Man-made CFC gases pose additional threat to ozone layer

Dealing with the hole in the ozone layer has been one of the most successful international science projects

Scientists have identified four new man-made gases that are contributing to the depletion of the ozone layer.

Two of the gases are accumulating at a rate that is causing concern among researchers.

Worries over the growing ozone hole have seen the production of chlorofluorocarbon (CFC) gases
restricted since the mid 1980s.

But the precise origin of these new, similar substances remains a mystery, say scientists.

Lying in the atmosphere, between 15 and 30km above the surface of the Earth, the ozone layer plays a critical role in blocking harmful UV rays, which cause cancers in humans and reproductive problems in animals.

Scientists from the British Antarctic Survey were the first to discover a huge "hole" in the ozone over Antarctica in 1985.

The evidence quickly pointed to CFC gases, which were invented in the 1920s, and were widely used in refrigeration and as aerosol propellants in products like hairsprays and deodorants.

Remarkably, global action was rapidly agreed to tackle CFCs and the Montreal Protocol to limit these substances came into being in 1987.

A total global ban on production came into force in 2010.

Now, researchers from the University of East Anglia have discovered evidence of four new gases that can destroy ozone and are getting into the atmosphere from as yet unidentified sources.

The Halley Research Station in Antarctica, where the hole in the ozone layer was first discovered

Three of the gases are CFCs and one is a hydrochlorofluorocarbon (HCFC), which can also damage ozone.

"Our research has shown four gases that were not around in the atmosphere at all until the 1960s which suggests they are man-made," said lead researcher Dr Johannes Laube.

Johannes Laube.

The scientists discovered the gases by analysing polar firm, perennial snow pack. Air extracted from this snow is a natural archive of what was in the atmosphere up to 100 years ago.

Grim discovery
The researchers also looked at modern air samples, collected at remote Cape Grim in Tasmania.

They estimate that about 74,000 tonnes of these gases have been released into the atmosphere. Two of the gases are accumulating at significant rates.

"The identification of these four new gases is very worrying as they will contribute to the destruction of the ozone layer," said Dr Laube.

"We don't know where the new gases are being emitted from and this should be investigated. Possible sources include feedstock chemicals for insecticide production and solvents for cleaning electronic components."

"What's more, the three CFCs are being destroyed very slowly in the atmosphere - so even if emissions were to stop immediately, they will still be around for many decades to come," he added.

The four new gases have been identified as CFC-112, CFC112a, CFC-113a, HCFC-133a 

• CFC-113a has been listed as an "agrochemical intermediate for the manufacture of pyrethroids", a type of insecticide once widely used in agriculture 
• CFC-113a and HCFC-133a are intermediaries in the production of widely used refrigerants 
• CFC-112 and 112a may have been used in the production of solvents used to clean electrical components

Other scientists acknowledged that while the current concentrations of these gases are small and they don't present an immediate concern, work would have to be done to identify their origin.

"This paper highlights that ozone depletion is not yet yesterday's story," said Prof Piers Forster, from the University of Leeds.

"The concentrations found in this study are tiny. Nevertheless, this paper reminds us we need to be vigilant and continually monitor the atmosphere for even small amounts of these gases creeping up, either through accidental or unplanned emissions.

"Of the four species identified, CFC-113a seems the most worrying as there is a very small but growing emission source somewhere, maybe from agricultural insecticides. We should find it and take it out of production."

The research 'Newly detected ozone-depleting substances in the atmosphere' has been published in the journal, Nature Geoscience.

ESA Mars Express: Seasonal Ozone Layer Over The Martian South Pole

Ozone production over Mars southern winter pole.
Credit: ESA/ATG medialab.

For the past decade, ESA's Mars Express orbiter has been observing atmospheric structure on the Red Planet.

Among its discoveries is the presence of three separate ozone layers, each with its own characteristics.

A new comparison of spacecraft data with computer models explains how global atmospheric circulation creates a layer of ozone above the planet's southern winter pole.

Ozone (O3) is a form of oxygen gas which contains three atoms, rather than two.

On Earth, ozone is a pollutant at ground level, but at higher altitudes it provides an essential protective layer against harmful solar ultraviolet (UV) light.

However, ozone molecules are easily destroyed by solar ultraviolet light and by chemical reactions with hydrogen radicals, which are released by photolysis (splitting) of water molecules.

The role of pollution in its destruction has been a major focus of attention since the mid-1980s, when a hole in the ozone layer was discovered above Antarctica.

Until the early 1970s, no one could be sure whether ozone existed on any of the other planets. Ozone was then detected on Mars and it has since been discovered on Venus by ESA's Venus Express mission.

ESA's Mars Express orbiter

On Mars, the ozone concentration is typically 300 times thinner than on Earth, although it varies greatly with location and time.

In recent years, the SPICAM UV spectrometer on board Mars Express has shown the presence of two distinct ozone layers at low-to-mid latitudes.

These comprise a persistent, near-surface layer below an altitude of 30 km, and a separate layer, which is only present in northern spring and summer, and whose altitude varies from 30 to 60 km.

In recent years, SPICAM has also provided evidence for the existence of a third ozone layer which exists 40-60 km above the southern winter pole, with no counterpart above the North Pole.

In a paper published in the journal Nature Geoscience, Franck Montmessin and Franck Lefevre, two scientists from LATMOS in Guyancourt, France, have analysed approximately 3000 occultation sequences and vertical ozone profiles collected by SPICAM on the night side of Mars.

ESA Weather Satellites: Antartica Ozone Holes Showing signs of closing

Time-series (1996 to 2012) of total polar ozone mean values over the months of September, October and November as measured by GOME, SCIAMACHY and GOME-2 flown on ERS-2, Envisat and MetOp-A, respectively. Smaller ozone holes are evident during 2002 and 2012. 

The maps were generated using total ozone columns derived with the GODFIT algorithm (BIRA/IASB, RT Solutions Inc.), which has been consistently applied to the three different satellite instruments. 

Credit BIRA/IASB.

Satellites show that the recent ozone hole over Antarctica was the smallest seen in the past decade. Long-term observations also reveal that Earth's ozone has been strengthening following international agreements to protect this vital layer of the atmosphere.

According to the ozone sensor on Europe's MetOp weather satellite, the hole over Antarctica in 2012 was the smallest in the last 10 years.

The instrument continues the long-term monitoring of atmospheric ozone started by its predecessors on the ERS-2 and Envisat satellites.

"The Ozone Layer, which protects the Earth from dangerous levels of uv-radiation, would be fatal to any animal that inhaled it, including humans. It is located approx 24 Kms above the earth's surface and smells faintly of geraniums."

Since the beginning of the 1980s, an ozone hole has developed over Antarctica during the southern spring - September to November - resulting in a decrease in ozone concentration of up to 70%.

Ozone depletion is more extreme in Antarctica than at the North Pole because high wind speeds cause a fast-rotating vortex of cold air, leading to extremely low temperatures. Under these conditions, human-made chlorofluorocarbons - CFCs - have a stronger effect on the ozone, depleting it and creating the infamous hole.

Over the Arctic, the effect is far less pronounced because the northern hemisphere's irregular landmasses and mountains normally prevent the build-up of strong circumpolar winds.

Reduced ozone over the southern hemisphere means that people living there are more exposed to cancer-causing ultraviolet radiation.

International agreements on protecting the ozone layer - particularly the Montreal Protocol - have stopped the increase of CFC concentrations, and a drastic fall has been observed since the mid-1990s.

However, the long lifetimes of CFCs in the atmosphere mean it may take until the middle of this century for the stratosphere's chlorine content to go back to values like those of the 1960s.

The evolution of the ozone layer is affected by the interplay between atmospheric chemistry and dynamics like wind and temperature.

If weather and atmospheric conditions show unusual behaviour, it can result in extreme ozone conditions - such as the record low observed in spring 2011 in the Arctic - or last year's unusually small Antarctic ozone hole.

To understand these complex processes better, scientists rely on a long time series of data derived from observations and on results from numerical simulations based on complex atmospheric models.

Although ozone has been observed over several decades with multiple instruments, combining the existing observations from many different sensors to produce consistent and homogeneous data suitable for scientific analysis is a difficult task.

Within the ESA Climate Change Initiative, harmonised ozone climate data records are generated to document the variability of ozone changes better at different scales in space and time.

With this information, scientists can better estimate the timing of the ozone layer recovery, and in particular the closure of the ozone hole.

ESA Venus Express finds has an ozone layer

Venus Express has two solar cell panels per wing comprising alternating rows of standard triple junction solar cells as well as highly reflective mirrors to reduce the operating temperatures. 

There is twice as much sunlight in Venus's orbit as there is in Earth's orbit, plus additional thermal input from the Venusian surface and atmosphere - 75% of sunlight being reflected up from it. In certain cases, this results in Venus Express receiving an equivalent of the thermal input from 3.5 Suns.

ESA's Venus Express spacecraft has discovered an ozone layer high in the atmosphere of Venus. Comparing its properties with those of the equivalent layers on Earth and Mars will help astronomers refine their searches for life on other planets.

Venus Express made the discovery while watching stars seen right at the edge of the planet set through its atmosphere. Its SPICAV instrument analysed the starlight, looking for the characteristic fingerprints of gases in the atmosphere as they absorbed light at specific wavelengths.

The ozone was detectable because it absorbed some of the ultraviolet from the starlight.

Ozone is a molecule containing three oxygen atoms. According to computer models, the ozone on Venus is formed when sunlight breaks up carbon dioxide molecules, releasing oxygen atoms.

These atoms are then swept around to the nightside of the planet by winds in the atmosphere: they can then combine to form two-atom oxygen molecules, but also sometimes three-atom ozone molecules. "This detection gives us an important constraint on understanding the chemistry of Venus' atmosphere," says Franck Montmessin, who led the research.

It may also offer a useful comparison for searching for life on other worlds.

Ozone has only previously been detected in the atmospheres of Earth and Mars. On Earth, it is of fundamental importance to life because it absorbs much of the Sun's harmful ultraviolet rays. Not only that, it is thought to have been generated by life itself in the first place.

The build-up of oxygen, and consequently ozone, in Earth's atmosphere began 2.4 billion years ago. Although the exact reasons for it are not entirely understood, microbes excreting oxygen as a waste gas must have played an important role.

Along with plant life, they continue to do so, constantly replenishing Earth's oxygen and ozone.

As a result, some astrobiologists have suggested that the simultaneous presence of carbon dioxide, oxygen and ozone in an atmosphere could be used to tell whether there could be life on the planet.

This would allow future telescopes to target planets around other stars and assess their habitability.

However, as these new results highlight, the amount of ozone is crucial.

The small amount of ozone in Mars' atmosphere has not been generated by life. There, it is the result of sunlight breaking up carbon dioxide molecules.

Venus too, now supports this view of a modest ozone build-up by non-biological means. Its ozone layer sits at an altitude of 100 km, about four times higher in the atmosphere than Earth's and is a hundred to a thousand times less dense.

Theoretical work by astrobiologists suggests that a planet's ozone concentration must be 20% of Earth's value before life should be considered as a cause.

These new results support that conclusion because Venus clearly remains below this threshold.

NASA Study Sheds Light On Ozone Hole Chemistry

NASA Study Sheds Light On Ozone Hole Chemistry

A new NASA study of Earth's polar ozone layer reinforces scientists' understanding of how human-produced chlorine chemicals involved in the destruction of ozone interact with each other.

A team of scientists led by Michelle Santee of NASA's Jet Propulsion Laboratory, Pasadena, Calif., examined how nighttime temperatures affect chlorine monoxide, a key chemical involved in ozone destruction.

Combining NASA satellite measurements with a state-of-the-art chemical model, they found this relationship to be more consistent with recent laboratory work than with some older laboratory and field observational data.

This verification is important, because scientists have not been able to conduct appropriate laboratory experiments relevant to understanding how polar chlorine monoxide behaves at night at the lowest temperatures of the stratosphere, Earth's second lowest atmospheric layer.

Santee and her team published their findings this month in the Proceedings of the National Academy of Sciences. The data came from the Microwave Limb Sounder instrument on NASA's Aura satellite.

"Our comprehensive study uses multiple years of Arctic and Antarctic satellite observations to quantify the nighttime balance of ozone-destroying chlorine chemical compounds," said Santee.

"By gaining a better knowledge of this balance, scientists will be able to make more accurate predictions of polar ozone loss, especially in twilight and in the Arctic, where conditions are often only marginally favorable for ozone destruction."

At night, chlorine monoxide molecules combine to form chlorine peroxide, and the balance between these two chemicals is highly temperature-sensitive. Studying this balance quantitatively is challenging.

Previous studies in the laboratory and using aircraft and satellites had found significantly different degrees of balance. The Microwave Limb Sounder's very large number of measurements has quantified this balance far better than before.

The new research contributes to scientific understanding of the phenomenon more commonly known as the "ozone hole." Each year in late winter and early spring in the southern hemisphere, chlorine and bromine from human-produced compounds cause the nearly total destruction of ozone in Earth's stratosphere in a layer about 20 kilometers (12 miles) above Antarctica.

These source gases that are responsible for the greatest destruction of the ozone layer are now declining in response to the 1985 Montreal Protocol and its amendments.

Since its launch in 2004, the Microwave Limb Sounder has monitored most of the polar regions of both hemispheres daily, compiling tens of thousands of measurements of nighttime chlorine monoxide levels, along with various other chemicals, including ozone.

These data are allowing scientists to test their understanding of chlorine-related chemistry on an unprecedented scale.