i-Tree Eco (originally the Urban Forest Effects or UFORE model) uses detailed field data from complete inventories or randomly sampled plots to quantify urban forest structure, environmental effects, and value to communities. The study area can range from a single tree to a park to an entire county’s urban forest. Eco provides accurate estimates of air pollutant removal, carbon storage and sequestration, effects of trees on building energy use and emissions, and compensatory value of the urban forest. In version 4.0, the air quality model has been refined to include improved simulations, updated monetary values, and charts and tables that now display yearly, monthly, or hourly results. Users must register to download and install the free iTree software suite.