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Environmental fate & pathways

Phototransformation in air

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Reference
Endpoint:
phototransformation in air
Type of information:
calculation (if not (Q)SAR)
Adequacy of study:
key study
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
accepted calculation method
Principles of method if other than guideline:
Calculation using SRC AOP v1.92
GLP compliance:
no
Estimation method (if used):
The Atmospheric Oxidation Program for Microsoft Windows (AOPWIN) estimates the rate constant for the atmospheric, gas-phase reaction between photochemically produced hydroxyl radicals and organic chemicals. It also estimates the rate constant for the gas-phase reaction between ozone and olefinic/acetylenic compounds. The rate constants estimated by the program are then used to calculate atmospheric half-lives for organic compounds based upon average atmospheric concentrations of hydroxyl radicals and ozone.

The estimation methods used by AOPWIN are based upon the structure-activity relationship (SAR) methods developed by Dr. Roger Atkinson and co-workers (Atkinson, 1985, 1986, 1987, 1991; Atkinson and Carter, 1984; Biermann et al, 1985; Kwok et al, 1992, Kwok and Atkinson, 1995; Kwok et al, 1996). AOPWIN incorporates updated fragment and reaction values as cited in Kwok and Atkinson (1995). In addition, Syracuse Research Corporation has derived some additional fragment and reaction values from new experimental data. Appendix I lists all fragment and reaction values used by AOPWIN.
DT50:
23.372 min
Test condition:
cis-isomer
DT50:
22.845 min
Test condition:
trans-isomer

PHOTOCHEMICAL REACTION WITH OH RADICALS

Atmospheric Oxidation (25 °C):

Hydroxyl Radicals Reaction:

OVERALL OH Rate Constant = 329.4985 E-12 cm3/molecule-sec [Cis-isomer]

OVERALL OH Rate Constant = 337.0985 E-12 cm3/molecule-sec [Trans-isomer]

Half-Life = 23.372 Min (12-hr day; 1.5E6 OH/cm3) [Cis-isomer]

Half-Life = 22.845 Min (12-hr day; 1.5E6 OH/cm3) [Trans-isomer]

No difference occurs in the estimated results using the acid form or the bound [Na] form.

Conclusions:
Half-Life = 23.372 Min (12-hr day; 1.5E6 OH/cm³) [Cis-isomer]
Half-Life = 22.845 Min (12-hr day; 1.5E6 OH/cm³) [Trans-isomer]
Executive summary:

The phototransformation in air was investigated using the SRC AOP v1.92 estimation tool. AOPwin is an application contained in the EpiSuite 4.1, the suite of physical/chemical property and environmental fate estimation programs developed by the EPA’s Office of Pollution Prevention Toxics and Syracuse Research Corporation (SRC).

Results

Half-Life = 23.372 Min (12-hr day; 1.5E6 OH/cm3) [Cis-isomer]

Half-Life = 22.845 Min (12-hr day; 1.5E6 OH/cm3) [Trans-isomer]

Description of key information

Hydroxyl Radicals Reaction:

OVERALL OH Rate Constant = 329.4985 E-12 cm³/molecule-sec [Cis-isomer]

OVERALL OH Rate Constant = 337.0985 E-12 cm³/molecule-sec [Trans-isomer]

Half-Life = 23.372 Min (12-hr day; 1.5E6 OH/cm³) [Cis-isomer]

Half-Life = 22.845 Min (12-hr day; 1.5E6 OH/cm³) [Trans-isomer]

Key value for chemical safety assessment

Half-life in air:
23.732 min

Additional information

Half-life and degradation rates have been estimated with AOPWIN v1.92.