HCFCs and the ozone layer

What is the ozone layer

Ozone is created by sunlight high in the stratosphere

Lower down in the stratosphere ozone is destroyed naturally in reactions with other atmospheric gases.

300.000.000 tons of ozone are produced and naturally destroyed by this cycle every day.

Ozone depletion occurs if the processes destroying ozone are augmented by, for example chlorine or bromine so that the balance is disturbed.

Because ozone absorbs solar UV radiation, lower ozone amounts in the layer coincide with an increase in the flux of UV-B into the lower atmosphere. The concern is that, if ozone depletion were to persist, the average UV-B flux could increase.

The recovery of the ozone layer

The principal parameters that are important for recovery of the ozone layer are:

  • The chlorine and bromine concentrations in the ozone layer now and in the future
  • The existence of particles in the stratosphere and Stratospheric temperature

The second and third of these moderate the effects of chlorine and bromine so that recovery of the ozone layer may not be simply what we might have expected from the fall in chlorine loading.

Nevertheless, chlorine loading is the most important factor and is continuing to fall as a result of the Montreal Protocol.

The best measure of ozone depletion substances: Chlorine Loading of the Stratosphere

graph_1Chlorine loading is a measure of the real contribution of a substance to ozone depletion. All ozone depleting substances are shown on a common scale that takes account of differences in potency.

Bromine is expressed as its equivalent in chlorine.

As a response to changes in society and to regulations, emissions of ozone depleting substances are falling. Chlorine loading shows how the environmental impact of ozone depleting substances changes in time in response to the change in emissions and removal of the substance from the environment by atmospheric processes.

Chlorine loading gives a measure of the actual environmental impact of an ozone depleting substance that is impossible to obtain just using its Ozone Depleting Potential.

The Potential Effect of Climate Change on Stratospheric Ozone Depletion

When the atmospheric concentration of CO2 increases, the stratosphere is expected to cool. This cooling favours the formation of Polar Stratospheric Clouds which strongly accelerate ozone depletion.

In the Antarctic, temperatures within the stratospheric vortex are well below the threshold for formation of PSCs, which means that no further deepening of the ozone hole might be expected.

In the case of the Arctic, the cooling of the stratosphere actually favours ozone depletion for a longer period than one would expect from the stratospheric chlorine decrease.

Water hazard classification

The most important fluorocarbons have been classified for their impact on aquatic environment in Water Hazard Classes. The classification is committed according to the German “Administrative Regulation on the Classification of Substances Hazardous to Waters into Water Hazard Classes” (Verwaltungsvorschrift wassergefährdende Stoffe – VwVwS).

Three Water Hazard Classes (WGK) are defined:

  • low hazard to waters
  • hazard to waters
  • severe hazard to waters

As you can see from the following table, all HCFCs and HFCs have been classified as “low hazard to waters”.
In the web site of German Federal Environmental Agency you can find more information on WGK classification.

Halocarbon n° Complete name WGK n° WGK class
CFC 11 trichlorofluoromethane 448 2
CFC 114 1,1,2,2-tetrafluoro-1,2-difluoroethane 1114 1
CFC 115 chlorpentafluorethane 115 1
HCFC 22 chlorodifluoromethane 2449 1
HCFC 123 dichlorotrifluoroethane 2518 1
HCFC 124 1-chloro-1,2,2,2-tetrafluoroethane 2519 1
HCFC 141b 1,1-dichloro-1-fluoro- ethane 2280 1
HCFC 142b chlorodifluoroethane 2811 1
HFC 23 trifluoromethane 4380 1
HFC 32 difluoromethane 4068 1
HFC 43 10mee 1,1,1,2,2,3,4,5,5,5-decafluoropentane 2034 1
HFC 125 pentafluoroethane 4066 1
HFC 134a 1,1,1,2 tetrafluoroethane 2350 1
HFC 143a 1,1,1-trifluoroethane 2782 1
HFC 152a 1,1-difluoroethane 4198 1
HFC 227 1,1,1,2,3,3,3-heptafluoropropane 4098 1
HFC 245fa 1,1,1,3,3- pentafluoropropane 3524 1
HFC 365 mfc 1,1,1,3,3-pentafluorobutane 4099 1