THE TOBACCO IS ESPECIALLY USED TO DETECT AND MEASURE ATMOSPHERIC OXIDATION POLLUTION BY OZON (O-3)

The tobacco react to the air pollution. A varietie of plant of tobacco is sensitive to a particular pollutant: the ozone. Form a certain leve of ozone in the atmosphere, the plant of tobacco react by developing necroses (zones of dead cells on the these sheets: these necroses show themselves in the form of small white spots to brunettes. We can estimate the level of pollution in ozone by estimating the percentage of surface necrosed on the leaf. We use survery stations: these are consituted by some plants of tobacco of sensitive varietie to the ozone ande some plants of resistant varietie, which serve as witnesses. We raise every week the quantity of necroses on the sensitive plants, and we calculate an average by biostation. Surveillance of the air quality sets up regularly bioresort to realize studies on the ozone. The bioindication or the biosurveillance does not aim at supplying quantified data on the concentrations of atmospheric pollutants. She allows, in complementarity of the physico-chemical measures which she cannot replace, to estimate the impact of present pollutants in the environment.The bioindication allows a qualitative approach of the pollution which brings a relative comparison of varous geographical zones. Besides a low cost, compared with the physico-chemical sensors and a relative ease of implementation, the bioindication has major interest: the use of plants allows to visualize the impact of the pollution on human beings and to make sensitive better the population in this problem. There is an increasing interest in the technique of using indicator plants as tobacco to detect and to monitor the ambient levels of photochemical oxidants. The bio-indicator plant ?tobacco BEL W-3? shows characteristic responses, visual foliair injuries, that are specific of ozone. The development of leaf necrosis is used to calculate the ?Leaf injury Index?. This index does not give the absolute concentration of ozon in the atmosphere, but it provides estimates of relative levels of this pollutant. From the information given by the different bio-stations with tobacco, position, leaf injury index, it is easy to map the spatial and temporal distribution of ozone at ground level.