CRC Report No. A-34 - Coordinating Research Council

April 2005
Figure 2-3. Average composition (weight percent) and range for PAMS species in 22
morning samples from Los Angeles in October 1995. Shown on an absolute scale (top)
and log scale (bottom).
The random variability introduced into the ambient samples, shown in Table 2-8, is described as
“measurement noise” because it was developed to address this issue. However, because of the
way that the measurement noise estimates were developed from real-world data, it is likely that
the random variability includes some effects of emissions source strength and source profile
variability in addition to measurement noise. This is consistent with the project objectives
because the photochemical model predicts concentrations that represent 25 km 2 grid cells
whereas urban monitoring sites are influenced by neighborhood scale variability that is not
captured by the grid model.
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