TREES grow better in cities than in the countryside.
Ecologist Jillian Gregg at Cornell University in Ithaca led a study of cottonwood saplings in New York city and the surrounding countryside. “They were always twice as big in the city,” she says. “It’s very dramatic.”
The effect is caused by traffic fumes creating the toxic gas ozone, Gregg’s team found. In the cities, ozone levels are kept in check as the gas is destroyed by other pollutants such as nitrogen oxides.
But ozone also drifts into the countryside where nitrogen oxide concentrations are low. There, because the ozone lingers longer…
