Trees aren't an insta-fix for city air pollution

Trees were supposed to be the urban jungle's salvation. After all, trees provide sweet, beautiful shade which helps cool the metropolis, a place prone to overheating thanks to a proliferation of surfaces like asphalt and concrete. And by pumping oxygen into the air—the same oxygen humans need to breathe— while also filtering out harmful air pollution, trees were supposed to help the eighty percent of Americans who live in urban areas breathe easy. But a new study out today in the jou