News of science:It’s a win-win situation: Take sulfur out of jet fuel and you can improve air quality and cool climate at the same time.
That’s good news, considering that air transportation is the fastest-growing fossil-fuel-based sector of the global economy: heat-trapping greenhouse gas emissions from jet planes are projected to double over year 2005 values as soon as 2025.
Until now, the push to remove sulfur from jet fuel has been motivated by a need to improve air quality around airports. Sulfur-rich exhaust particles get lodged in the lungs and can cause respiratory and cardiovascular illnesses. Since 2006, when the U.S. introduced an ultralow sulfur standard for emissions from diesel trucks on the nation’s highways, the Federal Aviation Administration has been interested in setting similar sulfur-reduction standards for jets.
So, if doing the right thing is so easy, why isn’t it already being done? One reason has been the fear that improving air quality might actually worsen global warming. Here’s why:
Burning sulfur-laden jet (or diesel) fuel produces sulfate. Sulfate particles down near the ground get lodged in your lungs; high in the atmosphere during the day, they act like tiny mirrors that scatter solar radiation back into space. Sulfate spewed from volcanoes, for instance, is well known to cool the atmosphere. So, removing sulfur from jet fuel might actually cause more warming—or so it seemed.
BLOG: Sulfur Smoke Slowed Global Warming Slightly
To see what really happens when sulfur is removed from the fuel, Nadine Unger of the Yale School of Forestry & Environmental Studies took advantage of newly available earth system computer models that allow scientists to simulate interactions among various chemicals and gases in the atmosphere in a more realistic way than ever before.
What she found is that more warming indeed occurs when you remove sulfur, but that warming is more than offset by a different cooling effect: nitrates, which form from nitrogen oxides in the jet exhaust, also reflect solar radiation back to space. Because of some complex interactions among these compounds, and their competition for ammonia, more nitrate forms when there is less sulfate around.
Looking at the red and orange blobs in Unger’s figure above, you can see that nitrate levels are notably higher in the desulfurized fuel scenario (below) than in the standard fuel scenario (above). The end result of Unger’s simulations is that desulfurization of jet fuel produced a small, net cooling effect.
Unger used a global-scale model that assessed the impact of reducing the amount of sulfur in jet fuel from 600 milligrams per kilogram of fuel to 15 milligrams per kilogram, which is the level targeted by the U.S. Department of Transportation. She simulated the full impact of sulfur removal on all aviation emissions, including ozone, methane, carbon dioxide, sulfate and contrails—those ribbons of clouds that appear in the wake of a jet. Previous studies examined each chemical effect only in isolation.
"In this study we tried to put everything together so that we account for interactions between those different chemical effects," Unger said in a press release.
Unger points out that the aviation industry is currently responsible for about 3% of all CO2 emissions from the burning of fossil fuels. But when you tally up all non‐CO2 effects, aviation’s share anthropogenic climate forcing may be as high as 14%.
If taking out the sulfur can lower those figures while improving air quality, it seems like a no-brainer.
News source:news.discovery
That’s good news, considering that air transportation is the fastest-growing fossil-fuel-based sector of the global economy: heat-trapping greenhouse gas emissions from jet planes are projected to double over year 2005 values as soon as 2025.
Until now, the push to remove sulfur from jet fuel has been motivated by a need to improve air quality around airports. Sulfur-rich exhaust particles get lodged in the lungs and can cause respiratory and cardiovascular illnesses. Since 2006, when the U.S. introduced an ultralow sulfur standard for emissions from diesel trucks on the nation’s highways, the Federal Aviation Administration has been interested in setting similar sulfur-reduction standards for jets.
So, if doing the right thing is so easy, why isn’t it already being done? One reason has been the fear that improving air quality might actually worsen global warming. Here’s why:
Burning sulfur-laden jet (or diesel) fuel produces sulfate. Sulfate particles down near the ground get lodged in your lungs; high in the atmosphere during the day, they act like tiny mirrors that scatter solar radiation back into space. Sulfate spewed from volcanoes, for instance, is well known to cool the atmosphere. So, removing sulfur from jet fuel might actually cause more warming—or so it seemed.
BLOG: Sulfur Smoke Slowed Global Warming Slightly
To see what really happens when sulfur is removed from the fuel, Nadine Unger of the Yale School of Forestry & Environmental Studies took advantage of newly available earth system computer models that allow scientists to simulate interactions among various chemicals and gases in the atmosphere in a more realistic way than ever before.
What she found is that more warming indeed occurs when you remove sulfur, but that warming is more than offset by a different cooling effect: nitrates, which form from nitrogen oxides in the jet exhaust, also reflect solar radiation back to space. Because of some complex interactions among these compounds, and their competition for ammonia, more nitrate forms when there is less sulfate around.
Unger used a global-scale model that assessed the impact of reducing the amount of sulfur in jet fuel from 600 milligrams per kilogram of fuel to 15 milligrams per kilogram, which is the level targeted by the U.S. Department of Transportation. She simulated the full impact of sulfur removal on all aviation emissions, including ozone, methane, carbon dioxide, sulfate and contrails—those ribbons of clouds that appear in the wake of a jet. Previous studies examined each chemical effect only in isolation.
"In this study we tried to put everything together so that we account for interactions between those different chemical effects," Unger said in a press release.
Unger points out that the aviation industry is currently responsible for about 3% of all CO2 emissions from the burning of fossil fuels. But when you tally up all non‐CO2 effects, aviation’s share anthropogenic climate forcing may be as high as 14%.
If taking out the sulfur can lower those figures while improving air quality, it seems like a no-brainer.
News source:news.discovery
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