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Chapter 10

Photochemical Reaction Kinetics in Surface Waters

The photochemical transformation kinetics of xenobiotics in surface waters can be modelled, based on a number of photochemically significant parameters of the xenobiotic (absorption spectrum, direct photolysis quantum yield, second-order reaction rate constants with OH, CO3−•, 1O2 and 3CDOM*) and on some environmental variables (water depth, dissolved organic carbon (DOC), concentration values of nitrate, nitrite, carbonate and bicarbonate). The latter define the ability of the water body to attenuate sunlight in the water column and/or to photochemically produce reactive transient species, while the photochemical parameters of the xenobiotic measure its ability to react via the different photochemical reaction pathways. All of the above calculations can be carried out using the APEX software (Aqueous Photochemistry of Environmentally-occurring Xenobiotics). The software is also able to predict the seasonal trends of the phototransformation kinetics and to assess the uncertainty of the model output.

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20 Nov 2015
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