What it shows
Dust and soot from traffic settle on leaves. Pressing clear tape on leaves from different places and sticking it on white paper gives a visible grey patch whose darkness shows how dusty the air is at each spot.
The science
Vehicle exhaust, brake wear, road dust and construction raise particles into the air, and the heavier ones settle within a few metres of the source. Leaves with a slightly rough or waxy surface hold the particles until rain washes them off. Tape lifts the layer and the darkness of the patch on white paper is roughly proportional to the amount of dust, so comparing patches from leaves of the same plant type and age ranks the sites.
Materials
Cost: under Rs 50. Many items come from home or from waste; spare parts such as LEDs, motors and wire are in the store.
- Clear cello tape
- White paper or index cards
- A hand lens
- A notebook
- Access to similar plants, such as hibiscus or a hedge, at five places: a busy road, a lane, a park, a school ground and near a construction site
Safety
For this project: Stay on the footpath near roads and go with an adult. Do not pick leaves from private gardens without asking.
Never use mains electricity: power models with cells, batteries or a low-voltage adapter. Sharp and hot tools, flames and lab chemicals need an adult or your teacher beside you. Keep magnets, button cells and small parts away from young children, and wash your hands after making.
Step by step
8 steps. Do them in order, and test each part before you go on to the next. Write what you notice in a notebook as you go.
Choose five sites and at each one find the same kind of plant at about the same height from the ground.
Note the date, the time, how many days since the last rain, and what is near the plant.
Press a 5 centimetre strip of tape firmly on the upper surface of a mature leaf, rub it, and peel it off.
Stick the tape on a white card and label it with the site.
Take three samples per site from different leaves.
Line up the cards and rank them from cleanest to dirtiest by eye, and with the lens count the dark specks in a 1 centimetre square.
Average the three counts per site and draw a bar chart.
Write which sites had the most dust and the likely sources.
What you should see
A card set where the busy road and construction site show grey or black patches with many specks per square centimetre, and the park usually shows a much cleaner tape.
Viva questions
A teacher or a judge will ask how it works. Try to answer each question before you open it, then compare.
01Where does road dust come from?
Exhaust, brake and tyre wear, and soil and construction dust raised by vehicles.
02Why take three samples per site?
Leaves vary; an average is fairer.
03Why use the same plant type everywhere?
Different leaves hold dust differently, which would spoil the comparison.
04How do trees help with dust?
Their leaves trap particles and rain washes them to the ground.
Take it further
Repeat the test the day after heavy rain and compare.
Change one thing, measure what happens, and add a table or chart of your readings: that is what turns a model into your own investigation.
Free ebooks for this project
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