The Nature Conservancy has a new study about the value of planting trees in cities. The study looked at both the impacts on reducing temperature in urban areas but also reducing particulates through absorption by the trees. You can read a description of the work at The Atlantic CityLab at http://www.citylab.com/design/2016/10/the-big-green-payoff-from-bigger-urban-forests/505913/. You can read the full 136-page PDF here. Atlanta is featured on pages 62-63.