Brighter Model For Global Warming: Some Pollutants Actually Slow Warming

From global warming to heavy metal pollution in groundwater, Martin, named Gordon McKay Professor of Environmental Chemistry last July, is using the tools of chemistry to shed light on how natural processes interact with human activities to affect the environment.

Martin has already made surprising findings on the effect of the particles responsible for acid rain on the amount of solar energy reaching the Earth's surface. If his research is correct, ammonium sulfate particles in the atmosphere act as tiny mirrors, reflecting sunlight back into space. This factor, unaccounted for in most models of global warming, can cut the amount of solar energy reaching the earth's surface by as much as 25 percent, Martin said.

This finding has important implications as nations seek ways to curb human-caused global warming. Martin has forwarded his findings on to the Intergovernmental Panel on Climate Change, the multinational body created in 1988 by the World Meteorological Organization and United Nations Environment Programme to study the problem.

"Greenhouse gases are important and fairly well understood. They lead to warming, but there's also cooling," Martin said.

The creation of ammonium sulfate in the atmosphere is a complex process, beginning with the release of sulfur in pollution such as that from coal-burning power plants. Ammonia is released in agricultural activities through the use of fertilizers and in animal waste.

Together in the atmosphere, the two form ammonium sulfate, which in dry air forms small crystals but in humid air can dissolve into water droplets, greatly increasing the particle's surface area and its reflectivity.

Martin said one of the exciting aspects of being at Harvard is the potential for interactions with other faculty. In this case, Martin collaborated with Daniel Jacob, Vasco McCoy Family Professor of Atmospheric Chemistry and Environmental Engineering in the Division of Engineering and Applied Sciences. They plugged Martin's results into Jacob's atmospheric models to see their potential effects. The findings raised new questions that Martin was able to take back to the lab to explore.

Martin has several other research projects under way as well, investigating topics as diverse as the effects of iron and manganese oxides on the fate and transport of heavy metal pollutants such as arsenic and chromium in groundwater to a collaborative effort with Cynthia Friend, Theodore William Richards Professor of Chemistry and Professor of Materials Science and associate dean of the Faculty of Arts and Sciences, and Heinrich Holland, Harry C. Dudley Research Professor of Economic Geology, to probe the chemical origins of life in the universe.

In his heavy metal work, Martin is examining how the elements iron and manganese, naturally present in the soil, affect the movement of heavy metal pollutants such as arsenic, cobalt, and chromium.

Under certain conditions, Martin said, iron and manganese oxides bind the metals and take a solid form. While the heavy metals are in that form, bound up with iron, they stay put.

But changing conditions, such as the change of seasons, causes the iron to change form, dissolving the oxide and releasing the pollutants back into the groundwater, into lake water, and into sediments.

Martin's newest work focuses on how the presence of cobalt changes the way the manganese compounds grow on surfaces such as soil particles as they solidify.

Martin came to Harvard from the University of North Carolina, Chapel Hill, in 2000 as an associate professor of environmental chemistry in the Division of Engineering and Applied Sciences. He had been an assistant professor of aquatic and atmospheric chemistry at North Carolina and before that had been a postdoctoral fellow in atmospheric chemistry at the Massachusetts Institute of Technology.

"When Scot Martin joined the Division more than five years ago, we had high expectations of his serving as a bridge between Environmental Science and Environmental Engineering," said Division of Engineering and Applied Sciences Dean Venkatesh Narayanamurti. "His research involves both atmospheric and aquatic chemistry and has brought fresh insight into an important area. Educationally, he has been a key player in teaching a broad-based environmental engineering sciences course. I am delighted that he recently got tenure. He is a stellar addition to the faculty."

Martin, who grew up in Indianapolis, said he developed a love of chemistry in high school, thanks to an enthusiastic chemistry teacher.

"I think I got on that train then and never got off," Martin said.

He received a bachelor's degree in chemistry at Georgetown University in 1991 and a doctorate in physical chemistry from the California Institute of Technology in 1995.

Martin said his high school chemistry experience made him understand the influence that a teacher - or a college professor - can have on his or her students. He said that at a place like Harvard, it's likely that future leaders, even a future president, is sitting in his class. One class he teaches, ES6, provides a broad introduction to environmental sciences and is taken by a diverse group of students, from freshmen to seniors concentrating in everything from the humanities to science. He realizes that, for some, this class may be the only one on the subject they'll take. For others, however, it may steer them toward a particular branch of science over another.

"This is my opportunity to get it right," Martin said. "With everything else I do, this may be the thing that has the most impact, depending on who's sitting in the class."