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Particulate Matter
Patrick N. Breysse, PhD, CIH
Peter S.J. Lees, PhD, CIH
Johns Hopkins University
Section A
Introduction and Definitions
Aerosols: Definition
Š Stable suspensions of solid or liquid
particles in air
Š Examples:
– Cigarette smoke
– Welding fume
– Sea mist
4
Types of Particulate Aerosols:
Dusts
Š Solid aerosols generated by the
handling, grinding, abrasion, or cutting
of a bulk material
Š Dust particle size is related to the
amount of energy involved in creation;
the higher the energy—the smaller the
particle created; the lower the energy—
the larger the particle created
Š Examples: Saw dust, coal dust
5
Types of Particulate Aerosols:
Mists
Š Liquid aerosols generated by
condensation from a gaseous state or
by the breaking up of a bulk liquid into a
dispersed state
Š Droplet size related to energy input as
in dusts and fibers
Š Examples: Metal working fluid from
lathe, paint spray, liquid mixing
operations
6
Types of Particulate Aerosols:
Smoke
Š Solid aerosols resulting from the
incomplete combustion of carbonaceous
materials
Š Wide range of particle sizes
Š Size related to combustion efficiency
– High efficiency = smaller particles
– Low efficiency = larger particles
Š Examples: Wood smoke, diesel exhaust
7
Types of Particulate Aerosols:
Fumes
Š Solid aerosols generated by the
condensation of vapors or gases from
combustion or other high temperature
processes
Š Usually very small and spherical
– Sources: Welding, foundry and
smelting operations, hot cutting or
burning operations
8
Types of Particulate Aerosols:
Bioaerosols
Š Solid or liquid aerosols from biological
sources
Š May be infectious, allergenic, and/or
irritating
Š Wide range of particle sizes
– Virus (0.002–0.03 um)
– Tree pollen (10–100um)
Š Examples: Mold spores, animal
allergens, anthrax
9
Types of Particulate Aerosols:
Fibers
Š A special (based on toxicological
properties) kind of dust that is fibrous in
nature (i.e., longer than it is wide)
Š Aspect ratio (L:W) defined as 3:1 or 5:1
Š Toxicity a function of composition, size,
and number of fibers
Š Examples: Asbestos, fiberglass,
refractory ceramic fibers
10
Quantification of Aerosols
mass of contaminan t
Concentrat ion =
volume of air
Š Typical Units: mg/m3, ug/m3
Š Special Units: f/cm3, cfu/m3, mppcf
11
Section B
Particle Size
Behavior of Aerosols
Airborne behavior,
such as settling
velocity, is a
function of:
Š Size
Š Specific gravity
Š Shape
Š Surface properties
Š Slip factor
Fluid drag forces
Buoyant forces
Particle
Gravity
13
Aerodynamic Equivalent
Diameter
Š The Aerodynamic Equivalent Diameter
(AED) of a particle is the diameter of a
unit density sphere that would have the
identical settling velocity as the particle
Continued
14
Aerodynamic Equivalent
Diameter
Š Measure of behavior of particle in air
Š Function of particle diameter, density,
shape, and surface characteristics
Š Determines site of deposition in lung
Š Effects air sampling characteristics
Š Referenced to spherical drop of water
with identical settling velocity
Continued
15
Aerodynamic Equivalent
Diameter
16
Section C
Particle Size Distributions
Particle Size Distributions
Particle sizes
of an aerosol
are typically
log-normally
distributed
Source: U.S. Government
Continued
18
Particle Size Distributions
Log
transformation of
particle size
distribution is
normally
distributed
Source: U.S. Government
Continued
19
Particle Size Distributions
Normalized size
distribution plotted
as cumulative
size distribution
Source: U.S. Government
Continued
20
Section D
Particles and Disease
Cytotoxic Dusts
Š Direct effect on the lungs
Š Examples
– Silica—Silicosis
– Asbestos—Asbestosis
– Coal Dust—Coal workers
pneumoconiosis
– Beryllium—Berylliosis and chronic
beryllium disease
Continued
22
Cytotoxic Dusts
Š Knowing how much and where a dust
will deposit in the lungs is important for
risk determination
23
Aerosols and Disease
Š Disease potential is a function of:
– Chemical properties of particle
– Site of particle deposition in
respiratory system
• Head region
• Thoracic region
• Respiratory region
– Particle clearance path/destination
24
Regional Particle Deposition
25
Site of Particle Deposition
26
Inspirable/Inhalable Dust
Definition
27
Thoracic Dust Definition
28
Respirable Dust Definition
29
Old Particle-Size Conventions
Š Non-respirable fraction (>10 µm AED)
– Can be breathed into nose or mouth,
penetrate head airways, and enter
lung airways
Š Respirable fraction (<10 µm AED)
– Can penetrate beyond terminal
bronchioles to gas exchange region
30
New Particle-Size Conventions
Š Inhalable fraction (<100 µm AED)
– Can be breathed into nose or mouth
Š Thoracic fraction (<25 µm AED)
– Can penetrate head airways and
enter lung airways
Š Respirable fraction (<10 µm AED)
– Can penetrate beyond terminal
bronchioles to gas exchange region
Continued
31
New Particle-Size Conventions
Š Outdoor or Ambient Air Pollution
Š Recommended by EPA
– Particulate matter <10 um (PM 10)
– Particulate matter <2.5 um (PM 2.5)
Š Not deposition-based
Š Roughly correspond to inhalable and
respirable dust
32
Section E
Mechanisms of Particle Deposition
Mechanisms of Particle
Deposition in the Lung
Š Inertial impactions
– Function of particle velocity and
mass
Š Interception
– Function of particle diameter
Continued
34
Mechanisms of Particle
Deposition in the Lung
Š Sedimentation (gravitational settling)
– Function of particle velocity
(residence time) and mass
Š Diffusion
– Function of particle diameter,
concentration, velocity (time), and
distance
Continued
35
Mechanisms of Particle
Deposition in Lung
Inertial impaction:
The process whereby a
particle moving in a gas
stream is unable to remain in
the streamline when the gas
changes direction (turns). As
a result, the particle strikes a
stationary obstacle (e.g.,
surface in respiratory system)
directly in its path and is
removed from the air.
Animated version at http://www.mfg.mtu.edu/cyberman/environment/air/depos.html
Continued
36
Mechanisms of Particle
Deposition in Lung
Interception:
The process whereby a
particle moving in a gas
stream remains in that
airstream but, because of its
dimensions, strikes a
stationary obstacle (e.g.,
surface in respiratory
system) and is removed from
the air.
Animated version at http://www.mfg.mtu.edu/cyberman/environment/air/depos.html
37
Mechanisms of Particle
Deposition in Lung
Sedimentation (gravitational settling):
The process by which a
particle in an airstream is
pulled downward by gravity
until it strikes a stationary
obstacle (e.g. surface in
respiratory system) and is
removed from the air.
Animated version at http://www.mfg.mtu.edu/cyberman/environment/air/depos.html
38
Mechanisms of Particle
Deposition in Lung
Diffusion:
The process by which the
molecules of two or more
substances (very small particles
having some molecular
characteristics) gradually mix as
a result of random thermal
motion, will strike a stationary
obstacle (e.g., surface in
respiratory system) and be
removed from the air.
Animated version at http://www.mfg.mtu.edu/cyberman/environment/air/depos.html
39