Chemical Analyses of Particle Filter Deposits* - Aerosols: Measurement, Dosimetry, and Health Effects - page 182

water or gases and has inherently low contamination levels, but chemicals have been found in some
batches by acceptance testing (Chow, 1995). Carbon cannot be measured on Telon-membrane il-
ters because of their high carbon content, although aerosol carbon has been inferred from hydrogen
measurements (Kusko et al., 1989). A variation on this ilter consists of a PTFE Telon-membrane
ilter mounted on a woven PTFE mat instead of a support ring (Pall Corporation, part number
P5PJ001). The membrane and mat sides look the same, and care must be taken to prevent mounting
it upside down on a ilter holder resulting in particles drawn through the mat rather than onto the
surface of the membrane.
Quartz-iber ilters (Pall Corporation, part number 7202; Whatman Inc., part number 1851-047)
consist of a tightly woven mat of quartz (SiO 2 ). These ilters can withstand high temperatures with-
out decomposing, making them suitable for different thermal analyses. Quartz-iber ilters adsorb
organic vapors passively before and after sampling, and actively during sampling (Chow et al.,
2010b; Sutter et al., 2010; Watson et al., 2009), so it is important to preire them for at least 3 h at
∼900°C and keep them sealed prior to and after sampling. The Whatman QM/A quartz-iber ilter
contains a 5% borosilicate glass binder that reduces its friability, but the binder also includes trace
elements and catalysts that may bias thermal carbon analyses (Lin and Friedlander, 1988). The
Palllex ® Tissuquartz™ 2500 QAT-UP ilter (Pall Corporation, part number 7202) is pure quartz
and undergoes a distilled water washing (thus the “UP,” or “ultra-pure,” designation).
Cellulose-iber ilters (Whatman, Inc., Clifton, NJ, part number 31 ET and 41) consist of a tightly
woven paper mat. These ilters are hygroscopic and require precise RH control in the ilter process-
ing environment to obtain accurate mass measurements (Demuynck, 1975). Cellulose-iber ilters
are most useful for impregnation with gas-absorbing compounds. The Whatman 31ET ilters are
thicker than the Whatman 41 ilters (0.5 versus 0.22 mm), so they absorb more of the impregnation
solution and have a higher collection capacity.
Etched polycarbonate-membrane ilters (Nuclepore™, Whatman, Inc., Clifton, NJ, part number
111107) are constructed from a thin polycarbonate sheet through which pores of uniform diameter
(e.g., 0.4 μm pore size) have been produced by radioactive particle penetration and chemical etching
(Spurny et al., 1969). These are the best ilter media for single particle analyses by electron micros-
copy because particles are easily distinguished from the lat ilter surface.
Glass-iber ilters should never be used for aerosol measurements. They consist of a mat of boro-
silicate glass ilaments with a high alkalinity that reacts with nitrogen oxide (NO x ), nitric acid
(HNO 3 ), and SO 2 (Coutant, 1977; Spicer and Schumacher, 1979). Blank levels for many elements are
high and variable (Witz et al., 1983).
When ilters are received from the vendor, one or two out of each 100 ilters should be ana-
lyzed for all species to verify that preestablished speciications have been met (Fehsenfeld et al.,
2004). Filters also are visually examined on a light table prior to labeling for discoloration, pinholes,
creases, separation of ring, loose material, or other defects.
7.3 SAMPLE PROCESSING
Figure 7.2 illustrates sample handling procedures and analysis methods for different observables.
Since ilter mass deposits are on the order of ∼1 mg and individual species concentrations are in the
nanogram to microgram range, potential contamination must be minimized. Filter handling in a
laboratory laminar low hood is always preferable to loading and unloading in the ield. Watson and
Chow (2011) and Lippmann (2001) describe different types of ilter holders in common use. Chain-
of-custody includes ilter preparation and acceptance testing, followed by pre-sampling gravimetric
analyses for mass and light transmission/absorption (b abs ) analyses as a surrogate for black carbon
(BC) (Chow et al., 2010c), if desired. Prior to sampling, ilter packs are assembled and transported
to the ield. After sampling, ilter packs are disassembled, followed by post-sampling gravimetric
and b abs analyses.