Chapter 3- Simple Models

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1、22CHAPTER3.SIMPLEMODELSTheconcentrationsofchemicalspeciesintheatmospherearecontrolledbyfourtypesofprocesses:•Emissions.Chemicalspeciesareemittedtotheatmospherebyavarietyofsources.Someofthesesources,suchasfossilfuelcombustion,originatefromhumanactivityandarecalledant

2、hropogenic.Others,suchasphotosynthesisofoxygen,originatefromnaturalfunctionsofbiologicalorganismsandarecalledbiogenic.Stillothers,suchasvolcanoes,originatefromnon-biogenicnaturalprocesses.•Chemistry.Reactionsintheatmospherecanleadtotheformationandremovalofspecies.•T

3、ransport.Windstransportatmosphericspeciesawayfromtheirpointoforigin.•Deposition.AllmaterialintheatmosphereiseventuallydepositedbacktotheEarth’ssurface.EscapefromtheatmospheretoouterspaceisnegligiblebecauseoftheEarth’sgravitationalpull.Depositiontakestwoforms:“drydep

4、osition”involvingdirectreactionorabsorptionattheEarth’ssurface,suchastheuptakeofCO2byphotosynthesis;and“wetdeposition”involvingscavengingbyprecipitation.Ageneralmathematicalapproachtodescribehowtheaboveprocessesdeterminetheatmosphericconcentrationsofspecieswillbegiv

5、eninchapter5intheformofthecontinuityequation.Becauseofthecomplexityandvariabilityoftheprocessesinvolved,thecontinuityequationcannotbesolvedexactly.Animportantskilloftheatmosphericchemististomakethejudiciousapproximationsnecessarytoconvertthereal,complexatmosphereint

6、oamodelsystemwhichlendsitselftoanalyticalornumericalsolution.Wedescribeinthischapterthetwosimplesttypesofmodelsusedinatmosphericchemistryresearch:boxmodelsandpuffmodels.Aswewillseeinchapter5,thesetwomodelsrepresentrespectivelythesimplestapplicationsoftheEulerianandL

7、agrangianapproachestoobtainapproximatesolutionsofthecontinuityequation.Wewillalsouseboxmodelsinchapter6toinvestigatethegeochemicalcyclingofelements.233.1ONE-BOXMODELAone-boxmodelforanatmosphericspeciesXisshowninFigure3-1.ItdescribestheabundanceofXinsideaboxrepresent

8、ingaselectedatmosphericdomain(whichcouldbeforexampleanurbanarea,theUnitedStates,ortheglobalatmosphere).TransportistreatedasaflowofXintothe