Page 16 - BBC Knowledge - October 2017 IN

Questions
& Answers

DO TREES REDUCE AIR
POLLUTION LEVELS?
The relationship between trees and air
pollution is a complicated one. Particulate
matter suspended in polluted air tends to
settle onto leaves, and certain gases including
nitrous dioxide (NO2) are absorbed by leaves’
stomata, filtering the air and reducing pollution
levels slightly. But trees and other vegetation
also restrict airflow in their immediate vicinity,
preventing pollution from being diluted by
currents of cleaner air. In particular, tall trees
with thick canopies planted alongside busy
roads can act like a roof, trapping pockets
of polluted air at ground level. To reliably improve
air quality, city planners need to give careful
consideration to how trees are placed. AFC

H OW I T WO R K S

MR TRASH WHEEL
At the mouth of the Jones Falls River, where it feeds into Baltimore Harbour in the US, sits Mr Trash Wheel. Since 2014, this
semi-autonomous floating rubbish collector has scooped up more than 500 tonnes of detritus, including 90,00,000 cigarette butts,
4,92,000 coffee cups and 3,76,000 crisp packets. Mr Trash Wheel cost $720,000 (£560,000) to build, and has now been joined by
Professor Trash Wheel, a ‘female’ version in a different part of the harbour.

The conveyors are powered by a water
wheel fed by the river current.
When the flow isn’t fast enough,
solar panels can take over.

As each skip fills,
A second conveyor belt scoops it’s towed away
up the rubbish, drains away the water and the rubbish
and carries the rest into a skip on a is incinerated
separate floating barge. to generate
electricity.
The river current drives
trash toward floating
booms, which funnel
rubbish to Mr Trash PHOTOS: GETTY, ZUMA PRESS/EYEVINE, ILLUSTRATIONS: RAJA LOCKEY
Wheel’s mouth.
Long forks attached to
a conveyor collect and
compact the debris. Most of the rubbish
isn’t thrown in
the river directly –
it’s land litter, washed
in by the rain.
A heavy storm can fill
12 skips!
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OCTOBER 2017