Weekend/Weekday Ozone Observations in the South Coast Air Basin

unlikely that one or two profiles adequately represent the emissions from all surface coatings.
The most recent data are those of Censullo et al., (1996). Eleven categories of coatings were
analyzed in this study. Detailed species profiles were obtained for 106 samples of water-based
and solvent-based coating samples. Surface coating profiles for solvent-based industrial
maintenance coatings, solvent-based medium gloss/high gloss, solvent-based primers and
sealers, quick dry primers and enamels, and thinning solvent were applied in the apportionments.
These are largely depleted in the species common to fuel use and production, with larger
abundances of styrene, n-decane, and especially “other” compounds. The “other” VOCs are
quantified and differ substantially among the different coatings tested. Most of these other
compounds are oxygenated compounds that are not measured in PAMS.
Consumer Products. This profile is a composite of various consumer products compiled
by the U.S. Environmental Protection Agency. This profile is also contained in the California Air
Resources Board’s list of profiles in the modeling emission data system.
Isoprene was used as a single-component biogenic profile. Biogenic NMHC emissions
are highly reactive in the atmosphere, and biogenic source contributions derived from CMB
modeling will supply only a lower limit to the actual contributions from biogenic emissions.
Regional Background is a composite of several ambient samples collected at sites located
off the coast of southern California from midnight to noon. It represents air masses transported
into the basin that are low in fresh emissions.
4.4.2 CMB Analysis of PAMS VOC Data for 1999-2000
CMB Version 8 was applied to the ambient site VOC data using the default set of source
composition profiles described in the previous section. These sources account for greater than
90 percent of the measured ambient NMHC in most cases. Source contribution estimates (SCEs)
were calculated for all valid samples collected at Azusa, Pico Rivera, and Upland by the
SCAQMD and at Los Angeles N. Main by CARB. The results were grouped by site, day-of-theweek,
and sample period and the average and standard deviation of the resulting apportionments
calculated. The statistics and diagnostic information and SCEs for the carryover, ozone
inhibition, ozone accumulation, and peak ozone periods are given in Tables 4.4-2 and 4.4-3 in
µg/m 3 of NMHC and percentage of NMHC, respectively. The source contributions are presented
graphically in Figure 4.4-1. Results for Los Angeles are only included in the tables due to the
different sampling schedule at that site (6:00 a.m. and 1:00 p.m.). Results from both years were
combined in the averages except for the Pico Rivera auto-GC/MS data, where only 1999 data
were used due to unusually high unidentified hydrocarbon concentrations in 2000 at that site. In
the CMB calculation, liquid gasoline represents the additional unburned gasoline (due to
misfiring and other engine malfunctions) that is not included in the exhaust profile, plus
evaporative emissions from gasoline spillage, hot soaks, and some portion of resting losses
(leaks, permeation). Previous studies showed that the source attribution between tailpipe and
liquid gasoline from receptor modeling can vary greatly depending on the particular profile
chosen for tailpipe emissions (Harley et al., 1992, Fujita et al., 1994, Pierson et al., 1999).
Gasoline exhaust is the predominant source, ranging from 40-60% for all sites during the
four periods studied. Diesel exhaust was not consistently identified, and was rarely apportioned
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