Industrial Hygiene

Indoor Particles:Fundamentals

Copyright © 2008 by DBS

Atmospheric particulate matter is inherently more difficult to study than gas-phase components of the atmosphere. It is highly variable in size and in chemical composition…

Harrison and van Grieken, 1998

Contents

• Size Distribution

• Classification

• Physical Properties

• Chemical Properties

• Biological Properties

• Sources and Source Characteristics

• Behavior and Transport

• Health Effects

Size Range of Particulate Matter

Morawska and Salthammer (2004)

Chemical, physical and biological classifications

Note: significant size variations – 5 orders of magnitude

Size Range of Particulate Matter

Morawska and Salthammer (2004)

Measurement is complex:What to measure?How to do it?Which instruments to use?

Further complication:Once airborne particles can change with time

Particles > 30 μm are subject to sedimentation

Classification of Particles and Terminology

• Classification based on:– Size– Generation process (primary or secondary)– Ability to enter respiratory systems

Classification of Particles and Terminology Classification by Size

e.g NH4Cl, SO4

2- / NO3- salts

Mineral dust from weathering of rocks and soils

Ultr

a-fin

eC

oa

rse

1 nm

Natural: forest fires, volcanoes etc.

Man-made: fossil-fuel combustion, industry

Fin

e

2.5 μm division is arbitrary, different authors use different values

Sources of Coarse Particles

• Most coarse particles are primary pollutants

• Natural sources: Soil dusts, (similar composition to soil or rocks – Al, Ca, Si, O), sand, sea salt spray, forest fire debris, leaf litter, pollen, volcanic eruptions

• Man-made sources: vehicle exhaust , stone crushing, land cultivation

• Basic due to high soil content

May begin existence as coarser matter

Sources of Fine Particles

• Most fine particles are secondary pollutants – form via chemical reactions and coagulation / nucleation of smaller species

• Natural sources: similar to course particles + aerosols

• Man-made sources: vehicle exhausts, tires, brakes, metal smelting– Diesel engines produce majority carbon particles (soot), gasoline engines

produce majority VOC’s

• The organic content of fine particles is greater than the coarse ones, e.g. urban smog, they are also more acidic

Because of their small size their settling velocity is very small. Most of them remain suspended in air

Most ultrafine particles in urban air are anthropogenic

Classification of Particles and TerminologyClassification by Source or Generation Process

Also nuclei mode, accumulation mode and coarse mode

Classification of Particles and TerminologyRegion of Deposition in the Lung Process

• Inhalable – total airborne particles inhaled

• Thoracic – particles that penetrate behind the larynx

• Extrathoracic – particles that fail to penetrate the larynx

• Respirable – particles that penetrate deep into the lungs

Physical Properties

• Physical properties underlie the behavior, removal processes, health effects

• Size distribution is a variation of concentration, i.e.

– Number and number size distribution

– Mass and mass size distribution

– Surface area

– Shape

– Electrical charge

• More common to measure number-weighted or mass-weighted distribution, due to cube dependence of volume on diameter the graphs are very different

Physical PropertiesShape (Morphology)

Varies with composition

Layers with age

Morawska and Salthammer (2004)

Physical PropertiesSize and Mass Distribution

• All sources generate particles with some distribution of sizes

• May be characterized statistically:

– Mean – average of all sizes

– Median – an equal no. of particles above and below this size

– Mode – the size with the maximum no. of particles

• Most sources have a log-normal distribution (bell-shaped when plotted on logarithmic scale)

• Can be sub-divided into three distinct ‘modes’

Physical PropertiesSize and Mass Distribution

Nucleation Mode: Small particles (0.01 µm) are formed by the condensation of vapors of pollutants (Condensation of H2SO4 and soot particles)

Accumulation Mode: These small particles serve as nuclei and undergo coagulation followed by deposition of gas molecules(Distribution peak 0.1 µm)

Coarse Particle Mode: Particles with distribution peak around 1µm are mainly soot or materials produced from mechanical grinding. Larger particles quickly settle

Different sources are characterized by different size distributions. Can be used as a source signature

Physical PropertiesNumber Distribution

Why no particles down here?

Small particles coagulate

cf. Fig. 2-17Vast majority of particles are ultra-fine

Physical PropertiesMass Distribution

• Number of particles does not represent the actual mass distribution

• Mass (volume) ~ (radius)3

• Larger particles contribute more mass

• Because of their small mass, peak corresponding to nuclei mode is not seen

CoarseUltrafine

cf. Fig. 2-19

Chemical Properties

• Depends on source and post-formation processes – adsorption/desorption, solubility etc.

• Important chemical properties:

– Elemental composition

– Inorganic ions

– Carbanaceous compounds (organic and elemental carbon)

Biological Particles

• Airborne solid particles (dead or alive) that are derived from living things

Matthias-Maser and Jaenicke (1995)

Particulate Matter

Sources and Source CharacteristicsSource Signatures

• Particles may be either:– Primary – emitted directly from sources; or– Secondary – formed within the atmosphere from gas-to-particle conversion

processes

• Particles may be formed through: – Attrition/disintegration processes– Combustion– homogeneous and heterogeneous nucleation processes– Droplet evaporation

• Several mechanisms can be present in a pollution source, resulting in a wide range of sizes and chemical compositions

• Coarse mode particles are mainly formed through mechanical attrition and disintegration processes making them quite distinct in their chemical composition

Sources and Source Characteristics

Morawska and Salthammer (2004)

Sources and Source Characteristics Nucleation Processes

• Involve the conversion of vapor phase materials to a particulate form

• Must cool to the dew point

• Each vapor phase element and compound has a different dew point. Therefore, some materials nucleate in relatively hot gas zones while others remain as vapor until the gas stream is cold.

• Homogeneous nucleation is the formation of new particles composed almost entirely of the vapor phase material. The formation of particles by homogeneous nucleation involves only one compound.

• Heterogeneous nucleation is the accumulation of material on the surfaces of existing particles. In the case of heterogeneous nucleation, the resulting particle consists of more than one compound.

Behavior and TransportPenetration of Outdoor Particles Indoors

• P

Behavior and TransportDeposition

• Bioaerosols:• Behavior is governed by physical characteristics• Concentration is usually significantly lower than non-biological particles• Very limited studies

Behavior and Transport‘Personal Cloud’

• Concentrations of gases and aerosols measured in the vicinity of an individual indoors are greater than concentrations measured away from the individual - ‘The personal cloud’

• Motion stirs up particles on clothes + nearby surfaces

• Body releases IR which stirs up and lifts pollutants

3-67 μg m-3 PM10 and 6-27 μg m-3 PM2.5 (Wallace, 2000)

Rodes et al, 1991 and McBride et al, 1999

Health Effects of Outdoor Pollutants

• Inferred from epidemiology• Main target organ – lungs• Ultrafine particles considerably more toxic than coarse particles

(Donaldson and MacNee, 1998)

Health Effects of Particulates

• Increase the risk of cardiovascular diseases and mortality

– Ultrafine may be especially dangerous(current drive to reduce PM2.5 may be dangerous)

– Particles penetrate the lungs, blocking and irritating air passages

– Toxic organic substances present in the particles

Health Effects

Relationship Between PM 2.5 and Daily Deaths in 6 Cities

Fine particles that originated from auto emissions and sulfate from burning of coal are responsible for increased mortality rate

Cities with high PM2.5 (~20 mg m-3) had 1.4% higher death rate than cities with 10 mg m-3

A 10 mg m-3 drop results in 36000 fewer earlier deaths per year

The shaded area represents uncertainty in data points

NO THRESHOLD!!!

Schwartz et al., 2002

References

• Becker, K., Seiwert, M., Kraus, S., Krause, C., Schultz, C., and Seifert, B. (2002) German Environmental Survey 1998 (GERES III): Pesticides and Other Pollutants in House Dust. Proceedings of the 9th International Conference on Indoor Air Quality and Climate – INDOOR AIR ‘02, Monterey, CA, Vol. 4, pp. 883-887.

• Harrison, R.M. (2004) Key pollutants-airborne particles. Science of the Total Environment pp. 334–335:3-8.

• Matthias-Maser, S. and Jaenicke, R.T. (1995) The Size Distribution of Primary Biological Aerosol particles with Radii greater than 0.2 mm in an Urban Rural Influenced Region. Atmospheric Research, Vol. 39, pp. 279-286.

• McBride, S.J., Ferro, A.R., Ott, W.R., Switzer, P., and Hildemann, L.M. (1999) Investigations of the proximity effect for pollutants in the indoor environment. Journal of Exposure and Analytical Environmental Epidemiology, Vol. 9, pp. 602-621.

• Pope, C.A., Dockery, D.W., and Schwartz, J. (1995) Review of epidemiological evidence of health effects of particulate air pollution. Inhalation Toxicology , Vol. 7, pp. 1-18.

• Pope, C.A. (2000) Epidemiology of fine particle air pollution and human health: Biologic mechanisms and who’s at risk? Environmental Health Perspectives, Vol. 208, Supplement 4, pp. 713.

References

• Rodes , C.E., Kamens, R.M., and Wiener, R.W. (1991) The significance and characteristics of the personal activity cloud on exposure assessment measurements for indoor contaminants. Indoor Air, Vol. 2, pp. 123-145.

• Schwartz, J. et al. (2002) The Concentration – Reponse Relation Between PM2.5 and Daily Deaths. Environmental Health Perspectives, Vol. 110, pp. 1025.

• Seaton, A., MacNee, W., Donaldson, K., and Golden, D. (1995) Particulate air pollution and acute health effects. Lancet , Vol. 345, pp. 176-178.

• Seifert, B. Becker, K., Helm, D., Krause, C., Schultz, C., Seiwert, M. (2000) The German Environmental Survey 1990/1992 (GerES II). Reference Concentrations of Selected Environmental Pollutants in Blood, Urine, Hair, House Dust, Drinking Water, and Indoor Air. Journal Exposure Analysis Environmental Epidemiology, Vol. 10, pp. 552-565.

• Wallace, L. (2000) Correlations of personal exposure to particles with outdoor air measurements: A review of recent studies. Aerosol Science and Technology, Vol. 32, pp. 15-25.

Books

• Brown, L.M. (2003) Ultrafine Particles in the Atmosphere. Wiley.

• Harrison and van Grieken (eds.) (1998) Atmospheric Particles. Wiley.

• 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.