CRC Report No. A-34 - Coordinating Research Council

April 2005
to 2.4 over the A-34 source categories. ROG tends to be greater than PAMS for many emissions
categories because PAMS is includes only 55 species and therefore omits many species (e.g.,
oxygenated and heavier compounds) that are part of ROG. However, PAMS can be greater than
ROG because ethane is included in PAMS but excluded from ROG (and VOC) on the basis of
low reactivity.
The ROG/TOG and PAMS/ROG ratios in Table 2-11 show that source category contributions
may vary significantly (by more than a factor of 2) depending upon how total organic
compounds are measured. It follows that comparing different measures of total organic
compounds between receptor modeling and emissions inventories will introduce biases (either
positive or negative) in comparisons of source category contributions. If source category
contributions are compared on a relative basis (e.g., percent of total) then a bias for one category
affects all others. Corrections may be applied by assuming certain PAMS/ROG ratios for each
category, but such assumptions are external to the receptor modeling process and the
experiments performed here are unable to characterize the resulting biases. These findings are
summarized as follows:
Findings on Measures of Total Organic Compounds
• Comparing different measures of total organic compounds (e.g., PAMS, ROG) between
receptor modeling and emissions inventories will introduce biases (either positive or
negative) in comparisons of source category contributions.
• Receptor modeling studies should state the measure of organic compounds that is
apportioned by the receptor model and define any conversion factors used to adjust this to
a different basis (e.g., PAMS/ROG ratios for each source category).
• If adjustment factors are used (e.g., PAMS/ROG ratios) they must be consistent with the
source profiles used for the receptor modeling and ideally should be developed
specifically for the study along with source profiles; i.e., the adjustment factors and
source profiles should be developed from the same set of detailed VOC measurements.
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