Sink terms

Research in the EPA test house; (2, 9, 10); and in the small chamber laboratory, (10) has shown that sinks (i.e., surfaces that remove pollutants from indoor air) play a major role in determining indoor pollutant concentrations. These sinks may be reversible or irreversible. A reversible sink re-emits the material collected in it, and an irreversible sink does not. Sink behavior depends on the pollutant, on the nature of the sink, and on environmental factors such as temperature, air velocity, and humidity. A sink may appear to be irreversible when the pollutant concentration is high and then become reversible when the pollutant concentration is low. Considerable research is necessary to define the behavior of sinks. Tichenor et al. (10) and Axley (11) have published sink models.

The sink model used in RISK is based on research of Tichenor et al.(10):

Rs = kaCAsink - kdMs nAsink(3)

Where

Rs = the rate to the sink (mass per unit time)

ka = the sink rate constant (length per time)

C = the in-room pollutant concentration (mass per length cubed)

Asink = the area of the sink (length squared)

Kd = the re-emission or desorption rate constant (1/time if n =1)

Ms = the mass collected in the sink per unit area (mass per length squared

n =an empirical constant. The recommended value of n, based on EPA research, is 1 (3).

Experimental data in the EPA test house and small chambers show that, for many gaseous organic pollutants of interest in indoor air, ka ranges from about 0.1 to 0.5 m/h, and the sink re-emission rate, kd, is about 0.008/h for carpet and 0.1/h for most other materials

The impact of sinks on individual exposure depends on the activity patterns. Sinks slightly reduce the peak exposure of individuals spending 24 h/day in a building and have no impact on their cumulative exposure. Sinks can have major impacts on the exposure of individuals with other activity patterns.

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