Nc Nc

" Adapted from Wolkoff (1998).

h A " + " sign means an increase of 20% or more in concentration. NC means less than 20% change.

' Texanol = isomers of 2,4,4-trimethyl-l,3-pentanediol monoisobutyrate.

Wolkoff, 1998; Haghighat and de Bellis, 1998). Table 15.7, for example, shows the effects of temperature and relative humidity on the emissions of particular compounds associated with carpet, PVC flooring, sealants, varnish, and wall paint (Wolkoff, 1998). Interestingly, exposure of these samples to N2 rather than air also increased the emissions in some cases. However, using increased temperatures to "bake-out" buildings and hence lower the concentrations of indoor VOCs does not appear to be particularly effective. For example, Bayer (1991) reports that the total VOC concentrations from particleboard are about the same after as before a 5-day bake-out at 88°C. Similarly, significant levels of HCHO have been observed in a mobile home even after 20 years of use in a hot ambient air environment (Pitts et al., 1989; see later).

The dependence of VOC emissions from building materials on relative humidity is more complex, with some emissions increasing with relative humidity, but others not. For example, Sollinger et al. (1994) report that the VOC emissions from carpets did not change with relative humidity over the range from 0 to 45% RH. On the other hand, the emissions of formic and acetic acids from latex paints have been reported to increase dramatically with relative humidity; for example, for one paint sample the emission rate for acetic acid almost tripled when the relative humidity was changed from 4-5% to 5-23% (Reiss et al., 1995b).

A number of different aldehydes have been measured indoors (e.g., see Crump and Gardiner, 1989; Lewis and Zweidinger, 1992; Zhang et al., 1994a; Daisey et al., 1994; and Reiss et al., 1995a), some of which are directly emitted and some of which are formed by chemical reactions indoors of VOCs such as styrene (see Section F). Of these, there is an enormous amount of evidence for direct emissions of HCHO from building materials. Interest in formaldehyde emissions and levels in homes and other buildings stems from its well-known health effects, which include possible human carcinogenicity and eye, skin, and respiratory tract irritation (Feinman, 1988). Formaldehyde is emitted from urea-formaldehyde foam insulation as well as from resins used in reconstituted wood products such as particleboard and plywood (Meyer and Reinhardt, 1986); urea-formaldehyde resins comprise about 6-8% of the weight of particleboard and 8-10% of medium-density fiberboard (Meyer and Hermanns, 1986). Other sources include permanent press fabrics (such as draperies and clothing), floor finishing materials, furniture, wallpaper, latex paint, varnishes, some cosmetics such as fingernail hardener and nail polish, and paper products (Kelly, 1996; Howard et al., 1998).

Many measurements of HCHO have been made in indoor air environments. In conventional homes, average concentrations are typically about 10-50 ppb (e.g., Stock, 1987; Zhang et al., 1994a; Reiss et al., 1995a). Sexton et al. (1989) measured concentrations of HCHO in 470 mobile homes in California and found geometric mean concentrations of 60-90 ppb, although maximum values of over 300 ppb were recorded in some cases. In a similar study in Wisconsin, levels up to 2.8 ppm were measured (Hanrahan et al., 1985). Higher levels are typically found in mobile homes because of the reconstituted wood products (e.g., particleboard and plywood) used in their construction. Interestingly, HCHO does not appear to be a significant product of natural gas combustion, as levels in dwellings with and without gas stoves turned on are not significantly different (e.g., Pitts et al., 1989; Zhang et al., 1994a).

Temperature is again an important determinant of HCHO levels. Figure 15.11, for example, shows the concentrations of HCHO as well as of formic acid and methanol measured using FTIR in a research mobile home as function of time as the temperature increased. At 70°F, the average HCHO concentration was 27 ppb but increased to 105 ppb at 100°F (Pitts et al., 1989).

Was this article helpful?

0 0

Post a comment