

Trees give us more breathing room

During the lazy, hazy days of summer, appreciate how trees clean the air. One way they do it is by scrubbing pollution from the air with their leaves.

"Think about how your clothes pick up lint, especially rough-textured clothing. That's essentially how trees pick up pollutants on their leaf surfaces," says John Dwyer, research associate at The Morton Arboretum.

Trees in the city of Chicago remove an estimated 888 tons of air pollution each year, according to the 2009 Chicago Urban Forest study. Trees are very good at capturing a type of pollution called particulate matter. This comes from car and truck emissions, power plants, road dust, and farming. It also forms in the atmosphere when other pollutants react.

The smallest particulate matter is called PM10 (smaller than 10 micrometers, which is one-seventh the width of a human hair). According to the Environmental Protection Agency, PM10 infiltrates deep into the lungs, triggers asthma attacks and damages lung tissue. Chicago's trees remove about 300 tons of PM10 per year, which is equal to the annual PM10 emissions from 809,000 automobiles.

Some trees are better than others at catching PM10. "The ones that do the best job are large, healthy trees with many small, rough leaves with jagged margins," says Dwyer. "Because evergreens work for us all year, they are usually at the top of the list."

Consider planting spruce, fir, cedar, pine, buckeye, hackberry and zelkova. If you already have a large shade tree, nurture it to help it live a long life. Large, healthy trees remove up to 70 times more pollution than small ones.

The 2010 Tree Census is gathering data to determine air pollution-removal capacity and other environmental benefits of the urban forest in the seven-county Chicago metropolitan region.

For free information on the Tree Census or general tree/shrub questions, call the Plant Clinic, 630-719-2424. Laurie Casey is a staff writer at The Morton Arboretum in Lisle (

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