CRC Report No. A-34 - Coordinating Research Council
CRC Report No. A-34 - Coordinating Research Council
CRC Report No. A-34 - Coordinating Research Council
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April 2005<br />
(c)<br />
Round 4: Experiments 1-8<br />
CMB vs. Actual Contribution, by Experiment<br />
90<br />
80<br />
70<br />
6<br />
CMB Contribution (%)<br />
60<br />
50<br />
40<br />
30<br />
3<br />
7<br />
812<br />
4 5<br />
3<br />
1<br />
5 74<br />
8<br />
2<br />
Gasoline<br />
Diesel<br />
Solvent<br />
Biogenic<br />
Backgd<br />
CNG and Aged<br />
LPG<br />
1:1<br />
20<br />
6<br />
3<br />
10<br />
5 1 82<br />
4<br />
7<br />
4<br />
3 6 8<br />
7 2 51<br />
6<br />
0 75846213 675281<strong>34</strong><br />
0 10 20 30 40 50 60 70 80 90<br />
Actual Contribution (%)<br />
Figure 4-2. Comparison of CMB contributions to actual contributions for experiments 1-8<br />
averaged over all receptors and hours in (a) Round 1 (b) Round 2 and (c) Round 4.<br />
Findings From Experiments 2-8<br />
• Overall CMB performance was relatively insensitive to higher atmospheric reactivity<br />
(experiment 2), weekend source mix (experiment 5), randomly varying source profiles<br />
(experiment 7) and higher random noise in the ambient data (experiment 8).<br />
• The results from experiments 7 and 8 showing that random changes did not impact CMB<br />
performance on average are expected because random changes tend to cancel when<br />
averaged by the atmosphere (experiment 7) or multiple samples (experiment 8).<br />
• CMB was robust against higher reactivity (experiment 2) because of receptor modeling<br />
protocols designed to avoid relying upon highly reactive species when ambient samples<br />
appear to be aged. However, the experiment 1 results for downwind receptors, discussed<br />
above, show that CMB performance can be degraded when air samples are highly aged at<br />
all times.<br />
• Introducing a weekend for 2 out of 4 days (experiment 5) did not degrade CMB<br />
performance because CMB was able to quantify emissions contributions on weekend<br />
days about as well as on weekdays.<br />
• When industrial emission levels were set to high levels (experiment 6) CMB tended to<br />
over-estimate the gasoline and solvent contributions by a factor of two, or more.<br />
Providing typically available source profile data in Round 2 did little to reduce these<br />
biases. Providing complete source profile data in Round 4 eliminated the bias for<br />
solvents and reduced the bias for gasoline to about 50%.<br />
H:\crca<strong>34</strong>-receptor\report\Final\sec4.doc 4-9
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