Environmental Engineering Reference
In-Depth Information
deposition of other trace compounds within the photochemical environment pro-
vided by the core model. Upon startup, CAMx reads, checks and compiles the
toxics mechanism and then configures the reactive tracer chemistry solver; hence
no solver development or coding is necessary on the user's part. During the model
simulation, the toxics chemistry receives oxidant information from the core model
and uses this to calculate the decay and/or production of toxic species. The current
implementation of RTCMC is for gas-phase reactions, i.e., gas-phase tracers reacting
with each other and/or gas-phase host model species. A suitable application for
RTCMC is simulating air toxic species that photolyze and/or decay according to
ambient concentrations of ozone and radicals such as OH, NO
3
, etc.
The format of the RTCMC input mechanism file is essentially the same as the
“IMC” input file format of the SCICHEM Lagrangian puff model (Santos and
Sykes, 2000). An example IMC format file is shown in
Fig. 1.
#Control
rate_species_units = 'ppm'
rate_time_units = 'min'
solver = 'dlsode'
Jacobian = 'numeric'
#Species, Type, Ambient, Tolerance, deposition vel, wet scav
O3 A 1.0 1.0E-12 0.0 0.0
OH A 1.0 1.0E-12 0.0 0.0
ATRAC F 1.0 1.0E-12 0.010 0.0
BTRAC F 1.0 1.0E-12 0.001 0.0
CTRAC F 1.0 1.0E-12 0.020 0.0
DTRAC F 1.0 1.0E-12 0.001 0.0
ETRAC F 1.0 1.0E-12 0.030 0.0
FTRAC F 1.0 1.0E-12 0.001 0.0
#Table
0 0. 15. 30. 45. 60. 75. 80. 86. 87. 88.
1 4.2E-04 4.1E-04 3.8E-04 3.3E-04 2.6E-04 9.5E-05 3.0E-05 4.9E-06 8.3E-08 1.0E-09
#Equations
1 [ATRAC] -> (2.0)[BTRAC] ; 0 0.000E-00
2 (1.5)[CTRAC] + [OH] -> (0.5)[DTRAC] ; 1 4.2000E+04
3 [ETRAC] + [O3] -> [FTRAC] ; 1 1.8000E-02
Fig. 1.
Example RTCMC chemistry input file
There are four sections in an IMC file that are identified by a keyword at the
start of each section, as follows. The “#Control” section defines which chemistry
solver to use (three are available), species and time units for chemical rates, solver
error tolerances, and whether to determine the Jacobian matrix of first-order
derivatives algebraically or numerically. The “#Species” section lists the chemical
species and associated data, including type (from the core photochemical model
[A] or independently solved [F]), species-specific error tolerances, and deposition
velocity (ambient and wet scavenging parameters are not used). The “#Table”
section provides photolysis rates as a function of solar zenith for any photolytic
reactions in the RTCMC mechanism; this is the only section that is optional if
there are no photolytic reactions defined. The “#Equations” section lists the
chemical reactions and rate constants for the RTCMC reaction mechanism. All
chemical species referred to in the equation section must appear in the species
