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Urban Forests for Clean Air
Researching the Relationship Between Trees and Local Air Quality
As far back as elementary school, we were taught that trees absorb carbon dioxide, turning it into wood and releasing oxygen. For most of us, this is the end of the story. If you believe more trees will help air quality, like the Sacramento Tree Foundation does, there is a bit more to understand.
Most trees emit some level of hydrocarbon gasses and these emissions cause air scientists to wonder about the actual air quality benefit of trees. The important question is: Given the many pluses and the one minus, are trees a net benefit to air quality?
In the fall of 2005, the Sacramento Tree Foundation teamed up with the United States Department of Agriculture Forest Service, the Sacramento Area Council of Governments, and the 5 Sacramento region Air Districts to study the effect of trees on air quality. We received a grant of $725,000 and started work in the spring of 2006. The joint project, known as the Urban Forests for Clean Air (UFFCA) demonstration project, is divided into three phases and will take over two years to complete.
The objective is to research and model the net benefit of trees to air quality. The plan is to understand how trees affect the air; decide when trees make the biggest improvement to our air quality; and where to best invest in our urban forest to improve the air.
The first phase of the UFFCA demonstration project is to develop initial estimates of the existing tree canopy on air quality using accepted science and simplified, mathematical models of air chemistry. This includes establishing the effects from the type and number of trees that make up our current urban forest.
The second phase is to build new urban forest computer models for enhanced tree populations and canopies and predict the resulting changes in the ways chemicals in the air react with each other and sunlight to make pollution.
The third phase of the project is to report the results so that policymakers and the public can make better-informed tree choices.
Early Results
The early results have shown great news. In completing the first phase of the study, we have found that we can establish a baseline for regional air quality including our tree canopy. We are now in the second phase of the study and so far the progress is encouraging and the numbers appear impressive. A smart and extensive tree planting campaign should remove seven tons of hydrocarbons, three tons of ozone, and almost one ton of nitrous oxides. The target number is a challenging doubling of the regional tree canopy. By 2025, the Sacramento region will need to plant 5 million new trees and replace 2.9 million existing trees that will die during that time frame.
Part of the Solution
The Sacramento area has a serious and stubborn ozone pollution problem. Over the years, a great many things have been done to reduce this problem, yet our region hasn't reached national and state air quality goals. Finding more ways to improve the air we breathe is proving difficult. The early results of our study show that trees, like most of us learned in grade school, will be a critical part of Sacramento's air quality solution.