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Ozone Pollution

In 1988, researchers in the School of Geophysical Sciences (now Earth & Atmospheric Sciences) reported in Science that natural hydrocarbons from trees play a larger role than originally believed in creating the ozone pollution that plagues many U.S. cities.

Georgia Tech file photo A 1990 Georgia Tech study of ozone pollution showed that reducing the number of trees in urban areas may raise temperatures, promoting an increase in the production of natural hydrocarbons and worsening air quality. Here, a researchers checks an air chemistry monitor.

Because ozone pollution is created from chemical reactions involving hydrocarbons and nitrogen oxides in the presence of sunlight, the scientists suggested that control strategies aimed at reducing nitrogen oxide emissions should be implemented. At the time, the nation's ozone abatement strategies focused almost exclusively on limiting hydrocarbon emissions.

In the intervening years since the 1988 Georgia Tech study, there has been an increasing awareness of the importance of natural hydrocarbons and the need for nitrogen oxide emission controls. Today, control of nitrogen oxide emissions from automobiles and power plants has become a key component in the nation's efforts to reduce ozone pollution.

Many people criticized the natural hydrocarbon theory. Some said the Georgia Tech study claimed that trees were causing pollution. But it actually meant that human-induced emissions of nitrogen oxides, instead of hydrocarbons, cause the pollution. Others argued that if the theory were correct, urban areas could control ozone problems by cutting down trees.

But a follow-up study published in the Journal of Geophysical Research in 1990 found that reducing the number of trees in urban areas may raise temperatures, promoting an increase in the production of natural hydrocarbons and worsening the pollution.

Trees and other plants actually moderate air temperature through the evaporation of water from their leaves, a natural air conditioning effect known as evapo-transpiration. Replacing trees with human-made materials that retain heat reduces evapo- transpiration, creating what is called an "urban heat island." Thus this follow-up study suggested that trees and green spaces may help alleviate urban pollution, instead of exacerbate it.

Dr. William Chameides and his colleagues R.W. Lindsay, J.L. Richardson, Chia S. Kiang and Carlos Cardelino conducted the research.

For more information, contact Dr. William Chameides, School of Earth and Atmospheric Sciences, Georgia Tech, Atlanta, GA 30332-0340. (Telephone: 404- 894-1749) (E-mail: william.chameides@eas.gatech.edu)

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Last updated: October 25, 1999