The effects on plant growth of radiation attenuation by atmospheric pollutants

Known species of air pollutants have been identified. Information has been tabulated on the sources, the concentrations, the absorption and scattering properties, the reactivities, and the photochemistry of these pollutants. Photostimulated plant processes have been identified and their action spectra examined. When available, information of the visible spectrum energy requirements, both intensity and quality, needed to drive these processes in higher order plants has been gathered and examined. Emphasis has been placed on economically important plants. A survey has been made of the recorded damage to plants by direct exposure to the above atmospheric pollutants and damage threshold levels have been established. Four models of polluted atmospheres have been developed. A calculation procedure has been generated for determining the magnitude of the spectral solar radiation intensity at the earth's surface after passing through the model atmosphere. Calculations for the intensities to be expected at three different latitudes in mid June, mid March, and mid December have been accomplished on a digital computer. Reasonable agreement was found between these calculations and the one available instance of measured attenuation through a vertical layer of pollution. The results show that in many situations there is considerable chance that important crops may suffer reduced yield or even damage from radiation attenuation by gaseous and particulate pollutants, selective absorption does not appear to govern the attenuation except in instances where particle concentrations have been held to unusually low limits. At pollutant concentrations below those which are known to cause direct harm to sensitive plants, there is reduced likelihood of deleterious effects on plants solely from the attenuation caused by the pollutants, except in the case of a few plants of importance. Recommendations for fruitful further study are given. [...]Mechanical Engineering, Department o