Air pollution in our cities, and even our suburbs, is a serious concern as we enter the twenty first century. The burning of fossil fuels has introduced a steady flow of deadly pollutants into our atmosphere, yet very few urban areas can meet national clean air standards. Luckily, we are surrounded by efficient air cleaning machines—trees. Trees sequester many pollutants from the atmosphere, including nitrogen dioxide (NO2), sulfur dioxide (SO2), ozone (O3), carbon monoxide (CO), and particulate matter of ten microns or less (PM10).

Dave Nowak, Ph.D., of the USDA Forest Service conducted research in 50 US cities and developed a methodology to assess the air pollution removal capacity of urban forests with respect to the above pollutants. American Forests uses this research to determine the work trees do to clean the air with CITYgreen software—a desktop GIS program that calculates the value of trees to urban environments. The program estimates the amount of pollution being deposited within a given study site based on pollution data from the nearest city then estimates the removal rate based on the area of tree and/or forest canopy coverage on the site.

Air Quality benefits are reported both in lbs removed per year, as well as annual dollar savings. Dollar values for pollutants are based on the median value of the externality costs set by the Public Service Commission in each state.

Trees and Air Quality around the Country

Additional Information can be found at:
CITYgreen Manual Air Pollution Removal Section