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
|
DATE |
SCHOOL |
WIND DIRECTION |
|
week 1 - day 1 |
A |
south |
|
week 1 - day 2 |
D |
south/east |
|
week 2 - day 1 |
C |
north/west |
|
week 2 - day 2 |
B |
west |
|
week 3 - day 1 |
D |
south/east |