BALTIMORE, Maryland, February 6, 2009 (ENS) – Increasing greenhouse gases could stall the recovery of stratospheric ozone in some regions of the Earth, according to new research by a team from Johns Hopkins University. The scientists warn that increased rates of skin cancer in those regions might result.

Darryn Waugh, a professor in the Department of Earth and Planetary Sciences at Johns Hopkins University, and his colleagues reported Thursday that climate change could provoke variations in the circulation of air in the lower stratosphere in tropical and southern mid-latitudes, including Australia and South America.

The circulation changes would cause ozone levels in these areas never to return to levels that were present before decline began, even after ozone-depleting substances have been wiped out from the atmosphere.

In tropical and southern mid-latitudes, Waugh says, “Global warming causes changes in the speed that the air is transported into and through the lower stratosphere. You’re moving the air through it quicker, so less ozone gets formed.”

Researchers at NASA Goddard Space Flight Center in Greenbelt, Maryland collaborated with Waugh in the study. The team forecast effects on ozone recovery by means of simulations using a computer model known as the Goddard Earth Observing System Chemistry – Climate Model.

On September 12, 2008, the Antarctic ozone hole reached its maximum size for the year. Though larger than it was in 2007, the 2008 ozone hole was still smaller than the record set in 2006. (Image courtesy NASA)

Waugh says this research will help scientists attribute ozone variations to the right agent.

“Ozone is going to change in response to both ozone-depleting substances and greenhouse gases,” he says, “If you don’t consider climate change when studying the ozone recovery data, you may get pretty confused.”

The research is published in the current issue of “Geophysical Research Letters,” a publication of the American Geophysical Union.

Dan Lubin, an atmospheric scientist who has studied the relationship between ozone depletion and variations in the ultraviolet radiation that reaches the Earth, says Waugh’s findings could cause health problems for people living in the tropics and southern mid-latitudes if ozone levels never return to pre-1960 levels in those regions.

“The risk of skin cancer for fair-skinned populations living in countries like Australia and New Zealand, and probably in Chile and Argentina too, will be greater in the 21st century than it was during the 20th century,” says Lubin, who is at Scripps Institution of Oceanography in La Jolla, California and did not participate in the research.

Ozone is a gas which is naturally present in the atmosphere and absorbs harmful ultraviolet radiation from the Sun. In the stratosphere, ozone blocks ultraviolet light that can cause skin cancers, cataracts, and other damage to animals and plants if it reached the surface.

This protective ozone layer has been in decline in the stratosphere since the 1970s due to an increase in atmospheric concentrations of human-made substances such as chlorofluorocarbon and bromofluorocarbon compounds such as refrigerants, solvents, and foam blowing agents.

Since the late 1980s, most countries have adhered to the Montreal Protocol, an international treaty to phase out production of such ozone-depleting substances.

The ozone layer has not grown thinner since 1998 over most of the world, and it appears to be recovering because of reduced emissions of ozone-depleting substances. Antarctic ozone is projected to return to pre-1980 levels by 2060 to 2075.

Not all regions face worse prospects for ozone recovery as a result of climate change, the Johns Hopkins scientists found.

In polar regions and northern mid-latitudes, restoration of ozone in the lower stratosphere will suffer little impact from increasing greenhouse gases, their projections indicate.

In the upper stratosphere, climate change causes a drop in temperatures that slows down some of the chemical reactions that destroy ozone. So, the Johns Hopkins team concludes, recovery might be reached in those parts of the atmosphere earlier than forecast, even decades before the removal of ozone-depleting substances.

While scientists have long suspected that climate change might be altering the dynamics of stratospheric ozone recovery, Waugh’s team is the first to estimate the effects of increasing greenhouse gases on the recovery of ozone by region.

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FORT LAUDERDALE, Florida, May 27, 2008 (ENS) – Using data from instruments in a constellation of NASA and French satellites, scientists are learning more about the link between clouds, pollution and rainfall.

Four NASA satellites – Aqua, Aura, CloudSat and CALIPSO and the French Space Agency’s PARASOL – make up the string of satellites in the Afternoon Constellation, more commonly called the A-Train.

They orbit only eight minutes apart and can be thought of as an extended satellite observatory, providing unprecedented information about clouds, aerosols and atmospheric composition.

“The A-Train is providing a new way to examine cloud types,” said Mark Schoeberl, A-Train project scientist at NASA’s Goddard Space Flight Center, Greenbelt, Maryland.

Details of the scientists’ findings were presented today at the American Geophysical Union’s 2008 Joint Assembly in Fort Lauderdale, Florida.

Jonathan Jiang of NASA’s Jet Propulsion Laboratory, Pasadena, California, and colleagues used these A-Train sensors to find that South American clouds infused with airborne pollution tend to produce less rain than their clean counterparts during the region’s dry season.

“Typically, it is very hard to get a sense of how important the effect of pollution on clouds is,” said Anne Douglass, deputy project scientist at Goddard for NASA’s Aura satellite. “With the A-Train, we can see the clouds every day and we’re getting confirmation on a global scale that we have an issue here.”

Jiang’s team used the Microwave Limb Sounder on the A-Train’s Aura satellite to measure the level of carbon monoxide in clouds. The presence of carbon monoxide implies the presence of smoke and other aerosols, which usually come from the same emission source, such a power plant or agricultural fire.

An artist’s rendition of six satellites moving
together (Image courtesy NASA)

With the ability to distinguish between polluted and clean clouds, the team next used Aqua’s Moderate Resolution Imaging Spectroradiometer to study how ice particle sizes change when aerosol pollution is present in the clouds.

The team also used NASA’s Tropical Rainfall Measuring Mission satellite to measure the amount of precipitation falling from the polluted and clean clouds.

All three measurements together show the relationship between pollution, clouds and precipitation.

The team found that polluted clouds suppressed rainfall during the June-to-October dry season in South America, which is also a period of increased agricultural burning. During that period it was more difficult for the smaller ice particles in aerosol polluted clouds to grow large enough to fall as rain.

This trend turned up seasonal and regional differences. Aerosol pollution was found, on average, to be less of a factor during the wet monsoon seasons in South America and in South Asia.

Other physical effects, such as large-scale dynamics and rainy conditions that clear the air of aerosol particles, might also be at play, the researchers suggest.

“The complexity of interactions between aerosols and clouds pose difficult problems that no one satellite instrument can solve,” said Jiang. “But when you put parameters from multiple satellites all together, you will find much more information than from a single instrument alone.”

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GREENBELT, Maryland, March 17, 2008 (ENS) – Close to 15 percent of the air pollution over the western United States and Canada originates in East Asia, according to NASA researchers using the latest, most accurate satellite sensors.

Their study offers the first measurement-based estimate of the amount of pollution from East Asian forest fires, urban exhaust, and industrial production that makes its way to western North America in as short a time as one week.

“We used the latest satellite capabilities to distinguish industrial pollution and smoke from dust transported to the western regions of North America from East Asia. Looking at four years of data from 2002 to 2005 we estimated the amount of pollution arriving in North America to be equivalent to about 15 percent of local emissions of the U.S. and Canada,” said study co-author Hongbin Yu.

Air pollution blankets a large region of
central China so thickly that in places
it completely obscures the surface
from the satellite’s view. As
acquired by the MODIS instrument
on the Aqua and Terra satellites,
early 2003. (Image courtesy NASA)

“This is a significant percentage at a time when the U.S. is trying to decrease pollution emissions to boost overall air quality,” said Yu. “This means that any reduction in our emissions may be offset by the pollution aerosols coming from East Asia and other regions.”

Satellite data confirmed that almost 40 billion pounds of pollution aerosols were exported to the northwestern Pacific Ocean and nearly 10 billion pounds reached North America annually from East Asia over the four year study period.

Yu, an associate research scientist of the University of Maryland working at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, grew up in China and taught there as a university professor, where he witnessed and studied how pollution from nearby power plants in China affected the local environment.

The world’s most populated country, China has experienced rapid industrial growth, massive human migrations to urban areas, and considerable expansion in automobile use over the last two decades.

In 20 years, the country has doubled its emissions of man-made pollutants to become the world’s largest emitter of pollution aerosols, tiny particles that are transported across the Pacific Ocean by rapid airstreams from East Asia.

Coal-fired power plant in the East China
province of Jiangsu (Photo by
China Resources Power Holdings Co)

Yu points out that the matter of pollution transport is global.

“Our study focused on East Asian pollution transport, but pollution also flows from Europe, North America, the broader Asian region and elsewhere, across bodies of water and land, to neighboring areas and beyond,” he said. “So we should not simply blame East Asia for this amount of pollution flowing into North America.”

In fact, in a model study published last November in the “Journal of Atmospheric Chemistry and Physics,” Mian Chin, also a co-author of this study and an atmospheric scientist at NASA Goddard, suggests that European pollution also makes a significant contribution to the pollution inflow to North America.

The Moderate Resolution Imaging Sprectroradiometer, MODIS, instrument can distinguish between broad categories of particles in the air, and observes Earth’s entire surface every one to two days. This enables it to monitor movement of the East Asian pollution aerosols as they rise into the lower troposphere, the area of the atmosphere where we live and breathe, and make their way across the Pacific and up into the middle and upper regions of the troposphere.

“Satellite instruments give us the ability to capture more accurate measurements, on a nearly daily basis across a broader geographic region and across a longer time frame so that the overall result is a better estimate than any other measurement method we’ve had in the past,” said study co-author Lorraine Remer, a physical scientist and member of the MODIS science team at NASA Goddard.

Map showing movement of pollution from East Asia to North America (Map courtesy NASA)

The research team found that pollution movements fluctuate during the year, with the East Asian airstream carrying its largest load in spring and smallest in summer.

The most extensive East Asian export of pollution across the Pacific took place in 2003, sent aloft by record-breaking wildfires across vast forests of East Asia and Russia.

The pollution aerosols travel quickly, crossing the ocean and entering the atmosphere above North America in as little as one week.

“Using this imaging instrument, we cannot determine at what level of elevation in the atmosphere pollution travels. So, we do not have a way in this study to assess the degree of impact the pollution aerosols from China have on air quality here once they cross over to North America. We need improved technology to make that determination,” said Remer.

“Nevertheless, we realize there is indeed impact,” said Remer. “Particles like these have been linked to regional weather and climate effects through interactions between pollution aerosols and the Sun’s heat energy. Since pollution transport is such a broad global issue, it is important moving forward to extend this kind of study to other regions, to see how much pollution is migrating from its source regions to others, when, and how fast.”

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GREENBELT, Maryland, February 2, 2008 (ENS) – Summertime storms in the southeastern United States drop more rainfall midweek than on weekends, and NASA scientists say air pollution from human activities, such as emissions from traffic, businesses and factories, is likely driving that trend.

The link between rainfall and the day of the week is evident in data from NASA’s Tropical Rainfall Measuring Mission satellite, known as TRMM.

“It appears that we’re making storms more violent,” said Thomas Bell, an atmospheric scientist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, lead author of the study published online this week in the American Geophysical Union’s “Journal of Geophysical Research.”

The data show that midweek storms tend to be stronger, drop more rain and span a larger area across the Southeast compared to calmer and drier weekends.

“It’s eerie to think that we’re affecting the weather,” said Bell.

Summer rainstorm in Atlanta,
Georgia (Photo credit unknown)

Rainfall measurements collected from ground-based gauges can vary from one gauge site to the next because of fickle weather patterns. So, to identify any kind of significant weekly rainfall trend, Bell and colleagues looked at the big picture from Earth’s orbit.

The team collected data from instruments on the TRMM satellite, which they used to estimate daily summertime rainfall averages from 1998 to 2005 across the entire Southeast. They found that, on average, it rained more between Tuesday and Thursday than from Saturday through Monday.

Newly analyzed satellite data show that summer 2007 echoed the midweek trend with peak rainfall occurring late on Thursdays. However, midweek increases in rainfall were more significant in the afternoon, when the conditions for summertime storms are in place. Based on satellite data, afternoon rainfall peaked on Tuesdays, with 1.8 times more rainfall than on Saturdays, which experienced the least amount of afternoon rain.

The team used ground-based data from gauges, along with vertical wind speed and cloud height measurements, to help confirm the weekly trend in rainfall observed from space.

To find out if pollution from humans indeed could be responsible for the midweek boost in rainfall, the team analyzed particulate matter, the concentrations of airborne particles associated with pollution, across the U.S. from 1998 to 2005.

The data, obtained from the U.S. Environmental Protection Agency, showed that pollution tended to peak midweek, mirroring the trend observed in the rainfall data.

“If two things happen at the same time, it doesn’t mean one caused the other,” Bell said. “But it’s well known that particulate matter has the potential to affect how clouds behave, and this kind of evidence makes the argument stronger for a link between pollution and heavier rainfall.”

Researchers know clouds are seeded by particulate matter. Water and ice in clouds grab hold around the particles, forming additional water droplets. Some researchers think increased pollution thwarts rainfall by dispersing the same amount of water over more seeds, preventing them from growing large enough to fall as rain. Still, other studies suggest some factors can override this dispersion effect.

In the Southeast, summertime conditions for large, frequent storms are already in place, a factor that appears to override the rain-thwarting dispersion effect.

When conditions are poised to form big storms, updrafts carry the smaller, pollution-seeded raindrops high into the atmosphere where they condense and freeze.

“It’s the freezing process that gives the storm an extra kick, causing it to grow larger and climb higher into the atmosphere,” Bell said.

Bell and his colleagues found that the radar on the TRMM satellite showed that storms climb to high altitudes more often during the middle of the week than on weekends. These invigorated midweek storms, fueled by workweek pollution, could drop measurably more rainfall.

The trend does not mean it will always rain on weekday afternoons during summertime in the Southeast, Bell said. Rather, “it’s a tendency,”

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