As discussed in Chapter 7.C.1, HONO is formed by the reaction of N02 with water on surfaces. The reac-
Plastic storm windows Galvanized metal duct Vinyl floor tile Asphalt floor tile Polyethylene sheet Formica® counter top Used furnace heat exchanger Window glass Waxed asphalt tiles Walltex® covering Spider plants (with soil covered) Cotton terrycloth Wool (80%) polyester (20%) fabric Ceramic tile Furnace filters (used) Particle board Vinyl-coated wallpaper Oak paneling Dehumidlfier Furnace filters (new) Acrylic carpet Polyester carpet Ceiling tile
Vinyl wall covering (paperbacked) Nylon® carpet Acrylic fiber carpet Plywood
Painted (flat latex) wallboard Cotton / polyester bedspread Masonite® Brick (used) Wool carpet Cement block Wallboard
FIGURE 15.4 Rate constants for N02 removal on 3.3-m2 samples of different materials commonly found in homes (adapted from Spicer et al, 1989).
tion is usually represented as
although the detailed mechanism is not known; gaseous HN03 is not generated in equivalent amounts, which has been attributed to its remaining adsorbed on the surface. This overall reaction occurs on a variety of surfaces in the laboratory and hence might be expected to also occur on surfaces in other environments, such as homes. This, indeed, is the case.
Pitts et al. (1985) first used differential optical absorption spectrometry (DOAS) to establish unequivocally that N02 injected into a mobile home forms HONO. interestingly, the dependence of the rate of HONO generation on the NOz concentration was similar to that measured in laboratory systems, consistent with production in, or on, a thin film of water adsorbed on surfaces. A number of studies have confirmed that the behavior is similar to that in laboratory systems; i.e., the rate of production of HONO increases with N02 and with relative humidity. Indoor levels of HONO as high as 8 ppb as a 24-h average and 40 ppb as a 6-h g 400 a.
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