Methods for Estimating Exposure


Exposure to air pollution is commonly measured by placing a monitor in the breathing zone of a subject. If the subject's activity patterns are recorded simultaneously, then it is possible to understand how a person's exposure profile is determined by places they visit, or by their activities or activities of those around them.

For example, if a person spends time around a smoker at home, or if they work in a factory with chemicals present, the monitor will register the elevated levels that coincide with the person being at home or at work.

Unfortunately, it is typically too burdensome or expensive to use a monitor on each subject. It may only be possible to monitor in fixed locations. Or what if monitoring cannot be accomplished at all?

Three-Zone Mass Balance Model


This tutorial is the third in a series that explores the mass balance model. Here, you can explore a three-zone model. Before using this tutorial, you should read the two previous tutorials containing an introduction to the mass balance model and an exploration of a two-zone model.

Exploring a Two-Zone Mass Balance Model


After you have read about and understood the single-box model as presented in the introduction to the mass balance model tutorial, you are ready to explore more complex arrangements of zones. In the real world, homes typically consist of more than just a single room.

This exercise allows you to interactively explore a two-zone box model for air pollutant emissions. The pollutant mass is emitted into the first zone (Room #1), but it can travel to the second zone at the flow rate that you specify. Pollutant mass is removed from both zones by ventilation or by deposition onto surfaces. The emissions are assumed to be instantly mixed throughout the zones.

Introduction to the Mass Balance Model


On this website, we use a simple mass balance model to simulate indoor levels of SHS. The essence of the mass balance model is that the rate of change in pollutant mass in a given space at any given instant is equal to the amount coming in, minus the amount leaving. In an equation:


For this tutorial you can use a Flash animation to explore a single-zone box model, one of the most simple applications of the fundamental mass balance equation. Although the model can be applied to either air pollution or water pollution, we are interested in emissions of pollution from cigarettes and other tobacco sources.

Box Model

The pollutant mass is assumed to be emitted into a confined space, in which the emissions are instantly mixed throughout the space. The air containing the mixture of pollutants can be exchanged with the outside. The pollution in the air can also be removed from the space by active filtration and by deposition onto surfaces present in the space.

How Do I Measure SHS? Answer: Using Real-Time Monitoring Instruments


When we at SimSmoke.Org developed the computer simulations used here to estimate secondhand smoke exposure levels, we validated them using real-time air pollution monitoring instruments. It was important for us to verify the results of exposure estimates using numerous measurements in bars, restaurants, homes, and cars.

The instruments for measuring airborne particles typically operate by drawing air into a tube and analyzing the amount of light that scatters off the particles in the air stream when struck by a laser beam or other light source. The amount of light scatter can be related to the mass of particulates that are present in the air.

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