Ozone Danger to Trees
September 25, 2008
Trees in urban and suburban settings directly affect air quality by
alerting the urban atmospheric environment. Yet, while trees contribute
to healthier air, they are also harmed by an unhealthy environment.
Urban trees affect air quality in four major ways.
Ozone is the result of a chemical reaction that converts car exhaust
into ozone in the presence of light. The regions that have the
highest automobile traffic and sunshine are the most at risk. Even
areas without congested traffic may suffer, since ozone is transportable
over long distances. The pollutant acts as an oxidant that
disrupts the chemical pathways in a plantís photosynthesis powerhouse,
the chloroplast. In response, the tree manufactures antioxidants
like vitamin E and C. This process may offer relief from low
levels of ozone, yet are no match for repeated exposure to toxic
- Temperature reduction. Trees reduce energy consumption in
summer by shading cars and buildings. A reduced air temperature
due to the cooling effects of trees can improve air quality because
the emissions of some pollutants and ozone-forming chemicals are
- Remove of air pollutants. Trees remove air pollution through
uptake by leaf stomata. Trees also remove pollution by intercepting
- Emissions of volatile organic compounds. Because VOC
emissions are temperature dependent and trees generally lower air
temperatures, increased tree cover can lower overall VOC emissions,
lowering ozone levels in urban areas.
- Energy effects on buildings. Trees reduce building energy
used by lowering temperatures and shading buildings during the
summer, and blocking winds in winter.
Ozone injury looks different on different species. On the leaves
of poplar and black cherry, the homeowner may see brownish lesions
on a leaf that appears water-soaked. On ash and hickory,
however, the lesions are white. On other species, damage appears
as a purple stippling all over the leaf. Evergreens appear to have
burnt needle tips.
"At present, the best thing homeowners can do to protect trees
from ozone injury is to keep them in an overall healthy state," stresses
Andersen. This includes protecting trees from wounding, and
keeping them well watered and judiciously fertilized."
What to do. A professional arborist can examine your trees to find the source
of the problem. A professional arborist can also recommend treatments,
including thinning dense woods, planting new trees, correcting
soil deficiencies, increasing water and nutrients, or pest management.
Partially Reprinted from Tree Care Industry Magazine.
Santa Ynez Valley Tree Care • 688-5580 • Lic. #750949
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