Many cities are notorious for their dangerously high levels of air pollution and the resulting health issues, such as asthma and emphysema. Summer heat and vehicle emissions are just a few of the contributing factors that increase air pollution levels. However, healthy trees planted effectively along roads, buildings and in parking lots can decrease overall air pollution levels for city residents.
Trees Remove Air Pollutants
Trees can remove both gaseous air pollutants and particulate matter. Gaseous air pollution enters a tree through leaf stomata and is either held in intercellular cavities or processed into usable nutrients. According to David Nowack’s report, "The Effects of Urban Trees on Air Quality" for the USDA Forest Service, particulate matter usually collects on the surface of trees. The particulates often enter the ground by either being washed off the tree by precipitation or falling to the ground with leaves and twigs. Larger trees tend to be much more effective, by approximately 70%, at removing air pollutants than smaller trees. Over the course of one year, trees removed an estimated 1,821 metric tons of air pollution in New York City.