Brighter model for global warming

To environmental chemist Scot Martin, chemistry is a way of understanding the Earth and some of its most pressing problems.
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.