Future Tree Effects on Air Quality and Human Health in the United States

Trees are critical green infrastructure for mitigating adverse effects associated with human population, land use, and climate change (e.g. urban heat island, greenhouse gasses, air pollution, and floods). i-Tree (www.itreetools.org) is a suite of software tools developed by the USDA Forest Service and The Davey Institute that allows users to assess urban forest structure and the ecosystem services provided. Using i-Tree, the annual effects of trees on air quality and human health in urban and rural areas of counties across the conterminous United States have been quantified for 2010 (Nowak et al. 2014). Here, we extended the study to incorporate future forest structure scenarios using a model that accounts for tree growth, mortality and new plantings. Computer simulations using local environmental data and the possible leaf area index (LAI) for deciduous or evergreen tree covers were performed in urban and rural areas of counties across the conterminous United States. The result is a tree effects database on air pollutant removal (CO, NO2, O3, PM10, PM2.5 and SO2), biogenic emission of volatile organic compounds (VOCs), and monetary values associated with human health quantified per unit tree cover area with deciduous or evergreen trees and LAI ranging from 0 to 18 within each modeling domain. With these data, the potential annual effects that trees have on air quality and human health under future scenarios of urban forest extent can be readily derived for anywhere in the conterminous United States. The developed database will be integrated into i-Tree's suite in 2015 to enhance its functionality in estimating tree effects under the future scenarios.