Wednesday, September 2, 2009

THE SKY IS NOT FALLING: POLLUTION IN EASTERN CHINA CUTS LIGHT, USEFUL RAINFALL

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New research shows that air pollution in eastern China has reduced the amount of light rainfall over the past 50 years and decreased by 23 percent the number of days of light rain in the eastern half of the country. The results suggest that bad air quality might be affecting the country's ability to raise crops as well as contributing to health and environmental problems.

The study links for the first time high levels of pollutants in the air with conditions that prevent the light kind of rainfall critical for agriculture. Led by atmospheric scientist Yun Qian at the Department of Energy's Pacific Northwest National Laboratory, the study appears August 15 in the Journal of Geophysical Research-Atmospheres.

"People have long wondered if there was a connection, but this is the first time we've observed it from long-term data," said Qian. "Besides the health effects, acid rain and other problems that pollution creates, this work suggests that reducing air pollution might help ease the drought in north China."

China's dramatic economic growth and pollution problems provide researchers an opportunity to study the connection between air quality and climate. Rain in eastern China — where most of the country's people and pollution exist — is not like it used to be.
Over the last 50 years, the southern part of eastern China has seen increased amounts of total rainfall per year. The northern half has seen less rain and more droughts. But light rainfall that sustains crops has decreased everywhere. A group of climate researchers from the U.S., China and Sweden wanted to know why light rain patterns haven't followed the same precipitation patterns as total rainfall.

Previous work has shown that pollution can interfere with light rain above oceans, so the team suspected pollution might have something to do with the changes over land. Light rain ranges from drizzles to 10 millimeters of accumulation per day and sustains agriculture. (Compared to heavy rain that causes floods, loss of light rain has serious consequences for crops.)

While the light rains have diminished, pollution has increased dramatically in China in the last half of the 20th century. For example, while China's population rose two and a half times in size, the emissions of sulfur from fossil fuel burning outpaced that considerably — rising nine times.

Air pollution contains tiny, unseen particles of gas, water and bits of matter called aerosols. Aerosols — both natural and human-caused (anthropogenic) — do contribute to rainfall patterns, but the researchers needed to determine if pollution was to blame for China's loss of rain and how.

To find out, the team charted trends in rainfall from 1956 to 2005 in eastern China, which has 162 weather stations with complete data collected over the entire 50 years.

From this data, the team determined that both the north and south regions of eastern China had fewer days of light rain — those getting 10 millimeters per day or less — at the end of the 50 year timespan. The south lost more days — 8.1 days per decade — than the north did, at 6.9 days per decade. However, the drought-rattled north lost a greater percentage of its rainy days, about 25 percent compared to the south's 21 percent.

"No matter how we define light rain, we can see a very significant decrease of light rain over almost every station," said Qian.

To probe what caused the loss of rainfall, the team looked at how much water the atmosphere contained and where the water vapor traveled. Most parts of eastern China saw no significant change in the amount of water held by the atmosphere, even though light rains decreased. In addition, where the atmosphere transported water vapor didn't coincide with light rain frequency.

These results suggested that changes in large-scale movement of water could not account for the loss of the precipitation. Some of pollution's aerosols can seed clouds or form raindrops, depending on their size, composition and the conditions in which they find themselves. Because these skills likely contribute to rainfall patterns, the researchers explored the aerosols in more depth.

Cloud droplets form around aerosols, so the team determined the concentration of cloud droplets over China. They found higher concentrations of droplets when more aerosols were present. But more droplets mean that each cloud droplet is smaller, in the same way that filling 10 ice cream cones from a quart of ice cream results in smaller scoops than if the same amount were put in only five cones.

This result suggested that aerosols create smaller water droplets, which in turn have a harder time forming rainclouds. The team verified this with computer models of pristine, moderately polluted or heavily polluted skies. In the most heavily polluted simulation, rain fell at significantly lower frequencies than in the pristine conditions.

An examination of the cloud and rain drops showed that these water drops in polluted cases are up to 50 percent smaller than in clean skies. The smaller size impedes the formation of rain clouds and the falling of rain.

Qian said the next step in their research is to examine new data from the DOE's Atmospheric Radiation Measurement Climate Research Facility in the central eastern Chinese city of Shouxian. The data was collected from April to December of 2008.

"This work is important because modeling studies of individual cases of pollution's effect on convective clouds have shown varying results, depending on the environmental conditions," said coauthor Ruby Leung. "The ARM data collected at Shouxian should provide more detailed measurements of both aerosols and clouds to enable us to quantify the impacts of aerosols on precipitation under different atmospheric and pollution conditions."

Pacific Northwest National Laboratory

SUPER PLANETARY NEBULAE

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A team of scientists in Australia and the United States, led by Associate Professor Miroslav Filipović from the University of Western Sydney, have discovered a new class of object which they call “Super Planetary Nebulae.” They report their work in the journal Monthly Notices of the Royal Astronomical Society.

Planetary nebulae are shells of gas and dust expelled by stars near the end of their lives and are typically seen around stars comparable or smaller in size than the Sun.

The team surveyed the Magellanic Clouds, the two companion galaxies to the Milky Way, with radio telescopes of the Commonwealth Scientific and Industrial Research Organisation (CSIRO) Australia Telescope National Facility. They noticed that 15 radio objects in the Clouds match with well known planetary nebulae observed by optical telescopes.

The new class of objects are unusually strong radio sources. Whereas the existing population of planetary nebulae is found around small stars comparable in size to our Sun, the new population may be the long predicted class of similar shells around heavier stars.

Filipović’s team argues that the detections of these new objects may help to solve the so called “missing mass problem” – the absence of planetary nebulae around central stars that were originally 1 to 8 times the mass of the Sun. Up to now most known planetary nebulae have central stars and surrounding nebulae with respectively only about 0.6 and 0.3 times the mass of the Sun but none have been detected around more massive stars.

The new Super Planetary Nebulae are associated with larger original stars (progenitors), up to 8 times the mass of the Sun. And the nebular material around each star may have as much as 2.6 times the mass of the Sun.

“This came as a shock to us”, says Filipović, “as no one expected to detect these object at radio wavelengths and with the present generation of radio telescopes. We have been holding up our findings for some 3 years until we were 100% sure that they are indeed Planetary Nebulae”.

Some of the 15 newly discovered planetary nebulae in the Magellanic Clouds are 3 times more luminous then any of their Milky Way cousins. But to see them in greater detail astronomers will need the power of a coming radio telescope – the Square Kilometre Array to be sited in either Australia or South Africa.

(Photo: E. Crawford & S. Griffith)

HOW MERCURY BECOMES TOXIC IN THE ENVIRONMENT

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Naturally occurring organic matter in water and sediment appears to play a key role in helping microbes convert tiny particles of mercury in the environment into a form that is dangerous to most living creatures.

This finding is important, say Duke University environmental engineers, because it could change the way mercury in the environment is measured and therefore regulated. This particularly harmful form of the element, known as methylmercury, is a potent toxin for nerve cells. When ingested by organisms, it is not excreted and builds up in tissues or organs.

In a series of laboratory experiments, Amrika Deonarine, a graduate student in civil and environmental engineering at Duke’s Pratt School of Engineering, found that organic matter and chemical compounds containing sulfur – known as sulfides -- can readily bind to form mercury sulfide nanoparticles. Since they are more soluble than larger particles, these nanoparticles may be the precursors to a process known as methylation.

“When the organic material combines with the mercury, it prevents the particle from accumulating with other mercury particles and growing larger,” said Deonarine, who presented the results of her analysis at the summer annual scientific sessions of the American Chemical Society (ACS) in Washington, D.C.

“Since the mercury remains in a nanoparticle size, it can easily collect on the surface of microbes where any mercury that dissolves can be taken in by the microbes,” Deonarine said. “Without the organic matter, the mercury sulfide nanoparticles would grow too large and become insoluble, thus reducing the availability of mercury for microbial methylation.”

It is while inside the microbe that the mercury is converted into the harmful methylmercury form, the researchers said.

These reactions can only take place in cold water environments with little to no oxygen, such as the zone of sediment just below the bottom of a body of water. Other such anaerobic environments can also be found in waste water and sewage treatment systems, the researchers said.

“The exposure rate of mercury in the U.S. is quite high,” said Heileen Hsu-Kim, Duke assistant professor of civil and environmental engineering and senior member of the research team. “A recent epidemiological survey found that up 8 percent of women had mercury levels higher than national guidelines. Since humans are on top of the food chain, any mercury in our food accumulates in our body.”

Because fish and shellfish have a natural tendency to store methylmercury in their organs, they are the leading source of mercury ingestion for humans. Mercury is extremely toxic and can lead to kidney dysfunctions, neurological disorders and even death. In particular, fetuses exposed to methylmercury can suffer from these same disorders as well as impaired learning abilities.

There are many ways mercury gets into the environment, with the primary sources being the combustion of coal, the refining of such metals as gold and other non-ferrous metals, and in the gases released during volcanic eruptions. The air-borne mercury from these sources eventually lands on lakes or ponds and can remain in the water or sediments.

“These initial laboratory findings could have far-reaching implications,” Hsu-Kim said. “That these reactions can take places in anaerobic environments suggests that the old paradigm of testing for toxic metals in sediments may provide an incomplete picture of how much methylmercury is there.”

The researchers plan to continue their studies with other types of organic matter and for longer periods of time.

(Photo: Pratt School of Engineering)

Duke University

A HARD RAIN'S GONNA FALL

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Heavier rainstorms lie in our future. That's the clear conclusion of a new MIT and Caltech study on the impact that global climate change will have on precipitation patterns.

But the increase in extreme downpours is not uniformly spread around the world, the analysis shows. While the pattern is clear and consistent outside of the tropics, climate models give conflicting results within the tropics and more research will be needed to determine the likely outcomes in tropical regions.

Overall, previous studies have shown that average annual precipitation will increase in both the deep tropics and in temperate zones, but will decrease in the subtropics. However, it's important to know how the magnitude of extreme precipitation events will be affected, as these heavy downpours can lead to increased flooding and soil erosion.

It is the magnitude of these extreme events that was the subject of this new research, which appeared online in the Proceedings of the National Academy of Sciences during the week of Aug. 17. The report was written by Paul O'Gorman, assistant professor in the Department of Earth, Atmospheric and Planetary Sciences at MIT, and Tapio Schneider, professor of environmental science and engineering at Caltech.

Model simulations used in the study suggest that precipitation in extreme events will go up by about 5 to 6 percent for every one degree Celsius increase in temperature. Separate projections published earlier this year by MIT's Joint Program on the Science and Policy of Global Change indicate that without rapid and massive policy changes, there is a median probability of global surface warming of 5.2 degrees Celsius by 2100, with a 90 percent probability range of 3.5 to 7.4 degrees.

Specialists in the field called the new report by O'Gorman and Schneider a significant advance. Richard Allan, a senior research fellow at the Environmental Systems Science Centre at Reading University in Britain, says, "O'Gorman's analysis is an important step in understanding the physical basis for future increases in the most intense rainfall projected by climate models." He adds, however, that "more work is required in reconciling these simulations with observed changes in extreme rainfall events."

The basic underlying reason for the projected increase in precipitation is that warmer air can hold more water vapor. So as the climate heats up, "there will be more vapor in the atmosphere, which will lead to an increase in precipitation extremes," O'Gorman says.

However, contrary to what might be expected, precipitation extremes do not increase at the same rate as the moisture capacity of the atmosphere. The extremes do go up, but not by as much as the total water vapor, he says. That is because water condenses out as rising air cools, but the rate of cooling for the rising air is less in a warmer climate, and this moderates the increase in precipitation, he says.

The reason the climate models are less consistent about what will happen to precipitation extremes in the tropics, O'Gorman explains, is that typical weather systems there fall below the size limitations of the models. While high and low pressure areas in temperate zones may span 1,000 kilometers, typical storm circulations in the tropics are too small for models to account for directly. To address that problem, O'Gorman and others are trying to run much smaller-scale, higher-resolution models for tropical areas.

Massachusetts Institute of Technology

TAKING SPACE IN STRIDE

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Anyone who has watched videos of the Apollo astronauts moving across the surface of the moon has noticed the unusual loping gait they sometimes adopted and their slow, almost graceful, movements. Now a new analysis by MIT researchers shows why astronauts moved around this way in their heavy Apollo-era space suits - and provides a mathematical method for evaluating new spacesuit designs for the moon and Mars and their effects on the efficiency of locomotion.

The loping gait of the lunar explorers was similar to a child's skipping, except that instead of switching back and forth on each stride between having the left or right foot in front, the same foot stayed forward the whole time, explains Christopher Carr, a research scientist in the Department of Earth, Atmospheric and Planetary Sciences. Carr is the lead author of a paper on the research appearing Aug. 12 in the online journal Public Library of Science One.

That way of moving, Carr says, "means they don't have to move as much" within the stiff pressurized suits. "They do whatever seems most efficient."

Trying to get around while inside the pressurized suits was "like being inside a balloon," Carr says. "When you bend it, it wants to spring back." When running or loping, that tendency can actually improve efficiency, acting like a spring that stores energy on each stride and then adds a little push on the next. "It can actually be a benefit," he says.

The spring-like nature of the space suit limbs, derived from the pressure used to supply the astronaut with oxygen, reduces metabolic expenditures by supporting the weight of the space suit. In the lab, lower gravity levels are simulated by reducing the weight supported by a subject, such as by having the subject wear a harness. Space suits have a similar effect: imagine hiking with a heavy backpack that is suspended from helium balloons so that you don't have to carry the weight of the pack. Like wearing a harness in the lab, this would feel like an effective reduction in the pull of gravity. For astronauts, this would result in switching, at lower velocities than normal, from walking to running, which is a more efficient gait in lunar and Mars gravity conditions.

But that springiness can also make it very hard to bend, as illustrated by a video of an Apollo astronaut attempting to pick up a hammer he had dropped. As described in the paper, he "can be seen jumping into the air in an attempt to provide (during the following impact) enough force (through body weight and impact loads) to buckle the knee joint and reach a hammer on the lunar surface." It takes the astronaut several such leaping attempts before he is able to retrieve it.

Analyzing how people move while wearing the spacesuits might seem straightforward, but because the suits are so heavy, running inside the suits under Earth's gravity requires more energy than a human can sustain. The suits can only function effectively under reduced gravity such as the moon's, which is one-sixth as strong as Earth's. In fact, the only way to achieve actual reduced gravity conditions on Earth is during "parabolic" flight, which is expensive and allows only brief (roughly 20 second) periods of lunar or Martian gravity. To evaluate gait transitions under real-world conditions the authors examined transcripts and videos from the Apollo missions to the moon

The analysis done by Carr and his co-author, recent Department of Aeronautics and Astronautics graduate Jeremy McGee '09, provides a mathematical way of determining when astronauts may switch gaits, which affects the amount of energy required to traverse a given distance, and may be helpful in the planning of future lunar or Mars surface missions, Carr says. For example, because running is more efficient than walking on the Moon, it may be possible for astronauts to venture farther than expected from a landing craft and still know that they would be able to return safely.

There is probably not enough time left to develop radically new spacesuit designs for planned NASA lunar missions beginning late next decade, Carr suggests, but there might be time to do so for human Mars missions, which are not yet part of firm plans but likely to take place at least a decade later.

Massachusetts Institute of Technology

GRAVITATIONAL WAVE OBSERVATORY LISTENS FOR ECHOES OF UNIVERSES BIRTH

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An investigation by a major scientific group headed by a University of Florida professor has advanced understanding of the early evolution of the universe.

An analysis of data from the Laser Interferometer Gravitational-Wave Observatory Scientific Collaboration, or LIGO, and the Virgo Collaboration has set the most stringent limits yet on the amount of gravitational waves that could have come from the Big Bang in the gravitational wave frequency band where LIGO can observe. In doing so, scientists have put new constraints on the details of how the universe looked in its earliest moments.

“Gravitational waves are the only way to directly probe the universe at the moment of its birth; they’re absolutely unique in that regard,” said David Reitze, a UF professor of physics and the spokesperson for the LIGO Scientific Collaboration. “We simply can’t get this information from any other type of astronomy. This is what makes this result in particular, and gravitational-wave astronomy in general, so exciting.”

Much like it produced the cosmic microwave background, the Big Bang is believed to have created a flood of gravitational waves — ripples in the fabric of space and time — that carry information about the universe as it was immediately after the Big Bang. These waves would be observed as the “stochastic background,” analogous to a superposition of many waves of different sizes and directions on the surface of a pond. The amplitude of this background is directly related to the parameters that govern the behavior of the infant universe.

Earlier measurements of the cosmic microwave background have placed the most stringent upper limits of the stochastic gravitational wave background at very large distance scales and low frequencies. The new measurements by LIGO directly probe the gravitational wave background in the first minute of its existence, at time scales much shorter than accessible by the cosmic microwave background.

The research also constrains models of cosmic strings, objects that are proposed to have been left over from the beginning of the universe and subsequently stretched to enormous lengths by the universe’s expansion. These strings, some cosmologists say, can form loops that produce gravitational waves as they oscillate, decay and eventually disappear.

Gravitational waves carry with them information about their violent origins and about the nature of gravity that cannot be obtained by conventional astronomical tools. The existence of the waves was predicted by Albert Einstein in 1916 in his general theory of relativity. The LIGO and GEO instruments have been actively searching for the waves since 2002; the Virgo interferometer joined the search in 2007.

The UF LIGO research group built one of the most important and complex parts of the gravitational wave detector, the input optics, said David Tanner, a UF professor of physics. The input optics takes light from the laser, shapes the beam into an ideal form, and directs it to the interferometer at the heart of the gravitational wave detector. UF scientists are working to design and build a second version of the input optics for a major upgrade to LIGO scheduled to go on line in three to four years.

“UF also plays important role in analysis of LIGO data, including searches for sharp bursts of gravitational waves, and for the stochastic background of gravitational waves … the subject of the just published paper,” Tanner wrote in an e-mail.

The authors of the new paper report that the stochastic background of gravitational waves has not yet been discovered. But the nondiscovery of the background described in the Nature paper already offers its own brand of insight into the universe’s earliest history.

The analysis used data collected from the LIGO interferometers in Hanford, Wash., and Livingston, La. Each of the L-shaped interferometers uses a laser split into two beams that travel back and forth down long interferometer arms. The two beams are used to monitor the difference between the two interferometer arm lengths.

“Since we have not observed the stochastic background, some of these early-universe models that predict a relatively large stochastic background have been ruled out,” said Vuk Mandic, assistant professor at the University of Minnesota and the head of the group that performed the analysis. “We now know a bit more about parameters that describe the evolution of the universe when it was less than one minute old.”

University of Florida

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