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

-------
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.

-------
     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
                                         U.S. GOVERNMENT PRINTING OFFICE' 1985-559-016/27030
                                                                                                 O.S.aPF'CiALL'AV
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
MAY 15-85   j ,";;.Aiepd
          1 jSf. SiOCi
& FEES W
     """ •
                                                                                                / B VFTfwRS PERMirNo  GT-3&
                                                                                                  i_ -i u r o ^ i I             ' _
Official Business
Penalty for Private Use $300
                                  0000329    PS

-------