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Environmental fate & pathways

Phototransformation in air

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Description of key information

The atmospheric lifetime of CTC is estimated to be 34 years.

Key value for chemical safety assessment

Half-life in air:
34 yr

Additional information

CTC is susceptible towards indirect photolysis by hydroxyl radicals in the troposphere (its estimated tropospheric half-life exceeds 330 years). Ultimately it diffuses upward into the stratosphere where it may be photodegraded (185-225 nm) to form the trichloromethyl radical and chlorine atoms.

Direct photolysis under stratospheric conditions is very efficient and the DT50 values range in the order of minutes. However the migration time to the troposphere is very long and the migration time limits the dissipation. On the other hand the direct photolysis of CTC is involved in global warming by ozone depletion.

The rate of photodissociation begins to become important at altitudes >20 km, and increases as altitude increases. Estimates of the atmospheric lifetime (the overall persistence of CTC in the troposphere and the stratosphere combined) range from 30 to 100 years, with 34 +/- 5 years being the most recently refined value.