Removal mechanisms atmospheric oxidation

Environmental Fate. Sensitized photolysis studies in water and oxidation/reduction studies in both air and water are lacking, as are biodegradation studies in surface and groundwaters. These kinds of studies are important, since they represent the fundamental removal mechanisms available to isophorone in the environment. In addition, the kinetic studies for the atmospheric reactions are important for understanding the significance of a removal mechanism and predicting the reactions that may control the fate of a chemical in the environment. 

Once PAHs enter the atmosphere, they are distributed between gas and particle phases and subject to removal mechanisms, such as oxidative and... 

In ambient air, the primary removal mechanism for acrolein is predicted to be reaction with photochemically generated hydroxyl radicals (half-life 15-20 hours). Products of this reaction include carbon monoxide, formaldehyde, and glycolaldehyde. In the presence of nitrogen oxides, peroxynitrate and nitric acid are also formed. Small amounts of acrolein may also be removed from the atmosphere in precipitation. Insufficient data are available to predict the fate of acrolein in indoor air. In water, small amounts of acrolein may be removed by volatilization (half-life 23 hours from a model river 1 m deep), aerobic biodegradation, or reversible hydration to 0-hydroxypropionaldehyde, which subsequently biodegrades. Half-lives less than 1-3 days for small amounts of acrolein in surface water have been observed. When highly concentrated amounts of acrolein are released or spilled into water, this compound may polymerize by oxidation or hydration processes. In soil, acrolein is expected to be subject to the same removal processes as in water. 

In summary, it appears [cf. Robinson and Robbins (214)] that photochemical reactions involving N02 and hydrocarbons and absorption by alkaline water drops with or without metal catalysts are the major mechanisms for oxidizing SC. The complex nature of these removal mechanisms will, however, make their inclusion in any atmospheric photochemical model difficult. This will be discussed in Section V. 

However, much of the methane produced in bottom sediments never reaches the atmosphere because it is oxidized to CO2 by microorganisms living in the surficial layers of the sediments and in the oxic, overlying waters. The oxidation of methane by sulfate reducers (or other organisms in the community) also has been examined and it is the principal removal mechanism of methane from shallow marine sediments (24, 25). Methane is also oxidized by certain chemoautotrophic bacteria in the presence of dissolved oxygen, although at much lower rates compared to those observed in sediments (27). 

In this chapter, we discuss the rate coefficients and the mechanisms of oxidation of ketones. The classes covered include alkanones, hydroxyketones, diketones, unsaturated ketones, ketenes, cyclic ketones, ketones derived from biogenic compounds, and halogen-substituted ketones. Photolysis is a major atmospheric process for many ketones, and will be discussed in chapter IX. The major bimolecular reactions removing ketones from the atmosphere are with OH. Although less important than the OH... 

---