Trees reduce pollution

In her speech this week to the District Council, the secretary of Sidmouth Arboretum talked about  'improving air quality' and how trees could help:
Futures Forum: Sidmouth Arboretum: how to protect trees and woodland 
In its final episode this week on BBC Two the series looking at health issues which are either overstated or - as in the case of air pollution and what it does to us - understated:

Trust Me I'm A Doctor

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The series that cuts through the confusing adverts, headlines and health advice to provide information you need to live healthily.

Michael Mosley and the team of doctors are in Lancaster to test if trees could be the answer to a hidden health threat that kills 29,000 people a year - air pollution.

The Big Air Pollution Experiment

Particulate Matter in the air (or PM) can be very bad for our health. Staying away from traffic as much as possible is one way to keep our exposure levels down, but what about in our actual houses? More often than not, houses are on roads – and roads carry traffic. So is there a way that we can help reduce the concentration of PM that creeps into our houses?

Michael Mosley and surgeon Gabriel Weston help test a new pollution filter developed by Professor Barbara Maher at the University of Lancaster: silver birch trees.

We set up a row of 24 young silver birch trees in tubs along the pavement of the busy A9 in Lancaster. Behind the trees were 4 terraced houses, and next to those, 4 identical terraced houses that didn’t have birch trees between them and the traffic on the road.

At the beginning of the fortnight experimental period, Barbara and Gabriel cleaned the TV screens and computer monitors inside each of the 8 houses. These were then left on standby for the next 2 weeks, and acted as very good dust-traps for the PM pollution.

Two weeks later, Gabriel and Barbara came to wipe down an identically sized area of the screens in the front room of each of the houses. Back in the lab, the magnetic properties of each of these wet-wipes was then measured in order to assess the quantity of (iron-bearing) particulate traffic pollution on each one, giving us a measure of the level of pollution in each of the 8 houses (4 protected by trees and 4 not protected by trees).

The results were astounding: the fortnight’s pollution in the 4 houses with trees was 50-60% lower than in those without.

So how were the trees giving so much protection?

Electron microscope images of the leaves of silver birch trees show why they are so good – they are covered in tiny hairs and ridges which help trap the pollution particles. Their sparse structure also helps keep the air circulating and flowing past the leaves to filter it effectively (rather than trapping pollution near the ground as bigger and denser trees do). Each time it rains, the PM pollution is washed off the leaves, allowing them to start trapping more. So whilst the birch trees are in leaf, at least, they are providing an excellent pollution filter. And given that heart disease (which is seriously affected by particulate air pollution) is Britain’s biggest killer, a couple of small silver birch trees in your front garden – or planted along the pavement by the local council – could be a huge boost to your health.

Useful links

• Prof Barbara Maher (www.lancaster.ac.uk)
• Prof Maher’s research showing that silver birches are particularly good at trapping pollution particles (PDF) (www.researchgate.net)

BBC Two - Trust Me I'm A Doctor - The Big Air Pollution Experiment
BBC Two - Trust Me I'm A Doctor - How does air pollution affect us?
Tree of life: birch filters out deadly diesel pollution | The Sunday Times


Trees Reduce Air Pollution

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Trees and other plants make their own food from carbon dioxide (CO₂) in the atmosphere, water, sunlight and a small amount of soil elements. In the process, they release oxygen (O₂) for us to breathe.
Trees:

• Help to settle out, trap and hold particle pollutants (dust, ash, pollen and smoke) that can damage human lungs.
• Absorb CO₂ and other dangerous gasses and, in turn, replenish the atmosphere with oxygen.
• Produce enough oxygen on each acre for 18 people every day.
• Absorb enough CO₂ on each acre, over a year's time, to equal the amount you produce when you drive your car 26,000 miles. Trees remove gaseous pollutants by absorbing them through the pores in the leaf surface. Particulates are trapped and filtered by leaves, stems and twigs, and washed to the ground by rainfall.

Air pollutants injure trees by damaging their foliage and impairing the process of photosynthesis (food making). They also weaken trees making them more susceptible to other health problems such as insects and diseases.
The loss of trees in our urban areas not only intensifies the urban "heat-island" effect from loss of shade and evaporation, but we lose a principal absorber of carbon dioxide and trapper of other air pollutants as well.
Some of the major air pollutants and their primary sources are:

• Carbon dioxide: Burning oil, coal, natural gas for energy. Decay and burning of tropical forests.
• Sulfur dioxide: Burning coal to generate electricity.
• Hydrogen floride and silicon tetrafloride: Aluminum and phospate fertilizer production, oil refineries, and steel manufacturing.
• Ozone: Chemical reactions of sunlight on automobile exhaust gases. Ozone is a major pollutant in smog.
• Methane: Burning fossil fuels, livestock waste, landfills and rice production.
• Nitros oxides: Burning fossil fuels and automobile exhausts.
• Chloroflorocarbons: Air conditioners, refrigerators, industrial foam.

The burning of fossil fuels for energy and large scale forest fires such as in the tropics are major contributors to the buildup of CO₂ in the atmosphere.
Managing and protecting forests and planting new trees reduces CO₂ levels by storing carbon in their roots and trunk and releasing oxygen into the atmosphere.

Trees Reduce Air Pollution
Trees cause pollution - RationalWiki
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