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25.
Quantitation, Detection and Measurement Precision of Organic Molecular
Markers in Urban Particulate Matter
Min
Li(1*), Stephen R. McDow(2), David Tollerud(3)
and Monica A. Mazurek(1)
(1)Department
of Civil & Environmental Engineering, Rutgers University,
Piscataway, NJ
(2)Environmental Characterization and Apportionment Branch, U.S.
EPA, Research Triangle Park, NC
(3)School of Public Health, Drexel University, Philadelphia, PA
*Corresponding author
Organic molecular markers have been quantified in
atmospheric particulate matter by gas chromatograph/mass spectrometer
(GC/MS) for nearly two decades (Mazurek et al., 1987; Rogge et
al., 1993; Schauer et al., 1996). However, little information
about the precision of analytical measurements has been provided
so far in the majority of these parts-per-billion determinations
of organic marker compounds in urban particular matter (PM). Such
information is critical to accurate source apportionment since
the uncertainty of analytical measurements is the primary quantifiable
uncertainty in source receptor models (Schauer et al., 1996).
The uncertainty of the analytical measurements has been estimated
only as ±20% for all the molecular markers due to lack
of accurate measurement of the analytical precision (Schauer et
al., 1996; Zheng et al., 2000). The problem with this estimation
is that different molecular markers have different analytical
uncertainties because of their various volatilities and chemical
structures within the analysis due to molecular properties such
as volatility, molecular weight and structure, and presence of
heteroatoms (e.g., O, N, S). If the molecular markers have significantly
different analytical uncertainties, the ±20% estimation
is not likely to generate accurate air pollution source apportionment
results using current receptor models. In this case, knowledge
of the analytical uncertainty for every molecular marker is critical
input to source receptor models. Therefore, an approach needs
to be developed to evaluate the measurement precision of molecular
markers in ambient particulate matter using GC/MS analysis.
This work focuses on organic molecular markers in airborne particulate
matter by Gas Chromatography/Ion Trap Mass Spectrometry (GC/IT
MS). The particulate samples used in the method development were
collected as PM10 in metropolitan Philadelphia area during 2000.
The method emphases a detailed compound identification procedure
by ion trap mass spectrometry, five-point mass calibration for
compound quantitation and estimates of measurement uncertainty
of ambient particulate samples with this method.
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