Philadelphia's recent Greenworks progress update noted that nearly 90,000 trees have been planted in the city since 2008.
According to the tree math of a new U.S. Forest Service study, that would mean fewer deaths from air pollution.
The study, published online by the journal, Environmental Pollution, attempted to quantify how much fine particulate pollution trees remove from the air, and what the beneficial health effects are.
"Trees can make cities healthier," said the forest service's David Nowak, one of the study authors, in a press release. "While we need more research to generate better estimates, this study suggests that trees are an effective tool in reducing air pollution and creating healthier urban environments."
Trees remove these fine particles, which can contribute to respiratory and heart problems, by capturing them on the leaf surface and, sometimes, absorbing the particles. Other times, the particles are rinsed off by rain. Either way, they're out of the air.
The authors studied several cities, including Philadelphia. They concluded that the trees here, as of 2011, were resulting in 1.2 fewer deaths per year -- which they valued at $9.7 million. Also avoided each year are 313 cases of acute respiratory symptoms and 2005 cases of asthma exacerbation. Some 53 potential lost work days aren't being lost.