AIR POLLUTANTS
A major air pollutant is sulfur dioxide (SO2) which upon contact with water forms sulfuric acid (H2SO4). Potato is relatively tolerant of SO2. Leaf symptoms start as dry papery blotches colored tan, straw or even white, and turn to interveinal browning or necrosis. Leaf veins remain green. Young and mid-aged plants and leaves are most sensitive. sensitivity is highest during days with bright sunlight and high relative humidity. Common sources of SO2 release are electric power plants, fossil-fuel furnaces, oil refineries, mining of cupper, iron and sulfur, smelters. Exposure to 0.5 ppm for four hours or 0.25 ppm for eight hours may be injurious to some crops which may show symptoms as far as 30 miles for a source. Potato is considered somewhat tolerant as is corn, onion and sorghum. If SO2 injury is suspected, one can check nearby, more sensitive crops such as alfalfa, beans, beets, soybean, and sunflower, or sensitive weeds such as pigweeds, ragweed and morning glory.
Ethylene (C2H4) is another pollutant from motor vehicle exhausts. It is also a natural hormone occurring in plants affecting growth and behavior. Ethylene can induce epinasty, plant twisting, defoliation etc. Potato is very sensitive to ethylene. Potato is rather tolerant of other pollutants such as chlorine and fluorine; They would give symptoms similar to SO2.