Ozone as a cause of tobacco injury

Abstract

Damage to tobacco plants, known as “weather fleck”, is now recognized as being due to ozone. Over the northern shores of Lake Erie ozone is believed to be mainly generated by photo-chemical processes from oxides of nitrogen and hydrocarbons emitted in industrial areas to the south. However, thunderstorm activity and stratospheric ozone might at times contribute to total ozone concentration, although only in small quantities. Indications are that on most occasions of high ozone concentration, lake breeze surges, and meso-scale systems forming as a result of the physiographical features of the Great Lakes area, dominated the weather picture and were the key mechanism by which ozone was advected and brought down to the surface. Severe flecking generally occurred with a particular combination of amounts of ozone dose and evapotranspiration. When the hourly ozone concentrations were modified by a coefficient of evapotranspiration derived from a simple form of the mass transfer equation, a much improved correlation between flecking severity and modified ozone dose was obtained, and several hitherto obscure results could be explained.