Photocatalytic degradation of organic water contaminants: Mechanisms involving hydroxyl radical attack

The present status of stratospheric science is discussed. The three basic elements of stratospheric science-laboratory measurements, atmospheric observations, and theoretical studies are presented along with an attempt to predict, with reasonable confidence, the effect on ozone of particular anthropogenic sources of pollution.

The stratosphere: Present and future

Halogen oxides: Radicals, sources and reservoirs in the laboratory and in the atmosphere

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Toxicological profile for malathion

The two major classes of perfluorinated acids (PFAs), perfluorocarboxylic acids (PFCAs) and perfluorosulfonic acids (PFSAs), are both likely to be ionized at environmental pH, suggesting they will be present primarily in the aqueous phase. Long-range transport through water occurs slowly, on the order of decades. The ubiquitous distribution of PFAs suggests a faster, atmospheric dissemination mechanism. In addition, not all PFAs observed in the environment have been commercially produced.

Atmospheric Perfluorinated Acid Precursors: Chemistry, Occurrence, and Impacts

The temperature dependence of two chlorine atom reactions of considerable fundamental importance to stratospheric chemistry was studied using the technique of flash photolysis-resonance fluorescence. The reactions of interest were: (1) Cl + O3 yields ClO + O2 studied at 220-350 K, and (2) Cl + CH4 yields CH3 + HCl studied at 218-401 K. In addition, the reaction Cl + H2O2 yields HCl + HO2 was studied at 300 K. The corresponding rate constants are provided for the three reactions. The new rate data implies the need to revise downward by a factor of 2.4-3 the magnitude of the ozone perturbation due to the presence of ClO/x/ species in the stratosphere, predicted by earlier model calculations.

A temperature dependence kinetics study of the reactions of Cl (2P3/2) with O3, CH4, and H2O2

Reported in this study are temperature dependent rate data for the reaction of OH with the partially halogenated methane species CH3Cl, CH2Cl2, CHCl3, and CH3Br. The nominal temperature range covered was 245–375 K. The appropriate Arrhenius expressions are kA= (1.84±0.18) ×10−12 exp[−(2181±70/RT)], kB= (4.27±0.63) ×10−12 exp[−(2174±161/RT)], kC= (4.69±0.71) ×10−12 exp[(2254±214/RT)], kD= (7.93±0.79) ×10−13 exp[−(1766±116/RT)]. Units are cm3 molecule−1⋅s−1. No simple correlations between Eact and C–H bond strengths were found. The impact of these halogenated species on stratospheric ozone is also discussed.

A temperature dependent kinetics study of the reaction of OH with CH3Cl, CH2Cl2, CHCl3, and CH3Br

A temperature dependent kinetics study of the reaction of hydroxyl radicals with chlorofluoromethane, dichlorofluoromethane, chlorodifluoromethane, 1,1,1-trichloroethane, 1-chloro-1,1-difluoroethane, and 1,1,2-trichloro-1,2,2-trifluoroethane

The flash photolysis resonance fluorescence technique has been utilized to determine the rate constants for three reactions involving the hydroxyl radical [OH(2≅)] and three halogenated C2 alkanes. The nominal temperature range covered was 250–375 K. The compounds studied and the resulting Arrhenius expressions in units of cm3/molec·sec are 






The error limits in these expressions are such that they include any possible systematic errors due to the presence of impurities in the halocarbon samples. Tropospheric lifetimes have been calculated for the above species by combining the above rate constant data with global seasonally and diurnally averaged hydroxyl radical concentrations.

G. Machado

Papers

A temperature dependence kinetics study of the reactions of Cl (2P3/2) with O3, CH4, and H2O2

A temperature dependent kinetics study of the reaction of OH with CH3Cl, CH2Cl2, CHCl3, and CH3Br

A temperature dependent kinetics study of the reaction of hydroxyl radicals with chlorofluoromethane, dichlorofluoromethane, chlorodifluoromethane, 1,1,1-trichloroethane, 1-chloro-1,1-difluoroethane, and 1,1,2-trichloro-1,2,2-trifluoroethane

A kinetics study of the temperature dependence of the reactions of OH(2Π) with CF3CHCl2, CF3CHClF, and CF2ClCH2Cl

A temperature dependent kinetics study of the reaction of OH with CH2ClF, CHCl2F, CHClF2, CH3CCl3, CH3CF2Cl, and CF2ClCFCl2