We know that trees eat greenhouse gases, and spit out breathable oxygen, but how much air pollution do they ingest, and how do humans benefit? The U.S Forest Service just released the first broad-scale estimate of how big an impact trees have on U.S. citizens and the economy. The study, published in Environmental Pollution, stated that trees in the U.S. save 850 human lives, and prevent 670,000 potential cases of acute respiratory symptoms annually. And that’s not all. The study calculates human health benefits of $7 billion a year thanks to the pollution that is cleaned up by trees.