Jamie S. Nakai

Atmospheric chemistry of chlorinated phenols

The quantum yields for the photodegradation of a series of chlorophenols have been used to estimate their rates of solar photodegradation In the atmosphere. The photochemical rates have been compared with the calculated rates of attack by atmospheric hydroxyl radicals. These two processes are complementary, with photolysis being faster for pentachlorophenol, and OH attack being faster for monochlorinated phenols. As a result, it is predicted that most chlorophenol congeners will have quite similar atmospheric half-lives.

A model for estimating the rate of chemical transformation of a VOC in the troposphere by two pathways: Photolysis by sunlight and hydroxyl radical attack

Abstract A simple model has been developed to describe the transformation of a tropospheric constitutent by two competing pathways: direct photolysis and attack by hydroxyl radicals. The model makes use of the observations of Platt et al . (1988) that under the condition of low NO x , the concentration of hydroxyl radicals appears to depend linearly on the rate of photolysis of ozone. It has been used to obtain a rapid but rough estimate of the rate of (photo)-chemical transformation of an organic tropospheric constituent and to estimate the tropospheric hydroxyl radical concentration under various conditions of geographical location, season, and time of day. In this work the model is used to describe the tropospheric chemistry of pentachlorophenol, but it is readily extended to other substances.

Estimates of the tropospheric lifetimes of short- and long-lived atmospheric pollutants

Abstract A computer model developed previously in our laboratory has been applied to substances with the potential for chemical reaction in the troposphere by two pathways: direct photolysis by sunlight and oxidation by hydroxyl radicals. A calculated value for the globally- and seasonally-averaged concentration of the hydroxyl radical is in reasonable agreement with previous reports. Compounds of the chlorobenzene, chlorobiphenyl and chlorophenol families are predicted to react with half-lives of several days at mid-latitudes. These lifetimes can be markedly dependent on season and on geographical location, showing the importance of using appropriate geographical and seasonal parameters to model the behaviour of pollutants in the atmosphere. Globally and seasonally averaged parameters have been used to estimate the tropospheric lifetimes of long-lived compounds such as chlorofluorocarbons.

In vitro thermal inactivation of hepatic Ah receptors from several mammalian species.

The thermal inactivation of the hepatic cytosolic Ah receptor was studied in vitro for several immature male rodents. The activation energies for receptor inactivation in C57BL/6 mice, Mongolian gerbils, golden Syrian hamsters, Hartley guinea-pigs, Sprague-Dawley rats and Wistar rats were 170, 142, 112, 131, 120 and 112 kJ/mol, respectively. The magnitude of the activation parameters pointed to a substantial change on inactivation, but not to complete unfolding of the protein. Statistical analysis indicated that attempts to interpret these results in terms of receptor heterology should be treated with caution. Among the species studied, the Ah receptor from the mouse offered the best possibility for in vitro studies at low temperature, free from the problem of thermal inactivation.

Solid state actinometers based on the photorearrangement of aromatic azoxy compounds in poly(methyl methacrylate)

Abstract The relationship between product formation and photon dose in the title actinometers is found to be described better by a rectangular hyperbola than by the single exponential proposed previously. Several methods have been investigated for decreasing the photosensitivity of azoxy compound-poly(methyl methacrylate) actinometers for use outdoors. The most successful method involves painting a UV-filtering substance directly onto the polymer surface. The sensitivity of these actinometers has also been found to depend upon the spectral distribution of the source. As a result, it is necessary to calibrate the device before it is used for the first time with each radiation source.

Interspecies differences in in vitro thermal inactivation of unliganded hepatic Ah receptor

Abstract The activation energies for the in vitro thermal inactivation of the hepatic cytosolic Ah receptor from the C57/BL mouse, gerbil, Syrian golden hamster, guinea pig, Sprague-Dawley and Wistar rats were 157, 167, 136, 122, 138 and 133 kJ/mol respectively.

Gas phase photochemistry in round bottomed flasks

Abstract Product and quantum yield studies may be carried out in the gas phase using ordinary laboratory equipment. The quantum yield values thus obtained appear consistent with previous literature data, e.g. chlorobenzene φ = 0.33, 1,2,4-trichlorobenzene φ = 0.47, 4-chlorobiphenyl φ = 0.078. Modelling studies indicate that the reactions occur principally in the gas rathern than on the surface of the equipment.