Not All Tree Planting Programs Are Great for the Environment

Countless cities have launched ambitious tree planting projects in the name of improving the environment—to suck up carbon dioxide and storm water, to provide cool shade on sunny days. But many trees also produce compounds that contribute ozone to the local atmosphere. That’s why communities considering planting large numbers of new trees in the next decade should pay special attention to exactly what they’re growing.

More recently, researchers have been trying to zero-in on how exactly this ozone production process works in urban areas, as well as which tree species emit more VOCs than others. Turns out, not all trees are equal. The unit for measuring VOC emissions from trees is micrograms per gram of leaf mass per hour. This table lists average VOC emission rates for several popular urban trees under standard conditions of temperature and light.