Clean air - Danish efforts
The hole in the
sky
– the CFC gasses and the Montreal Protocol
CFC (chloro-fluoro carbons) is a common name for a series of industrially produced gasses. They are under normal conditions extremely stable and completely nontoxic. They have therefore had a series of practical applications, e.g. as heat medium in refrigerators, as propellant in spray cans or fire extinguishers, and in the production of insulating foam. For many years they were considered an environmental asset.
In the beginning of the 1980's, however, it became evident that their great stability might be the explanation of a newly observed global environmental threat: the depletion of the atmosphere's ozone layer.
Depletion of the ozone layer
Ozone (O3) is at low altitudes an air pollutant that harms both vegetation and human health. In the stratosphere 15-50 km above the ground, however, ozone provides a necessary shield against biologically active ultraviolet radiation from the sun - the so-called UV-B radiation. The great stability of the CFC gasses and thus their long lifetime in the atmosphere mean that they can be mixed only poorly in the stratosphere. Here they are broken down by the ultraviolet radiation and form free chlorine atoms that transform ozone to ordinary oxygen. In a chain process a single CFC molecule can decompose many ozone molecules.
Depletion of the ozone layer will result in an increase of the UV-B at ground level and a range of unwanted effects. Most feared is the increased incidence of i.a. skin cancer. It is, thus, estimated that a 1% reduction of the ozone layer will increase the risk of nonmelanomium by 2%. The significance for the far more dangerous malignant melanomium is, however, less clear.
Sunlight is an essential condition for higher forms of life. For humans the lack of sunlight can cause serious health and sometimes mental problems. But direct radiation from the sun also contains ultraviolet radiation that is harmful to biological systems. Normally it is partly filtered out by the ozone layer in the stratosphere. It is therefore a serious matter if the ozone layer is depleted.
On a larger scale i. a. plankton algae can be harmed. As they constitute the first link in the marine food chain, it may have consequences that can escalate through the whole system.
International efforts
Already in 1985 the Vienna Convention on the Protection of the Ozone Layer was signed, and in 1987 the more concrete Montreal Protocol. It has later been tightened, in step with the provision of new knowledge on ozone depleting compounds and the possibilities for phasing them out. The industrialised countries committed themselves to stopping the use of the five most important CFC's before 1996, whereas the developing countries must stop the use before 2010. There are also agreements for three halones (similar compounds that contain bromine), which have been used especially for fire extinguishers. Further, it has been planned to phase out a series of substitutes with minor ozone depleting efficiency.
The development in Denmark and the World
Denmark has rapidly outphased the use of ozone depleting compounds. For practical reasons the effect of all the relevant compounds is expressed in terms of the most important CFC, CFC-11. In 2001 the Danish consumption measured as CFC11 equivalents had fallen by 99%.
Also internationally phasing out has been successful, although a fall in the production of CFC has been accompanied by rising production of the less harmful substitutes. In the future the most important challenges will be to ensure that the developing countries can meet the requirements of the Montreal Protocol to phase out HCFC (hydrochloro fluorocarbons) and methyl bromide, to fight illegal trade and, finally, to identify and control new ozone depleting compounds.
The problem thus appears to be on its way towards a solution. But even with fulfilment of the most recent international agreement, the ozone layer will not be fully restored until approx. the middle of this century.
Danish consumption of ozone depleting compounds
Since international work with protection of the ozone layer started in the beginning
of the 1980's, the Danish consumption of ozone depleting compounds has by and large been
phased out. Here is shown - in amount of controlled ozone depleting compounds - the
consumption expressed in terms of CFC11 equivalents.
(Source: Danish Environmental Protection Agency).
The global average of the CFC-11 concentration
Although the global mean value of CFC-11 concentrations appears to have peaked, it
will take at least decades before the impact on the ozone layer is below the critical
level.
(Source: IPCC).
The ozone column over Denmark
The average ozone column over Denmark has, since measurements started in 1978, fallen
by about 10%. Under cloud-free conditions, when people preferably enjoy the sunlight, the
harmful ultraviolet radiation increases by nearly 15%. Nevertheless, this is still
significantly less than possible exposure during the summer holiday in Southern Europe.
(Source: DMI).