Investigation on Injury to Plants from Air Pollution in the Los Angeles Area

Abstract

Spinach, beet, endive, oat, and alfalfa plants were used for the determination of crop damaging pollutants in the air of metropolitan Los Angeles. The air pollution, or smog, symptoms on these indicator plants are well known through previous studies. The production of a metallic glaze or silvering on the lower surface of leaves on spinach, beet and endive especially distinguishes this damage from the effect of previously known toxic materials. Activated carbon filters were devised which removed the toxic agents from the polluted air. The filters demonstrated that sublethal concentrations of smog had a depressing effect on the growth of the plants. Principal attention was given to the reaction products which are formed in the air from natural components and air pollutants, as well as from the air pollutants with each other, after earlier tests with a series of pure compounds of organic nature failed to produce smog symptoms. The reaction products of ozone with unsaturated hydrocarbons produced typical smog damage on all of the indicator plants. The damaging factor must therefore be attributed to the peroxides formed in the ozonization process. Optimum effects were obtained by using olefins with five and six carbon atoms with the double bond in the end position. However, the end position of the double bond is not essential, since 3-n-heptene, 4-n-nonene and cyclohexene gave typical smog damage upon ozonization. The concentration of ozone at which damage occurs with the olefins is well within the range of ozone concentration found in the atmosphere as determined by the rubber cracking test. The optimum activity of the C5 and C6 series is attributed to the stability of the intermediate products in the reaction process. The catalytic oxidation of the olefins with NO2 under the influence of sunlight produces oxidation products very similar to those produced by ozone. In the plant fumigations with oxidation products of olefins, lachrymatory effects were often observed. These investigations demonstrate the utility of plants in analyzing air pollutants. They further show for the first time that hydrocarbons, normally harmless air pollutants of organic nature, can cause severe damage through their reaction with substances known to be in the air. In this way these experiments have contributed to a better understanding of the smog problem.