Ozone vegetation effected

For any pollutant, air quality criteria may refer to different types of effects. For example. Tables 22-1 through 22-6 list effects on humans, animals, vegetation, materials, and the atmosphere caused by various exposures to sulfur dioxide, particulate matter, nitrogen dioxide, carbon monoxide, ozone, and lead. These data are from fhe Air Quality Criteria for these pollutants published by the U.S. Environmental Protection Agency. 

However, ozone may have some undesirable effects. There have been a few reports of changes in aroma and surface colour of some fruits and vegetables (Kim etal., 1999 Perez etal., 1999). Ozone can also be hazardous to humans. A concentration above 0.1 ppm in air has a strong odour that causes irritation of the nose, throat and skin (Sharma, 2005). In addition, long-term exposure to the gas may lead to mutagenic effects and even death. 

When a monitoring site is selected, it is important to take account of environmental features. For example, ozone measured in or near automotive traffic can drop to 50% of the areawide value, owing to reaction with the nitric oxide firom exhaust emission. Ozone measured 7.5 m from a large tree in green leaf can drop to 70% of the areawide value, but it may also be reduced within 1 m of shrubs and grass. Paint, asphalt, concrete, dry soil, and dead vegetation are not as reactive and so have less effect. Peak ozone values observed in sunlit windscreened. 

This includes data obtained from laboratory studies of chemical reactions, plant and material damage, and animal and human toxicology from field studies of air quality and vegetation and ecosystem effects and from population exposures. In all such studies, irrespective of the method used, the measurement of oxidants is based on a standardized source of ozone. 

A number of reviews of varied quality cover general or special effects of photochemical oxidants on vegetation (Table 11-1). Thomas fairly comprehensively covered the available information on the effects of photochemical oxidants on plants. Middleton gave the first comprehensive coverage of the phytotoxic effects of photochemical oxidants in 1961. A number of excellent reviews have appeared since 1%1. Rich presented an early review of ozone effects. Dugger and associates presented the physiologic and biochemical effects of oxidants on plants. Heck covered factors that influenced the expression of oxidant dam-... 

Heck and Brandt discussed the effectiveness of green belts in relation to vegetation as a pollutant sink and concluded that vegetation probably acts as a major sink for air pollutants, including oxidants and ozone, over time, but has a relatively minor effect on oxidant concentrations during high-pollution episodes is more effective in some seasons than others or with some cultural and management practices than others and should not be considered an important contributor to short-term reductions in oxidant or ozone concentrations. 

The ozone dose responses and the specific effects on the photosynthetic activity of both herbaceous and woody plants, principally in controlled short exposures, are discussed in Chapter 11. The main aim of this section is to evaluate the effects of the chronic exposure of vegetation in natural ecosystems to total oxidants (more than 90% ozone) under field conditions or simulated field conditions. The effects of chronic exposure on agroecosystems are also discussed to a limited extent in Chapter 11. 

Both in vivo and in vitro systems have been utilized to try to elucidate the effects of ozone on vegetation, but one must be cautious about assuming that they are equal. In vitro studies reveal the potential of ozone to injure organelles, enzyme systems... 

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