B1 Intermediate US 65 Folder Collection
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Search Google Earth for China and you'll
see this.

But an unedited satellite photo might look
more like this.

That gray smudge is air pollution and it's
coming from Chinese cars, factories, and power plants.

But it's not only here.
In cities around the world, air pollution
is a big problem.

A majority of humans now live in cities and
that number is only going to rise,

which means more cars, more factories, and
more power plants.

As officials explore options for fighting
air pollution, there is one tool that is often overlooked:

trees.
Cities are centers of industry, but the resulting
pollution is filling our lungs and making us sick.

One major culprit is particulate matter: airborne
particles of dust, soot and smoke that are

released when we burn fossil fuels or kicked
up during construction and farming.

When we inhale them, they can cause asthma
and they can also enter our bloodstream to cause strokes and even death.
Experts estimate that outdoor air pollution
kills over three million people a year and

as cities grow, leaders are funding creative—and
often expensive—solutions for the problem.

In London, the mayor spent over a million
pounds spraying city streets

with an adhesive that was supposed to glue pollutants to the road.
and in the Netherlands, designers have created
a giant air purifier they call

"The Smog Free Tower",
which is cool, but there is another,
simpler solution…

A new report from The Nature Conservancy shows
that planting trees can be

a cost-effective way to improve public health, which they do in two ways:
First, a tree removes particulate matter when
polluted air blows through its branches.

The particulate matter settles on the leaves
and when it rains

the dust is washed down the gutter so we don't inhale it.
Second, trees cool temperatures by providing
shade and releasing water through photosynthesis,

which cools summer temperatures by about two
to four degrees fahrenheit.

But there is a catch!
Trees can only clean and cool the air within
a close radius: about one hundred feet,

so city officials need to be careful where they plant.
Officials can maximize pollution reduction
by planting trees where population density and air pollution overlap.
The Nature Conservancy report uses data from
Washington D.C. to create a map showing where

planting trees will have the highest return
on investment.

And some trees work better than others:
trees with larger, stickier leaves, like maples and elms
are more effective, but they also
need to be considered within the larger ecosystem.

Compared to DC, many cities around the world
have even more to gain from planting trees:

this map shows where return on investment
is highest for reducing particulate matter.

With proper targeting, planting trees can
be just as cost-effective as other strategies

like converting public transportation to use less diesel fuel.
But there is one major limiting factor: water
access.

What might work in Boston, will be less feasible
in a city like Doha, Qatar,

where water is a scarce resource.
And on top of that, many mayors don't yet
think of trees as a public health resource.

Trees might not look like giant air filters,
but that's exactly what they are,

and the sooner we start thinking of them that way,
the sooner the air we breathe might be cooler and cleaner in cities around the world.
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Why cities should plant more trees

65 Folder Collection
April Lu published on November 19, 2018
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