Re: Is there an inexpensive way to measure particulate air pollution?

Tania,

I talked over this one with my boss, and we agree it's a tricky one, experimentally. However, first we should clear up some things about the science behind this experiment that we hope will give you some ideas on how to proceed experimentally.

Smoke is made up of several different components, which all interact differently with plants. The component of smoke you can see with the naked eye consists of water vapor and small particles known as aerosols. The chemical makeup of these aerosols determines the color of smoke, ranging from the very black smoke produced by diesel engines to the nearly white smoke produced after lighting of damp wood. Besides aerosols, any combustion process will also produce a gaseous component, of which the main ingredients will nearly always be carbon dioxide and carbon monoxide.

In the experiment you describe, the carbon dioxide will be actively reduced by the activity of the plants, but the removal of carbon monoxide and aerosols will be controlled by deposition, or settling. The plants will have some influence on this as well, because of the higher surface area provided by the leaves, but the active process of photosynthesis should have minimal effect on removing smoke from the atmosphere, at least in ways that can be easily observed. You might also consider the effect the smoke will have on plants, in terms of comparing their growth and performance to plants in cleaner air: on the one hand, the enhanced CO2 from the smoke should promote growth, but on the other hand, the smoke haze will reduce the light available to the plant and retard growth (I would expect this effect to be greater in an aquarium-sized experiment with a visible smoke layer).

As for measuring smoke, the two simplest mechanisms rely on the two simplest properties of smoke: first, it has mass, and second, it blocks light.

The first mechanism uses filters, like coffee filters, which are carefully weighed and then exposed to smoke with fixed rates of airflow through them. While you do not need calibrated flow for the simple purpose of comparing an experiment with a control, provided both have the same airflow conditions, this method does require a highly sensitive balance, ideally one capable of measuring just a few micrograms [1 microgram = one millionth of a gram, or 0.000001 grams] of change in the weight of the filter.

The second mechanism requires just a fixed light source and a sensitive light meter, you can probably get OK results with the kind of meter used by professional photographers provided you can control the illumination of the chambers well enough.

Thanks for a good question, and best of luck with the experiment,

Edward J. Hyer
Naval Research Laboratory
Monterey, CA