In the first broad-scale estimate of air pollution removal by trees nationwide, scientists have calculated that trees are saving more than 850 human lives a year and preventing 670,000 incidences of acute respiratory symptoms. The study considered four pollutants for which the U.S. EPA has established air quality standards: nitrogen dioxide, ozone, sulfur dioxide, and particulate matter less than 2.5 microns (PM2.5) in aerodynamic diameter.http://feeds.sciencedaily.com/~r/sciencedaily/~3/-...