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I NBSIR 82-2561

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I NBS Portable Ambient Particulate

I Sampler

U.S. DEPARTMENT OF COMMERCE

National Bureau of Standards

Center for Analytical Chemistry

Washington, DC 20234

November 1982

Final Report

Issued January 1983

Prepared for; ^wwwivlronmental Monitoring Systems Laboratory

nvironmental Protection Agency

esearch Triangle Park, NC 2771

1

2561

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NBSIR 82-2561

NBS PORTABLE AMBIENT PARTICULATE

SAMPLER

Robert A. Fletcher and David S. Bright

U.S. DEPARTMENT OF COMMERCE

National Bureau of Standards

Center for Analytical Chemistry

Washington, DC 20234

November 1982

Final Report

Issued January 1983

Prepared for; Environmental Monitoring Systems Laboratory

Environmental Protection Agency

Research Triangle Park, NC 2771

U.S. DEPARTMENT OF COMMERCE, Malcolm Baldrige, Secretary

NATIONAL BUREAU OF STANDARDS, Ernest Ambler, Director

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ABSTRACT

The NBS portable ambient particulate sampler is designed to collect the

respirable and inhalable particle size fractions at a sampling rate of 6 L/min

for 24 hour sampling periods. Particulates are fractionated and collected

by series filtration. The collection efficiency of the inlet is measured by

comparison with isokinetic probes in the wind tunnel. The collection

efficiency and sampling size characteristics of two small personal cyclone

samplers are also reported.

This work was sponsored by the Environmental Protection Agency under

Interagency agreement no. AD-13-F-1-535-0.

iii
CONTENTS

Abstract ............ ill

Figures v

Acknowledgements vi

1. Introduction 1

2. Conclusions 3

3. Recommendations for Future Work 4

4. Designing the NBS Sampler 5

5. Testing of Sampler Components 10

6. Sampler Noise Measurements 16

7. Wind Tunnel Test of Inlet 18

8. Cut Test of Cyclones 23

9. Atomizer Size Calibration 27

References 29

Appendices

A. Parts List 31

B. User Instructions 35
FIGURES

Number Page

1 Schematic of sampler 2

2 Schematic of inlet 7

3 Pump efficiency test 9

4 Battery life time test 11

5 Pulsation dampening test 12

6 Coarse filter particle size cut test and effects of filter

loading 14

7 Sampler inlet cut test 15

8 Sampler noise measurements 17

9 Wind tunnel 19

10 Effect of wind speed on inlet sampling efficiency 20

11 Horizontal particle concentration profile 22

11 Effect of wind speed on inlet collection efficiency 22

12 Cyclone cut test 25

13 Effect of wind speed on cyclone collection efficiency 26

14 Atomizer size distribution 28

V
ACKNOWLEDGEMENTS

The authors wish to thank Dr. John D. Spengler and co-workers (Harvard

School of Public Health) for helpful discussions and the loan of a sampler.

The authors would also like to thank Drs. Larry Doemeny and Paul Baron of

NIOSH and T. Dzubay and R. K. Stevens of EPA for advice during the early

stages of the project. We would like to thank Dr. Ben Liu for his advice

with respect to wind tunnel sampler testing and Dr. Walter John and

Steve Wall for use of their inlet design.

vi
SECTION 1

INTRODUCTION

We have developed a portable ambient particulate sampler that collects

both inhalable (_f^l5 ym) (1) and respirable (up to 3 ym) particulates for use

in personal exposure monitoring applications. The NBS sampler is designed to

complement and supplement exposure monitoring data obtained by existing area sampling programs. This has become an important issue based on evidence that

personal exposure is often not accurately reflected by area sampling (2)

Also, exposures can be appreciable in confined areas (3) where area samplers

are rarely placed. Although existing personal samplers might perhaps be

modified to collect the Inhalable fraction as well as the respirable fraction,

there are other reasons for developing another sampler. First, to fit easily

into the present sampling program, the sampler has to run for 8 to 24 hours

per battery charging. Also, ambient atmospheric particle mass concentration

levels are 10 to 100 micrograms per cubic meter. Obtaining sufficient sample

for gravimetric analysis at such concentrations requires a flow rate that is

greater than that available with any current personal sampler or pump.

This paper describes the design of the NBS sampler shown in Figure 1 and

reports the results of tests performed on prototypes. The particle collection efficiency of the sampler inlet has been characterized for wind

conditions representative of indoor and calm outdoor air. We describe

results indicating that for particles larger than 5-7 micrometer diameter

the sampler may either over sample or under sample, depending on wind

velocity and direction.

Two small cyclone samplers, the 10 mm Nylon and the H&H cyclone sampler*,

have received wide use in industrial and mining environments. This report

also discusses our test results for these samplers.

•k In order to adequately describe materials and experimental procedures, it was occasionally necessary to identify commercial products by manufacturer's

name or label. In no instance does such identification imply endorsement

by the National Bureau of Standards nor does it imply that the particular

products or equipment is necessarily the best available for that purpose.

1
Inlet

2
SECTION 2

CONCLUSIONS

The NBS portable particulate sampler collects the respirable and inhalable size fractions of airborne particles. The collection efficiency has

been characterized for wind speeds ranging from indoor (0.15-0.5 m/s) to

moderate outdoor (2.4 m/s) conditions. Flow rates of 5.5 to 6.5 L/min can be sustained from 20 to 60 hours by the 1.6 kg (4 pound) sampler.

The sampling efficiency of the two cyclone samplers tested were found

to be slightly wind directional and orientation independent for 1 ym mass mean diameter particles in the wind tunnel. The cut-points (diameter of

particle having 50% penetration through the cyclone sampler) were found to be

the expected values.

3
SECTION 3

RECOMMENDATIONS FOR FUTURE WORK

Our reconnnendations for future research on the NBS sampler are:

1. To continue modification and testing of the inlet to reduce the effects

of wind speed and direction.

2. To adapt gas monitors for inclusion into the portable particle

sampler.

3. To field test and further refine the sampler to make it more rugged and

dependable.

4
SECTION 4

DESIGNING THE NBS SAMPLER

The NBS sampler was designed to be as small and portable as possible

and yet comply with the following design constraints:

• The sampler should have well defined, stable cut points with respect to

particle size.

• The samples (as with the standard EPA area samplers) should be

collected on filters for subsequent weighing and chemical analysis.

• The sampler should have as high a sampling flow rate as possible since

ambient particle concentrations are typically low and a ^100 yg particle

sample per filter is necessary for a gravimetric measurement uncertainty

of £10%.

• X-ray fluorescence, a widely used method for elemental analysis of

filter samples, requires the sample be in an even, homogeneous

layer on the filter (4)

• To be acceptable to volunteers participating in exposure studies, the

sampler must be light, quiet and inconspicuous.

• To be able to sample at high flow rates for long time periods and

still be small and light weight, the sampler must have energy efficient

components. This means that the sampler air path must have a low

pressure drop and that the motor-pump unit have low internal losses.

DEVICE FOR THE 3 ym RESPIRABLE CUT

The NBS sampler (figure 1) uses a 6.8 ym pore size, Apiezon L coated

Nuclepore filter to achieve the separation (5,6) of the inhalable and

respirable fractions. In addition to serving as the collection substrate

for the coarse or inhalable particle fraction, it has the advantages of

being inexpensive, light weight, and having only 2.5 cm (one inch) of water

pressure drop. The size cut characteristics are adequate despite the

inherent problems of loading and bounce (7,8) associated with membrane

filters

5
The following samplers were also considered for separating the respirable and inhalable particle size fractions, but were not chosen for the

reasons indicated:

a. Cyclone: A 10 mm nylon cyclone is commonly used for industrial (9) and

ambient (10) samplers that collect only the respirable fraction. If it were

used for the NBS sampler to collect the inhalable fraction it would be

necessary to wash the cyclone to retrieve the inhalable fraction, and subsequent handling and preparation would be required for analysis.

b. Impactor: Single orifice impactors have been used for personal samplers

(11), however, a heavy grease coating is needed to minimize bounce, and the

sample is deposited in a spot rather than evenly over the filter. Both of

these sampling effects complicate subsequent analysis.

c. Micro-orifice Impactor: This device (12) may be used without a greased

surface, and will deposit the sample in a sufficiently even layer for x-ray

fluorescence analysis. It is a future possibility for the NBS sampler, but

it is still in the developmental stage and would be very expensive.

d. Virtual impactor: This device is used in the dichotomous sampler, but is

not used for the NBS sampler because it is heavy and complicated. Also,

unless cascade Impactors are used, some of the fine fraction would always

contaminate the coarse fraction.

e. Electrical Mobility Analyzer: This device has a very low pressure drop

and works well for particles smaller than 1 micrometer, but not well for

larger particles. It is large and thus would not be practical as a portable/

personal sampler. Also, the high voltages required by the Instrument are a potential personal hazard.

DEVICE FOR INHALABLE CUT AND INLET

All particles greater than the upper size limit of the inhalable fraction

(10 or 15 pm (13-17) must be eliminated by the inlet. Also, the sampling

efficiency of the inlet should be minimally affected by wind speed and

direction (18-20) . Several Inlets were designed and tested for the dichotomous sampler (21,22), but most of these inlets, even when scaled down to

operate at 6 L/min were larger than our entire sampler. Therefore, we used

part of an inlet (Figure 2) designed by Walter John (22). When scaled for

6 L/min, this inlet is small and includes an impactor which can be designed

to cut at 7, 10, or 15 pm and to minimize bounce even when heavily loaded.

6
Figure 2. Cross section of the inlet, to scale. Full length = 9.5 cm, 15 ym

insert shown, (critical dimensions in cm)

Critical Dimensions for Funnel Inserts

Cut Point A B

(ym) (cm) (cm)

15 3.696 2.372

10 3.863 2.568

7 3.871 2.675

7
FINE FILTER

Ideally, the fine filter should be an absolute filter and have a low

pressure drop. Glass fiber filters that have these characteristics are too

flimsy, massive, and/or hydrophilic. We chose a porous polytetrafluoroethylene (PTFE) fiber filter (23) as the fine filter for collecting the respirable

(j<3 ym) fraction.

FILTER PACKAGE

The coarse and fine filters are strong enough to be mounted without

support pads between the 37 mm plastic rings of a filter cassette. This

filter cassette provides a disposable container for collection and storage,

it minimizes filter contamination, promotes smooth sample deposition, and has

a low pressure drop. The total sampler pressure drop at 6 L/min is only 13

to 15 cm of water. The inlet, impactor, and tubing add only a few mm water

pressure drop to that of the filter cassette.

MOTOR-PUMP UNIT

Batteries make up over half of the total weight of the sampler. Battery

weight, within a given battery type, is roughly proportional to the stored

energy. Therefore, we chose the commercial pump-motor unit that was most

efficient at 6 L/min and 15 cm (6 inches) of water pressure drop (Figure 3).

Fortunately, the Bendix unit, besides being the most energy efficient for

these operational conditions, was also the quietest unit when inside the

sampler case.

AUXILLIARY PARTS

To keep the sampler weight at a minimum, a battery charger was not

incorporated in the sampler. The batteries may be charged externally and

changed when the filter pack is changed. There is easy access to both the

battery and filter packs.

8
%

Efficiency

.22 r

46 46 46 4 46 46 46 4

Flow Rate - L/min

Figure 3. Pump efficiency. Efficiencies of various commercial motor-pump

units for a pressure drop (load on pump) of 15 cm (6 inches) of water.

Efficiency is calculated by dividing the work done per unit time in drawing

air through a restriction, by the electrical power consumed by the motor.

Comparative efficiencies may be very different at other pressure drops.

9
SECTION 5

TESTING OF SAMPLER COMPONENTS

BATTERY - PUMP

Because particle concentration values are dependent on sampler flow

rate, a uniform, stable flow is desirable. The best flow rate control over

long periods of time was obtained using nickel- cadmium batteries connected

directly to the motor (see page 34) . This combination held the flow rate

constant to within 10% (Figure 4). To determine the effect of changes in

flow rate on sampler performance, we compared measurements at 6 L/min and

4 L/min. This reduction in flow rate (33%) Increases by only 7% the diameter

of particles collected at 50% efficiency on the coarse filter. Assuming that

the inlet impactor behaves similarly to a single round jet impactor, a reduction of the flow rate from 6 L/min to 4 L/min would raise the diameter for

50% collection efficiency by only 7%. For normal atmospheric conditions,

l.e., 20-50 ug/m^ particles of <3 ym diameter, the flow restriction due to

the fine filter clogging will reduce the flow rate less than 10%. The

uncertainty in air volume measurement is not critical since at these particle

concentrations, particle mass can only be determined to 10%. We therefore

judged additional flow control for the sampler not to be necessary. In a 8 or 24 h integral sampling period, filter clogging may become a problem when

ambient particle concentration levels are exceedingly high. A short sampling

interval solves this problem.

CASE

We selected a strong, aluminum case, 10 x 10 x 18 cm, which has a handle

and hinged, gasketed lid. Because the case can be made airtight, the

internal volume serves as a pulse dampener which compares favorably with other

methods of pump pulsation dampening (Figure 5) . The sealed case also muffles

the pump noise.

FINE FILTER

Both the fine and coarse filters are sturdy and are weight-stable to a few micrograms. To obtain filter weights to this precision, however, it is

necessary to equilibrate the filters in the weighing room and neutralize

surface electrical charge on the filters and balance compartment with 500

microcurie Polonium ionizing units.

The fine filter causes most of the pressure drop in the sampler. To

minimize the power requirements (pump capacity) of the sampler, we therefore

10
7

F Cells

1.1 kg

Figure 4. Battery pack lifetime. A freshly charged battery pack was

inserted into the sampler and the flow rate monitored with a strip

chart recorder. Note the maintenance of a fairly constant flow rate

for most of the life of the battery pack.

11
10 msec

i I "v\/\/\/\/\/VAyv B

Figure 5. Pulsation dampening tests. Because the suction from diaphragm

pumps is highly pulsatile, a dampener is needed between the pump and the

particle collection elements. The oscilloscope tracings here compare the air

flow through the inlet and coarse filter with various dampeners by showing

the time variation of the pressure differential with respect to ambient

pressure, measured just behind the coarse filter. In A, with no dampener

present, the pulses are 50% excursions from the steady flow rate. This is

improved in B, with a flexible rubber thimble dampener (used in the Bendix

Super Samplers). The NBS sampler, C, gives virtually steady flow. D shows

the corresponding measurement for the Harvard sampler (see acknowledgement)

with different components: single piston Brailsford pump (1.7 1/min) , 3 cm bladder dampener, low porosity PTFE membrane filter, 2 cm "tee" connection

(pressure measured here), and a 10 mm cyclone. The small excursions below

the baseline show that the pulses are large enough to momentarily reverse the

direction of flow.

12
selected the most porous filter available that still collects most of the

fine (respirable) particles. The filter selected is a 3 ym pore PTFE fiber

filter. This filter causes only 8 to 10 cm of water pressure drop at 6 L/min,

yet it collects over 98% of all the fine particles. The worst loss (2%) occurs for monodisperse 0.1 ym NaCl particles. These particles were generated

with an atomizer, dried, and the monodisperse 0.1 ym diameter fraction

selected by an aerosol mobility classifier. The aerosol was detected with a condensation nuclei counter. These tests gave results similar to those of

Liu et al . , (23)

To determine the filter loadings that can be achieved before clogging

occurs, the filter was loaded by sampling in a cigarette smoke-laden room until a reduction in the flow rate was observed. This took several days of

sampling. No reduction in the flow rate for filter loadings up to 100 micrograms was observed; and flow rate changes of only -7% and -12% for filter

loadings of 220 and 400 micrograms, respectively, were noted.

COARSE FILTER

The particle size cut point of the coarse filter was determined for clean

and ambient dust loaded filters. The filter penetration characteristics of

monodisperse aerosol (produced by a vibrating orifice monodispers generator

(24)) were measured with a Cllmet optical particle counter. If C = number of

particles without the filter and = number of particles with the filter in

the particle counter inlet, then the collection efficiency is defined as (C-C^)/C. The aerodynamic diameters of the aerosol particles were determined

by measuring their sedimentation velocity in air and calculating their

diameter using Stokes law. Diameters smaller than 3 or 4 ym were obtained by

dilution of the solution used to generate larger particles of known diameter.

Liquid test particles were generated using DOP and solid particles using

solution of ammonium fluoroscein or ammonium sulfate. No difference was noted

between the two types of solid particles in these tests. Results of the tests

are shown in Figure 6. The cut curves are broad, but the curves for solid

particles closely match the AEG definition (9) for the respirable size distribution. The filter collects the liquid particles more efficiently. This

indicates that the solid particles still experience some particle bounce

despite the grease coating on the filter. The filter becomes more efficient

as the loading increases for both liquid and solid particles because the

effective pore size becomes smaller. The change with loading is less for

solid particles. John ^ al . , (8) attribute this to the fact that grease

coating on the periphery of the pore is partly covered with dust, resulting in

more bounce of the solid particles which counteracts the effect of decreasing

pore size. The cut point for liquid particles is 2.3 ym and for solid

particles is 3.5 ym. The cut data (figure 6) indicates there is considerable

variability in the cut point depending upon the sticking properties of the

particles passing through the Nuclepore filter. However, the range of

variability (2. 3-3. 5 ym) fortuitously coincides with the broad minimum in the

natural ambient particle mass distribution (25) . Thus the coarse and fine

particle fractions collected by the NBS sampler should correlate well with

analogous fractions taken by accepted sampling devices such as the dichotomous

sampler.

13
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14
INLET I^IPACTOR

The cut characteristics of the inlet (Figure 7) were determined with the same test apparatus as above except that oleic acid particulate was used.

Results are also shown in Figure 7 for other Inserts which were designed to

cut at 10 and 7 pm in addition to the 15 ym cut.

Figure 7. Sampler inlet cut test. The results of a pseudostatic test on the

inlet impactor show the inlet impaction or removal efficiency for large

particles. The data points for the 15 ym insert fall within the recommended

region for inhalable particles as of 1980 (26) . The boxed in region in the

upper left and lower right are forbidden regions. If C is the particle count

with the funnel insert removed, and is the particle count with the funnel

in place, then impaction efficiency = (C-C^)/C. The 7 and 10 ym inserts were

designed and tested to meet possible revised definitions of inhalable

particles

15
SECTION 6

SAMPLER NOISE MEASUREMENTS

To obtain the quietest sampler possible we made noise measurements of

various motor-pumps and sampler configurations. The measurements consisted

of frequency spectra and total RMS noise measurements. Measurements were

made in a 55 x 55 x 75 cm cardboard box completely lined with 5 to 10 cm

of foam rubber with a high quality microphone placed 60 cm from the sampler.

Signals from the microphone were amplified and then analyzed with a Nicolet

440A audio spectrum analyzer. Each spectrum is a summation of 32 single

spectra minus 32 background noise spectra taken with the pump turned off.

With the sampler case closed, differences between various pumps were hard to

detect above 500 Hz. This is because the case muffles high frequency sounds.

Representative 500 Hz spectra for two pumps and for the case being open or shut are shown in Figure 8. Curves 1 and 2 show the reduction in noise

attained by closing the case. The most notable difference is the elimination

of the peak at 350 Hz (curve 3) when the case is closed (curve 2) . This peak

corresponded to an annoying pulsing or rattling sound of the pump. The

differences between curves 2 and 3 and the corresponding RMS noise differences

(see caption of Figure 8) do not seem to adequately reflect the large difference in "annoyance level" that occurs when the sampler case is closed.

Curves 1 and 2 compare the much more subtle difference between two makes

of motor-pump. Both were pumping at the same flow rate, and generated pulses

of about the same frequency. These are the fundamental peaks in each spectrum

below 100 Hz. These curves indicate a problem with evaluating the noise

level of the sampler in this way: although curve 1 has larger noise components than curve 2, and a greater overall RMS level as well, curve 1

represents the least annoying or quieter pump, as judged by several people.

This may be because the fundamental component of the Bendix pump is at a lower frequency and the peaks between 100 and 300 Hz are absent, thus making

the pump harder to hear.

16
1.0

Figure 8. Sampler noise measurement. These frequency spectra are representative of measurements taken to select the most quiet sampler configuration.

Relative noise amplitude, in Pa/Hz, is plotted against frequency in Hz. The curves represent: 1. The normal NBS sampler configuration, Bendix pump, case

shut (total relative RMS noise, 0.67); 2. Gilian pump, case shut (total

RMS = 0.55); 3. Gilian pump with case open (total RMS = 1.13). See text for

discussion

17
SECTION 7

WIND TUNNEL TEST OF INLET

Sampling efficiency is defined as the ratio of the number of particles

per volume of air drawn through the inlet to the number of particles per

volume of ambient air. Determination of the latter requires the use of ideal

or isokinetic probes, which in turn requires that one know the air velocity.

This is most easily accomplished by using a wind tunnel test facility (9,21,

27,28). Therefore we have designed and built a low velocity wind tunnel for

particulate and gas sampler testing (Figure 9)

The tunnel has an 0.46 m square cross section, and can provide wind

speeds over the range from 0.3 to 2.4 m/s. The variation of wind speed over

the cross section of the tunnel is within 7% of the average wind, speed except

in the 5 cm boundary layer at the walls. The turbulence ranges from 2% at

0.3 m/ s to 4% at 2.4 m/s. Turbulence is the RMS value of the fluctuating

component of the wind velocity (parallel to the flow) divided by the steady

component. Air velocities and turbulences were measured with a fast response

thin film anemometer which was calibrated with a vane anemometer, which in

turn was calibrated in a special low velocity wind tunnel at NBS (29).

Aerosol is injected into the tunnel, just downstream from the turbulencegenerating "mixing” grid, through a tube with an airfoil attached to its

trailing side. The airfoil helps maintain a stable aerosol plume position.

We kept the aerosol plume narrow so as not to dilute the test aerosol.

The monodisperse test aerosol consisted of either ammonium fluorescein

dye or oleic acid tagged with the dye. All particles were sized by sedimentation. The particles were sampled through the inlet or through isokinetic

probes and collected on filters. The mass of aerosol collected was determined indirectly from spectrophotometric determination of 490 nm absorbance

of the fluorescein dye in 3 mL of 0.1 N ammonia solution. The filters used were 37 mm, 0.3 ym pore size Nuclepore high flow filters. The aerosol was easily recovered from the filter by washing with the ammonia solution and the

filters gave low blank readings.

Sampling efficiency was measured by determining the ratio of the particle

concentration sampled with the inlet to the concentration sampled with

isokinetic probes. The results are shown in Figure 10. The inlet is about

100% efficient for small particles, regardless of wind speed and inlet

orientation. The collection efficiency decreases as particle size increases

and wind speed increases so that, for example, less than 20% of 15 ym particles

are collected at 2.4 m/s, regardless of inlet orientation. For 10 ym

particles, there is a pronounced orientation effect above 1 m/s. For

18
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20
intermediate particle sizes the inlet is 75 to 100% efficient, with a slight

orientation effect, and a slight efficiency decrease with increasing wind

speed. The inlet over-samples large particles at low wind speeds as predicted

by Davies (14) and Fuchs (28) . Data taken with the NBS sampler when wind

speeds are in the range of 2.4 m/s will have to be adjusted for these effects.

Average outdoor wind velocities are about 2.4 m/s. Indoor air velocities

rarely exceed 0.5 m/s (100 ft/min) and are usually below 0.15 m/s (30 ft/min)

out of drafts. From Figure 10, then, we expect the sampler to sample all

particles efficiently indoors.

WIND TUNNEL PARTICLE PROFILES

The particle concentration in the wind tunnel is not uniform. We have

chosen to introduce the particles in a plume in order to not dilute the

concentration. We have characterized the shape and stability of the plume.

Figure 11 shows the relative density of a typical particle plume as a function

of position across the test section of the wind tunnel. This particular

curve shows the particle plume to be skewed to the right, and the test probes

and inlet would be moved over accordingly. The asymmetry of the plume

position is probably due to slight asymmetries in the airfoil of the aerosol

injection tube: the vortex that is formed sheds more off of one side of the

tube. These effects are hard to prevent though we attempted to minimize

them, and have taken account of the asymmetries of plume position in our experiments. The data in figure 11 was taken by continuously traversing the

test section with the probe of the optical particle counter. The multichannel

analyzer, operating in the multiscaling mode, records all counts from the

optical particle counter occurring during a short time period ("^C.b s) and

stores each count total (during the 0.6 s) in a single channel (there are

512 channels) . This counting technique is employed during the probe traverse

and generates a particle concentration profile in about 5 min (0.6 s /channel

X 512 channels 2 307 s or 5 min)

f The characterization of the particle concentration profile helped detect

and explain an effect that gave incorrect sampler efficiencies for the NBS

and Harvard sampler when the samplers were tested intact in the tunnel. Both

samplers were large enough that they had to sit on the tunnel floor in order

to place the inlet near the tunnel centerline. There is a boundary layer in

the tunnel, close to the walls, where the velocity is low and the particle

concentration is low. The sampler cases, resting on the tunnel floor,

deflected some of this boundary layer up and over the sampler, creating a "dead space" very sparse in particles around the inlets of the samplers.

When the inlet or cyclone was isolated from the body of its sampler, this

effect disappeared even when the inlets were placed exactly where they would

have been had they been mounted on the respective sampler case. This effect

made the collection efficiencies of the samplers appear artificially low,

except for the NBS sampler with the inlet fully extended. In this latter

case, the inlet extends far enough that it projects into an unperturbed

region of the aerosol plume.

21
Our wind tunnel is too small to test intact samplers because we are not

able to fill the tunnel homogeneously with aerosol and even the smallest

samplers block more than 5% of the tunnel cross section. When more than 5%

blockage occurs, usually aerodynamic testing becomes invalid.

Horizontal Particle

Concentration Profile

0

.>

0

QC

1

Normalized Horizontal Distance

Figure 11. Horizontal particle concentration profile. This curve is an example of a particle profile in the test section of the wind

tunnel. The relative number of particles counted is plotted vs. probe position across the tunnel. This curve shows the aerosol plume

to be skewed to the right.

0.25 0.5 0.75

22
SECTION 8

CUT TEST OF CYCLONES

On request, we measured the collection efficiencies of two cyclone

samplers as a function of particle diameter. The collection efficiency of a cyclone is the number of particles collected by the cyclone divided by the sum of the number of particles that penetrate the cyclone plus the number

that are collected by the cyclone. The first cyclone is the 10 mm nylon unit

used widely in the U.S. for industrial hygiene applications. This cyclone

was tested under typical conditions, l.e. , highly pulsating flow averaging

1.7 L/min as with the Harvard sampler (John Spengler, Harvard Medical

School) . The second cyclone is an aluminum unit made by H & H of Toronto

,

Canada, and loaned to us by Bob Stevens (ESRL of EPA, Research Triangle Park,

N.C.). The H & H cyclone flow rate was 1.7 L/min smooth flow. The tests

were run under pseudo-static conditions using oleic acid aerosol tagged with

fluorescein dye as the test aerosol. Collection efficiencies were calculated

as the ratio of the amount of dye Inside the cyclone to this amount of dye

plus the amount in the backup filter. The cyclones and backup filters were

washed with ethanol. The ethanol wash (3 mL) was recycled three times

through cyclone during the wash process. The amount of fluorescein particulate found on the filter and in the body of the cyclone sampler was measured

at 490 nm using a laboratory spectrophotometer. The measured collection

efficiencies are shown in Figure 12, along with the respirable curve for

comparison. (Note that the H & H cyclone was not intended to have the AEG

respirable cut characteristics, but to sample larger particles.) The 50%

cut point for the nylon cyclone as used with the Harvard sampler is 2.5 ym.

In general, the cut curve is shifted to slightly smaller sizes in comparison

to the respirable distribution curve, but the steepness of the cut and the

respirable distribution curve are about the same. The H & H cyclone has a 50% cut point at about 5.5 ym, with a slightly broader cut curve.

WIND TUNNEL TESTING OF CYCLONES

The nylon cyclone and the H & H cyclone were tested in the wind tunnel

to measure the effects of wind speed on sampling efficiency. The tests were

run with nominal one micrometer aerodynamic diameter particles made with an atomizer and fluorescein solution (as described on page 29 in this report — a mass size distribution is given there). The results are shown in Figure 13,

where the angle of orientation is the angle between the wind tunnel axis and

a line from the center of the cyclone through the center of the air inlet.

Zero degrees is with the inlet facing head-on into the wind. The inlets of

both cyclones are canted with respect to this latter direction by 90 and 180

degrees). There is a lot of scatter in the data, due to the difficult nature

23
of the experiments and that the data points represent single measurements —

not averages. The effects of wind speed are slight with the nylon cyclone

showing a larger decrease in efficiency at the higher wind speed than the

H & H cyclone. Effects of orientation also were measured for the H & H

cyclone. The effects are minimal, with a slight reduction in efficiency when

the opening is downwind ( 180 °).

Note that these wind tunnel tests were done on isolated cyclones,

not on cyclones mounted on a sampler or attached to a person as they

would normally be used in practice.

24
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26
SECTION 9

ATOMIZER SIZE CALIBRATION

To make a concentrated plume of respirable aerosol In the wind tunnel,

we atomized an ammonium fluorescein solution. The atomizer generates a high

concentration of small polydisperse particles. Because wind tunnel characterization and sampler efficiency measurements depend on collecting measurable

amounts of particles, we used an atomizer generator for some of the tests in

order to decrease the length of the tests. For example, one collection of

2 pm aerosol made with the vibrating orifice generator took over two hours to

get the required mass of dye for an absorption reading. The same collection

using aerosol generated by the atomizer took 5 minutes. The aerosol was generated as follows: a 4 mL aliquot of .69 g/L solution of ammonium fluorescein was put into a DeVilbiss glass medicinal atomizer (glass nebulizer #40)

The atomizer was supplied with dry air at 4.5 L/min. The atomizer was not

modified in any way, except that the rubber squeeze bulb was replaced with

the air supply hose. After generation, the aerosol followed the same procedure

for introduction into the tunnel as an aerosol generated with the vibrating

orifice generator. This procedure included dilution with 1 m^/h dry air and

charge neutralization. For size calibration runs or for testing, the aerosol

was sampled at the other end of the wind tunnel. The atomizer was run for

5 min, then the remaining solution was discarded and the atomizer loaded with

fresh solution for another run. The size distribution shifted slightly

during the 5 minutes of a collection, presumably due to increased concentration

of the solution in the atomizer resulting from evaporation of the solvent.

Therefore, all size measurements are averaged over the 5 minute collection

time. The mass size distribution was calculated from the number size

distribution, which was measured with a Climet CI-208 optical particle counter

and a pulse height analyzer. Because the fluorescein particles absorb

strongly, they appear to the Cimet to be roughly half the diameter of clear

liquid particles that were actually the same aerodynamic diameter. The

optical particle counter was therefore calibrated with monodisperse fluorescein

particles made with the vibrating orifice generator. The largest particles

were sized by sedimentation in air. The sizes of the smaller ones were

calculated by dilution factors (24) from the larger sizes. The mass size

distribution is shown in Figure 14. The mass mean diameter is 0.95 pm, and

most of the mass is confined to aerodynamic diameters between 0.3 and 2 pm.

This aerosol is nominally called 1 pm, for the wind tunnel tests of the

samplers, where the other larger sizes of aerosol were made with the vibrating

orifice generator. Note that very little, if any, of the aerosol is larger

than 3 pm: all of this test aerosol is clearly respirable.

27
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Pm "H 'T3 ,J3

28
REFERENCES

1. Miller, F. , D. E. Gardner, et al.: J. Air Pollut. Control Assoc. 29:610

(1979).

2. Dockery, D. W. and J. D. Spengler: J. Air Pollut. Control Assoc. 31:153

(1981).

3. Repace, J. L. and A. H. Lowrey: Science 208:464 (1980).

4. Dzubay, T. : EPA, Research Triangle Park, Personal communication, 1980.

5. Parker, R. D., G. H. Buzzard, T. G. Dzubay, and J. P. Bell: Atmos.

Envirn. 11:617 (1977).

6. Cahill, T. A., et al.: J. Air Pollut. Control Assoc. 27:675 (1977).

7. John, W. , G. Reischl, S. Goren, and D. Plotkin: Atmos. Envirn. 12:1555

(1978).

8. John, W. , S. Hering, G. Reischl, and J. J. Wesolowski: Final Report,

Interagency Agreement ARB A7-139-30 Air and Industrial Hygiene Laboratory Section, Lab. Services, Berkeley, CA CA/DOH/AIHL/SP-21 (February

1980)

9. Caplan, K. J. , L. J. Doemeny, and S. D. Sorenson: Am. Ind. Hyg. Assoc.

J. 38:83 (February 1977).

10. Turner, W. A., J. D. Spengler, D. W. Dockery, and S. D. Colome: J. Air

Pollut. Control Assoc. 29:747 (1979).

11. Treaftis, H. N. , T. F. Tomb, and C. D. Taylor: Am. Ind. Hyg. Assoc. J.

39:891 (1978).

12. G. A. Kuhlmey, B. Y. H. Liu, and V. A. Marple: A Micro-orifice Impactor

for Sub-micron Aerosol Size Classification. The 89th National Meeting

of the American Institute of Chemical Engineers in Portland, Oregon.

Particle Technology Laboratory Publ. No. 427, August 20, 1980.

13. Fuchs, N. A.: Atmos. Envirn. 9:697 (1975).

14. Davies, D. N.: Brit. J. Appl. Phys. (J. Phys. D.) 1:921 (1968).

15. Bien, C. T. and M. Corn: Am. Ind. Hyg. Assoc. J. 32:453 (1971).

29
16. Agarwal, J. K. and B. Y. H. Liu; Am. Ind. Hyg. Assoc. J. 41:191 (March

1980)

17. May, K. R. , N. P. Pomeroy, and S. Hlbbs: J. Aerosol Sci. 7:53 (1976).

18. Ogden, T. I. and J. L. Birkett: Ann. Occup. Hyg. 21:41 (1978).

19. Pattenden, N. J. and R. D. Wiffen: Atmos. Envirn. 11:677 (1977).

20. Raynor, G. S.: Am. Ind. Hyg. Assoc. J. 31:294 (December 1970).

21. Liu, B. Y. H. and D. Y. H. Pui: p. 383 in EPA Proceedings; Advances in

Particle Sampling and Measurement, Daytona Beach, FI (1979) EPA-600-9-

80-004 (January 1980)

22. John W. S. M. Wall, arid J. J. Wesolowski; Final Report. EPA Grant Number

R806414-02. CA/DoH/AIHL/SP27 Nov. 1981.

23. Liu, B. Y. H. , D. Y. H. Pui, K. L. Rubow, and G. A. Kuhlmey: EPA Progress

Report, May 1978, EPA Grant R 804600, T. G. Dzubay, project officer.

24. Berglund, R. M. and B. Y. H. Liu: Envirn. Sci. Technol. 7:147-153 (1973).

25. Whitby, K. T. , R. B. Husar, and B. Y. H. Liu: J. Colloid Interface Sci.,

29:177 (1972).

26. Smith, W. B. , K. U. Cushing, M. C. Thomas, R. P. Wilson, and D. B. Harris:

Some Aerodynamic Methods for Sampling Inhalable Particles, p. 316 in

Proceedings; Advances in Particle Sampling and Measurement (Daytona

Beach, FL, October 1979) EPA-600/9-80-004 Environmental Protection

Agency (January 1980)

27. Wedding, J. B., A. R. McFarland, and J. E. Cermak: Envirn, Sci. Technol.

11:387 (1977).

28. Fuchs, N. A.: The Mechanics of Aerosols . Pergamon Press, New York,

1964, p. 111.

29. Purtell, L. P. and P. S. Klebanoff: A Low-Velocity Air Flow Calibration

and Research Facility. NBS Tech Note 989 (March 1979).

30
SAMPLER PARTS LIST

FILTER HOLDERS

Company; Millipore Corp. , Order Service Department, Bedford, MA 01730

Telephone: (617) 275-9200

Item: Aerosol Monitor Case, 37 mm diameter, 50/pk

Cat #M000037A0 $46.30 (8/21/80)

Extra rings are needed:

Item; Styrene monitor rings 100/pk

Cat #M000-037-RS $27.20 (8/80)

FILTER HOLDER PRESS

A 1.630" rod sliding in 1.690" id. tubing works well.

Portable drill press mount might work well for loading many samples.

COARSE FILTERS

Company: Nuclepore Corp. , 7035 Commerce Circle, Pleasanton, CA 94566

Telephone: (415) 462-2230

Item; 8 pm (nominal) pore Apiezon coated 37 mm polycarbonate filters

Cat //110832, Lot //51ABC-3-4 $94.00/100 filgers (8/80)

FINE FILTERS (PTFE fiber)

Company; Ghia Corp. 7071 Commerce Circle, Pleasanton, CA 94566

Telephone: (415) 846-8270

Item: 3 ym pore size Zeflour filters, 37 mm diameter (heavy backing)

$98.00/100 filters (8/80)

IONIZING UNITS (polonium 210 - half-life = 138.4 days - reorder regularly)

NOTE: The Nuclepore filters are very difficult to handle and to

weigh without neutralizing the static electrical charges that

easily build up on them.

Company: Nuclear Products Corp., 2519 N. Merced Ave. , South Elmont,

CA 91733

Telephone; (213) 283-2603

31
CASE

Company: Zero East Division, 288 Main St., Monson, MA 01057

Telephone: (413) 267-5561

Roger St. Martin - Local Representative*

Pyttronics, 8220 Wellmoor Ct., Savage, MD 20863

Telephone: (301) 972-0780 Attn: Vernell Jackson

North Carolina Representative

Kirkman Electronics, Inc., 901 W. Second St. (Drawer K - Alem Station),

Winston Salem, NC 27108

Telephone: (919) 722-9131

Item: Aluminum Carrying Case

Cat #ZC 7010 $42.10 (7/80)

NOTE: Inlet hole punched with 1" conduit (chassis) punch - approx.

1 6/16" hole.

RUBBER FEET

Blobbs of RTV silicone rubber cement make functional, though not elegant,

feet

Company: Green Rubber Co., 160 Second St., Cambridge, MA 02142

Telephone: (617) 547-7655

Item: white bumbers SJ5018 $30/100 (3/81)

FOAM

(For case lining to damper noise, vibration)

Company: Green Rubber Co., 160 Second St., Cambridge, MA 02142

Telephone: (617) 547-7655

Item: 3" x 12" #580 polyfoam, 1/4" thick

$2.88/sq. yd. (3/81)

Item: 5" x 5" polyfoam #2 density, 3/4" thick (not used)

$7.14/sq. yd. (3/81)

BATTERIES

Company: Gould Inc., Portable Battery Division, 931 Van Dalia St.,

St. Paul, MN 55114 Attn: Greg Taylor

Item: NiCad cells plastic insulation, solder lugs

C cells (15 hours) - Cat #2.0SCL (18 hours) $6.05 (10/80)

D cells (35 hours) - Cat #4.0SCL (38 hours) $9.90

F cells - Cat #7.0SCL (64 hours) $15.85

32
MSCL. ITEMS

Item: Velcro tape, used to attach battery pack and motor to case.

Item: GE RTV Silicone rubber cement, used to make all rivets air tight.

Item:

NOTE:

(Kodak) Plastic 35 mm film can 9 muffler for pump exhaust).

The output of the motor goes via 1/4" id. flexible rubber hose

to one film can, then via 1/4" id. tygon to the other film can and

then to the outlet fitting, which is a plastic hose-hose connector

cut in half. The tygon is used only if^ it is stiff and can be

force-fit into undersize holes in the plastic film can.

Item: Rubber hose and fitting for case exhaust)

(Exhaust line must not leak into case)

Item: Battery connector, any small 2 lead connector to make battery pack

removable. Note: the batteries have pins that are recessed so that

when the battery is unpluged (sampler off), there is no chance of

NOTE:

metal parts inside the case causing a short.

The battery connector serves as the on/off switch. The batteries

are intended to be changed and charged separately, probably where

the filter packs are changed.

Item: Duct tape to wrap batteries together and insulate them.

Item: 2" X 6" board - holds battery pack with velcro.

Item: hookup wire

Item: 1/4" (copper) elbow to make sharp bends in exhaust line

(3/8" O.D. for 1/4" tubing), swagelok

grommet 5/16" I.D. for 7/16" panel hole

INLET

See accompanying drawing and notes

NOTE: A collar of aluminum is used to securely attach the inlet to the

case. A shoulder may be machined directly on the head instead.

Item: 1.5" aluminum bar stock

Item: Fritted stainless steel, (1/16" thick filters)

Company: Pacific Sintered Metals, 16120 S. Figueroa St. Gardena, CA 90248

Telephone: (213) 321-4595

2" disc., 1/16" thick, 2-5 pm, pore size

Cat. //FCR-2030 $5.62 (6/80)

NOTE: $25 minimum order

33
PUMP

NOTE: There are three Bendlx pumps — the BDX35, BDX55, and BDX60

self contained pump units — all having the same pumping

characteristics. Any of the three will perform equally

well in the sampler, however, the BDX55 pump and item "b" are the only ones that will fit sideways in the case without

removing the rear shaft extension. The shaft extension on the

BDX60 is for a motor speed controller, and is not used in the

sampler. The extension on item "a" is for a worm gear to

drive a mechanical counter to count total pump cycles. This

might be a useful indication of total volume.

Company: Industrial Products Corp., 21 Cavot Blvd., Langhorn, PA 19047

Telephone: (800) 523-3944 Attention: Jeanette Laster

Normal delivery, 1 month, Jeanette's file is under the name D. Bright.

Item a: BDX30 pump. Part #241 7110-0005 $130 (2/81)

Item b: BDX30 pump. Part #241 7110-0003 $120 (2/81)

Item a has a revolution counter, item b does not.

Possible alternative source of item a: John Spengler, Harvard School

of Public Health, 665 Huntington Ave. , Boston, MA 02115

Telephone: (617) 732-1946

Associate: William Turner 732-1245

Spengler used 50 complete BDX55 units as backups for some studies and is

now through with them. He has expressed Interest in selling the units:

they might be less expensive than new replacement motor-pump assemblies

from Bendix.

PUMP (Alternate Source)

Company: Gillan Instrument Corp., 1275 Route 23, Wayne, NJ 07470

Telephone: (201) 696-9244

Item: OEM pump, 4-6 1/m, large cam. P/N 10027

$250 (2/81)

NOTE: This pump is slightly less efficient, noticeably more noisy,

but durable.

Company: Brailsford & Company, Inc., Milton Road, Rye, NY 10580

Telephone: (914) 967-1820

Item: TD-4x2L, 6 volt pump

$140.00

NOTE: Only half as energy efficient as the Bendix, but very durable.

34
NBS PARTICLE SAMPLER OPERATION AND MAINTENANCE

o Schematic of sampler (page 2)

o Filters

1. Handling

2. Storage

3 . Weighing

4. Mounting in holders

5. Loading into sampler

6. Flow rate measurement

o Batteries and charging

o Inlet

1. Impactor ring replacement

2. Extension to full length

35
o Filters

A 6.8 pm grease coated Nuclepore filter is used for coarse particle

collection and a 3 ym pore size Ghia Zeflour teflon fiber filter for fine

particle collection. The filters are neutralized with a 500 yc polonium

source to remove static charges. The Nuclepore fiber is especially hard to

handle directly from the package, but after neutralization it becomes flat

and flexible. It can be mounted with either side up since both sides are

identical. The Zeflour filter should be mounted with the soft, smooth

(velvet-like) PTFE side up. This can be easily determined by touching one

of the filters although that filter can not then be used for collection.

However, with practice, one can recognize the back side by observing the

grain like structure of the support material.

After the filters are neutralized and ready for weighing, an identification number is placed near the filter edge which contributes less than 1 y

to the weight.

The filters are weighed on a Me22 (Mettler) microbalance. The Nuclepore

typically weighs '^10 mg and the Ghia Zeflour weighs from 100 to 150 mg. For

weighing, the filters are fully neutralized and the relative humidity of the

weighing room is held as constant as possible 50 ± 11%. An aluminum foil is

used as a tare weight with each filter to detect balance fluctuation and

systematic weighing errors.

After weighing, the filters are mounted in a 37 mm Mlllipore holder.

This requires 3 rings and a top and bottom cap. The filters should be placed

in the three ring assembly and then the assembly should be pressed tight with

considerable force to make sure the filters do not slip out. Nothing else

supports the filters, so this ring tightening procedure is essential . Once

the filters are mounted, they can be stored with the top and bottom closed.

The series filter assembly is mounted on the back end of the inlet after

the top and bottom caps are removed. An elastic strap helps to hold the

filter unit tightly in place. No tubing is attached to the filter pack (see

schematic of sampler). Once the filters are loaded, fully extend the inlet.

Connect the pump to the battery pack and close the lid. Take care that none

of the exhaust tubes are pinched in the process. Make a flow rate measurement using the rubber adapter provided in the shipment. Slip the adapter

over the inlet entrance so that the openings clear the sealing part of the

adapter. Hook adapter to a low resistance flow meter such as a model TSI

thermocouple gauge. Rotometers and units with several inches of H2 O will

restrict the flow and will not give an accurate measure of the flow rate. A

bubble meter will work if its pressure drop is 2.5 cm of water or less. The

flow should be 6 L/min ±0.5 L/mln.

36
o Batteries and Charging

The sampler should be able to run at 6 L/mln for 25—35 hours without

charging the battery packs. Charging of the battery packs Is done by removing

the battery and connecting them overnight to the charger provided. The

charger light (LED) Indicates either battery charging or when the charger

power cable Is disconnected, battery discharging through the LED.

After completing a sampling period, the filters are removed, capped, and

stored In the humidity temperature controlled weighing room. After 24 hours

equilibration the filters are rewelghed. The foil tare Is used as comparative

"standard" to correct for balance drift.

o Inlet

The Impacting surface Inside the Inlet Is a sintered stainless steel

disc, soaked with vacuum pump oil. The disc Is held In place by friction and can be removed by pushing from the bottom of the Inlet, through the small

hole In Its mounting shoulder. Loose discs can be made to fit snuggly by

drying a layer of glue on the outer edge of the disc before Insertion.

When the discs become dirty, they may be wiped clean and a few drops of

vacuum pump oil added. Allow It to sit overnight and blot away any excess

oil. An alternate procedure. If preferred. Is to remove the disc, clean It

In acetone, soak It overnight In vacuum pump oil, and then drain and blot off excess oil before reinserting the disc Into the Inlet.

37
NBS-114A <REV. 2 *80 ) U.S. DEPT. OF COMM.

BIBLIOGRAPHIC DATA

SHEET (See instructions)

4. TITLE AND SUBTITLE

PUBLICATION OR

REPORT NO.

NBSIR 82-2561

2. Performing Organ. Report No. 3. Publication Date

January 1985

NBS Portable Ambient Particulate Sampler (Interagency Agreement No. AD-13-F-1-535-0)

5. AUTHOR(S)

Robert A. Fletcher and David S. Bright

6. PERFORMING ORGANIZATION (If joint or other than NBS, see instructions) 7. Contract/Grant No. NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE 8. Type of Report & Period Covered

WASHINGTON, D.C. 20234

9. SPONSORING ORGANIZATION NAME AND COMPLETE ADDRESS (Street, City, State, ZIP)

10. SUPPLEMENTARY NOTES

Document describes a computer program; SF-185, FIPS Software Summary, is attached.

11. ABSTRACT (A 200-word or less factual summary of most significant information. If document includes a significant

bi bi iography or literature survey, mention it here)

The NBS portable ambient particulate sampler is designed to collect

the respirable and inhalable particle size fractions at a sampling rate

of 6 L/min for 24 hour sampling periods. Particulates are fractionated

and collected by series filtration. The collection efficiency of the

inlet is measured by comparison with isokinetic probes in the wind

tunnel. The collection efficiency and sampling size characteristics of

two small personal cyclone samplers are also reported.

This work was sponsored by the Environmental Protection Agency

under interagency agreement no. AD-13-F-1-535-0.

12. KEY WORDS (Six to twelve entries; alphabetical order; capitalize only proper names; and separate key words by semicolons)

inhalable aerosol; inlet efficiency; isokinetic probes; portable aerosol sampler;

respirable aerosol

13. AVAILABILITY 14. NO. OF

Unlimited For Official Distribution. Do Not Release to NTIS

PRINTED PAGES

43

1 1 Order From Superintendent of Documents, U.S. Government Printing Office, Washington, D.C.

15. Price 20402.

[}^ Order From National Technical Information Service (NTIS), Springfield, VA. 22161 $7.50

USCOMM-DC 6043-P80
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