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.

  • 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 temperature dependent.
  • Remove of air pollutants. Trees remove air pollution through uptake by leaf stomata. Trees also remove pollution by intercepting airborne particles.
  • 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 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 levels.

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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Santa Ynez Valley Tree Care
P.O. Box 1147, Santa Ynez, California 93460

(805) 688-5580

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