Damage, symptoms and biology
Ozone, a gas that is present in the upper atmosphere, specifically in the stratosphere, plays a beneficial role by absorbing much of the ultraviolet radiation from the sun. While natural ozone concentrations do exist at ground level, they are very weak and do not pose a serious environmental threat. Human activities, coupled with the oxidizing effect of solar radiation, induce the formation of additional ground-level ozone. Polluting emissions resulting from the use of fossil fuels cause the formation of toxic gases such as NOx and SOx. When there is a build-up of these gases and smog forms, incoming solar radiation oxidizes the oxygen molecules, thus causing more ozone to form. The build-up of ozone concentrations causes a change in the colour of foliage, wilting and, in some cases, premature leaf-fall.
Warm, humid days with little wind are favourable for ground-level ozone formation. Most large cities have a smog alert system.
Canadian Forest Service Publications
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