Environmental Engineering Reference
In-Depth Information
(Watson and Chow, 2011). PM ilter analyses are used to identify and quantify source contribu-
tions (Watson and Chow, 2005, 2007; Watson et al., 2002, 2008), estimate visibility impairment
(Watson, 2002), evaluate adverse effects on human health (Mauderly and Chow, 2008; Pope and
Dockery, 2006), and determine causes of material damage (Hu et al., 2009a,b). PM concentrations
for mass, elements, water-soluble ions, and organic and elemental carbon (OC and EC, respectively)
are measured on ilters acquired at ∼400 sites in urban and nonurban U.S. networks (Flanagan et al.,
2006; Hansen et al., 2006; Watson, 2002). More useful information could be obtained from these
and other ilter samples at a small incremental cost. Source samples acquired by dilution sampling
systems (ASTM, 2008; Deuerling et al., 2010; England et al., 2007a,b; Hildemann et al., 1989) are
also amenable to the same measurements described here and are becoming more in demand for
multi-pollutant air quality management strategies (Chow and Watson, 2011; Chow et al., 2010a;
Hidy and Pennell, 2010).
This chapter summarizes and updates relevant information from previously published reviews
(Chow, 1995; Chow et al., 2002a, 2007c, 2008; Fehsenfeld et al., 2004; Landsberger and Creatchman,
1999; Lodge, 1989; Solomon et al., 2001; Vincent, 1994; Watson and Chow, 1994; Wilson et al.,
2002) and draws from recent experience of the authors. Chow et al. (2008) provide more detailed
lists of chemical species, detection limits, and comparison studies that are not repeated here.
7.2 FILTER SAMPLING
Sampling systems, ilter media, and analysis methods must be considered as a unit and comple-
mented with comprehensive sample handling and analysis protocols. A multi-channel sampling
coniguration is shown in Figure 7.1. Sampling system and inlet details are speciied by Watson and
Chow (2011). PM
2.5
and PM
10
(particle fractions less than 2.5 and 10 μm aerodynamic diameter,
respectively) inlets are commonly used for 16.7 L/min low rates (1 m
3
/h), which provide ample
material for analyses when 24 h mass concentrations exceed ∼5 μg/m
3
. Lower low rates (e.g.,
5-7 L/min) may be needed for higher PM concentrations (>50 μg/m
3
) to minimize ilter clogging
(Davies, 1970). An even lower low rate (e.g., 2-5 L/min) is used for microscopic analysis as the
particles should not overlap for accurate automated detection.
The Figure 7.1 system consists of four parallel channels using low rates of 5-16.7 L/min to
acquire PM deposits on front ilters along with gaseous precursors for ammonia (NH
3
) (Appel
et al., 1988; Cao et al., 2009; Chow et al., 1993a; Ferm, 1979) and sulfur dioxide (SO
2
) (Axelrod and
Hansen, 1975; Huygen, 1963) on impregnated backup ilters. Impregnated ilters also can be used to
collect nitrogen dioxide (NO
2
) (Gotoh, 1980; Hedley et al., 1994), hydrogen sulide (H
2
S) (de Santis
et al., 2006; Duckworth, 1971; Nash and Leith, 2010), ozone (O
3
) (Grosjean and Hisham, 1992;
Miwa et al., 2009; Monn and Hangartner, 1990), and some volatile organic compounds (VOCs)
(Kume et al., 2008; Mason et al., 2011; Miller et al., 2010; Shields and Weschler, 1987; Stock et al.,
2008). Figure 7.1 includes a quartz-iber backup ilter to evaluate organic vapors adsorbed onto the
front quartz-iber ilter (Cheng et al., 2009, 2010; Chow et al., 2010b; Vecchi et al., 2009; Watson
et al., 2009) that may positively bias the OC concentration. A backup nylon-membrane or sodium
chloride (NaCl)-impregnated cellulose-iber ilter can be used to determine ammonium nitrate
evaporation during sampling (Chow et al., 2002b, 2005b). Denuders (Kitto and Colbeck, 1999) may
be placed downstream of the inlet to remove gases from the airstream.
No single ilter medium is appropriate for all analyses, so it is necessary to sample on mul-
tiple substrates for chemical speciation. Ringed Telon
®
-membrane ilters (Pall Corporation, Ann
Arbor, MI, part number R2PJ047; Whatman Inc., Clifton, NJ, part number 7592-104) consist of a
thin, porous polytetraluoroethylene (PTFE) Telon-membrane sheet stretched across a polymeth-
ylpentane ring. The thin membrane collapses without the ring, and the ilter cannot be accurately
sectioned into smaller pieces. The white membrane is nearly transparent (thickness of 30-46 μm)
and has been used to estimate light transmission/absorption (b
abs
) (Campbell et al., 1995; Chow
et al., 2009, 2010c; Moosmüller et al., 2009). PTFE Telon membrane absorbs negligible amounts of
Search WWH ::
Custom Search