Sulfur Aerosol Particles And Climate Change
May 15, 2013

Climate Models Underestimate Cooling Effect Of Sulfur Aerosol Particles In The Atmosphere

Brett Smith for - Your Universe Online

A new study on cloud formation shows that climate change models may have underestimated the cooling effect of sulfur aerosol particles in the atmosphere.

These aerosols mitigate greenhouse gases by reflecting sunlight. They also act as seeds for cloud condensation by allowing humidity to accumulate around them — forming droplets and then clouds.

To investigate the role of sulfur aerosols in cloud formation and climate change, Eliza Harris, with the Max Planck Institute for Chemistry at the time of the study, began by looking at atmospheric sulfur compounds and the behavior of sulfur isotopes.

“The relative reaction rates of isotopes are like fingerprints, which tell us how the sulfate was formed from the sulfur dioxide,” Harris said.

A unique feature of the study was how the researchers looked at cloud formation on top of a mountain. There, scientists said they could trace how the aerosol behaved while the cloud was forming.

Harris looked specifically at how sulfate in clouds forms through the oxidation of sulfur dioxide by oxygen. This reaction can be catalyzed by the atmospheric dust of so-called transition metal ions like iron or manganese.

“As my colleagues and I compared the basic assumptions of climate models with my results we were very surprised, because only one of twelve models considers the role of transition metal ions in the formation of sulfate,” Harris said.

According to the study, which appears in the journal Science, sulfates that were catalyzed by transition metal ions are formed on fairly large mineral dust particles. These particles are much bigger than those formed by a less prevalent reaction involving hydrogen peroxide. Because of their larger size, the particles fall from the air at a fast rate, making the time frame for climate cooling by sulfate particles shorter than previously thought.

The Max Planck research team said in a recent statement that they could not quantify how their study will impact past or future climate models. They did suggest that future models should consider the effect of transition metal ions in the role of the oxidation of sulfur dioxide.

Harris said that the study´s impact on climate models would differ by region. The effect on European models might be low, since mineral dust concentrations in the regional atmosphere are diminutive and sulfur dioxide emissions are on the decline.

“In India and China, however, where sulfur dioxide emissions are expected to rise in the near future, combined with significantly higher concentrations of mineral dust in the air, the effect could be stronger,” Harris said.

Climate change continues to be an issue around the world and a particularly divisive one in the political conversations of the United States. Speaking this week in Sweden, Secretary of State John Kerry praised the Scandinavian country and called climate change a “life and death” issue.

"It is not a challenge that can be solved by any one nation, and in our discussions with the Prime Minister he pointed out to me that, in fact, Sweden´s contribution to the problem of — to the problem of climate change is a tiny point percentage of the total problem,” Kerry said. “And yet Sweden´s contribution to the solution is much more significant than anything that might be expected because of the level of its own contribution to the problem. “

“So Sweden is way ahead of the curve,” he added.