nanosafety assessment methodology kaarle hämeri professor in aerosol physics university of helsinki...
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Nanosafety assessment methodology
Kaarle Hämeri
Professor in Aerosol physics
University of Helsinki
Finnish Institute for Occupational Health
Take home -message
• Aerosol particles have wide range of sizes and other properties
• Exposure assessment requires determination of relevant aerosol characteristics using right measurement techniques
Content
• Exposure • Health effects• Aerosol particle properties:
– Number– Size– Surface area
• Case studies
Exposure assessment
• Analysis of processes leading to human contact to pollutants after release:– inhalation, ingestion, dermal contact
• Exposure - Event when there is contact with human and environment with pollutant for an interval of time
• Dose - Amount of contaminant absorbed or deposited in the body
Condensation particle counter (CPC)
• Single particle is illuminated with laser and light scattering is measured.
• Before counting, particles are grown by condensation process
TSI CPC model 3007
TSI CPC model 3776
Aerosol particle properties
Particle properties:• Size• Shape (Shape factor χ)
– Surface area– porosity– Volume
• Mass, density• Chemical compositon
– Hydrophobicity, solubility– Surface charge– Electromagnetic properties
Collective properties:• Mass concentration (μg/m3)• Number concentration (1/cm3)• Surface area (m2/m3)
• Size distribution (number, surface area, mass)
Different sizes
• Aerodynamic size– Impactor, APS
• shape, density, size
• Electrical mobility size– Electrostatic classification
• shape, size
• Optical size– Amount of scattered light
• refractive index, shape, size
• Geometric size– Microscope
Size and shape depends on the detection method and the physical principle used
Kuva:Mikko MoisioDekati Oy
Differential Mobility Analysis
E
QaerosolQsheath
Qclassified
Qexhaust
Qsheath + Qexcess
Qaerosol + Qclassified
R ≈
• Aerosol particles are charged by gas ions• Charged particles migrate across a particle-free sheath flow• Particles within a narrow range of mobilities migrate to a sample flow where they are extracted for counting• Pecision is determined by flow rates• Resolution is approximately
scanning mobility particle sizer, SMPS
• Neutraliser, DMA and CPC (+ high voltage supply and flow controls)
Analogy
Particle size classes 1 nm – 100 µm
-> Football hall vs. globe
Or spoonful vs. km3 (1012 l)
Need for investigations of:
-several properties, several intruments and methods...
Nanoparticle surface area monitor
• Detects particles between 10 nm and 1 µm• Concentration range 0.01-2500 µm2/cm3
• 1 s time resolution• Counter-flow diffusion charging of particles• Detection of the total charge (corresponds to
total active surface, condensation sink)
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Nanoparticles
Consepts of nanoparticles (NP) (~1 nm < Dp < 100 nm):
• Natural NPs, i.e. ultrafine particles (UFP) (from vegetation, sea, volcanoes, …)• Incidental NPs (UFP) (combustion, cooking, welding, …)• Engineered NPs (NPs, purposely manufactured)
NPs at work place:• Measurements are needed for exposure assessment and
to control emissions.• NPs are concidered to be potentially most harmful for health.• In occupational environment inhalation is the most significant exposure route for nanoparticles.
Health effects
• Mass? • Number? • Surface area? • Composition?
Importance of the size distribution!
Main open questions:
• Are engineered nanoparticles harmful and how harmful?
• Main sources and emissions?• Health relevant properties and measurables?
– What type of detectors and instruments should be used in determining exposure?
• Chain: emission-concentration-exposure-dose-effect
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Lung deposition
ENPsNanomaterials (CNTs, agglomerates, …)
Lung deposition curves defined by International Comission on Radiological Protection
Suburban, natural ventilation Suburban, mechanical ventilation
Urban, high mech. ventilation Urban, low mech. ventilation
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Particle concentration time series during the work day
TiO2
Nanocoatings
Cu
x Oy
Mn
x Oy
Mn
x Oy
Nanocollection
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Particle size distribution time series
Nanoparticles
1 Background particles
Particles from burning of impurities
Residualparticle
Nucleatedparticles
Respirator protection factor
TH2 class:
APF = 20
Assigned protection factor (APF)Level of respiratory protection that can be expected to be achieved in the work place by 95% of adequately trained and supervised wearers using a properly functioning and correctly fitted respiratory protective device (European standard: EN529).
TH3 class: APF = 200
Schematic of Filter Efficiency vs. Particle Size
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Summary
Concentration levels• Discrimination of NPs from background particles is challenging• Contribution of NPs to particle number concentration was ~99% and
to mass concentration was < 0.01%
Exposure• 70 % of particles were deposited in alveolar region where ~99%
was NPs• 70 % of mass was deposited in head airways where <0.01% was
NPs
RecommendationsMass concentration is not proper metric in exposure assessment for
synthesized NPs.