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Patrick N. Breysse, PhD, CIH
Peter S.J. Lees, PhD, CIH
Johns Hopkins University

Introduction

Exposure Assessment Methods
Š General air-sampling methodology
Air
Pump
Flow
Adjust
Collection
Media
Air + Contaminant
4

General Sampling Methodology
Š Personal sampling
– Battery powered pump worn by worker
Š Sample from “breathing zone”
Š Area sampling
– Sample from fixed location
5

Concentration
Concentrat ion
=
Mass conta min ant
Volume air
Š Contaminant mass from laboratory analysis
Š Air volume from product of calibrated air flow rate and sampling time
6

Sample Pumps and
Volume Determination

Personal Sampling Pumps
Source: Patrick Breysse 8

Sample Volume
V
=
Q T
Š Where V is volume, L
Š Q is flow rate, L/min
Š T is sample time, min
( 2 .
5 L / min)
(
480 min
)
=
1 , 200 L
( 1 , 200 L ) ( 1 m
3
/ 1000 L )
=
1 .
2 m
3
9

Source: U. S. Government
10

Pump Calibration
Soap bubble flow meter
Pump
Tubing
Cassette
11
Source: Patrick Breysse

Frictionless Piston Flow Meter
Calibrator
Tubing
Source: Patrick Breysse
Sample collector
Pump
12

Soap Bubble Flow Meter
Š Measure time required for bubble to move through specified volume in burette
1
30
.
0 L sec
60 sec min
=
2 .
0 L / min
13

Sample Collection

Sampling for Aerosols
Š Filtration is method of choice
Š Filter defined by composition, diameter, and pore size
Š General classes of filters used:
– Membrane filter
– Nuclepore filter
Source: Peter Lees
15

Filter Selection
Š Membrane filter types
– Mixed cellulose ester (MCE)
– Teflon
– Polyvinyl chloride
Š Filter type selected primarily for compatibility with analytical method
Continued 16

Filter Selection
Š MCE filters
– Clears for microscopy
– Particle counting and sizing
– Fiber counting (asbestos)
Š PVC filters
– Do not absorb water vapor
– Stable for gravimetric analysis
Continued 17

Filter Selection
Š Teflon filters
– Low tare weight
– Low mass gravimetric analysis
18

37 mm Filter Cassette
Š Plastic cassette holds filter paper
Š Filter collects
“total” dust
Š Filter diameter is
37 mm
Retaining
Ring
Filter paper
Support
Pad
Source: Peter Lees
Continued 19

Source: Patrick Breysse
37 mm Filter Cassette
20

Filter Analysis
Š Gravimetric (pre-weight minus postweight)
Š Specific contaminant analysis
– Metals
– Silica
– Fibers
– Polyaromatic hydrocarbons
21

Impingers
Š Old dust methods used microscopic counting of particles (mppcf)
Š Current bioaerosol method (fungal spores and bacteria)
Source: U. S. Government
Continued 22

Size-Selective Samplers

Exposure Assessment Methods
Š Size-selective air-sampling methodology
Air
Pump
Flow
Adjust
Collection
Media
Size
Selector
Air + Contaminant
Š Size selector permits collection of more biologically-relevant aerosol fraction
– Respirable fraction, thoracic fraction, inhalable fraction, PM10, PM 2.5
24

Size Selection: Impactors
Š Multistage or single stage
Š Multiple fractions of varying size ranges possible
– Can be used to determine complete size distribution
Š Flow rate dependent
Š Commonly used for bioaerosol assessment
Š Mostly area-type measurement because high flow rate required
25

S-Stage Impactor Schematic
Adapted by CTLT 26

Size Selection: Cyclones
Š Cyclones are commonly used sizeselective samplers
Š Used to define respirable particle sampling criteria
– Cyclone removal mimics respiratory system when operated
– Flow rate is critical
27

Cyclone Samplers
To sample collection filter
Inertial
Impaction
Source: U.S. Government
28

10 mm Dorr-Oliver Cyclone
Filter cassette
Cyclone inlet
Cyclone body
Source: Patrick Breysse
29

Personal P10 and
PM2.5 Impactors
Š EPA regulates particles <10 um (PM10) and <2.5 um (PM2.5)
Š Sampled using impactors (personal and area samplers)
Š Used in non-occupational sampling associated with ambient air pollution
– Childhood asthma studies
– Effects of PM on mortality
– COPD Studies
30

Adapted by CTLT
Cyclone/Impactor
Performance
31

Direct-Reading Instruments

Direct-Reading Instruments
Š Based on light scattering
– Intensity of scatter light is proportional to concentration
– Require calibration
– Effected by humidity
Š Incorporate data logger so can get concentration over time
33