Industrial Hygiene

Indoor Particles:Technology

Copyright © 2008 by DBS

Contents

• Introduction

• Mass Measurement

• Number Measurement

• Size Distribution Measurement

• Overview of technologies

Introduction

• Active and passive collectionrequired for further physical + chemical + biological analysis

• In-situ techniquesmeasure physical particle characteristic in real time (mass, number, size distribution, surface area)

– Maybe direct (e.g. optical counting) or indirect (oscillating microbalance)

– Developing technology: real-time chemical/biological characterization (Gard et al., 1997; Hairston et al., 1997)

IntroductionAnalysis of Airborne Particles

McMurry, 2000; Willeke and Baron, 2001; Schwela et al., 2002

Mass Measurement

• MethodsGravimetric Methods

Beta Attenuation Methods

Vibration Microbalance Methods

Light-Scattering Methods

Mass MeasurementGravimetric Methods

• Determines mg/m3

• Draws large volume of air over 24 hr period

– Glass fiber or membrane filter– Weighed before and after– 0.3 to ~100 μm particle size

• ‘Hi-Vols’ are not suitable for indoor use due to flow rate

Reeve, 2002

Mass MeasurementBeta Attenuator Methods (BAM)

• Beta particles from 14C source are attenuated (lose signal strength) as they pass through particulate deposits on a filter tape

• Absorption of radiation is proportional to mass of PM

– Contunuous real-time measurement (no weighing required!)

• Range: 30 - 300 µg/m3 • Temperature: -30° to +45°C

• New version is heated to remove moisture effects http://www.thermo.com

Willeke and Hinds, 2001

Mass MeasurementVibrational Microbalance Methods

Tapered Element Oscillating Microbalance (TEOM)

• Air is drawn through a filter at the end of a tapered oscillating glass tube

• Change in frequency is directly related to the mass of PM accumulated

• Range: 30 - 300 µg/m3 • Temperature: -30° to +45°C

Patashnik and Ruprecht, 1980

Mass MeasurementLight-Scattering Methods

• Concentration of airborne particles

• In-situ, real-time measurements

• Categories:

– Nephelometers (wider angle)

– Photometers

Mass MeasurementLight-Scattering Instruments: Photometers

• Most common direct-reading instrument

• Pros:

– Real-time

– Simpler to use, direct reading

– Less expensive (long-term)

• Signal is proportional to total volume (not mass),particle density must be used to derive mass concentration

• Introduces uncertainty in measurements

• pp.66-72 Morawska and Salthammer, 2004

Morawska and Salthammer, 2003

Number Concentration Measurement

• Optical particle counters (OPCs) based on principle of light scattering by particles

– Coincidence error – when 2 particles cross the beam at once

– Limited to particles > 0.1 μm

• Condensation particle counters (CPC)

– Particles drawn through n-butanol vapor

– Magnifies particles by growth via condensation

– Detects down to 10 nm

Size Distribution Measurements

• Mass distribution with particle size

Multistage Impactor (gravimetric or TEOM)

- Larger particles stick to impaction plates

• Number distribution with particle size

Light scattering

or Electrical Low-Pressure Impactor (ELPI)

- Measures electric current of charged particles

at each impaction stage(Marjamaki et al., 2000)

Surface Area Measurements

• Epiphaniometer – determines Fuchs aurface area of particles using radioactivity (Gaggeler et al 1989)

Technology Overview

Question

There are currently several investigations to compare the results of different PM analyzers. What reasons could contribute to this concern?

Measurements are dependent on atmospheric conditions

Absorbed water may be difficult to control during operationsMeteorological conditions may affect flow rate

Each technique responds differently to individual particle sizes

Some components are volatile and may be lost due to heat (TEOM)

References

• *Baron, P.A. and Willeke, K. (eds.) (2001) Aerosol Measurement. Wiley-Interscience, New York.• *Gard, E., J. E. Mayer, B. D. Morrical, T. Dienes, D. P. Fergenson and K. A. Prather (1997). "Real-time

analysis of individual atmospheric aerosol particles: Design and performance of a portable ATOFMS." Analytical Chemistry, Vol. 69, No. 20, pp. 4083-4091.

• *Hairston, P. P., Ho, J., and Quant, F. R. (1997) Design of an Instrument for Real-Time Detection of Bioaerosols Using Simultaneous Measurement of Particle Aerodynamic Size and Intrinsic Fluorescence. Aerosol Science Technology. Vol. 28, pp. 471–482.

• Willeke and Hinds, 2001• *Lai, A.C.K. (2002) Particle Deposition Indoors: A Review (Summary Version). Indoor Air, Vol. 12, pp.

211-214.• Marjamaki, M., Keskinen, J., Chen, D.R., and Pui, D.Y.H. (2000) Performance Evaluation of the

Electrical Low-Pressure Impactor (ELPI). Journal of Aerosol Science, Vol. 31, No. 2, pp. 249-261.• *McMurry, P.H. (2000) A Review of Atmospheric Aerosol Measurements. Atmospheric Environment, Vol.

24, pp. 1959-1999.• *Schwela, D., Morawska, L., and Kotzias, D. (eds.) (2002) Guidelines for Concentration and Exposure-

Response Measurements of Fine and Ultra-Fine particulate Matter for Use in Epidemiological Studies. World Health Organization.

• Patashnik, H. and Ruprecht, G. (1980) A New Real Time Aerosol Mass Monitoring Instrument: The TEOM. Paper presented at the Proceedings of Advances in particulate Sampling and Measurement.

• *Willeke, K. and Baron, P.A. (eds.) (2001) Aerosol Measurement: Principles, Techniques and Applications (2nd ed.). Van Nostrand Reinhold, New York.

Books

• Jacobson, M.Z. (2002) Atmospheric Pollution. Cambridge University Press, Cambridge.

• Morawska, L. and Salthammer, T. (eds.) (2003) Indoor Environment: Airborne particles and Settled Dust. Wiley-VCH.

• Vincent, J.H. (2007) Aerosol Sampling: Science, Standards, Instrumentation and Applications. Wiley.