ImpactsoftheLegalizationofMarijuanaonEmissionsandAirQualityinUSKirsti Ashworth1 andChristineWiedinmyer2

1UniversityofMichigan,2NationalCenterforAtmosphericResearch

1.INTRODUCTIONRecentchangesinUSstateregulationsallowforlegalmarijuanacultivationfacilities(MCFs,Figure1)anduseinColoradoandWashington.Marijuanaplants(Cannabisspp.)emitprimarilybiologicalparticles(e.g.,Fungi,Pollen[1,2])andahostofbiogenicvolatileorganiccompounds(VOCs).Theemissions,however,areveryuncertainandarenotwellconstrained.Wehypothesizethat,asthenumberofMCFsincreaseacrossthesestates,particularlyinandnearurbanareas,emissionsofbiogenicVOCswillincreaseandpotentiallyresultinimpactsonregionalairquality(O3 andPM).

Questions:WhatcompoundsarebeingemittedbyCannabisspp.andhowmuch?WhatisemittedreleasedtotheatmospherefromindoorandoutdoorMCFs?AretheemissionsfromMCFssignificantonlocalandregionalscales?Dotheseemissionsimpactozoneandparticulatematterformationonlocalandregionalscales?

AstheregulationsonmarijuanagrowingandusechangeacrosstheUS,theimpactsofthesechangesshouldbeevaluated.Byperformingassessmentsoftheemissionsandairqualityimpacts(orlackof)thatresultfromincreasesinMCFsinColoradoandWashingtonstates,wecanprovideaframeworkofforunderstandingtheairqualityimpactsofthechangingregulationsofmarijuanagrowingandusageacrosstheUS.

2.VOLATILESFROMCANNABISSPP.MeasurementsofemissionsfromCannabisspp.arelimited.EmissionfactorsforCannabisspp. forbiogenicVOCemissionsmodelingarenotcurrentlyavailable.

KnownvolatilesfromCannabis spp. includemonoterpenes (a-pinene,b-mycrene,b-pinene,andlimonene),delta-9-tetrahydrocannabinol(THC,C21H30O2),oxygenatedVOCs,andsesquiterpenes (Figure2;[3-6]).

Incultivationfacilities,a-pinene,b-mycrene,b-pinene,andlimonenewerefoundtobepresentinhighconcentrations(50to100ppb)inthegrowingrooms.AlloftheairborneTHClevelswerebelowthedetectionlevel(0.10μg/sample)exceptforonesample(0.70μg/sample)thatwasnearthedetectionlimit[2].

3.QUICKEMISSIONESTIMATESFORCOLORADOCurrently,inColorado,marijuanacultivationfacilitiesmustbeinafullyenclosed,lockedarea.Asof15June2014,thereareontheorderof1,000cultivationsstatewide.Thesizeandlocationofthesearenotknownatthispoint,butthenumberoffacilitiesischangingrapidly(N.Bryant,StateofColorado,Personalcommunications,13June2014).

Jankauskiene andGruzdeviene [7]reportthatthedrybiomassfromtwocultivarsofCannabissativa rangedfrom162– 227g/m2 (average195g/m2).

AssuminganaverageMCFsizeof½hectare(5,000m2),thatequatesto973metrictonsofdrybiomass.Atotalmonoterpene emissionfactorof5mgg-1 hr-1,assumingthatCannabisspp. havetotalmonoterpeneemissionfactorsonthesameorderasotherhighemittingspecies(e.g.,Eucalytpus spp.andArtemisiaspp.(sage))[8].

Giventheseinitialassumptions,totalmonoterpene emissionsfromMCFsareontheorderof43metrictonyr-1.Theseestimationmethodsarevalidforcultivationfacilitiesintheoutdoors.However,inColorado,whereMCFsmustbeenclosed,emissionstotheatmospherewillalsobereduced.There,theamountofbiogenicVOCsreleasedintotheatmospherewillbeafractionofthetotalanddependentontheventilationsystemateachMCF.

4.IMPLICATIONSOverall,thesefirstestimatesarefairlysmallcomparedtootherVOCsourcesinthestateofColorado.However,asthenumberoffacilitiesincreases,thepotentialtoemitsignificantamountsofbiogenicVOCstotheatmospherebecomesapossibility.Thiscouldbeveryimportantwhenevaluatingimpactsonozoneandparticulatematterformation.

IntheFrontRangeregionofColorado,muchoftheDenvermetropolitanareaincludingDenver,Boulder,andpartsofWeldcountieshaveozoneproductionthatisVOC-limited(G.Tonnesson,US.EPARegion08,Personalcommunications,10June2014).Therefore,itispossiblethatincreasesinVOCs,includingemissionsfromMCFs,couldcauseincreasesinozoneconcentrationsincertainareas.

Figure2:VolatilesfromCannabisspp.

alpha-pinene

beta-pinene

myrcene

limonene

beta-caryophellene

ocimene

otherMTs&SQTs

other

oxygenatedVOCs

Figure1:PictureofMarijuanaCultivationFacility

5.FUTUREWORKTheemissionsproposedherearehighlyuncertainduetothelackofdataneededtobetterconstraintheestimationprocess.WerecommendthefollowingforadvancingtheknowledgewithregardtoquantifyingtheatmosphericimpactsofthelegalizationofmarijuanaintheUS:• QuantifyemissionfactorsandbiomassdensitiesassociatedwithCannabis

spp.• Determinethenumber,sizeandlocationofMCFsinlegalizedareas• Performsensitivitysimulationswithchemicaltransportmodelsto

determineif,where,andwhenemissionsfromMCFsareimportanttoozoneandparticulateformation.

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