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Veerabhadran Ramanathan was collecting air samples in Southeast Asia when he heard about an important upcoming event: the Beijing Olympics.

Although he cared little about Michael Phelps or the U.S. women’s gymnastics team, Ramanathan was psyched. That’s because the climatologist at the Scripps Institution of Oceanography found out the Chinese government planned to close polluting factories in Beijing and ban more than 1 million cars from the city’s streets before and during the Olympics to help athletes breathe better.

“I thought this was a fantastic opportunity,” Ramanathan said. “Scientists are always waiting for chances to do experiments. If the government was suddenly decreasing pollution, that would be a huge manmade experiment, and I wanted to get scientific knowledge from it.”

The government’s cutback on a specific type of pollution — the burning of fossil fuels –gave Ramanathan and his team the rare opportunity to isolate the impact of diesel pollution on the air. Because fossil fuel pollution was reduced during the Olympics, the team could compare and contrast air pollution from cars, wood burning and coal burning in a way that wouldn’t be available under normal circumstances.

This “manmade experiment” allowed Ramanthan to conduct research that produced surprising results. He found that so-called “black carbon” emissions created by burning fossil fuels contribute more to global warming than black carbon emissions made from burning wood. Their results were published recently in the journal Nature Geoscience.

“We really didn’t expect to see this, so I was pleasantly surprised,” Ramanathan said.

Although Ramanathan’s team hasn’t finished a detailed analysis of their results yet, he thinks the reason for this differing impact on global warming is that fossil fuel emissions trap more of the sun’s heat than wood-burning emissions. If this proves to be correct, the team’s study will show that fossil fuels contribute more to global warming, which means measures to control fossil fuel pollution could be more effective than controlling burning wood.

The team also found that another ingredient produced during the burning of fossil fuels can help mitigate the effect of these emissions on global warming. Pieces of a salt called sulfate (which are also responsible for acid rain) reflect the sun’s heat instead of absorbing it. This means that cutting back on sulfate pollution without also reducing black carbon could make global warming worse.

“We found that when we initiate air pollution laws, when you cut down on sulfur emissions, you have to make sure you cut down on black carbon by same amount, if not more,” Ramanathan said. “Both contribute to air pollution and human death, but black carbon also contributes to global warming.”

But there is hope. The team found that efforts to cut back on air pollution during the Olympics reduced the amount of black carbon pollution produced.

“Using the knowledge we got, we need to ask if the Chinese example can be used to clean up the rest of the planet,” Ramanathan said.

(Full disclosure: My boyfriend is a graduate student at the Scripps Institution of Oceanography, but does not work in this area and does not know Dr. Ramanathan.)

— CLAIRE TRAGESER

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