NASA Celebrates World Ozone Day

Minimum concentration of ozone in the southern hemisphere for each year from 1979-2013 (there is no data from 1995). 

Each image is the day of the year with the lowest concentration of ozone. A graph of the lowest ozone amount for each year is shown.

Credit: NASA

Miles above the surface of the Earth, a thin layer of ozone gas acts as a shield that protects us from harmful ultraviolet light. 

Image Credit: NASA

What is ozone, and why is some ozone “good" while some is "bad?"

Just as humans need sunblock, the Earth needs protection too. Earth’s sunscreen is called ozone.

The ozone that protects us, and all life on Earth, from the Sun’s harmful UV radiation is high in the atmosphere, in the stratosphere.

But there is also ozone closer to Earth in the troposphere and that is harmful to the health of people, plants and animals.

Decades ago scientists discovered that the Earth’s “good” ozone layer was thinning. It was being depleted by chlorofluorocarbons (CFCs), but the international community came together with an agreement to vastly curtail the use CFCs.

The UN General Assembly proclaimed September 16 the International Day for the Preservation of the Ozone Layer, commemorating the date of the signing of the Montreal Protocol on Substances that Deplete the Ozone Layer.

The theme for this year’s celebration is “Ozone Layer Protection: The Mission Goes On.”

The Montreal Protocol has so far been successful in meeting some of its targets, as a result, the abundance of ozone-depleting substances in the atmosphere is declining and the ozone layer is expected to recover around the middle of this century.

International Action Against Ozone Depleting Substances Claim Gains

Minimum concentration of ozone in the southern hemisphere for each year from 1979-2013 (there is no data from 1995). 

Each image is the day of the year with the lowest concentration of ozone. A graph of the lowest ozone amount for each year is shown.

Image Credit: NASA's Goddard Space Flight Center/M. Radcliff

Worldwide action to phase out ozone-depleting substances has resulted in remarkable success, according to a new assessment by 300 international scientists.

The stratospheric ozone layer, a fragile shield of gas that protects Earth from harmful ultraviolet light, is on track to recovery over the next few decades.

The Assessment for Decision-Makers, a summary of the Scientific Assessment of Ozone Depletion 2014, provides new information to affirm that the 1987 international agreement known as the Montreal Protocol on Substances that Deplete the Ozone Layer has successfully resulted in global international policies to reduced levels of ozone-depleting substances.

The report is conducted by the World Meteorological Organization (WMO), and the United Nations Environmental Program (UNEP), and co-sponsored by NASA, National Oceanic and Atmospheric Administration (NOAA), and the European Commission.

Science teams from these organizations and other countries have been monitoring the ozone layer on the ground, by balloon and with a variety of satellite instruments dating back to NASA's Nimbus 4 satellite, launched in 1970.

The most current ozone hole satellite data comes from the Ozone Monitoring and Profiler Suite (OMPS) instrument on the NASA-NOAA Suomi National Polar-orbiting Partnership satellite (Suomi NPP), and the Ozone Monitoring Instrument and Microwave Limb Sounder (OMIMLS) on NASA's Aura satellite.

"It is particularly gratifying to report that the ozone layer is on track for recovery to 1980 benchmark levels by mid-century," said Paul A. Newman, chief scientist for atmospheres at NASA's Goddard Space Flight Center in Greenbelt, Maryland, and a co-chair of the WMO/UNEP report.

"Many of these early signs of ozone improvements are due to decades of work and contributions by NASA and NOAA instruments and scientists."

Ozone depleting substances are also powerful greenhouse gases. The Montreal Protocol provided a double benefit: stopping ozone depletion, and slowing the growth of greenhouse gases.

“Substitutes for ozone depleting substances are ozone safe, but many are powerful greenhouse gases.

These substitutes could offset the climate gains achieved by the Montreal Protocol in the future," Newman said.

The Assessment for Decision-Makers, a summary of the Scientific Assessment of Ozone Depletion 2014 is the first comprehensive update in four years.

The full report will be available in early 2015.

Plutonium and Caesium: Nuclear-test legacy in stratosphere bigger than thought

Plutonium cycle in the atmosphere. Credit: : J.A. Corcho Alvarado

Levels of radioactive plutonium in Earth's stratosphere from nuclear tests and accidents is higher than previously thought, but probably not dangerous to humans, scientists in Switzerland said Tuesday.

It was previously thought that plutonium radionuclides—radioactive atoms which can take decades or thousands of years to degrade—were present in the stratosphere only at negligible levels.

It was also believed that levels of these pollutants were higher in the troposphere, the layer of the atmosphere that is closest to the ground, than in the stratosphere.

Both ideas turn out to be wrong, according to the new study, whose authors also found no likelihood of a hazard to health.

Radiation levels in the stratosphere are "more than three orders of magnitude higher than previously thought," study co-author Jose Corcho of the Swiss Federal Office for Civil Protection told reporters.

The team also found that volcanic eruptions may shift those pollutants from the stratosphere into the troposphere, closer to Earth.

But Corcho said there was no evidence of danger.

"The levels of plutonium and (caesium) currently found in the stratosphere are low, and comparable to the levels measured at ground level air (troposphere) at the end of the sixties and in the seventies," he explained.

The aerosol collection devices mounted on the wings of a Tiger (F5E/F), aircraft of the Swiss Air Force. 

Credit: Swiss Federal Office of Public Health

"Although I'm not a health specialist, I would say that the current levels of plutonium found in the stratosphere do not represent a risk for the population."

The study, published in the journal Nature Communication, said the radioactive particles in the stratosphere mainly came from above-ground nuclear weapons tests in the 1950s and early 1960s.

Other sources were the burn-up of an ill-fated US navigation satellite in 1964 that spilled its plutonium fuel into the atmosphere, and nuclear power plant accidents like Chernobyl and Fukushima.

The team used aerosol samples taken by Swiss military aircraft since the 1970s as part of the country's environmental surveillance programme.

More information: Paper: dx.doi.org/10.1038/ncomms4030

NASA ATTREX: Climate Change Clues In The Stratosphere

ATTREX is one of the first investigations in NASA's new Venture-class series of low- to moderate-cost projects.

Starting this month, NASA will send a remotely piloted research aircraft as high as 65,000 feet over the tropical Pacific Ocean to probe unexplored regions of the upper atmosphere for answers to how a warming climate is changing Earth.

The first flights of the Airborne Tropical Tropopause Experiment (ATTREX), a multi-year airborne science campaign with a heavily instrumented Global Hawk aircraft, will take off from and be operated by NASA's Dryden Flight Research Center at Edwards Air Force Base in California.

The Global Hawk is capable of making 30-hours of continuous flight.

Water vapour and ozone in the stratosphere can have a large impact on Earth's climate. The processes that drive the rise and fall of these compounds, especially water vapor, are not well understood.

This limits scientists' ability to predict how these changes will influence global climate in the future. ATTREX will study moisture and chemical composition in the upper regions of the troposphere, the lowest layer of Earth's atmosphere.

The tropopause layer between the troposphere and stratosphere, 8 miles to 11 miles above Earth's surface, is the point where water vapour, ozone and other gases enter the stratosphere.

Studies have shown even small changes in stratospheric humidity may have significant climate impacts. Predictions of stratospheric humidity changes are uncertain because of gaps in the understanding of the physical processes occurring in the tropical tropopause layer.

ATTREX will use the Global Hawk to carry instruments to sample this layer near the equator off the coast of Central America.

"The ATTREX payload will provide unprecedented measurements of the tropical tropopause," said Eric Jensen, ATTREX principal investigator at NASA's Ames Research Center in Moffett Field, Calif.

"This is our first opportunity to sample the tropopause region during winter in the northern hemisphere when it is coldest and extremely dry air enters the stratosphere."

Led by Jensen and project manager Dave Jordan of Ames, ATTREX scientists installed 11 instruments in the Global Hawk.

The instruments include remote sensors for measuring clouds, trace gases and temperatures above and below the aircraft, as well as instruments to measure water vapor, cloud properties, meteorological conditions, radiation fields and numerous trace gases around the aircraft.