOD
5.0 storm code. Since these expressions
are described in the PLUVIUS User's
Manual, they are not discussed at length
in this report.
The Version 1.2 described in this report
has been written in standard FORTRAN
77 code and, other than for architectural
features, has not been prepared for vec-
torization on an array-processor. In par-
ticular, many of the innermost loops con-
tain conditional statements, which will
prevent direct vectorization. This choice
was made with Version 1.2 because the
primary objective of this version is to
coordinate development and illustrate in-
formation exchange, and inclusion of the
conditional statements results in a much
more easy-to-follow text. A vectorized
replica of Version 1.2 will be prepared for
initial blending with the RADM on the
NCAR Cray array processor. Upgraded
versions of the Advanced Scavenging
Module will become available periodically
during the next two years.
Conclusion
Version 1.2 of the ASM should be con-
sidered as a partial guide for host-code
development and as a form for the im-
plementation of wet chemical reaction
schemes. The potential user is encour-
aged to familiarize himself with the ASM
by reproducing the example in the report,
and progressively augmenting it as
desired. While the ASM's subroutines will
undergo extensive development in the
future, the framework of the module is
essentially at a final stage. Thus, it should
be relatively easy to incorporate higher
versions into existing host codes, once
they are formatted to interact with Ver-
sion 1.2. Several new and improved ver-
sions are anticipated during the coming
year.
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J. M. Hales is with Battelle Northwest Laboratory, Richland, WA 99352.
Jack L. Durham is the EPA Project Officer (see below).
The complete report, entitled "An Interim User's Manual for the Advanced
Scavenging Module: Version 1.2," Order No. PB85 173 9Q4/AS; Cost: $10.00,
subject to change) will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield. VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Atmospheric Sciences Research Laboratory
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
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