Pine Tree Pollution

forestNeil Donahue

Neil Donahue

Pine trees are one of the biggest contributors to air pollution.

They give off gases that react with airborne chemicals — many of which are produced by human activity — creating tiny, invisible particles that muddy the air.

And new research from a team led by Carnegie Mellon University's Neil Donahue shows that the biogenic particles formed from pine tree emissions are much more chemically interesting and dynamic than previously thought.

The study provides the first experimental evidence that such compounds are chemically transformed by free radicals, the same compounds that age our skin, after they are first formed in the atmosphere.

These findings, published in the Proceedings of the National Academy of Sciences, can help make climate and air quality prediction models more accurate, and enable regulatory agencies to make more effective decisions as they consider strategies for improving air quality.

"We have been able to show conclusively that biogenics are chemically transformed in the atmosphere. They're not just static. They keep going, they keep changing and they keep growing," said Donahue, professor of chemistry, chemical engineering, engineering and public policy, and director of CMU's Center for Atmospheric Particle Studies (CAPS).

"Quite a few atmospheric models, which are commonly used to inform research and policy, have been assuming that that doesn't happen. What we really need to have in the models is an accurate representation of what's really going on in the atmosphere, and that's what this lets us do."

The air that we breathe is chock-full of particles called aerosols. These tiny liquid or solid particles come from hundreds of sources including trees, volcanoes, cars, trucks and wood fires.

The small particles influence cloud formation and rainfall, and affect climate and human health. In the United States each year, 50,000 premature deaths from heart and lung disease are attributable to excess concentrations of aerosols, especially particles less than 2.5 micrometers in diameter.

"There's a very, very strong body of data that establishes that fine particles in the air we breathe have a significant bad effect on people. What is less well understood is how the size and chemical composition of those particles influences that effect," Donahue said.

What complicates matters is that the atmosphere is a highly oxidizing, highly reactive place, which means that aerosols are transformed very rapidly into particles that can have completely different chemical compositions.

Donahue and colleagues in CAPS were the first to describe the chemical processes involving free radicals that transform aerosols emitted by man-made sources like diesel exhaust.

Researchers in CAPS are focused on understanding more about atmospheric particles to get a better handle on how they affect our health and impact our climate.

CMU has a longstanding commitment to the environment and a sustainable energy future, with 10 Silver or Gold LEED certified (green) buildings, including the nation's first green dormitory on its Pittsburgh campus.

Most recently, CMU announced it will purchase green power to offset 100 percent of the university's electric consumption for 2012.

"We practice what we preach. Carnegie Mellon is committed to sustainability in education, research and our own practices," said CMU president Jared L. Cohon.

Related Links: Read More | Mellon College of Science | Environment at CMU

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