P.1 

OAR Box 1128 

Prepped by Ollie Stewart 

Document Number: 

61)11-1-239 

Docket Number: 

A-83-22 

Printed 4/21/2008 11:07:13 AM Sheet 61 of 198 
fr~*3 -. 

f?jrO. O v~F 

nil " J, 

•'.•.• » i '... 2 

EPA AIR DOCKET 

^cCUft(. 

<TP.2 

9~^A 

CHARACTERISTICS OF AEROSOL SAMPLERS USED IN 

AMBIENT AIR MONITORING 

C 

BY: Andrew R. McFarland 

Carlos A. Ortiz 

Civil Engineering Department 

Texas A&M University 

College Station, Texas 77843 

Charles E. Rodes 

Environmental Monitoring and Support Laboratory 

U.S. Environmental Protection Agency 

Research Triangle Park, North Carolina 27711 

Paper Presented At 

86th National Meeting 

American Institute of Chemical Engineers 

Houston, Texas 

April 1-5, 1979 
P.3 

ABSTRACT 

c 

Aerosol collection characteristics of the 15" x 15" (0.38 x 0.38 m) 

Hi-Vol, 11 V x 14" (0.29 x 0.36 m) Hi-Vol, membrane, cascade impactor, 

ERC dichotomous (early model) and Beckman dichotomous ambient air samplers 

were evaluated by wind tunnel testing. 

The systems were tested to determine the effects of typical sampling 

variables such as wind speed (2, 8, and 24 km/hr) and direction (for samplers 

with assymetric inlets), aerodynamic particle size over the range of 1-30 ym, 

sampling flow rate, and internal wall losses. Wind velocity was a major 

cause of bias for the six samplers when collecting aerosol particles > 10 ym.. 

Characteristic curves were very similar for the 15" x 15" Hi-Vol and the 

1 1V x 14" Hi-Vol. At 28 ym and wind speeds of 2, 8, and 24 km/hr, sampling 

effectiveness values respectively were 81, 58, 43 percent for the 15" x 15" 

Hi-Vol and 72, 50, and 43 percent for the 11%" x 14" Hi-Vol. Sampling 

effectiveness at 24 km/hr when the Hi-Vol roof ridge was either perpendicular 

or parallel to the flow for 23.5 ym was approximately 25 percent less than 

when the roof ridge was oriented 45° to the flow. Determinations were made 

of the collection of wind driven particulate matter by a Hi-Vol when the 

sampler is not in operation. This deposition in the standby mode was noted 

to increase with larger particle sizes and higher wind speeds. 

The rainshield inlet of the membrane and cascade impactor samplers 

showed less than 10 percent collection at 24 km/hr as compared to more than 

75 percent at 2 km/hr for 28 ym particles. Wall losses as.high as 95 percent for 10 ym and 50 percent for 3.75 ym particles were measured for the 

cascade impactor system. 
P.4 

Collection characteristics of the ERC dichotomous sampler show that 

the particle size associated with 50 percent effectiveness is reduced from 

approximately 15.5 to 6.3 ym as wind speed is increased from 2 to 8 km/hr. 

For the Beckman sampler the corresponding values of particle size for the 

two wind speeds are 15.5 and 13 ym. 

V 
P.5 

I, 

INTRODUCTION 

Characterization of the concentration of suspended particles in the 

ambient atmosphere is primarily accomplished through the use of several 

thousand Hi-Vol samplers spread across the United States. These samplers 

have an efficiency approaching 100 percent for particles for which the 

gravitational and inertial forces are small (less than approximately 5 ym); 

however, for larger-sized particles the efficiency is quite variable and 

depends not only upon particle size but also upon wind speed and direction (1), 

and to a limited extent upon air sampling rate. In field applications, 

characterization of aerosol concentration is difficul t when the upper size 

limit of the sampler is variable. Also, since the Hi-Vol samplers are not 

size segregated near the center of the atmospheric aerosol distribution 

(e.g., fractionation of respirable, <2.5 ym, from non-respirable particles, 

>2.5), long term particle concentration trends may be misleading. Public 

Health Service (2) studies for the period 1957 to 1966 showed that in urban 

regions the particle concentration had decreased, whereas, a corresponding 

increase had occurred in non-urban areas. This may simply reflect a shift 

in particle size distribution in urban areas. I t is possible that the concentration of respirable particles actually increased in urban areas during 

the period, but because of a decrease in the emissions of large particles 

due to the application of abatement technology, the overall concentration 

measured with the Hi-Vol approach would show a decrease. To enable interpretation of both historical data and data which are currently being accumulated 

with the aid of Hi-Vols, i t is highly desirable to acquire additional understanding of the inlet particle transport characteristics of the system. 
P.6 

I 

Analysis of data from most other ambient air samplers suffers from the 

same problems as the Hi-Vol, that is, a lack of information on the inlet 

fractionation characteristics as functions of the environmental.conditions. 

It would be expected, however, that systems which employ internal classification devices (e.g., impactors or the dichotomous sampler) would yield 

information on the concentration of respirable-sized material which would 

not be strongly influenced by inlet design. 

Several investigators (3-16) have examined the basic fluid and particulate mechanics modeling for simple inlet configurations. However, such 

is not the case for the more complex inlet configurations that are used in 

the field. 

Davies (3) conducted a study to determine theoretically and experimentally the conditions for efficient sampling with respect to the size of 

inlet tubes in relation to particle size, sampling flow and velocity, and 

wind speed. Agarwal (5) studied the mechanics of aerosol sampling and 

transport with the objective of characterizing efficient systems. The 

numerical solution of the Navier-Stokes equation indicated that the sampling 

efficiency of a cylindrical-shaped inlet depends primarily on the Stokes 

number and the relative settling velocity. 

Sampling efficiencies for large windborne particles using 17 different 

sampling devices in the field was measured by May et_ al_. (7). A small portable wind tunnel, 20 x 20 cm square, was used to sample with a standard 

knife-edged orifice under isokinetic conditions for establishment of true 

aerosol concentration. 

McFarland e_t al_. (15) developed an all weather sampler inlet for a 

2.8 s,/min (1 cfm) out-of-doors ambient air sampler that minimizes sampling 

biases from such variables as particle size, wind velocity and direction, 

2 
P.7 

and turbulence intensity. The collection efficiency was examined by generating monodisperse aerosol particles with the aid of a vibrating orifice 

atomizer and introducing the aerosol in a 3.65 x 1.83 m wind tunnel. Efficiency was based on the comparison of aerosol collected by the sampler to 

that of an isokinetic rake. 

A 566.4 £/min (20 cfm) ambient aerosol Hi-Vol cascade impactor was 

fiel d tested by Burton et. al_. (16). I t was also evaluated by Sehmel (17) 

for particle sampling bias caused by interstage losses and by non-wind 

direction sampler orientation. Particle sampling bias was decreased by 

use of a wind oriented inlet on the system. 

Wedding et al_. (1) conducted a study to determine the large particle 

collection characteristics of ambient aerosol samplers. Of the four samplers 

tested, the two that are commercially available are a 23.8 2,/min cascade 

impactor and a Hi-Vol sampler. 

Studies conducted by Steen ejt aK (16, 17, 18) were focused on determination of the sampling efficiency of samplers commonly used in Europe'to 

collect ambient aerosols. To investigate inlet sampling bias, Steen and 

co-workers undertook a program to evaluate samplers in the field and in a 

0.4 x 0.4 m wind tunnel. Hi-Vol samplers were equipped with symmetrical 

inlets, one of these being an isokinetic inlet used as a reference to 

evaluate a modified Hi-Vol in the field . The results confirmed the importance of inlet design to sampling efficiency. 

EXPERIMENTAL APPARATUS 

The wind tunnel testing program was accomplished with the use of three 

different size wind tunnels. A small wind tunnel, 15 cm diameter by 180 cm 
I 

long, was used to obtain high concentrations of monodisperse aerosols to 

facilitat e determination of wall losses and fractionation efficiency for the 

dichotomous samplers and cascade impactor. A medium sized wind tunnel, 61 x 

61 cm by 3.6 m long, was used for the evaluation of the inlet s and sampler 

effectiveness of the dichotomous and membrane sampler and, a large wind 

tunnel 1.5 x 1.5 m cross-section by 9.8 m long, was used to accommodate ful l 

size samplers, where environmental fiel d conditions of wind velocity and 

direction effects could be simulated. For the latte r system, the tes t section was set up with a one RPM turntable to evaluate the effect of wind 

direction on non-circular inlets . 

A vibrating orific e monodisperse aerosol generator system (20, 21) was 

used to generate uniformly-sized oi l droplets from solutions of ethanol and 

olei c acid tagged with uranine. Since particles may possess an electrical 

charge after generation, the freshly formed aerosol was neutralized with a 

10 millicuri e Kr-85 radioactive source. 

Particle size was determined by taking samples of the aerosol with 

the aid of a Casella impactor (22). The particles were collected on clean 

o i l phobic microscope slides treated by immersion in a fluorocarbon surfactant (23). The aerosol samples were checked for size and homogeneity 

under a Nikon LKE microscope with fla t fiel d objective. Particle diameter 

was measured on the projected screen of a Model TVM 302A Pulse System, Inc. 

television monitor. The image was transmitted by an RCA television camera, 

Model TCIOOO, mounted on the microscope. Particle diameter, measured on the 

screen with the aid of a machinist's comparator, was converted to equivalentspherical diameter using a flattening factor (23), 0.690 of the measured particle. 

Also, particle diameter of oi l droplets was converted to aerodynamic particle 
P.9 

diameter as follows: 

D a2 " s '9-*D p2 

where Da - aerodynamic particle diameter 

s.g. = particle specific gravity 

D = particle diameter of oil droolets 

P 

In computing aerodynamic size, the specific gravity of the particle was 

taken to be that of oleic acid, 0.895. 

(D 

L 

METHODOLOGY 

For the evaluation of a sampler in the 1.5 x 1.5 m wind tunnel, the 

device was placed in the test section. In the case of the Hi-Vol, the unit 

was either mounted on the one RPM turntable or set stationary in the appropriate direction. During a test, aerosol was introduced at the wind tunnel 

entrance, mixed and uniformized with the aid of a turbulence grid located at 

the entrance of the wind tunnel, and transported to the test section. Aerosol concentration profiles were determined with the aid of nine isokinetic 

samplers, positioned at 25 cm intervals in both the horizontal and vertical 

directions. These were mounted on a rake at the downwind end of the test 

section, and the flow in each sampler was monitored with a separate rotameter. 

For smoke particles, and small and large monodisperse aerosol particles the 

concentration profiles proved to be a valuable tool for checking the mixing 

at the test section. 

Collection effectiveness of the sampler was determined by comparing the 

concentration determined with the aerosol sampler to that determined with 

the aid of a 8.5 m3/hr (5 cfm) isokinetic sampler (9, 10, 12, 24). 
P.10 

( 

Tests of the small-sized inlets of the dichotomous and the membrane 

sampler were conducted in the 61 x 61 cm wind tunnel. The same testing procedure as that used with the 1.5 x 1.5 m tunnel was employed with only minor 

differences. The mixing of the aerosol particles was accomplished with the 

aid of a Stairmand disc at the entrance of the wind tunnel and then uniformized with a turbulence grid 1.2 m downstream. Also, only the inlets were 

placed in the test section while the sampler set underneath the wind tunnel. 

To determine wall losses of the cascade impactor and to determine wall 

losses and fractionation efficiency of the dichotomous sampler, tests were 

conducted in the 15 cm diameter wind tunnel. Freshly generated aerosol was 

transported to the test section where a portion of the flow was drawn through 

a sample intake tube to the fractionating units. A vacuum blower with a 

cleaning filter was used to maintain a slightly negative pressure in the tunnel 

For the analysis of aerosol collected by the sampler on the filter, and 

particles deposited on the walls of the sampler, a fluorescence technique was 

used to quantify concentrations of uranine. 

Filters and any components of the sampler to be analyzed were placed in 

solutions of ethanol to extract oleic acid and uranine. The volume of ethanol 

wash for the filters ranged from 20 to 250 md, and the filters were left in 

solution for at least one hour before dilution with an equivalent volume of 

distilled water. Sampler components to be analyzed for particle collection 

were thoroughly washed in a detergent solution, rinsed with tap water and 

rerinsed with distilled water and ethanol. After the test, the sampler was 

taken apart; each component to be analyzed was placed in a separate container 

and a measured volume of ethanol was added. By mild agitation of the container for several minutes, the oleic acid and fluorescent material were removed and the solution was diluted with distilled water. 

6 
P.11 

I 

From well-mixed, ethanol-distil led water solutions, about 4 m!, of the 

wash was poured into a cuvette and duplicate readings of fluorescence were 

taken. To stabilize and maximize the fluorescence of sodium fluorescein one 

drop of 1 N NaOH was added to the solution in the cuvette. 

RESULTS 

The data acquired from the experimental study are assimilated in graphical 

form. The collection effectiveness for each of the aerosol samplers is plotted 

as a function of sampling variables: aerodynamic particle size, wind velocity, 

and wind direction for assymetric inlets. Here effectiveness, E, is defined as 

C. 

E = sam 

'iso 

x 100% (2) 

where C„,„ = concentration determined with the test 

s am sampler 

C = concentration determined with the isokinetic 

sampler 

For devices which have high aerosol losses in the internal components, 

(e.g., the cascade impactor and the dichotomous sampler), the total wall 

losses (percent of total aerosol entering the system which is deposited on 

internal surfaces other than the actual collection surfaces) are plotted as 

a function of aerodynamic particle size. 

Duplicate tests were performed for most of the experimental conditions. 

Additional data was acquired if the average value of E, T, was greater than 

50 percent and the ratio of the range of values, R to E was 

> 15% 
P.12 

Also, for the case of E < 50%, if 

i-r 

> 15% 

additional tests were conducted. 

I 

Hi-Vol Samplers 

The Hi-Vols were operated at a flow rate of 1.41 m3/min (50 cfm) to 

determine the sampling effectiveness as a function of particle size and 

wind velocity . The results of these tests for a range of particle sizes 

from 1-30 ym and for wind speeds of 2, 8, and 24 km/hr with the sampler 

rotating at one RPM are shown in Figures 1 and 2. The characteristic 

curves are ^ery similar for the 15" x 15" and the 11%" x 14" Hi-Vols. For 

particles <10 ym sampling effectiveness is over 90 percent for the three 

wind speeds. For particles larger than 10 ym the collection depends on wind 

velocity . At 28 ym the 15" x 15" Hi-Vol (Figure 1) has sampling effectiveness values of 81 , 58 and 43 percent for 2, 8, and 24 km/hr; and for the 

11%" x 14" Hi-Vol (Figure 2) the corresponding effectiveness values are 

72, 50 and 43 percent, respectively. 

To determine the influence of the flow rate on sampling effectiveness, 

the 11%" x 14" Hi-Vol was tested with 29 ym particles at a wind speed of 

2 km/hr with three levels of flow rate: 0.57, 1.41, and 1.92 m3/min (20, 

50 and 68 cfm). The results (Figure 3) show flow rate has littl e influence 

upon performance of the sampler at the conditions tested. However, for 

flow rates lower than those tested, the sampling effectiveness may increase 

due to the sedimentation of wind driven particles on the sampling filter . 
P.13 

L 

100-

£ 80-

UJ 

o 

cr 

UJ 

°-60 

•• 

CCO O 

UJ 

£ 40 

o 

UJ 

fc 2C 

c 

, 1—— i r iii' ' 

n

 o 

0 *"^^ ^ 

o 2 Km/hr V 

o 8 Km/hr \ 

® 24 Km/hr ^ 

> • 

" 

i * — ' 

• i i • * -

1 —•—•—* • • — 

>j 3 ^ 7 10 30 

AERODYNAMIC PARTICLE DIAMETER, }xm 

FIGURE 1. SAMPLING EFFECTIVENESS OF 

15" x 15" HI-VOL. 

9 
P.14 

( 

I00 l-o 

a 

80 

UJ 

o 

cr 

ui 

OL 60 

CO 

CO 

UJ 

£ 40 

o 

UJ 

UL 

^ 20 

0 

— i 1—i—i—r i i 

o ® 

o 2 Km/hr 

© 8 Km/hr 

® 24 Km/hr 

| il l I 1—L_l 

3 5 7 10 

AERODYNAMIC PARTICLE DIAMETER, Mm 

FIGURE 2. SAMPLING EFFECTIVENESS OF 

lUs" x 14" HI-VOL. 

10 
P.15 

c 

0^ 

* 

t 

* 

CD 

I N 

^s» 

do 

N 

§ 

fr 

• s 

vS 

rJ 
P.16 

( 

100 -

0.5 1.0 1.5 2.0 

VOLUMETRIC FLOW RATE, m3/min 

FIGURE 3. EFFECT OF FLOW RATE ON PERFORMANCE 

OF 11V x 14" HI-VOL. 

AERODYNAMIC PARTICLE DIAMETER = 29 ym. 

11 
P.17 

Figure 4 illustrates the deposition of wind driven particles on the 

filte r when the sampler was not in operation. An H V x 14" Hi-Vol was 

set in the wind tunnel in the standby mode and subjected to monodisperse 

aerosols (4-30 ym) at wind speeds of 2 and 8 km/hr. A deposition parameter, 

m/c , is plotted as a function of aerodynamic particle size, where: 

m = deposition rate on Hi-Vol filter , yg/day 

c = mean aerosol concentration collected by isokinetic 

sampler, yg/m3 

( 

The rate of deposition, yg/day, of wind driven particles can be determined 

for a specific particle size by knowing the ambient air concentration, c , 

yg/m3. From Figure 4, the deposition parameter, m, m3/day, is defined by the 

particle size and the wind speed. Rate of deposition of a given particle 

size is the product of the deposition parameter and the ambient air concentration. 

Wind velocity and direction effects on sampling effectiveness are plotted 

in Figure 5. Tests with the 11V' x!4" Hi-Vol yielded results which show a 

variation of sampling effectiveness with sampler orientation. The sampler 

was tested at four different positions: 0° (Hi-Vol roof ridge parallel to 

the flow), 45°, 90° and rotating one RPM. When the Hi-Vol is operated in 

the rotational mode, one RPM, the sampling effectiveness is approximately 

the average of the effectiveness values for the various orientations tested. 

The sampler is less sensitive to wind velocity effects for the roof ridge 

at 45° to the flow, and <15% difference for wind speeds of 2 and 24 km/hr. 

This is not the case for the 90° orientation where the difference is >50?S. 

12 
P.18 

e 

10001 I I I 1111 1—I I I 111 

5 

to 

E 

o 

a 

100 

hi 

hu 

< 

< 

CL 

o 

CO 

O 

a. 

UJ 

o 

10 

1.0. 1.0 

O 2 Km/hr 

• 8 Km/hr 

1 i « i i m 

3 10 

i i i.ii n 

30 100 

AERODYNAMIC PARTICLE DIAMETER, /im 

FIGURE 4. DEPOSITION IN STANDBY MODE, 

11%" x 14" HI-VOL. 

13 
100 T r 1—r—nr 

*m. 

80 

UJ 

o 

cc 

UJ 

Q- 60 

CO 

CO 

Ul 

UJ 

> 40 

ro 

UJ 

u_ 

u_ 

UJ 20 

G 

0 

0 

© 

SAMPLER 

POSITION 

0° 

45° 

90° 

1 RPM 

' I I I I I 

2 4 6 8 10 

WIND VELOCITY, Km/hr 

20 

FIGURE 5. EFFECT OF WIND VELOCITY AND DIRECTION ON 

PERFORMANCE OF 11V x 14" HI-VOL. 

AERODYNAMIC PARTICLE DIAMETER = 23.5 ym 

•o 

co 
P.20 

Membrane Sampler 

The evaluation of aerosol penetration into the rainshield inlet of the 

membrane system is shown in Figure 6 for a sampling rate of 119 fc/min (4.2 

cfm). It may be noted that wind velocity does have a pronounced effect on 

the effectiveness of collection. For particles <5 ym collection is greater 

than 90 percent regardless of the wind speed. For wind velocity up to 

8 km/hr, the effect is not noticeable for particles smaller than 10 ym. 

Particle size associated with 50 percent effectiveness is reduced from 21 ym 

at 8 km/hr to 10 ym at 24 km/h4. 

C 

Cascade Impactor (25, 26, 27) 

During preliminary testing with 10 ym particles at 2 and 8 km/hr, effectiveness values of approximately 10 percent were observed with the cascade 

impactor as opposed to 90 percent for the membrane sampler which has an 

identical inlet configuration. Based on this observation and known facts 

from other studies (27, 28, 29, 30), a detailed study was made to determine 

the wall losses of the impactor as a function of particle size. 

For the cascade impactor operating at 112 i/min (3.94 cfm) the 

results showing total wall losses as a function of aerodynamic particle 

size are given in Figure 7. It may be noted that for aerosol particles 

greater than 2 ym, wall losses increase rapidly from 2 percent to 95 percent for 10 ym and that 50 percent wall losses correspond to 3.75 ym. 

These data support the results of only 10 percent collection effectiveness 

for 10 ym. 

15 
r^-

EFFECTIVENESS, PERCENT 

(Ti 

CD 

cz 

TO 

OO 

3> 

CD 

to 

Co 

O 

-n 

o 

o 

CD 

to 

3=» 

m 

73 

ro 

o o 

> 

m 70 

o 

o 

- < 

21 

> 

S OJ 

o 

> Ol 

30 

H 

o ^ 

r~ 

m 

-, o 

o 

> 

< : 

m H 

m 

70 

•5 o 

3 

I I 

-

~ 

-

-

• * 

- J® *&* 

...... . 

•^ 3 

o o 1 1 1 

® © 0 

ro oo ro Km/hr Km/hr 

4 Km/hi ^ 

i . „ i i , . i ,,i 

00 

o 1 ' " 

1 

o 

o 

• e o 

0J°° 

/ 

M TM 

' 

> 

. 

-

• » 
P.22 

I 

100 

H 

Z UJ 

2 80 

UJ 

CL 

** 

CO 

UJ 

« 60 CO 

o _J 

_J 

_J 

< 40 

55 

_J 

< 

ri n i " 

-

_. 

i i i i r\——C 

1 1 'r-T— 

s^J 

GTo 

/o 

" > ^ ! Il l 

1 1 1 1. 

1 1 1 1 

-

— 

-

_ 

— 

_^ 

-

^ « a i P 4 6 8 10 20 

0.6 0.8 I z ^ 

AERODYNAMIC PARTICLE DIAMETER, pm 

FIGURE 7. WALL LOSSES OF CASCADE IMPACTOR. 

FLOW RATE =112 £/min 

17 
P.23 

ERC Dichotomous Sampler 

The performance of an aerosol fractionator is generally characterized 

in terms of the fractional collection efficiency as a function of particle 

size and the internal wall losses as a function of particle size (31). 

The fractional efficiency curve for the early version of an ERC dichotomous 

sampler, Figure 8, was determined by testing the fractionator head separately in the small aerosol wind tunnel. The quantity of particulate matter 

collected on the large and small collection filters was determined and the 

efficiency, n, calculated as follows: 

I 

m. 

n = m£

 + ms + mw 

where m = aerosol collected on large filter 

m = aerosol collected on small filter 

m = aerosol collected on internal walls 

w 

(3) 

The results of these tests show a cutpoint (particle size for which the 

efficiency is 50 percent) of 2.7 ym. 

Wall losses, WL, were determined in a similar manner and were computed 

from: 

m. 

WL = w 

m w + \ + m s 

(4) 

Wall losses as a function of particle size are also shown in Figure 8. For 

particles between 2.8 and 10 ym, wall losses are S 7 percent. High losses 

for larger particles are due to deposition of aerosol in the upstream 

region of the acceleration nozzle. This could be reduced .by making minor 

modifications in the nozzle geometry. 

18 
P.24 

i 

100 

UJ 

o 

DC 

UJ 

>-

O 

UJ 

o 

U_ 

u_ 

u 

o 

UJ 

_J 

_l 

o 

o 

80 

60 

40 

20 

3 5 7 10 30 

AERODYNAMIC PARTICLE DIAMETER, /*m 

100 

80 

60 

UJ 

o 

cr 

UJ 

CL 

CO 

UJ 

co 

co 

o 

4 0 _J 

20 

FIGURE 8. EFFICIENCY AND WALL LOSSES OF ERC DICHOTOMOUS FRACTIONATOR. 

19 
I 

The ERC system has twin inlets which each sample 14 i/min—one inlet 

for the dichotomous fractionator and the second for a total filter. The 

characteristic dimension of these inlets is small (an opening normal to 

the wind and 3.5 mm in size). The results of tests for these two inlets 

giving effectiveness as a function of particle size and wind velocity are 

given in Figure 9. As may be expected, considering the small opening 

for both inlet systems, the effectiveness is strongly dependent upon wind 

speed. The particle size associated with 50 percent effectiveness for the 

total inlet system is reduced from 16 to approximately 6 ym for an increase 

in wind speed from 2 to 8 km/hr. 

It may be noted from Figure 9 that there is a large difference in 

effectiveness for the total and the fractionator systems. Collection of 

16 ym particles decreases from 50 percent to 24 percent when sampling with 

the fractionation head. The difference in results is due to the internal 

wall losses of the fractionation head. 

Beckman Dichotomous Sampler 

The Beckman dichotomous sampler is an automated system which is designed 

to collect material on as many as 36 sequential filter pairs at pre-programmed time periods. The unit samples ambient air at 16.7 n/min and has 

a nominal cutpoint of 2.5 ym for the internal fractionator. The inlet is 

similar to a unit designed by McFarland et_ al_. (14) and it has a nominal 

cutpoint of approximately 15 ym. 

The results of laboratory testing of the internal fractionator are 

shown in Figure 10 , wherein it may be noted that the cutpoint size is 2 .5 ym 

and that the wall losses associated with the cutpoint are 6 percent. Losses 

20 
r100 

80 

1-

2 

UJ 

o 

cc 

UJ 60 

#» 

CO 

CO 

UJ 

z 

£ 40 

P FEC 

u_ 

L• aU t 

20 

r\ 

1 1 

^ - ^ ""V^^ 

* N\ < * \ 

\ \ 

\ 

_ ^v 

-

— 

-

INLET 

SYSTEM 

TOTAL 

FRACTIONATOR 

' i 

• T " • 1 1 

\ 

\ 

Km/hr 

2 8 

O O 

A A 

i i i 

" T — I -' 1 " " — 

\ Xp 

\ ck \ ^ \ \ \ 

\ A \ 

^ \ 

\ 

\ 

\ 

\ 

\ 

V 

1 1 

— 

-

-

_ 

— 

\ 

o\ 

V \ 

\ \ V \ 

\ \ 

** \ \ \ ^ \ x ^ \ X -J 

V ^-—^^ © " 

1 1 \ Nfc- , ^-^V L 

5 7 10

 3 0 

AERODYNAMIC PARTICLE DIAMETER,Jim 

FIGURE 9. SAMPLING EFFECTIVENESS OF ERC DICHOTOMOUS SAMPLER 
ro 

100 

z 

UJ 

o 

cr 

UJ 

> 

o 

z 

UJ 

o 

80 

6 0 

u. 

u_ 

UJ 4 0 

ro 

UJ 

o 

o 

20 

_QT 1—I—r 

100 

COLLECTION EFFICIENCY 

WALL LOSSES 

FIGURE 10. 

2 3 5 7 10 

AERODYNAMIC PARTICLE DIAMETER, /tm 

EFFICIENCY AND WALL LOSSES OF BECKMAN DICHOTOMOUS FRACTIONATOR. 

FLOW RATE = 16. 7 JL/MIN. 

H80 

UJ 

o 

a. 

UJ 

160 Qco" 

UJ 

co 

co 

o 

40 

< 

20 

-Jo 

30 
for particles as large as 75 ym are less than 10 percent. 

With respect to wind tunnel evaluation of the system, the effectiveness 

as a function of particle size for a wind speed of 2 km/hr is shown in 

Figure 11. The cutpoint for the inlet is 15.5 ym. Tests at wind speeds of 

8 and 24 km/hr showed the cutpoint to be shifted to 13 and 10.5 ym, respectively. 

I 

SUMMARY AND DISCUSSION 

Ambient aerosol samplers were evaluated under simulated field,conditions 

as a function of aerodynamic particle size and wind speed. The following 

conclusions may prove to be helpful to gain insight into the validity of 

usage of present aerosol samplers and to encourage modifications to the 

standard method for sampling particulate matter: 

1. Wind velocity is a major cause of data bias in aerosol sampling. 

For particles >10 ym, sampling effectiveness for all the samplers 

tested decreased with increasing wind velocities. 

2. For Hi-Vol samplers the effectiveness for 30 ym particles can vary 

from 70 to 40 percent as wind speed is increased from 2 to 24 km/hr. 

Other biases in the inlet system of the Hi-Vol are the wind directional effects and standby mode collection. The sampler is most 

effective when the roof ridge is oriented at an angle of 45 degrees 

to the wind flow. Wind driven particles, such as would exist in 

high concentrations in the case of a sand storm, can be deposited 

when the sampler is not in operation. The inlet system of the 

Hi-Vol sampler could be modified to provide a better defined cutpoint size, one which is less dependent upon wind speed and 

23 
100 

UJ 

CJ 

CC 

UJ 

CL 

CO 

CO 

UJ 

z 

UJ 

> 

rO 

UJ 

u. 

u. 

UJ 

AERODYNAMIC PARTICLE DIAMETER, /im 

FIGURE 11. EFFECTIVENESS OF BECKMAN DICHOTOMOUS SAMPLER. 

FLOW RATE = 16.7 Jl/min. WIND SPEED = 2 km/hr. 

J 
P.30 

i 

direction (a symmetrical inlet) and which precludes deposition of 

wind driven particles. 

3. Aerosol collection with the rainshield inlet of the membrane and 

cascade impactor samplers is somewhat variable with wind speed. 

High internal wall losses of the cascade impactor raise questions 

of the validity of results derived from its use in the past. 

Quality data could be obtained with the impactor if either the 

flow rate is reduced to 28.3 «,/min or the stages are designed to 

accommodate higher flow rates. An adequate flow control system 

and the reshaping of the rainshield inlet would also improve the 

sampling capabilities of the systems. 

4. An early version of the ERC dichotomous sampler, because of the 

small inlet openings (3.5 mm), proved to be the least desirable 

inlet system since particles as small as 3.0 ym seem to be impacted on the inlet walls by wind effects. The sampler is a 

valuable tool for fractionating respirable from non-respirable 

particles, but should not be used as an ambient sampler with the 

small-sized inlet. It should be noted that the manufacturer has 

changed the inlet design since the time at which these tests were 

performed. The Beckman dichotomous sampler provides an internal 

fractionation of 3.5 ym and has low wall losses for particles as 

large as 15 ym. The inlet is not highly sensitive to wind speed, 

but should probably be improved. 

Based on the results of this study, further research of ambient aerosol 

samplers should consider the design and evaluation of inlet systems with 

collection characteristics which are less sensitive to wind effects. 

25 
P.31 

L 

LITERATURE CITED 

1. Wedding, J.B., McFarland, A.R., Cermak, O.E., "Large Particle Collection Characteristics of Ambient Aerosol Samplers", Environ. Sci. 

.Technol.. 11, 4, 387 (1977). 

2. Spirtas, R., Levin, H.J., "Characteristics of Particulate Patterns", 

National Air Poll. Control Adm., Raleigh, N.C., March 1970. 

3. Davies, C.N., "The Sampling of Aerosols", Staub 28, 1 (1968). 

4. Davies, C.N., "The Entry of Aerosols into SamDling Tubes and Heads", 

Brit. J. Appl. Phys., 2, 1, 921 (1968). 

5. Agarwal, J.K., "Aerosol Sampling and Transport", Particle Technology 

Lab., Mechanical Technology Lab., Publication No. 265, University of 

Minnesota, May 1975. 

6. Raynor, G.S., "Variation in Entrance Efficiency of a Filter Sampler 

with Air Speed, Flow Rate, Angle and Particle Size", AIM Journal 31, 

294 (1970). 

7. May, K.R., Pomeroy, N.P., Hibbs, S., "Sampling Techniques for Large 

Windborne Particles", J. Aerosol Science 7, 53 (1976). 

8. Watson, H.H., "Errors Due to Anisokinetic Sampling of Aerosols", AIM 

Journal 15, 21 (1954). 

9. Vitols, V., "Theoretical Limits of Errors due to Anisokinetic Sampling 

of Particulate Matter", J. Air Pollution Contvo. Assoc. 16, 79 (1966). 

10. Sehmel, G.A., "Particle Sampling Bias Introduced by Anisokinetic 

Sampling and Deposition within the Sampling Line", AIM Journal 31, 

758 (1970). 

11. Selden, M.G., "Nozzle Sampling Bias", AIHA Journal 36, 549 (1975). 

12. Parker, G.J., "Some Factors Governing the Design of Probes for Sampling Particle and Drop-Laden Gas Streams", Atm. Env. 2, 477 (1968). 

13. Breslin, J.A., Stein, R.L., "Efficiency of Dust Sampling Inlets in 

Calm Air", AIHA Journal 36, 576 (1975). 

14. McFarland, A.R., Wedding, O.B., Cermak, O.E., "Wind Tunnel Evaluation 

of a Modified Andersen Impactor and an All Weather Sampler Inlet", 

Atm. Env. 11, 535 (1977). 

15. Burton, R.M., Howard, J.N., Penley, R.L., Ramsay, P.A., Clark, T.A., 

"Field Evaluation of the High-Volume Particle Fractionating Cascade 

Impactor", J. Air Pollution Control Assoc. 23, 277 (1973). 

26 
• 

-1 i Cascade Particle 

r ,'If

 Paci'fic Northwest 

C., 1973. 

Parameters on the Sampling 

is for Measuring Particle Con- • 

is, Chalmers Institute of 

Efficiency of Two Types of 

f Aerosols in Ambient Air" 

i Labs., B 230, Gothenburg,' 

Measurements of Particle Confound Station with Different 

Water and Air Pollution Labs., 

of Techniques for Generating 

Droplet Generator", In Fission 

Energy Comm. (1970). 

ion of Monodisperse Aerosol 

. 147 (1973). 

la 1 is", American Medical 

fc K , 481 (1956). 

Single Particle Optical 

Sci. Technol., 1, 10, 801 

ing with a Side Port Probe", 

ir Surveillance Cascade 

Measurements of Suspended 

Tech. 6, 12, 1019 (1972). 

c Method for Determining 

•ended in the Air", Paper 

ociation annual meeting, 

* 

Z,4 "The Evaluation of 

es in Air", Atm. Env. 6, 

Andersen Impactor", M.S. 

ilson, W.E., Stevens, R.K., "The Size 

the Air", Science 183, 1098 (1974). 

deal Collection Characteristics, of 

ors", AIM Journal 38, 174 (1977). 

lertch, R.W., Jr., "Particle Collection 

ige Dichotomous Sampler", Environ. Scv. 

ie Environmental Monitoring and Support 

vironmental Protection Agency (EPA) under 

support is gratefully acknowledged. 

.." 

28 

P.32