Cleaner air: the black cloud, exhaust and factories
Pollution often comes from incomplete combustion. The black cloud over parts of the Nile Delta appears in October and November, when rice straw is burned in heaps. Piled straw burns incompletely and gives carbon monoxide, carbon dioxide and soot in dense smoke, which reduces visibility and worsens asthma and chest allergies. Reusing straw as compost, animal feed, boards or mulch avoids it. Car exhaust holds carbon monoxide, carbon dioxide, soot and nitrogen oxides, and is a main cause of city air pollution, especially when engines are poorly kept. Measures are regular maintenance, cleaner fuels such as natural gas or electric cars, and public transport. A catalytic converter uses catalysts to turn carbon monoxide and nitrogen oxides into carbon dioxide and nitrogen by redox reactions. It does not remove carbon dioxide. Power stations and factories burn fuel for heat and steam. Natural gas gives less pollution than coal, but it is cleaner, not clean. Filters in chimneys catch particles, and an acid-gas scrubber neutralises acid gases, leaving salts that settle out.
| Problem | Cause | Measure |
|---|---|---|
| black cloud | straw burned in heaps | reuse the straw |
| city exhaust | busy engines | maintenance, public transport |
| factory gases | burning coal | natural gas, filters, scrubbers |
Filter model, with a grown-up. Stir flour or soil in a jug of water. Pour it through a coffee filter paper or a cloth into a clean cup. Describe what is caught and what passes through. Say what this model can show about chimney filters (they catch particles) and what it cannot (gases pass through a filter like this). Then make a problem–cause–measure poster for the black cloud, in your own words and without blaming anyone.