Mathematical Modeling of Indoor Air Quality
Indoor settings are important for analyzing human exposure to pollutants, because people spend so much time indoors. Although the most accurate way to determine pollutant concentrations in indoor air is by measurement, mathematical models capable of predicting indoor concentrations have a variety of uses and can complement indoor measurements. Indoor air quality models, once validated, offer a practical methodology for understanding and predicting indoor concentrations for use in exposure analysis and for assessing health risks. This chapter derives the basic equations used to model indoor air quality in a well-mixed chamber, which is relevant to a room, a house, or a motor vehicle under certain conditions. There are three important cases: (a) a source emitting inside the indoor setting, (b) a pollutant inﬁltrating from outdoor ambient air into the indoor setting, and (c) a combination of the two cases by the principle of superposition. This chapter discusses a source emitting pollutants within a microenvironment, and Chapter 8 discusses a pollutant inﬁltrating from outdoors. Analytical solutions for the single-compartment model have a variety of practical applications, and these solutions always depend on the source emission rate as a function of time. The validity of the assumption of a well-mixed microenvironment is supported by experiments after the source ends its emissions. Practical formulas are useful for estimating the source strength from experimental data, and indoor modeling requires information on parameters such as the air change rate, deposition rate, and physical volume of the indoor setting. Indoor source emission rates are useful for generalizing the ﬁndings from one indoor setting to another, and indoor
models allow the exposure analyst to ask “what if” questions about changes in indoor air quality and human exposure.