I live near a busy street and concerned about the vehicular pollution. Could you please advice on what trees I could grow along my property to reduce the impact. Thank you!
Thank you for contacting the Toronto Master Gardeners. All trees absorb carbon dioxide, however some trees are better than others at filtering pollutants from the air, in particular particulate matter (PM), that is tiny particles of organic chemicals, acids, metals and dust, emitted from fossil-fuel-burning vehicles, factories and construction sites. On the other hand, some trees emit volatile organic compounds (VOCs) which can interact with the gases emitted by vehicles and in the presence of sunlight this interaction can contribute to ground-level ozone which is harmful to human health. Other considerations for tree selection include ability to adapt to an urban environment eg. sensitivity to road salt, whether or not it is invasive eg. Norway maple is one of the most effective trees for trapping air pollutants but it is highly invasive, and the garden / planting environment eg. hours of sunlight daily, soil type (clay, sand, loam), garden size.
In general :
- Larger leaves can trap more pollutants than smaller leaves, and leaves with rough, rugged and hairy surfaces are the most effective filters for PM. The leaves trap PM, which is then washed away when it rains.
- Conifers, like pines and cypresses, are good natural purifiers. The dense canopy of needle-like leaves typical of conifers is very effective at trapping pollutants. And conifers are evergreen, so they work year-round to reduce air pollution, unlike deciduous trees that are without leaves for many months of the year.
Trees that are recommended for their ability to reduce air pollution, based on the few studies that have been done include :
Deciduous : Maple – Acer rubrum, A. saccharinum, Linden – Tilia tamentosa, T. americana, T. europea, T. euchlora, T. cordata, T. platyphylios, T. tomentosa, Tulip tree (Liriodendron tulipifera), Maidenhair tree (Ginkgo biloba), Birch – Betula pendula, B. nigra, and Honey locust (Gleditsia Triacanthos).
Evergreen : Chinese juniper (Juniperus chinensis), American arborvitae (Thuja occidentalis), Eastern white pine (Pinus strobus), Canadian hemlock (Tsuga canadensis), Norway spruce (Picea abies).
For further reading, below are a couple of articles that might be helpful. The first one includes information about a couple of tools (iTree, Photo-sensor) that provide lists of plants that have been proven to be effective at reducing particulate matter.