Indicator: A-10 stratospheric chlorine from the major ozone-depleting substances
Data
Stratospheric ‘chlorine’ (ppb - parts per 109 molar) from the major ozone depleting substances (ODS) comprising CFCs, chlorinated solvents, halons, methyl bromide, methyl chloride and HCFCs.
Source: CSIRO Atmospheric Research and Cape Grim Baseline Air Pollution Station, The Australian Antarctic Division and Australian Bureau of Meteorology.
What the data mean
The data shows atmospheric observations of ozone-depleting substances: CFCs, chlorinated solvents, methyl chloride, methyl bromide, halons and HCFCs. These are also expressed as ‘total stratospheric chlorine’.
The stratospheric chlorine observations are compared with scenarios to 2020 under the Montreal Protocol. These scenarios assume global compliance to the Protocol, with consumption of ozone-depleting substances being largely phased out:
- in the 1990s in the developed world, and
- by 2010 in the developing world.
CFCs and chlorinated solvents are the largest contributors to total stratospheric chlorine accounting for about 41 percent and 23 percent respectively. All chlorine species, except HCFCs, are expected to decrease over the scenario period. Actual observations, for the most part, support these predictions.
Total stratospheric chlorine peaked in the mid 1990s and is now in decline by about one percent per year. Total stratospheric chlorine levels are below those predicted under the Montreal Protocol scenario. Stratospheric chlorine from:
- CFCs peaked in 1999 and are now declining at 0.3% per year
- chlorinated solvents peaked around 1994 and 1995 and have since declined by five percent per year
- methyl chloride peaked in 2001 and has declined by about three percent per year
- methyl bromide peaked in 2002 and is now in decline by about six percent per year
- halons are still rising by about two percent per year and should peak around 2007 according to the Montreal Protocol scenario - however, CSIRO consider that the prediction may be optimistic
- HCFCs have risen by about nine percent per year over the past 30 years with the most current growth rate being around six percent. The Montreal Protocol scenario predicts ongoing increases in HCFCs, although HCFCs contribute just one percent of total stratospheric chlorine.
Data Limitations
Nil known
Issues for which this is an indicator and why
Atmosphere — Stratospheric ozone - General stratospheric ozone
Chlorine released from the earth’s surface, breaks down in the stratosphere, releasing chlorine species that can cause ozone destruction.
The chlorine species of interest are atmospheric concentrations of chlorofluorocarbons (CFCs), chlorinated solvents (methyl chloroform and carbon tetrachloride), methyl chloride (CH3Cl), methyl bromide (CH3Br), halons and hydro-chlorofluorocarbons (HCFCs). Their combined concentrations can be expressed as ‘equivalent effective stratospheric chlorine’, or simply ‘total stratospheric chlorine’, which is a way of representing their ability to destroy stratospheric ozone. Total stratospheric ozone is a direct indicator for this issue.
Other indicators for this issue:
- A-11 Summer mean total ozone column
- A-12 Trend in the area of the ozone hole
- A-13 Surface ultraviolet radiation in Australia
- A-14 Consumption of ozone-depleting substances - Australian consumption of ozone-depleting substances
- A-15 Skin melanoma rates
Key
Links to another web site
Links to data in the DRS
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