### Concentrations of halocarbons

#### Indicators:

concentration of chlorinated compounds (CFCs, HCFCs and other CCs) concentration of hydrofluorocarbons | concentration of bromocarbons concentration of perfluorocarbons & SF6

Halocarbon are carbon compounds that contain chlorine, fluorine, bromine or iodine. In the model we distinguish between:

- halocarbons contributing to ozone (O3) depletion in the lower stratosphere (an indirect cooling effect). These halocarbons include CFCs, HCFCs and other CCs, and bromocarbons. Their emissions are controlled under the Montreal Protocol and its Adjustments and Amendments.
- halocarbons that act as direct greenhouse gases. These (fluorinated) halocarbons include hydrofluorocarbons (HFCs), perfluorocarbons (PFCs) and sulphur hexafluoride (SF6) and are included in the Kyoto Protocol with the gases CO2, CH4 and N2O.

The concentrations of the different halocarbons are presented for the different compounds included in the groups of chlorinated compounds (CFCs, HCFCs, other CCs), hydrofluorocarbons (HFCs), perfluorocarbons (PFCs) and SF6 and bromocarbons (see definitions - chemical compounds).

| #### Concentration of chlorinated compounds
| unit: pptv (parts per trillion by volume) dimension: compound

Chlorinated compounds consist of the groups of chlorofluorocarbons (CFCs), hydrochlorofluorcarbons (HCFCs) and other chlorocarbons (CCs). All chlorinated compounds stem from anthropogenic sources, except for the chlorocarbon CH3Cl (methylchloride). The values for the global warming potential (GWP) of these chlorinated compounds are much higher than that of CO2 (if only the direct effect is considered).

The CFCs included in the model are CFC-11 (CCl3F), CFC-12 (CCl2F2), CFC-113 (CCl2FCClF2), CFC-114 (CClF2CClF2) and CFC-115 (CF3CClF2) (see also definitions - chemical compounds).

CFCs are broken down in the stratosphere by dissociation. The CFC concentrations are calculated using a constant lifetime taken from the IPCC. The slow-down in the growth rates of the concentrations of chlorofluorocarbons (CFCs) is consistent with the rapid phase-out of CFC consumption required by the Montreal Protocol and its Amendments (Copenhagen).

The HCFCs included in the model are HCFC-22 (CHClF2), HCFC-123 (CF3CHCl2), HCFC-124 (CF3CHClF), HCFC-141b (CH3CFCl2), HCFC-142b (CH3CF2Cl) and HCFC-225ca (C3HF5Cl2) (see also definitions - chemical compounds). HCFCs have been used as interim substitutes for CFCs. These compounds are less inert in the troposphere than CFCs because they are oxidized by OH· as well. The loss due to the oxidation by OH· is proportional to both the concentration of the trace gas and the concentration of OH·. Hence, the change in the concentration of HCFCs depends on the balance between anthropogenic emissions, stratospheric loss (represented by a loss term) and oxidation by OH·.

The other chlorocarbons included in the model are perchlorocarbon (CCl4), chloroform (CHCl3) and methyl chloroform (CH3CCl3) (see also definitions - chemical compounds). CCl4 is modelled in the same way as the CFCs and CHCl3 and CH3CCl3 are modelled in the same way as the HCFCs.

| #### Concentration of hydrofluorocarbons
| unit: pptv (parts per trillion by volume) dimension: compound

The group of hydrofluorocarbons (HFCs) is increasingly being used as longer-term substitutes for CFCs and HCFCs. The HFCs included in the model are HFC-23 (CHF3), HFC-32 (CH2F2), HFC-43-10mee (C5H2F10), HFC-125 (C2HF5), HFC-134a (CH2FCF3), HFC-143a (CH3CF3), HFC-152a (CH3CHF2), HFC-227ea (C3HF7), HFC-236fa (C3H2F6) and HFC-245ca (C3H3F5) (see also definitions - chemical compounds).

The values of GWP of the HFCs are typically lower than those of the CFCs they replace, but high compared to carbon dioxide (CO2). HFCs are completely oxidized in the troposphere by OH·. The loss due to the oxidation by OH· is proportional to both the concentration of the trace gas and the concentration of OH·.

| #### Concentration of bromocarbons
| unit: pptv (parts per trillion by volume) dimension: compound

Bromocarbons include methyl bromide (CH3Br), halon-1211 (CBrClF2) and halon-1301 (CBrF3) (see also definitions - chemical compounds).

Bromocarbons stem from anthropogenic sources, except for CH3Br which is also emitted by natural sources. the atmospheric concentration is calculated from the emissions through a conversion factor minus a stratospheric loss term calculated with the lifetime of the compound considered taken from IPCC.

| #### Concentration of perfluorocarbons & SF6
| unit: pptv (parts per trillion by volume) dimension: compound

This group of trace gases has very long atmospheric lifetimes (greater than 1000 years) and large GWP values. The perfluorocarbons (PFCs) included in the model are tetrafluoromethane (CF4), hexafluorethane (C2F6). The model also includes sulphur hexafluoride (SF6) (see also definitions - chemical compounds).

CF4 (tetrafluoromethane) and C2F6 (hexafluorethane) are by-products of the production of aluminium and sulphur SF6 (sulfurhexafluoride) is primarily used as a dielectric fluid in heavy electrical equipment. The only sink for these compounds is photodissociation in the stratosphere, represented by the lifetime (similar to the group of CFCs).