Environment 360: Trees are saving more than 850 human lives each year and preventing 670,000 cases of acute respiratory symptoms in the U.S., according to the first broad-scale estimate of trees' air pollution removal by U.S. Forest Service researchers. Looking at four common air pollutants -- nitrogen dioxide, ozone, sulfur dioxide, and particulate matter with a diameter less than 2.5 microns -- researchers valued the human health benefits of the reduced air pollution at nearly $7 billion annually in a study published...