Greenland ice sheet carries evidence of increased atmospheric acidity

Dec 07, 2012
This ice core from Summit, Greenland, kept in the laboratory of Jihong Cole-Dai at South Dakota State University, provided data that Lei Geng used in his research. Credit: Jihong Cole-Dai

(Phys.org)—Research has shown a decrease in levels of the isotope nitrogen-15 in core samples from Greenland ice starting around the time of the Industrial Revolution. The decrease has been attributed to a corresponding increase in nitrates associated with the burning of fossil fuels.

However, new University of Washington research suggests that the decline in nitrogen-15 is more directly related to increased acidity in the atmosphere.

The increased acidity can be traced to sulfur dioxide, which in the atmosphere is transformed to sulfuric acid, said Lei Geng, a UW research associate in atmospheric sciences. Following the , increased steadily because of coal burning.

"It changes the chemical properties of the lower troposphere, where we live, and that can have a lot of consequences," Geng said. He presents his findings Friday (Dec. 7) at the fall meeting of the in San Francisco.

Greenland ice sheet carries evidence of increased atmospheric acidity
Ice core data show concentrations of nitrate (top line), hydrogen ions (middle line) and nitrogen-15 (bottom line) from 1772 through 2006. Credit: Lei Geng/University of Washington

The gradual buildup of acidity in the atmosphere over a century got a boost around 1950 with a sharp increase in nitrogen-oxygen compounds, referred to as NOx, mainly produced in high-temperature combustion such as occurs in coal-fired power plants and motor vehicle engines. NOx is easily converted to nitric acid in the atmosphere, further increasing the acidity.

NOx carries a chemical signature – the abundance of nitrogen-15, one of two nitrogen isotopes – which changes depending on the source. That means it is possible to distinguish NOx that came from a from NOx produced as a result of lightning, soil emissions, car exhaust and power plant emissions. The level of nitrogen-15 can be measured in that formed from NOx and were deposited in ice sheets such as those in Greenland.

Current evidence indicates NOx from coal-fired power plant and motor vehicle emissions likely carries more nitrogen-15 than NOx produced by natural sources, so nitrogen-15 levels in deposited nitrate could be expected to go up. However, those levels actually went down in the late 1800s, following the Industrial Revolution, Geng said. That's because increasing sulfuric acid levels in the atmosphere triggered chemical and physical processes that allowed less nitrogen-15 to remain in vaporized nitrate, which can be carried to remote places such as Greenland.

The growing acidity in the atmosphere was occurring decades before acid rain was recognized as a threat, particularly in industrial areas of North America.

from sheets reflect a correlation between -15 levels and atmospheric acidity, Geng said. Data he studied came primarily from a core that is part of combined research between UW and South Dakota State University, funded by the National Science Foundation.

Geng noted that the core reflects a decline in signals for both NOx and emissions in the 1930s, during the Great Depression. The signals increased again following the Depression until the early 1970s, when Western nations experienced an economic downturn and an oil shortage. Shortly after that, the Clean Air Act in the United States began to have an impact on vehicle and power plant emissions.

"We've seen a huge drop in sulfate concentrations since the late 1970s," Geng said. "By 2005, concentrations had dropped to levels similar to the late 1800s."

Ice core data show nitrate levels have stabilized during that time, he said, because while emission levels from individual vehicles might have decreased substantially, the number of vehicles has increased significantly.

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Royale
2.1 / 5 (13) Dec 07, 2012
Isn't a volcano a high-temperature combustion? Does that get wrapped in with exhaust levels?
tadchem
2.6 / 5 (9) Dec 07, 2012
Only 2 isotopes of nitrogen are tracked: N-14 and N-15. There are multiple possible sources of oxides of nitrogen mentioned: forest fires, lightning, soil emissions, car exhaust and power plant emissions.
Since NOx from all possible sources is blended in the atmosphere, and no single nitrogen atom of any mass carries a pedigree, it is mathematically impossible to quantify the amount coming from 5 sources with measurements of only 2 isotopes.
Urgelt
4.5 / 5 (8) Dec 07, 2012
"...it is mathematically impossible to quantify the amount coming from 5 sources with measurements of only 2 isotopes."

True as far as you went, tadchem.

But the larger point is, since the start of the industrial revolution, atmospheric acidity has gone up, and that can be tracked.

It's just one study, one datum, but it confirms many, many other analytical methods.

Industrialization, relying on coal and other hydrocarbons, is changing the troposphere. Rapidly. CO2 is rising by leaps and bounds. The Arctic is warming rapidly, threatening release of massive stores of carbon and reducing the Earth's albedo. Oceans are acidifying. Species are migrating away from the equator. Tropical diseases are migrating to temperate zones, too. A huge extinction event is well underway - one of the six largest since life began, some scientists observe. The evidence is there.
VendicarD
4.3 / 5 (8) Dec 08, 2012
No. Of course not.

"Isn't a volcano a high-temperature combustion?" - Royale

Do you think that volcano's burn rock?
Lurker2358
2.1 / 5 (10) Dec 08, 2012
Do you think that volcano's burn rock?


Not primarily, but some materials in magmas could well be above their flash point, which would actually cause combustion when they reach the surface and contact oxygen.
barakn
2.3 / 5 (3) Dec 08, 2012
The components of magma are typically well-oxidized, but that's beside the point. Both precursors of NOx, oxygen and nitrogen, are in the air itself. They simply require high temperature and/or high pressure, such is occur in a combustion engine or lightning plasma channel, to combine. I'm not certain magma is hot enough to create much, especially since there's not much exposed magma surface area on the planet at any given point and it tends to cool off rapidly.
maxberan
1.6 / 5 (7) Dec 08, 2012
I wonder why the title wasn't something along the lines of "Greenland ice sheet carries evidence that atmospheric acidity has peaked"?
Actually I don't wonder, I know why.
VendicarD
5 / 5 (6) Dec 08, 2012
I need not wonder either. It is because it hasn't peaked.

As CO2 levels continue to increase, so too will the acidity of precipitation and surface water.

JoeBlue
1 / 5 (11) Dec 08, 2012
I need not wonder either. It is because it hasn't peaked.

As CO2 levels continue to increase, so too will the acidity of precipitation and surface water.



You again? Look at the chart, do you understand what a down trend is? Nope, that's right you only understand scare tactics and pseudo-science.
VendicarD
4.5 / 5 (8) Dec 08, 2012
JoeBlueTard is not smart enough to realize that the downward slope shown in the graph is a downward slope in PH, and lower PH levels indicate higher levels of acidity.

PH = -log(J Concentration)

So the acidity hasn't peaked, it has traufed.

Sadly, Idiots like Joe Blue will never have enough brain power to realize that they are idiots.
ScooterG
1.1 / 5 (9) Dec 09, 2012
I wish more of that acid would fall on my little plot of alkaline soil.
VendicarD
4.2 / 5 (5) Dec 09, 2012
Sad how the grain belt of the U.S. is reverting to desert, isn't it ScooTard?

Some people might consider that Justice for the crimes against humanity committed by America.

ScooterG
1 / 5 (8) Dec 09, 2012
Sad how the grain belt of the U.S. is reverting to desert, isn't it ScooTard?

Some people might consider that Justice for the crimes against humanity committed by America.



It figures that you would blame the alkalinity of my soil on mankind, even though you don't even know where I live.

VendicarD
4.7 / 5 (3) Dec 09, 2012
Even sadder that you see fit to lie with every breath.

It is very Conservative of you.

"It figures that you would blame the alkalinity of my soil on mankind" - ScooTard
Royale
1 / 5 (3) Dec 10, 2012
Sad how the grain belt of the U.S. is reverting to desert, isn't it ScooTard?

Some people might consider that Justice for the crimes against humanity committed by America.



It figures that you would blame the alkalinity of my soil on mankind, even though you don't even know where I live.



LOL. And then you're down-voted twice. Any chance either of those are NOT from VendicarD and his/her sockpuppets.

To be fair though, Vendicar, you said "some people might consider" and I am one of those folks. I might consider it delayed retribution. I didn't notice you blaming it on mankind.. only the possibly that some might think "serves em' right, damn Americans".

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