Photochemical degradation transformation

Fig. 7 Conceptual representation of processes influencing the atmospheric transport and fate of POPs. (1) Primary emissions of POPs to the atmosphere, (2) atmospheric deposition and photochemical degradation/transformation, (5) re-volatilisation from secondary sources in the different environmental compartments and burial in sediments, (4) bioaccumulation and biotic transport, (5) accumulation in glaciers and ice caps, with probable releases due to melting...

The major fate mechanism of atmospheric 2-hexanone is photooxidation. This ketone is also degraded by direct photolysis (Calvert and Pitts 1966), but the reaction is estimated to be slow relative to reaction with hydroxyl radicals (Laity et al. 1973). The rate constant for the photochemically- induced transformation of 2-hexanone by hydroxyl radicals in the troposphere has been measured at 8.97x10 cm / molecule-sec (Atkinson et al. 1985). Using an average concentration of tropospheric hydroxyl radicals of 6x10 molecules/cm (Atkinson et al. 1985), the calculated atmospheric half-life of 2-hexanone is about 36 hours. However, the half-life may be shorter in polluted atmospheres with higher OH radical concentrations (MacLeod et al. 1984). Consequently, it appears that vapor-phase 2-hexanone is labile in the atmosphere. 

Hexa- and other higher brominated biphenyls are expected to be present in the particle-adsorbed state in the atmosphere. These PBBs photolyze in solution and in soil (Hill et al. 1982 Ruzo and Zabik 1975 Trotter 1977). Since PBBs present in surface soil are known to photolyze, particle-sorbed PBBs present in the atmosphere may also undergo photolysis. The importance of the photochemical reaction under sunlight illumination conditions for the degradation/transformation of PBBs in air cannot be evaluated due the lack of information. 

Transport from the atmosphere to land and water Dry deposition of particulate and gaseous pollutants Precipitation scavenging of particulate and gaseous pollutants Adsorption of gases onto particles and subsequent diy and wet deposition Transport within the atmosphere Turbulent dispersion and convection Atmospheric transformation Diffusion to the stratosphere Photochemical degradation Oxidation by free radicals and ozone Gas-to-particle conversion... 

Sorption by sediment and suspended solids Sedimentation and resuspension of solids Aerosol formation at the air-water interface Uptake and release by biota Transport within water bodies Turbulent dispersion and convection Diffusion between upper mixed layer and bottom layer Transformation Biodegradation Photochemical degradation... 

Kujawinski, E. B., Del Vecchio, R., Blough, N. V., Klein, G. C., and Marshall, A. G. (2004). Probing molecular-level transformations of dissolved organic matter Insights on photochemical degradation and protozoan modification of DOM from electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry. Mar. Chem. 92, 23—37. 

In addition to the applications reported here, gas chromatography-mass spectrometry has been employed in the characterization of photochemical degradation products of p,p -DDT and p,p -DDE (27), synthetic intermediates in p,p -DDT metabolism studies (28), and transformation products of herbicidal chloroanilines in soil (29). 

Wetzel, D.L and Carter, R.O., III (1998) Synchrotron powered FT-IR microspectroscopic incremental probing of photochemically degraded polymer films, in Fourier Transform Spectroscopy (ed. ).A. deHaseth), American Institute of Physics, Woodbury, New York, pp. 567-70. 

Photooxidation Photooxidation is considered another factor involved in the transformation of crude oil or its products released into the marine environment. The photochemical degradation can yield a variety of oxidized compounds that are highly soluble in water. However, it should be noted that for most oils, photooxidation is probably a minor process in terms of changing their fate or mass balance after a spill. 

In order to predict the fate of an anthropogenic pollutant in natural waters, it is necessary to know how it is transported and how it is transformed, either biologically or abiotically, in the environment. For many compounds, photochemical degradation reactions are important destruction pathways. The behavior of a photochemically active compound in a surface layer, either one made up of surface-active or water-insoluble compounds, is likely to be dissimilar to its behavior in aqueous solution. Only a few studies have examined the question of the photochemical fates of organic compounds in natural surface layers in one recent example, Zadelis and Simmons reported that the photolysis of... 

Katoh Takahashi studied photochemical degradation under pulsed laser irradiation in order to examine the decomposition behaviour of l-methyl-3-butylimidazolium bis[(trifluoromethyl)sulphonyl]amide and iodide. They concluded that the excited state l-butyl-3-methylimidazolium cation ([BMIM ] ) underwent degradation efficiently and suggested that the neutral l-butyl-3-methylimidazolium radical ([BMIM] ) was relatively stable (Katoh Takahashi, 2009). The majority of studies have looked at the photodegradation of imidazolium-based ILs. Nevertheless, there is some information on the photochemical transformations of pyridinium salts, which could be a good starting point for later IL degradation studies (Damiano et al., 2007). 

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