treasure valley road dust study: final report - ResearchGate

?? Sieving each sample to obtain a suspendable fraction (< 38 µm geometric diameter),
injecting this fraction into an enclosed chamber, and sampling onto Teflon-membrane
and quartz-fiber filters through PM 10 and PM 2.5 impactor inlets (Chow et al., 1994a).
In the laboratory, the soil samples were air-dried in a low-relative-humidity (approximately
20% to 30%) environment and sieved through a Tyler 400-mesh screen (< 38 ?m geometric
diameter) prior to resuspension in the laboratory chamber following the procedures described by
Chow et al. (1994a).
Filter samples were drawn through PM 10 and PM 2.5 inlets. Most of the mass of geological
material is in the coarse particle portion of PM 10 (Houck et al., 1989a), and similar compositions
were found for the PM 2.5 and PM 10 geological profiles (Chow and Watson, 1994b).
Two additional samples were collected during the winter sampling period on board the
TRAKER vehicle. Particles suspended from the road surface behind a moving tire were sampled
through a tube into a plenum. A portion of the sample stream was drawn through a filter pack
preceded by impactors with aerodynamic size cuts of either 10 ?m or 2.5 ?m. These filters were
analyzed directly for mass and chemical speciation.
All source profile samples were weighed and chemically characterized at the Desert
Research Institutes Environmental Analysis Facility in Reno, Nevada. Samples were analyzed
using Ion Chromatography (IC) for major ions, Automated Colorimetry (AC) for ammonium, X-
Ray Fluorescence (XRF) for elements, and Thermal Optical Reflectance (TOR) for organic and
elemental carbon. Table 7-1 lists all the chemical species analyzed and their corresponding
mnemonics.
Coarse particle Al, Si, P, Cl, K, and Ca values determined by XRF were originally
adjusted for large particle self-absorption using the theoretical formulation developed by Dzubay
(1975). This adjustment is a function of particle size distribution and composition. Since the
actual particle size distribution and composition is unknown, the uncertainty of these adjustments
is up to ± 25%, and is reflected in the reported uncertainty. Particle size effects for Na and Mg
are so large and variable that we cannot make accurate corrections for these two elements. Their
raw, uncorrected concentrations are included in the data files, but they should not be considered
quantitative for fine or coarse samples.
A standard quality assurance test for speciated aerosol samples is to compare the
reconstructed mass to the measured mass. Reconstructed mass should be less than or equal to the
measured gravimetric mass within the limits of analytical uncertainties. Typical ratios of
reconstructed mass to measured mass for PM10 range from 75% to 95%. Reconstructed mass is
calculated from major species mass concentrations using the following equations to account for
the unmeasured components of the aerosol (i.e., oxygen associated with mineral oxides and
hydrogen associated with organic carbon compounds):
[Soil] = 2.2*[Al] + 2.49*[Si] + 1.63*[Ca] + 2.42*[Fe] + 1.94*[Ti]
[Organic Carbonacious Material (OCM)] = 1.4*[OC]
7-2