CRC Report No. A-34 - Coordinating Research Council

April 2005
CRC project A-42-2 (ENVIRON, 2002a). In RTRAC, an arbitrary number of additional tracer
species can be added to a CAMx simulation where they are emitted, transported and deposited
using the core model algorithms. The core model chemistry drives the chemical decay of
RTRAC tracers by reactions with OH radical, NO 3 radical, ozone and photolysis. Compared to
the alternate approach of adding “live species” to the core model the RTRAC approach has
several advantages for this study:
• Reactive tracers are much more computationally efficient than live species.
• The oxidant fields are decoupled from uncertainties in the chemistry of the tracers.
• The source strengths of the tracers may be varied without changing the oxidant fields
allowing experiments to be more controlled.
RTRAC was used to model atmospheric concentrations of 55 PAMS species from 22 source
categories giving a total of 1210 unique tracers in each simulation. The total concentration of a
PAMS species at a receptor location is the sum of tracers for that species over the 22 source
categories modeled, plus a background. Sampling noise was added to this total concentration as
described below. The 55 PAMS species are listed in Table 2-1 along with reaction rate constants
at 298 K and background concentrations. Each PAMS species was assigned a unique “A-34”
number for this study. Table 2-1 also provides the short names that DRI uses for PAMS species
in receptor modeling studies. Reaction rate constants at 298 K and 1 atmosphere are given in
units of cm 3 molecule -1 s -1 and are from Calvert et al. (2000, 2002), JPL (1997), Atkinson (1989)
and Carter (2000). Temperature dependencies of rate constants also were accounted for in the
modeling. The background concentrations shown in Table 2-1 are averages of data from San
Nicolas Island (in the Pacific Ocean to the west of Los Angeles) collected during SCOS and
provided by DRI.
Table 2-1. PAMS species included in the modeling analysis with reaction rate constants at 298
K and background concentrations.
A-34
Num
Short
Name
Full
Name
M.Wt.
(g) k(OH) # k(O3) # k(NO3) # Background
(ppbC) $
1 ETHENE ethene 28.05 8.52E-12 1.59E-18 2.05E-16 0.503
2 ACETYL acetylene 26.04 8.97E-13 0.475
3 ETHANE ethane 30.07 2.68E-13 1.393
4 PROPE propene 42.08 2.63E-11 1.01E-17 9.49E-15 0.292
5 N_PROP n-propane 44.10 1.15E-12 0.590
6 I_BUTA isobutane 58.12 2.34E-12 0.383
7 LBUT1E 1-butene 56.11 3.14E-11 9.65E-18 1.35E-14 0.048
8 N_BUTA n-butane 58.12 2.54E-12 0.608
9 T2BUTE t-2-Butene 56.11 6.40E-11 1.90E-16 3.90E-13 0.000
10 C2BUTE c-2-butene 56.11 5.64E-11 1.25E-16 3.52E-13 0.000
11 IPENTA isopentane 72.15 3.90E-12 0.613
12 PENTE1 1-pentene 70.13 5.14E-11 1.06E-17 1.38E-14 0.057
13 N_PENT n-pentane 72.15 3.94E-12 0.367
14 I_PREN isoprene 68.11 1.01E-10 1.28E-17 6.78E-13 0.000
15 T2PENE t-2-pentene 70.13 6.70E-11 2.96E-16 3.70E-13 0.000
16 C2PENE c-2-pentene 70.13 6.50E-11 2.09E-16 3.70E-13 0.000
17 BU22DM 2,2-dimethylbutane 86.17 2.32E-12 0.047
18 CPENTA cyclopentane 70.13 5.16E-12 0.000
19 BU23DM 2,3-dimethylbutane 86.17 6.20E-12 0.088
20 PENA2M 2-methylpentane 86.17 5.60E-12 0.382
21 PENA3M 3-methylpentane 86.17 5.70E-12 0.152
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