A book out of the Netherlands called 'The Green City Guidelines, Techniques for a Healthy Liveable City' (Michelle de Roo & Niek Roozen, Zwaan Printmedia, Sept 2011) has prompted a look at the role trees play in the absorption of pollutants in the air.
Keeping it simple (and there is a lot of very technical information relating to this topic) large leafed deciduous trees are top of the list for absorbing ozone (which is dangerous to nose and lung tissue in concentrated amounts at ground level), gaseous pollutants such as nitrous oxide and sulphur dioxide from industry as well as particulate matter covering ash, pollen and smoke.
The NGIA is now commissioning its own research on this matter with the aim of identifying absorption rates and filtering capabilities of native trees in the Australian climate.
Regardless of outcomes here, one fundamental point remains true and above debate: that trees (some more than others, but all regardless) have the ability to filter the air we breathe.
Gingko biloba
In large leafed trees such as Gingko biloba (pictured), Ulmus, Zelkova, Cercis, Cotinus and Canadian Maples such as Acer rubrum 'Autumn Red', pollutants are absorbed by the stomata of leaves (the outer skin layer). The larger the leaf surface, the greater its ability to filter out nasties such as carbon dioxide, ozone and nitrous oxide which is linked to nitric oxide and the production of greenhouse gases (with impact far greater than that associated with carbon dioxide).
Particulate matter such as that found in smoke and ash is captured on leaves too. In a process called impaction, and with the assistance of wind and water, the captured pollutants travel to the ground as fallen leaves where they are either washed away as run-off or fixed into the soil via decomposition.
Conifer species such as Picea and Pinus are very effective here as their needles permanently cover the tree as well as densely surround the tree all year round.
Allocasuarina torulosa
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