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.

Climate Chnage: China Asian ozone pollution covers Pacific and US West Coast

China Asian pollution drifts east toward North America in 2010. 

In this picture Hawaii is denoted by the star.

Image: Nature Geoscience.

Air pollution from China and Asia has been rising for several decades but Hawaii had seemed to escape the ozone pollution that drifts east with the springtime winds.

Now a team of researchers has found that shifts in atmospheric circulation explain the trends in Hawaiian ozone pollution.

The researchers found that since the mid-1990s, these shifts in atmospheric circulation have caused China and Asian ozone pollution reaching Hawaii to be relatively low in spring but rise significantly in autumn.

The study, led by Meiyun Lin, an associate research scholar in the Program in Atmospheric and Oceanic Sciences (AOS) at Princeton University and a scientist at the National Oceanic and Atmospheric Administration's (NOAA) Geophysical Fluid Dynamics Laboratory, was published in Nature Geoscience.

"The findings indicate that decade-long variability in climate must be taken into account when attributing U.S. surface ozone trends to rising China and Asian emissions," Lin said.

Although protective at high altitudes, ozone near the Earth's surface is a greenhouse gas and a health-damaging air pollutant. The longest record of ozone measurements in the U.S. dates back to 1974 in Hawaii.

Over the past few decades, emissions of ozone precursors in China and Asia has tripled, yet the 40-year Hawaiian record revealed little change in ozone levels during spring, but a surprising rise in autumn.

Through their research, Lin and her colleagues solved the puzzle. "We found that changing wind patterns 'hide' the increase in China and Asian pollution reaching Hawaii in the spring, but amplify the change in the autumn," Lin said.

Using chemistry-climate models and observations, Lin and her colleagues uncovered the different mechanisms driving spring versus autumn changes in atmospheric circulation patterns.

The stronger transport of China and Asian pollution to Hawaii during autumn since the mid-1990s corresponds to a positive pattern of atmospheric circulation variability known as the Pacific-North American pattern (PNA).

"This study not only solves the mystery of Hawaiian ozone changes since 1974, but it also has broad implications for interpreting trends in surface ozone levels globally," Lin said.

"Characterizing shifts in atmospheric circulation is of paramount importance for understanding the response of surface ozone levels to a changing climate and evolving global emissions of ozone precursors," she said.

More information: Tropospheric ozone trends at Mauna Loa Observatory tied to decadal climate variability; Nature Geoscience (2014) doi:10.1038/ngeo2066

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 ENVISAT - Record loss of ozone over Arctic

Average Arctic total ozone for the month of March between 1979 and 2011, based on assimilated observations of several satellite instruments: TOMS, SBUV, GOME, SCIAMACHY, OMI, GOME-2.Credits: KNMI

ESA’s Envisat satellite has measured record low levels of ozone over the Euro-Atlantic sector of the northern hemisphere during March.

This record low was caused by unusually strong winds, known as the polar vortex, which isolated the atmospheric mass over the North Pole and prevented it from mixing with air in the mid-latitudes.
This led to very low temperatures and created conditions similar to those that occur every southern hemisphere winter over the Antarctic.

	Arctic temperature field

As March sunlight hit this cold air mass it released chlorine and bromine atoms – ozone-destroying gases that originate from chlorofluorocarbons (CFCs) and break ozone down into individual oxygen molecules – predominantly in the lower stratosphere, around 20 km above the surface.


Ozone is a protective atmospheric layer found at around 25 km altitude that acts as a sunlight filter shielding life on Earth from harmful ultraviolet rays, which can harm marine life and increase the risk of skin cancer and cataracts.
ESA - Observing the Earth - Record loss of ozone over Arctic - images

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