Urban forests clean our air
Avon-Otakaro Forest Park will not just tie up greenhouse gasses – it will also help to solve Christchurch’s air pollution problem.
Urban forests take pollution out of the air. As trees remove most air pollution through their leaves, evergreen trees (as most natives are) could make our winter air cleaner.
Christchurch’s air pollution problem
High levels of the pollutants known as PM10 are linked with cancer, breathing problems and heart disease. The Ministry of the Environment says that because of PM10, “We incur major costs, for example, for hospitalisation and medical treatment, premature deaths, and lost work days.”
Every year in Christchurch, 150 people die earlier than they should, because of air pollution. In 2014, Christchurch had 19 high-pollution days, when PM10 levels were higher than national standards. We have to get this down to one high-pollution day by 2020.
How trees help improve air quality
All trees take carbon dioxide, sulphur dioxide and PM10 particles out of the air. They do this by absorbing them through their leaves and stems. Trees currently remove around 300 tonnes of air pollution from Christchurch every year.
But large trees are better at taking pollutants out of the air than small trees are. A 76cm-diameter tree removes about 70 times more air pollution a year than a 7.6cm-diameter tree!
Forests are much better at removing air pollution than any other form or arrangement of vegetation. Individual street trees just don’t do as well. And highly maintained parks and street trees might actually give off more pollution and use more water than those in resilient natural areas.
In Christchurch, the winter air quality in the centre of Riccarton Bush is significantly better than outside the bush. And the worst air quality is outside the bush, near deciduous silver birch trees.
Evergreen trees take pollution from the air all year round, but only some deciduous trees can still do so during winter. So if we want to use trees to improve Christchurch’s winter air pollution, we need to plant native evergreens.
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