EVALUATION OF VEGETATION NEAR COAL-BURNING POWER-PLANTS IN SOUTHWESTERN PENNSYLVANIA .2. OZONE INJURY ON FOLIAGE OF HYBRID POPLAR

The objective ot this study was to determine if the incidence or sever ity of foliar injury induced by regional, ambient ozone was influenced by local emissions from a complex of coal-burning power plants in sou thwestern Pennsylvania. Plantings of an ozone-sensitive hybrid poplar clone (Populus maximowizii x trichocarpa, clone NE 388) were establish ed in 1972 at various distances and directions from the power plants. Foliar injury caused by ambient ozone was evaluated annually from 1973 to 1990 in early to mid-August. Data are presented for the 12-year pe riod, 1979 to 1990 inclusive, for which the most complete data sets we re available. Injury from ambient ozone varied spatially and temporall y, but with little relationship to power plant location. There was an apparent negative relationship between emission trends and ozone-induc ed symptoms, but only for one power plant. The correlation between ann ual mean levels of ozone-induced stipple and frequency of days (per ye ar) with a 1-hr ozone maximum exceeding 0.04 ppm was weak, but signifi cant. Ozone-induced bifacial necrosis was not observed on the foliage of the hybrid poplar during the drought year of 1988 in spite of recor d high levels of ozone; however, ozone-induced stipple was observed.