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

winter

summer

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)

ΔT CPC

NANO-DMPS

CPC-PAIR

FMPS

AIS

APS

IMPACTOR

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...

Number

Surface area

Volume

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)

21

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

Occupational aerosols

Suburban, natural ventilation Suburban, mechanical ventilation

Urban, high mech. ventilation Urban, low mech. ventilation

Paint shop

33

Particle concentration time series during the work day

TiO2

Nanocoatings

Cu

x Oy

Mn

x Oy

Mn

x Oy

Nanocollection

34

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

36

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.