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Environmental fate & pathways

Phototransformation in air

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Rate constant for photodegradation with OH radicals: 2.6 +/- 0.6 * 10^-11 cm^3*mol^-1*sec^-1, atmospheric half-life 3.7 hours according to a study by Aschmann et al. (2001). This half-life is < 2 days being the cut off for potential long range transport (http://www.unece.org/fileadmin/DAM/env/documents/2000/ece/eb/ece%20eb%20air.60.e.pdf). The substance does not have an ozone depletion potential because it does not contain halogens and does not have the potential to reach the stratosphere.

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Additional information

The photodegradation of HHCB was studied by Aschmann et al. (2001) under laboratory conditions using blacklamps for irradiation (l > 300 nm) at 25 °C and 740 mm Hg (0.986 bar) total pressure of purified air at ~5% relative humidity. The rate constant was measured for the gas phase reaction of OH radicals. The measured rate constant (in cm3molecule-1s-1) is 2.6 ± 0.6.10 -11. Combined with estimated ambient atmospheric concentrations of OH radicals, an atmospheric lifetime of 5.3 hours is calculated (t½ = 3.7 h) based on a 12 -hour daylight average atmospheric concentration of 2.0.106molecule cm-3, assuming a daylight period of 12 h and 1.5.106OH cm-3, t½ based on the empirical rate is 4.96 h. This data indicates that the atmospheric lifetime of HHCB is sufficiently short that it will not undergo long-range transport to any significant extent (Aschmann et al. 2001).