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Environmental fate & pathways

Phototransformation in air

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Description of key information

Hypochlorous acid degrades in the atmosphere with a DT50 of 114.6 days (24-hr day), corresponding to 2750 hours. As hypochlorous acid contains no olefinic carbon-carbon double and acetylic triple bonds, it is not supposed to react with ozone.

Key value for chemical safety assessment

Half-life in air:
115 d

Additional information

The photochemical and oxidative decomposition of hypochlorous acid in air was calculated according to Atkinson.

Reaction rate constant kOH= 0.14× 10-12cm3molecule-1sec-1

The DT50for hypochlorous acid was estimated to be 114.6 days (24-hr day), corresponding to 2750 hours, using the reaction rate constant kOH.

As hypochlorous acid contains no olefinic carbon-carbon double and acetylenic triple bonds, it is not supposed to react with ozone.

Atmospheric degradation

At environmental pH values (6.5-8.5) half of the hypochlorite is in the undissociated form of hypochlorous acid and half is dissociated to the hypochlorite anion. Only the hypochlorous acid fraction is volatile, but the amount of hypochlorous acid that could volatilise from water into air is expected to be very low. The calculated half life (Atkinson calculation) for hypochlorous acid in the atmosphere is 2750 hours, but there are indications that the half life is shorter (only a few hours).

Photolysis of hypochlorous acid generates atomic chlorine and hydroxyl radicals OH°:

HOCl + hv => HO° + Cl°

Thus, hypochlorous acid could participate in the atmospheric chlorine reaction routes.

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