Clean Air Day (Thurs 20th June) is an important reminder that we need to keep raising awareness of air quality, and the benefits of planting trees. Our Community Engagement Officer Jo has broken down the ways in which trees are the most helpful tool to combat air pollution:

Lowering the air temperature

When you sit in the shade on a hot day, or when you feel cooler air when you walk through the forest, what you’re experiencing is mainly a process known as transpiration. Moisture evaporates – mainly from leaves – and this process cools the air. So underneath woodland canopies, you feel refreshingly cool.

graphic of cars in the sun and shade

Even when your car isn’t running…

Emissions of many pollutants and/or ozone-forming chemicals increases with temperature. A great example of this takes place in car parks every day. You know how hot your car is after just a few minutes of sitting in the full sun? Well, hot seats and door handles are not the only undesirables happening at that moment when you get in and start to wilt.

Forest Service researchers in Davis, California found that parking under a tree in a car park reduced vehicle surface temperatures up to 36ºF, inside (cabin) temperatures by 47 degrees and, importantly, petrol tank temperatures by 7 degrees! When your petrol tank gets hot, petrol or diesel evaporates from it. At present, most of our car parks are places where high temperatures increase pollutant emissions and so the formation of smog and ozone.

graphic of trees and a car saying -60% pollution

Reducing airborne particles

Airborne particles, or particulate matter, are emitted when fuel is burned, especially diesel. It is removed (at least temporarily) from the air when it lands on leaf surfaces. While the particles float around in the air, their microscopic size enables them to be breathed deep into our lungs, potentially causing serious health problems or just a temporary irritation. Trees reduce street-level particulates by up to 60%, removing both gaseous pollutants and airborne particles.

Gaseous pollutants include ozone, sulphur dioxide (21% comes from refining and the combustion of petroleum products), nitrogen dioxide, carbon monoxide and CO2 (which causes half of the greenhouse effect, alone) These are taken out of the air by trees mainly through tiny “windows” on green leaves (called stoma). which let carbon dioxide in and oxygen out. They also let gaseous pollutants in, where they diffuse into spaces between leaf cells and from there are handled various ways.

graphic of trees and a car saying 1140 hectares of woodland = 2000 family cars

We need more trees

Well-placed trees can significantly lower temperatures in buildings by shading them. This reduces the need for air conditioning by up to 30 percent - which in turn reduces the amount of fossil fuels burned to produce electricity.

The combination of CO2 removal from the atmosphere, carbon storage in wood and the cooling effect makes trees extremely efficient tools in fighting the greenhouse effect. Planting trees remains one of the most cost-effective means of drawing excess CO2 from the atmosphere.

The Worldwatch Institute, in its Reforesting the Earth paper, estimated that the earth needs at least 321 million acres of trees planted just to restore and maintain the productivity of soil and water resources, annually remove 780 million tonnes of carbon from the atmosphere and meet industrial and fuel wood needs in the third world. For every tonne of new-wood growth, about 1.5 tons of CO2 are removed from the air and 1.07 tons of life-giving oxygen is produced.

We’ve created over 1,140 hectares of new woodland in the Forest so far, which is about 4917 tonnes of CO2 that’s being stored from the atmosphere every year – that’s the equivalent of 2000 family cars. Obviously we’re very proud of what we’ve achieved, but we still want to plant another 5 million trees.

If you want to help us – donating any amount can go towards more trees and therefore more harmful chemicals being taken out of the air we’re breathing, in the long term. Love your Forest!


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