Table of Contents - The Atmospheric Studies Group at TRC

Section 9: CALPUFF
9.7 Boundary Concentration Module File (BCON.DAT)
The impact of significant regional pollution transport on concentrations and deposition fluxes computed
within the modeling domain can be included in a CALPUFF analysis either by adding a spatially uniform
(and either constant in time or varying by hour) field at the post-processing step with CALPOST, or by
selecting the boundary concentration (BCON) module within CALPUFF. The latter choice is preferable
if there are known spatial gradients in regional concentrations outside the modeling domain, or if
chemical transformation and removal processes associated with the regional pollution must be explicitly
modeled.
Regional air-mass characteristics are defined and assigned to segments along each boundary of the
computational domain when the boundary concentration module is used. A segment is equivalent to the
length of one side of a grid cell. The number of air-mass types can be equal to the number of cells along
the perimeter of the domain if sufficient information exists on this scale, or the number can be far fewer in
typical applications where an entire side of the domain is characterized by a single air-mass. Air-mass
characteristics include the concentration of each species advected into the domain and the thickness of the
layer that contains these species. These concentrations are used to initialize puffs that are well-mixed in
the vertical and the horizontal. The vertical depth of a puff is the thickness of the layer assigned to the
air-mass, and the radius of the puff is related to the length of the segment and the component of the
transport wind that is perpendicular to the segment (the mass flux into the domain and the initial
concentration are conserved). The concentration of each species for each air-mass type may be scaled by
factors that vary in one of the following ways: by hour of the day (24 factors); by month (12 factors); by
hour and season (96 factors); by wind speed and stability class (36 factors); or by temperature (12
factors). These are the same factors provided for sources specified in the CALPUFF control file. If more
detailed variation is needed for one or more air-mass types, air-mass characteristics for these can be
provided hourly. When this method is used, the layer thickness may change as well as the concentrations.
Otherwise, the layer thickness is constant for each air-mass type.
The configuration of the boundary properties is provided to CALPUFF in a "BCON.DAT" file. Two
formats are available for this file. The first is a formatted file prepared specifically for use with the
BCON option (MBCON = 1). It is constructed using the CALPUFF control file conventions. A sample
file is shown in Table 9-32, and a description of the input parameters is provided in Table 9-33. The
second (MBCON = 2) is a standard CALPUFF unformatted “CONC.DAT” output concentration file.
Receptors in this file must lie along the boundary of the modeling region, providing near-surface
concentrations for the air mass transported across the boundary into the modeling domain. This format
may be chosen if CALPUFF results from a larger domain are available.
Input Group 1 in the BCON.DAT file identifies the grid information for the computational domain, the
units for the concentrations that are provided, the number of air-mass types, and the type of temporal
variation used in describing air-mass properties. Four air-mass types are used in this example. Three of
these use the temporal variation factors provided in Input Group 3 and one uses an explicit sequence of
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