Canadian Forest Service Publications

Tropospheric ozone: a continuing threat to global forests? 2003. Percy, K.E.; Legge, A.H.; Krupa, S.V. Pages 85-118 (Vol. Chapter 4) in D.F. Karnosky, K.E. Percy, A.H. Chappelka, C.M. Simpson, and J. Pikkarainen, editors. Air Pollution, Global Change and Forests in the New Millenium. Elsevier Ltd., Amsterdam, The Netherlands.

Year: 2003

Issued by: Atlantic Forestry Centre

Catalog ID: 22976

Language: English

Availability: Order paper copy (free), PDF (download)

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Ozone (O3) has a critical role in tropospheric chemistry. it absorbs radiation in the infrared and ultraviolet regions and is very reactive and biologically toxic at appropriate levels of exposure. At the earth's surface, O3 is subject to long-range transport and is the most pervasive air pollutant affecting the world's forests today. The existence of O3 has been known since 1840 and smog-induced foliar injury on plants was first identified in the 1950s. Levels were ~10-15 ppb during the second half of the 1800s, compared with 30-40 ppb measured as the global background today. By 2100, fully 50% (17 million km2) of world forests are predicted to be exposed to O3 at concentrations >60 ppb. Ozone induces a variety of symptoms and pattern of injury that are dependant upon species, genotype, leaf position on the plant, leaf age, exposure dynamics, and meteorological factors or growth conditions. It is absolutely essential to have knowledge on species sensitivities, O3 profiles and toxicity concentrations for the species under investigation before diagnosis can be confirmed. Ozone is generally detrimental to tree growth and ecosystem productivity, often through induced changes in patterns of carbon allocation or pre-disposition to insects and disease. The development of ozone exposure-forest response relationships that are scientifically defensible and applicable in air quality regulation has been difficult due to serious limiations encountered in scaling-up experimental data. In terms of air quality regulations, North America and Europe have adopted different approaches toward ambient ozone standard setting, with Europe opting for an approach that protects vegetation. The US and Canada, in their individual countries, implement separate or identical standards to protect both human health and the environment.