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Sally Ng

Assistant Professor Sally Ng led a study of how certain emissions from cars and power plants interact with natural emissions from trees to form particulates. (Photo: Nick Burchell)

ARBOREAL PARTNERS IN POLLUTION

By Brett Israel

A new study has found that certain emissions from cars and coal-fired power plants promote processes that transform naturally occurring emissions from trees into organic aerosols. Organic aerosols make up a substantial fraction of ambient particulate matter that can affect climate, air quality, and human health.

Combining laboratory studies and ambient measurements from multiple sites in and around Atlanta, Georgia, and rural Alabama, scientists found that sulfur dioxide and nitrogen oxides directly and substantially mediate the formation of aerosols from the volatile organic compounds produced by trees.

“This finding is good news for pollution control. If we are able to further reduce sulfur dioxide and nitrogen oxide emissions, we will not only decrease sulfate aerosols but also organic aerosols, thus lowering the total aerosol burden in the southeast United States,” said Nga Lee (Sally) Ng, an assistant professor in Georgia Tech’s School of Chemical & Biomolecular Engineering and School of Earth and Atmospheric Sciences.

Scientists have known that human-made pollutants can interact with vegetation-emitted organic compounds, turning them into airborne particles. Those particles may affect air quality, human health, and climate. However, to what extent and how exactly human-made pollutants affect aerosol formation from vegetation in the ambient environments are poorly understood.

Anthropogenic sulfate, produced mainly by coal-fired power plants, and nitrogen oxides, produced mainly by vehicle emissions, control between 43 and 70 percent of the total measured organic aerosol load in the southeastern United States during summer months, the study found.

Published in the journal Proceedings of the National Academy of Sciences, the study was sponsored by the National Science Foundation, the Environmental Protection Agency, and the National Oceanic and Atmospheric Administration.

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