Transcript Environmental Chemistry - Robert Morris University

Industrial Hygiene
Indoor Particles:
Technology
Copyright © 2008 by DBS
Contents
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Introduction
Mass Measurement
Number Measurement
Size Distribution Measurement
Overview of technologies
Introduction
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Active and passive collection
required for further physical + chemical + biological analysis
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In-situ techniques
measure 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)
Introduction
Analysis of Airborne Particles
McMurry, 2000; Willeke and Baron, 2001; Schwela et al., 2002
Mass Measurement
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Methods
Gravimetric Methods
Beta Attenuation Methods
Vibration Microbalance Methods
Light-Scattering Methods
Mass Measurement
Gravimetric Methods
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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 Measurement
Beta Attenuator Methods (BAM)
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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!)
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Range: 30 - 300 µg/m3
Temperature: -30° to +45°C
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New version is heated to remove moisture
effects
http://www.thermo.com
Willeke and Hinds, 2001
Mass Measurement
Vibrational Microbalance Methods
Tapered Element Oscillating Microbalance (TEOM)
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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 Measurement
Light-Scattering Methods
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Concentration of airborne particles
In-situ, real-time measurements
Categories:
– Nephelometers (wider angle)
– Photometers
Mass Measurement
Light-Scattering Instruments: Photometers
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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
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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
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Condensation particle counters
(CPC)
– Particles drawn through nbutanol vapor
– Magnifies particles by growth
via condensation
– Detects down to 10 nm
Size Distribution Measurements
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Mass distribution with particle size
Multistage Impactor (gravimetric or TEOM)
- Larger particles stick to impaction plates
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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
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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 operations
Meteorological 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
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*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 ExposureResponse 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
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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.