Which one of the following is NOT an assumption of the indoor air quality model?

In the context of indoor air quality models, constant volume refers to the consideration that the volume of air in the space does not change over time, which simplifies the modeling process. Uniform concentration assumes that the concentration of pollutants is evenly distributed throughout the space, allowing for straightforward calculations regarding exposure levels. The decaying pollutants assumption considers that certain pollutants will decrease in concentration over time due to natural decay processes, which is a critical factor in understanding the dynamics of indoor air quality.

The assumption of variable emission rates deviates from standard practice in many indoor air quality models, which typically assume a constant emission rate for pollutants. This simplification helps in creating more manageable equations and analyses for predicting air quality, as fluctuating emission rates complicate the modeling processes and would require more dynamic approaches to accurately capture the changes in indoor air composition. Thus, while real-life emission rates may indeed vary due to different sources and activities, the assumption of variable emission rates is not a foundational premise in many indoor air quality models, making it the correct choice for this question.