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.