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Environmental fate & pathways

Phototransformation in air

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Description of key information

A photooxidation half-life of 13.124 days (hydroxyl radicals) has been reported using a recommended rate constant of 0.8150 E-12 cm3/molecule/sec. In addition a half-life of 382 days for ozone radicals has been reported.

Key value for chemical safety assessment

Half-life in air:
13.124 d

Additional information

Atkinson (1989) is a review article, with no data reported on the test methods or conditions of the original data source. Nevertheless, the data are taken from a published, peer-reviewed journal article and are considered to be suitable for this endpoint. Measured data from author and other investigators were quality assessed and then used to develop rate constants for different chemicals. The data have been used within the AOP (Atmospheric Oxidation Program (AoPWin) V.1.92 within EPISuite 4.0 2008) to calculate a rate constant for atmospheric gas phase reaction between photochemically produced hydroxyl radicals and organic chemicals.

As most acetylene will distribute to the atmosphere, the most dominant environmental fate process will be photooxidation. Acetylene has been shown to react rapidly with hydroxyl radicals, ozone and NO3 in the vapour phase. The reaction with ozone is less rapid, and therefore less important than the reaction with hydroxyl radicals. However, at night, when the concentration of hydroxyl radicals falls to negligible levels, this removal mechanism will become more important. acetylene is expected to be rapidly removed from the atmosphere by photooxidation.