?url_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Adc&rft.relation=http%3A%2F%2Fmiis.maths.ox.ac.uk%2Fmiis%2F317%2F&rft.title=Transport+and+Reaction+Processes+in+Soil&rft.creator=Arab%2C+N&rft.creator=Bazarganzadeh%2C+Reza&rft.creator=Ceseri%2C+M&rft.creator=Gallimore%2C+Laura&rft.creator=Lacey%2C+Andrew&rft.creator=Lustri%2C+Chris&rft.creator=Majdodin%2C+Rooholah&rft.creator=Ockendon%2C+John&rft.creator=Please%2C+Colin&rft.creator=Seguis%2C+Jean-Charles&rft.creator=Shabala%2C+Alex&rft.creator=Smith%2C+Amy&rft.creator=Smith%2C+Nadia&rft.creator=Somfai%2C+E&rft.creator=Whittaker%2C+Robert&rft.subject=Environment&rft.subject=Food+and+Drink&rft.description=In+order+to+register+agrochemicals+in+Europe+it+is+necessary+to+have+a+detailed+understanding+of+the+processes+in+the+environment+that+break+down+agrochemicals.+The+existing+framework+for+environmental+assessment+includes+a+consideration+of+soil+water+movement+and+microbial+breakdown+of+products+in+soil+and+these+processes+are+relatively+understood+and+represented+in+models.+However+the+breakdown+of+agrochemicals+by+the+action+of+light+incident+on+the+soil+surface+by+a+process+termed+photolysis+is+not+so+well+represented+in+models+of+environmental+fate.%0D%0A%0D%0AThe+problem+brought+by+Syngenta+(one+of+the+worlds+leading+agrochemical+companies)+to+the+workshop+was+how+to+include+the+effects+of+light+degradation+of+chemicals+into+predictive+models+of+environmental+fate.%0D%0A%0D%0APhotolysis+is+known+to+occur+in+a+very+thin+layer+at+the+surface+of+soil.+The+workshop+was+asked+to+consider+how+the+very+rough+nature+of+the+upper+surface+of+a+ploughed+field+might+affect+the+degradation+of+chemicals+by+sunlight.+The+discussions+were+directed+down+two+avenues%3A%0D%0A-+firstly+to+determine+how+the+very+small+distances+over+which+photolysis+occurs+might+be+adequately+incorporated+into+models+of+transport+in+soils+and%2C%0D%0A-+secondly+to+consider+how+the+rough+surface+might+modify+the+illumination+of+the+surface+and+hence+alter+degradation.%0D%0A%0D%0AThe+rate+of+degradation+by+photolysis+is+measured+in+the+laboratory+by+illuminating+a+thin%2C+typically+about+1+or+2+mm%2C+layer+of+soil+with+very+strong+xenon+lamps.+The+amount+of+chemical+is+measured+at+various+intervals+and+is+fitted+to+a+first-order+process.+Field+experiments+where+the+chemical+is+sprayed+on+a+bare+field+show+evidence+of+photolysis+indicated+by+biphasic+degradation+patterns+and+the+presence+of+breakdown+products+only+formed+by+photolysis.%0D%0A%0D%0AThis+report+addresses+methods+for+mathematically+modelling+the+action+of+photolysis+on+particular+relevant+chemical+species.+We+start+with+a+general+discussion+of+mechanisms+that+transport+chemicals+within+soil+%C2%A72.+There+is+an+existing+computational+model+exploited+by+Syngenta+for+such+modelling+and+we+discuss+how+this+performs+and+the+predictions+that+can+be+derived+using+it+%C2%A73.%0D%0AThe+particular+mechanism+of+photolysis+is+then+considered.+One+aspect+of+this+mechanism+that+is+investigated+is+how+the+roughness+of+the+surface+of+the+soil+could+be+adequately+incorporated+into+the+modelling.+Some+results+relating+to+this+are+presented+%C2%A74.2.+Some+of+the+original+experimental+data+used+to+derive+aspects+of+the+model+of+photolysis+are+revisited+and+a+simple+model+of+the+process+presented+and+shown+to+fit+the+data+very+well+%C2%A75.%0D%0ABy+considering+photolysis+with+a+constant+diffusion+coefficient+various+analytical+results+are+derived+and+general+behaviour+of+the+system+outlined.+This+simple+model+is+then+applied+to+real+field-based+data+and+shown+to+give+very+good+fit+when+simply+extended+to+account+for+the+moisture+variations+by+utilising+moisture+dependent+diffusion+coefficients+derived+from+the+existing+computational+model+%C2%A75.3.+Some+consequences+of+the+simple+model+are+then+discussed+%C2%A76.&rft.date=2010&rft.type=Study+Group+Report&rft.type=NonPeerReviewed&rft.format=application%2Fpdf&rft.language=en&rft.identifier=http%3A%2F%2Fmiis.maths.ox.ac.uk%2Fmiis%2F317%2F1%2Freport_v6.pdf&rft.identifier=++Arab%2C+N+and+Bazarganzadeh%2C+Reza+and+Ceseri%2C+M+and+Gallimore%2C+Laura+and+Lacey%2C+Andrew+and+Lustri%2C+Chris+and+Majdodin%2C+Rooholah+and+Ockendon%2C+John+and+Please%2C+Colin+and+Seguis%2C+Jean-Charles+and+Shabala%2C+Alex+and+Smith%2C+Amy+and+Smith%2C+Nadia+and+Somfai%2C+E+and+Whittaker%2C+Robert++(2010)+Transport+and+Reaction+Processes+in+Soil.++%5BStudy+Group+Report%5D+++++