Nitrogen Dioxide and fine particulate are two key components of smog and soot, which can damage lungs, make outdoor exercise unsafe and send asthmatics running to the emergency room at high rates. Both pollutants, however, can be reduced by as much as 40% to 60% if trees, shrubs, ivy and even grass are planted in so called "urban street canyons." Trees, in fact, may be less effective than smaller greenery, since pollutants may be trapped beneath the tree canopy in some cases.
Trees have many benefits in urban, suburban, or rural environments. Strategically planted, trees can also reduce home energy use by as much as 30%, according to the Arbor Day Foundation, and street trees may boost home values in the neighborhood by more than $10,000, according to a 2010 Forest Service Study.
