Environmental Engineering Reference
In-Depth Information
methods.already.described;.and.(2).counting.or.mass.measurements.to.determine.par-
ticulate.numbers.and.surface.areas.for.exposure.assessment..It.should.be.emphasized,.
however,.that.even.in.relatively.controlled.environments,.the.challenges.for.protective.
monitoring.are.considerable..As.noted.in.Chapter.9.of.this.topic,.the.current.state.of.
knowledge.on.the.mechanisms.of.action.and.toxicology.of.speciic.nanomaterials.is.
very.limited..The.critical.parameters.or.appropriate.range.for.monitoring.for.worker.
safety.is.not.well.understood.for.most.nanomaterials;.and.given.the.uncertainties,.the.
design.of.worker.safety.monitoring.programs.that.are.protective.and.cost-effective.
remains. dificult. at. best.. As. presented. in. Section. 5.4,. governmental. agencies. on. a.
global.basis.have.made.monitoring.for.worker.safety.a.research.priority.
5.2.1 C
OndensatiOn
p
artiCle
C
Ounter
(CpC)
Condensation. particle. counters. (CPCs). measure. the. number. of. particles. in. an. air.
sample..Commercially.available.models.operate.on.the.principle.that.small.particles.
serve.as.condensation.nuclei.for.vapors..A.constant.low.of.air.is.pulled.through.the.
meter,.irst.entering.a.chamber.saturated.with.water,.alcohol,.or.other.organic.vapor..
The.sample.and.vapor.then.enter.a.cooled.chamber.where.the.vapor.condenses.onto.
the.particles,.forming.droplets.large.enough.to.be.detected.optically..Units.currently.
on.the.market.include.hand-held.and.ixed.monitors,.with.some.capable.of.detect-
ing.particles.down.to.2.5.nm.[43]..This.technique.provides.no.information.on.actual.
particle.size,.shape,.or.composition,.and.particles.larger.than.nanoparticles.will.be.
counted.unless.there.is.some.pre-iltering.or.separation..This.technology.is.useful.
for.air.measurements.where.the.particulates.themselves.have.been.characterized.by.
other. techniques. or. for. monitoring. where. the. absolute. number. of. particles,. either.
total.or.below.a.predetermined.size.cutoff,.will.meet.the.monitoring.objective.
5.2.2 s
urFaCe
a
rea
: t
Otal
e
xpOsure
As.noted.above,.particle.counting.may.not.be.suficient.to.evaluate.potential.risks.of.
exposure.to.nanoparticles..For.each.type.of.nanomaterial,.the.surface.area.of.indi-
vidual.particles.can.signiicantly.affect.the.activity.of.the.material.toward.biological.
tissues.[44].
Development.of.a.real-time.instrument.that.can.monitor.exposure.as.opposed.to.
a.single.parameter.represents.an.important.advance.toward.ensuring.safe.working.
environments.for.the.engineered.nanoparticle.industry..The.electrical.aerosol.detector.
(EAD).measures.a.unique.aerosol.parameter.called.aerosol.diameter.concentration,.
or.total.aerosol.length..This.measurement.(reported.as.mm/cm
3
)
.
represents.a.number.
concentration. multiplied. by. average. diameter,. and. thus. is. directly. related. to. sur-
face. area.. The. aerosol. diameter. concentration,. when. complemented. by. CPC. data.
for.particle.number,.can.be.used.to.calculate.the.average.particle.size..Continuous.
measurements.of.aerosol.diameter.concentration.with.the.EAD.correlate.well.with.
the.surface.area.of.deposited.particles.and.are.believed.to.provide.a.better.estimate.of.
actual.inhalation.exposure.than.either.the.mass.or.number.concentration.of.particles.
could..EAD.has.been.used.in.ambient.air.studies.at.the.St..Louis.Supersite.[45].
