The Ups and Downs of Ozone
"We've seen a turnaround in the amount of ozone destroying chemicals," said Michael Kurylo, manager with NASA's upper atmosphere research program. "We're beginning to see, at certain altitudes, the turnaround in the halogen burden or the chlorine burden in the stratosphere."
Above: NASA satellites show the size of the region of depleted Antarctic ozone (shown in blue) extended to a record 10.5 million square miles on Sept. 19,1998. In this image obtained on October 3, 1999 the size of the Antarctic ozone hole is smaller than it was at the same time in 1998. Red colors denote high ozone levels; blue denotes low. [More images and credits]
Kurylo addressed scientists gathered in early May for the annual meeting of NASA's Total Ozone Mapping Spectrometer (or TOMS) hosted this year by the University of Alabama in Huntsville (UAH).
In fact, says Mike Newchurch, associate professor of atmospheric science at UAH and host for the conference, it might not be recovering at all.
"While the halogen burden is declining, the result of the halogen change on the ozone layer is not at all clear," says Newchurch. "We don't know how well or how soon the ozone will bounce back. This subject is an area of very active research."
Above: This image from the TOMS web site shows how the size and depth of the 1999 Antarctic ozone hole (plus symbols) compare with 1998's (solid line) and with the entire Nimbus 7 TOMS climatology (shaded). [more information]
TOMS instruments aboard four spacecraft have monitored the ozone since 1978. The four products derived from these data are total column ozone, aerosol index, UV exposure and reflectivity.
1) Normal oxygen gas is a molecule consisting of two oxygen atoms. Ozone, on the other hand, is made up of three oxygen atoms. It comprises a thin layer in the upper atmosphere and protects animal and plant life from harmful solar ultraviolet radiation. Ozone is also found near the surface of the earth. But here, it can be a dangerous and unhealthy pollutant in high concentrations. Lower level ozone is caused by a variety of natural and human activities.
2) Aerosols are tiny and microscopic particles of dust, smoke and ash. Volcanoes, deforestation, desert storms,and fires, both natural and man-made, may generate these aerosols.
Above: Near realtime displays of global aerosols will soon be available at the TOMS web site.
3) UV exposure has served as a focal point for most stories dealing with ozone depletion. Erythemal UV exposure is described as the daily amount of radiation that gets through the atmosphere to ground level. Measured by TOMS in terms of kilojoules per square meter, it is the intensity of solar ultraviolet radiation reaching plant and animal life after it has been filtered through stratospheric ozone, clouds and aerosols multiplied by its biological damage potential. Erythema is the scientific word for sunburn.
4) Reflectivity is derived from the percentage of sunlight reflected up to the instrument from the surface of the earth. Everything reflects light, including soil, water, ice, vegetation and clouds. Studying this percentage of light, researchers can determine cloud reflectivity and see significant weather phenomena over both land and sea. The latest TOMS satellite passes over the equator during each orbit at local noon, providing the instrument with the maximum amount of reflected light for more precise measurements.
Throughout the worldwide scientific community, TOMS is now considered the standard in ozone studies. Through an impressive web site, visitors are provided with near-real-time access to today's ozone. Web surfers can select their geographic location, check the level of ozone and ultraviolet exposure and even compare their levels with other locations around the globe. In the not too distant future, web site visitors will be able to check aerosol levels anywhere around the globe in the same manner.
TOMS is supported from the ground by the Southern Hemisphere ADditional OZonesonde program or SHADOZ. Anne Thompson, an atmospheric chemist at Goddard Space Flight Center in Greenbelt, Maryland, addressed the conference about the SHADOZ program.
Ozonesondes are measuring devices attached to a weather balloon. They measure temperature, moisture and ozone up to a height of around 100,000 feet (35km). One of the highlights of the conference was the launch of an ozonesonde from the parking lot of the Bevill Center on the UAH campus.
Above: Conference participants launch an ozonesonde from a parking lot on the UAH campus.
Although the TOMS conference displayed a collective, positive attitude among researchers, findings that show an ozone turnaround do not necessarily mean that NASA's work is done.
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Mike Newchurch echoed McPeter's feelings.
"Due to complex atmospheric interactions with CO2 increases and resulting climate changes, the ozone recovery may not be as quick or as obvious as we would like," said Newchurch.
"We must, therefore, be extremely diligent in our focus on the TOMS and other ozone measurements to determine when and how fast our protective ozone layer recovers from its significant decline in recent decades."
Above: These plots show total ozone over the southern hemisphere averaged during the month of October for specific years. Colors from blue to red indicate increasing column density in Dobson Units (DU). A DU is the equivalent physical thickness of the ozone layer if it were brought to the earth's surface (300DU = 3mm). The steady growth of an "ozone hole" from 1970 to 1997 is denoted by an expanding blue region over Antarctica.
TOMS-EP and other ozone-measurement programs are important parts of a global environmental effort of NASA's Earth Science enterprise, a long-term research program designed to study Earth's land, oceans, atmosphere, ice and life as a total integrated system.
TOMS Web Site -- data and information about the Total Ozone Mapping Spectrometer (TOMS) instrument aboard NASA's Earth Probe (TOMS-EP) satellite.
Stratospheric Ozone: An Electronic Textbook -- a comprehensive tutorial about the chemistry and dynamics of the ozone layer
Recent Ozone Hole Measurements -- QuickTime movies and still images from NASA
Ozone and the Atmosphere -- a tutorial on Earth's present day atmosphere, ozone creation and depletion, and the complex interactions under study by scientists worldwide
SHADOZ -- Southern Hemisphere ADditional OZonesondes