CRC Report No. A-34 - Coordinating Research Council

April 2005
2.4 EXPERIMENTS FOR ROUNDS 1 AND 2
For Rounds 1 and 2, ENVIRON provided DRI with virtual PAMS samples for 8 receptors, four
days (August 4-7, 1997) and 8 different experiments for a total of 6144 simulated air samples.
The 8 experiments differed in modeling assumptions used to prepare the simulated air samples
(e.g., relative source contributions, atmospheric reactivity, sampling noise, source profiles). For
Round 1, DRI had no additional supporting information beyond the sample identification
number. For Round 2, ENVIRON provided DRI with additional information that a receptor
modeler would typically have available to support a real-world receptor model application. For
example, a virtual tunnel study was performed to provide DRI with information on the mobile
source emissions profiles.
The 8 experiments for Rounds 1 and 2 are described below and the relative emission levels for
the source categories in each experiment are shown in the Table 2-9. The emission levels by
source category were varied for each experiment as shown in Table 2-9 so that each experiment
would be different, in some cases substantially different. The base emissions for each day shown
in Table 2-10 were multiplied by the ROG percentages from Table 2-9. This conserves total
ROG emission levels, but not necessarily the total TOG and PAMS emission levels as illustrated
in Table 2-11 for experiment 1 on August 5, 1997.
1. Base Case: A simulation representing nominal 1997 weekday conditions. Random
measurement noise was added to the species concentrations at each receptor.
2. Higher Atmospheric Reactivity: Essentially a re-run of the base case with higher ambient
reactivity to produce more rapid chemical aging of VOC emissions. The 1997 base case has
a relatively low VOC-NOx ratio that results in suppression of ozone (and related
photochemical activity) over a wide area of the LA basin for much of the night and morning.
Photochemical reactivity was enhanced by substantially reducing the NOx emission
inventory (by 50% for surface emissions and 75% for point sources) to raise the VOC/NOx
ratio. In addition, a 300 m deep mixed layer was maintained at night to reduce NOx titration
of ozone and suppression of nocturnal chemistry. The source contributions will be varied
from the base case by a moderate amount to provide a different receptor model solution
without completely changing the nature of the problem. The source profiles were the same
as the base case but the measurement noise will be different (but with the same form and
magnitude). Random measurement noise was added to the species concentrations at each
receptor with the same magnitude as the base case but initialized using a different random
number. The objective of this experiment was to investigate the influence of high chemical
aging on receptor model performance.
3. Alternate Source Profiles: Re-run the base case using alternate source profiles. Mobile
source profiles were based on a Houston tunnel study and related fuel samples. The
replacement of profiles is summarized in Tables 2-12 and 2-13. In total, 19 base case
profiles were replaced by 7 alternate profiles affecting 53 source categories and about 50% of
the ROG emissions. The source profiles were the same as the base case. The source
contributions were varied from the base case by a moderate amount and the measurement
noise was initialized using a different random number. The objective of this experiment was
to investigate how receptor model performance is related to chemical speciation, especially
for mobile sources.
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