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U.S. National Ambient Air 1-h CO Standard and OSHA Occupation 8-h CO Standard

U.S. National Ambient Air 8-h CO Standard

FIGURE 15.7 Measured concentrations of CO in eight homes using unvented kerosene heaters: dark shading, hourly average concentrations with heater off; no shading, hourly average concentrations with heater on; light shading, peak 1-h concentration (adapted from Mumford et al., 1991).

45 ppb. When the exhaust hood (which was externally vented) above the range was turned on, the N02 and HONO decreased substantially. Similar production of HONO from kerosene and propane space heaters has been observed (e.g., see Pitts et al., f989; Brauer et al., f990; Febo and Perrino, 1991; and Vecera and Das-gupta, 1994). While the mechanism generating such substantial concentrations is not known, it may involve the recombination of OH with NO as the combustion gases cool.

In a house used for investigating indoor air pollution that had natural gas fueled applicances (a convective heater, a radiant heater, and a range with four burners), both the surface reaction of NOz and the direct combustion emissions contributed significantly to the measured indoor HONO. When an appliance was operational, the contribution of direct emissions was the more important source (Spicer et al., 1993).

In short, the "dark reaction" of N02 with water on surfaces is ubiquitous and occurs not only in laboratory systems but also indoors. The combination of this heterogeneous reaction with combustion sources of HONO can produce significant concentrations of HONO indoors. As a result, there is a concern regarding the health impacts of nitrous acid, not only because it is an inhalable nitrite but also because it is likely the airborne acid present in the highest concentrations indoors.

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