By absorbing and filtering out nitrogen dioxide (NO₂), sulfur dioxide (SO₂), ozone (O₃), carbon monoxide (CO), and particulate matter less than 10 microns (PM10) through their leaves, trees perform a vital air cleaning service that directly affects the well-being of people and reduces the greenhouse gases that are a contributing factor to Global Warming. AMERICAN FORESTS’ CITYgreen software calculates the annual air pollution removal rate of trees using a scientific model developed by the US Forest Service and the pollutants are those that are identified by EPA as the major greenhouse gases. The dollar values are derived by “externality” costs, (a method developed by economists) which are indirect costs borne by society.

The values in this web-based calculator are based on the coefficients from CITYgreen. To use this calculator you will need to estimate the number of acres of trees in your community and choose the nearest major city. Estimating tree canopy with a high degree of precision requires sophisticated software and experienced image processing specialists. At American Forests, landcover assessment is the basis for all of our analysis projects.

There are a couple of ways to get a ‘ball park’ estimate of your tree canopy.

• Estimate your number of trees and use a rough estimate of 200 trees per acre (don’t include trees with a crown spread of less than 10 feet).



• Using a sampling method, choose a representative area of your community from an image at http://maps.google.com and estimate the percentage tree cover. Multiply the percent tree cover of your sample to the total acreage of your area.



• If you are looking for very precise values, you will need to use GIS (Geographic Information Systems) and CITYgreen software to create and analyze a landcover map.

The Air Pollution Removal program is based on research conducted by David Nowak, PhD, of the U.S. Forest Service. Dr. Nowak developed a methodology to assess the air pollution removal capacity of urban forests with respect to pollutants such as Nitrogen Dioxide (NO₂), Sulfur Dioxide (SO₂), Ozone (O₃), Carbon Monoxide (CO), and particulate matter less than 10 microns (PM10). Pollution removal is reported in pounds and U.S. dollars, on an annual basis. Removal rates were estimated for 55 cities.

For more information see: airpollution.pdf