Trees Improve Air Quality

Urban areas often experience higher levels of air pollution than areas outside of the city, due to a higher population density and resulting larger amounts of vehicles, equipment, industrial activities and overall human impact. Pollutants are given off as byproducts of these uses and as their concentration in the air increases, they can lead to severe respiratory health problems for some people living within these areas.

One major asset that Edmond has to alleviate against impaired air quality is a vast and healthy urban forest. The trees in our yards and throughout our community greatly improve the air we breathe in a few different ways. For example, trees release oxygen into the atmosphere. This occurs during the process of photosynthesis, in which a tree makes its own food. Carbon dioxide is taken into the tree during the process of photosynthesis, and when the reaction is complete, oxygen is given off as a byproduct. Trees in Edmond’s residential areas give off about 141,000 tons of oxygen per year. The amount of oxygen produced increases with the size and health of a tree, and larger, older trees that are in better condition produce the most oxygen.
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In addition to producing clean air for us to breathe, trees also remove pollutants from the air that could otherwise contribute to health problems for residents. Gaseous pollutants such as ozone, carbon monoxide, nitrogen dioxide, and sulfur dioxide are absorbed into a tree through tiny openings in leaves, "stomata", and then are broken down within the tree. The largest pollutant type consists of particulate matter that is less than 2.5 microns in size. According to the International Society of Arboriculture, “particulates are solid rather than gaseous, generated by combustion of fossil fuels, construction and demolition, industrial processes, soil tillage and erosion, and complex reactions between sunlight and gaseous pollutants. Particulates have been associated with respiratory (asthma) and cardiopulmonary (heart and lung) diseases, and cancer.” These particulates are not absorbed by trees the way that gaseous pollutants are, but they do collect on the surfaces of leaves and are removed from the atmosphere in that way.

Overall, trees growing in Edmond’s residential areas remove 1,630 tons of air pollution per year. See Table 1 for each pollutant removed by Edmond’s residential trees each year and the number of vehicles or single family homes with annual emissions equivalent to the amount of the pollutant removed from the air by trees. The air quality improvements from these trees result in savings of approximately $7.68 million. This quantity is based on the estimated local incidence of adverse health effects, such as costs associated with respiratory health issues linked to air quality.

Table 1. Air Quality Impacts Due to Trees in Edmond's Residential Areas

Pollutant Type
Pollutant Removal is Equivalent to Annual Emissions of...
Carbon Monoxide
47 Automobiles or 195 Single-Family Homes
Nitrogen Dioxide
4,040 Automobiles or 2,700 Single-Family Homes
Sulfur Dioxide
39,800 Automobiles or 667 Single-Family Homes
Particulate Matter (< 2.5 Microns)
2,349,000 Automobiles or 227,000 Single-Family Homes
As a community grows, the importance of taking action for clean air and healthy communities becomes increasingly important. Fortunately, trees are part of the answer for this dilemma, and improved air quality is but one of many, many reasons that trees create better quality of life in urban areas.

The air quality data within this article was generated by a study conducted in 2012 using an Urban and Community Forestry Cost-Share Assistance Grant provided through the Oklahoma Urban and Community Forestry Council and Oklahoma Forestry Services. This study utilized iTree, a software suite developed by the USDA Forest Service which provides urban forestry analysis and benefits assessment tools. Last season's information on the energy conservation benefits of Edmond's residential trees resulted from the same study.

Check out other topics from the Winter 2015 issue of Edmond Tree Mail