Scientists discovered that urban pollution is stunting the growth of trees in the countryside.
Researchers from Cornell University traced the growth of identical cottonwood trees in New York City and in rural areas. The trees planted among New York's congested streets grew twice as large.
Ozone created in urban areas, where emissions interact with sunlight to form ozone, is blown out of cities to the countryside. In rural areas, where nitric oxide concentrations are low, the ozone remains in the atmosphere longer ... and affects the growth of trees.