Thespecificdustmixinanyhouseholddiffersaccordingtoclimate,ageofthehouseandthenumberofpeoplewholiveinit—nottomentiontheoccupants'cooking,cleaningandsmokinghabits.Butnearlyeverywhere,dustconsistsofsomecombinationofshedbitsofhumanskin,animalfur,decomposinginsects,fooddebris,lintandorganicfibersfromclothes,beddingandotherfabrics,tracked-insoil,soot,particulatematterfromsmokingandcooking,and,disturbingly,lead,arsenicandevenDDT.
"Therearemore[components],"Beamersays."Dustisahodgepodgeofallsortsofthings.Itwouldprobablybeimpossibletomakealistofallthepossibleitems."
Butdust'singredientlabelisnotthewholestory,sinceallofthoseflecksandbitsbehavedifferentlyandpresentdifferentlevelsofhealthrisk.Toinvestigatethosefactorsmoreclosely,LaytonandBeamerdevelopedacomputeralgorithmthatlookedatthesize,sourceandtoxicityofdustparticlesaswellashoweasilytheyenterthehouse,iftheyeverexitand,ifso,bywhatroute.Thatinformation,byextension,canprovideatleastaroughsenseofthedustloadinyourownhome.
Asageneralrule,themajorityofhouseholddust—about60%—comesfromoutside,throughwindows,doors,ventsand,significantly,onthesolesofyourshoes.Smallerdustparticles—from28to49microns,orthousandthsofamillimeter—tendtostayonyourshoes.Therestisshakenoffinside.Ahighershareofthedustthatfloatsintheairgetsdeposited,butagain,there'salotthatdetermineshowmuchanyonehomewillget.
"HereinArizona,"saysBeamer,"whereweleaveourwindowsopenmostoftheyearandhaveanaridclimate,wewouldprobablyhaveahigherratio."Industrialcentersorsootycitieshaveplentyofdusttoo,thoughfordifferentreasons.
