CRC Report No. A-34 - Coordinating Research Council

April 2005
4.4 ACTUAL VERSUS EMISSIONS CONTRIBUTIONS
Source apportionment methods are often used to gain insight into the real-world sources of
emissions in order to evaluate emission inventories. Therefore, the relationships between actual
contributions and emissions contributions (defined above as emissions from the 9 5-km grid cells
centered on the receptor) are of interest. The actual contributions present in an air sample could
differ from the local emissions contributions for two main reasons:
• The emissions inventory is spatially inhomogeneous. Air samples integrate source
contributions over some upwind area (footprint) that depends upon wind direction/speed
and atmospheric dispersion properties.
• Emissions from different source categories have different photochemical removal rates
according to their VOC speciation (e.g., see Figures 4-8 and 4-9, above).
The actual emissions contributions for each receptor in experiments 1 on August 5, 1997 are
shown in Figure 4-10 and Table 4-2. The emissions are summarized by the A-34 categories,
which are listed in Table 4-2. Figure 4-10 shows qualitatively that the distributions of emissions
by source category varied substantially among the receptor locations, with the exception of
Hawthorn and LAX. The same information is provided quantitatively in Table 4-2.
A-34 category contributions to emissions for 9 cell areas surrounding each receptor
100%
Percent of PAMS
90%
80%
70%
60%
50%
40%
30%
20%
10%
a34_22
a34_21
a34_20
a34_19
a34_18
a34_17
a34_16
a34_15
a34_14
a34_13
a34_12
a34_11
a34_10
a34_9
a34_8
a34_7
a34_6
a34_5
a34_4
a34_3
a34_2
a34_1
0%
Anaheim Crestline Diamond Bar Hawthorn Lake Perris LAX Long Beach Van Nuys
Receptor
Figure 4-10. Source category contributions to the sum of PAMS emissions for 9 cell areas
surrounding each receptor in experiment 1 on August 5, 1997.
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