Airwatch – Odour as a source indicator

1. Preliminary class activity

Test odour perception in class: open a bottle of peppermint or similar at the back of the class and time how long it takes for pupils in different rows to smell it. Plot the time vs distance and draw conclusions about the speed of diffusion in the room.

Repeat with an odour of very different molecular weight. Perhaps a dependence on molecular weight of the odorous material can be obtained?

2. Regional odour study

The objective is to map out the source of an odour in the community. An area may have a recognisable odour and the community may already know its source. Hence the following study may be an exercise to confirm what is already known. If the source of an odour is not known then this exercise is a worthwhile activity to discover the source.

The method is very simple but powerful: collect over a number of days/weeks the location or direction of a particular odour and at the same time, the wind direction. Combine this information on a map to pinpoint the source of the odour.

The study can be carried out by one school over a period of time, or it can be a collaborative project between three or four participating AIRWATCH schools. It may be difficult for one school to study a large area around a source, so by sharing data a meaningful result can be obtained.

Procedure:

• Set up two teams of pupils with a street map or topographic map of the region where an odour is known to occur.
• The teams locate the odour and make their way cross-wind in opposite directions until the odour is definitely not apparent. The distance that the groups will have to travel will vary depending upon the spread of the odour, and may be as much as two or three kilometres or as little as a hundred metres.
• Then each team retraces their path and marks on the map when the odour is first apparent. Mark this spot with an ‘X’.
• Record the wind direction on the map.
• Draw a line parallel with the wind direction halfway between the two ‘X’ marks. The odour source lies somewhere along this line in the upwind direction.

By repeating this procedure on different days when the wind direction changes, the lines on the map will cross, locating the odour source.

Example: Regional Odour Study by Schools A, B, C, D

TABLE OF RESULTS

The results are plotted on the map below. The rough intersection of the lines points to a site marked S (for source). The source on this fictitious map could be a garbage tip.

Contact: peter.manins@csiro.au

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Modified: 16 May 2002