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Trees and Air Quality

A Great Combination

May 4, 2010

We all know that trees make oxygen and clean the air. Now trees are being recognized as an innovative solution for dealing with air pollution in our region.

Thanks to a partnership called “Urban Forests for Clean Air” with the Sacramento Metropolitan Air Quality Management District (SMAQMD), four other local air quality districts, and the Sacramento Tree Foundation, trees are included in the Air Quality District's plan to reduce ground level ozone, which is an air pollutant. Once approved, the plan will become an update to the California State Implementation Plan for Air Quality.

Analysis of the current tree population and species data shows that a small, gradual change in the regional tree species mix can help reduce ground level ozone, which is a public health concern. Ozone at high levels in the atmosphere protects the earth, but at ground level it is an irritant that increases susceptibility to respiratory infections and diseases.

Different tree species emit different levels of biogenic gases, which help create ground level ozone. Even a small shift in tree species population can help improve the air.

As with all successful tree programs, this solution is based on the philosophy of “the right tree in the right place.” When choosing to plant a new tree, site considerations such as microclimate, soil type, and water usage need to be considered. This program adds a new layer to the selection criteria, air quality. In order to help the Sacramento region improve air quality, the largest appropriate tree species possible for the given site with the best possible air quality rating should be selected.

Currently the air quality rating is based solely on biogenic emissions of the tree species; however there are other important air quality benefits from trees. Trees capture air pollutants such as nitrogen oxides, ground level ozone, and particulate matter. Some of these benefits are currently being studied by cooperating agencies and some still require further research.

Click here  to download the Greeprint Recommended Tree List.

A long term goal of SMAQMD and the Tree Foundation is for this voluntary control measure to drive the research required to accurately quantify the complete net effect of trees on air quality. At some future date, new research findings may be the basis for a revised control measure reflecting all the benefits of trees on air quality.

The Tree Foundation thanks all of our partners on this ground-breaking project:

Air Quality Districts

Sacramento Metropolitan Air Quality Management District

El Dorado County Air Quality Management District

Feather River Air Quality Management District

Placer County Air Pollution Control District

Yolo-Solano Air Quality Management District

Research Partners

Altostratus Inc.

USDA Forest Service – Center for Urban Forest Research

University of California, Davis – Dept. of Land, Air and Water Resources