High volume air samplers (hi vols) are described which utilize a brush-type electric motor to power the fans used for pulling air through the filter. Anomalously high copper values were attributed to removal of copper from the commutator into the air stream due to arcing of the brushes and recirculation through the filter. Duplicate hi vols were set up under three operating conditions: (1) unmodified; (2) gasketed to prevent internal recirculation; and (3) gasketed and provided with a pipe to transport the motor exhaust some 20 feet away. The results of 5 days' operation demonstrate that hi vols can suddenly start emitting increased amounts of copper with no discernible operational indication, and that recirculation and capture on the filter can take place. Copper levels found with hi vols whose exhaust was discharged at a distance downwind were among the lowest found, and apparently provides a satisfactory solution to copper contamination

King, R. B.

Toma, J.

English

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NASA TECHNICAL NASA TM X-71693
MEMORANDUM
I-
Z (NASA-TM-X-71693) COPPER EMISSIONS FROM A N75-19535 ,
HIGH VOLUME AIR SAMPLER (NASA) 9 p HC $3.25
CSCL 09A
Unclas
G3/33- 13413
COPPER EMISSIONS FROM A HIGH-VOLUME AIR SAMPLER
Robert B. King and John Toma 3
Lewis Research Center
Cleveland, Ohio 44135
March 1975 c +
81. Y
https://ntrs.nasa.gov/search.jsp?R=19750011463 2020-03-22T23:47:11+00:00Z
TECHNICAL MEMORANDUM
COPPER EMISSIONS FROM A HIGH-VOLUME AIR SAMPLER
by Robert B. King and John Toma
SABSTRACT
co
Many high volume air samplers (hi vols) utilize a brush-type electric motor
to power the fans used for pulling air through the filter. Anomalously high copper
values have been attributed to removal of copper from the commutator into the
air stream due to arcing of the brushes and recirculation through the filter.
Duplicate hi vols were set up in this study under three operating conditions:
(1) unmodified; (2) gasketed to prevent internal recirculation; and (3) gasketed
and provided with a pipe to transport the motor exhaust some 20 feet away. The
results of 5 days' operation demonstrate that hi vols can suddenly start emitting
increased amounts of copper with no discernible operational indication, and that
recirculation and capture on the filter can take place. Copper levels found with
hi vols whose exhaust was discharged at a distance downwind were among the lowest
found, and apparently provides a satisfactory solution to copper contamination.
COPPER EMISSIONS FROM A HIGH-VOLUME AIR SAMPLER
by Robert B. King and John Toma
Lewis Research Center
SUMMARY
Many high volume air samplers (hi vols) utilize a brush-type electric
motor to power the fans used for pulling air through the filter. Anomalously
high copper values have been attributed to removal of copper from the commuta-
tor into the air stream due to arcing of the brushes and recirculation through
the filter. Duplicate hi vols were set up in this study under three operating
conditions: (1) unmodified; (2) gasketed to prevent internal recirculation;
and (3) gasketed and provided with a pipe to transport the motor exhaust some
20 feet away. The results of 5 days' operation demonstrate that hi vols can
suddenly start emitting increased amounts of copper with no discernible opera-
tional indication, and that recirculation and capture on the filter can take
place. Copper levels found with hi vols whose exhaust was discharged at a
distance downwind were among the lowest found, and apparently provides a
satisfactory solution to copper contamination.
INTRODUCTION
A number of investigators (refs. 1 and 2) have reported anomalously
high values for copper in the suspended particulate matter in the ambient
air using samples collected with high volume air samples (hi vols) and have
attributed them to various pollution sources. Hoffman and Duce (ref. 1)
have suggested that arcing at the brush-commutator interface may cause
copper to be entrained in the air stream passing through the hi vol motor
-2-
and subsequently exhausted to the immediate vicinity of the hi vol. It
can then be recirculated through the hi vol, depositing the entrained
copper on the filter. Since the use of hi vols with brush-type motors
is well established for both total suspended particulates (TSP) and trace
element determinations, it is important to determine if the hi vol itself
is a copper source.
Experimental
Six hi vols were positioned north to south on a roof about 20 feet
(6 m) above ground on the western edge of a building. They were divided
into 3 groups about 50 feet (15 m) apart; the 2 hi vols in each group
were similarly oriented and were about 8 feet (2.5 m) apart. The centrally
located hi vols were unmodified as supplied by the manufacturer except that
variable voltage transformers had been added to control air flow rate.
The northerly positioned set had gaskets attached under the supporting
edge of the funnel to prevent the exhaust from the motor from being trans-
ported vertically within the hi vol case into the air stream that passes
through the filter. The exhaust from these hi vol motors was thus expelled
to the air surrounding the hi vol and if it were to pass through the filter
would have to travel external to the hi vol case. The southerly positioned
set was also similarly gasketed but in addition had 20 feet (6 m) long
4" (10 cm) stove pipes attached to the exhaust end of the motor to carry
the exhaust away to the east from the immediate vicinity of the hi vol
(fig. 1). In addition, the possibility of contribution of copper by the
hi vol was materially reduced since the wind blew from the west (ref. 3)
on the five test days.
-3-
Particulate matter was collected upon 8" x 10" Whatman No. 41 filter
medium using filter holder cassettes (ref. 4). The hi vol was operated at
an initial flow rate of about 40 cubic feet per minute (0.02 m 3 /sec) as
described by Neustadter, et al (ref. 5). Each run was for 24 hours. Con-
centrations of copper and calcium on the filter were measured on a piece
of the filter and determined by energy dispersive X-ray fluorescence analysis
using a tungsten target X-ray tube at 60 kV and 10 milliamp current for ex-
citation with a cadmium filter and a Si(Li) detector (ref. 6). Analytical
precision for copper was ±10% and for calcium ±20%. Analyses were performed
by Dr. David Liu of this laboratory.
RESULTS AND DISCUSSION
The concentrations of copper and calcium found at each of the sampling
locations for the five test days are shown in Table I. Individual daily
values for each hi vol sample are shown. The significant difference between
the values for the unmodified set of hi vols and the values for the other hi
vols should be noted. The copper levels for the gasketed and piped exhaust
set of hi vols are quite low and reasonably consistent ranging from a mini-
mum of <6.9 ng/m3 to a maximum of 50.5 ng/m3 for an average of about 23.6
ng/m3 . The gasketed-only set of hi vols exhibit somewhat higher copper
values and are reasonably consistent on a daily basis except for one day
(09/30/74). The values ranged from a minimum of 32.8 ng/m 3 to a maximum of
120 ng/m3 for an average of 77.0 ng/m 3 . In contrast to these two sets, the
unmodified set of hi vols shows highly divergent values after the first day's
run, the copper level of hi vol No. 1 of this set suddenly increasing. Appar-
ently this hi vol started emitting larger amounts of copper, probably due to
-4-
increased arcing of the brushes and commutator.
The somewhat higher values of the gasketed set of hi vols could be
due to higher hi vol production of copper or to a higher ambient level
due to variability in TSP collected. However, comparison of the concen-
trations of calcium on the same filters indicates that the level of an
element not associated with the brush-commutator phenomenon was about the
same for all filters on a given day. This is shown specifically in Table
II where the means (p) and then standard deviation (a) are tabulated for
copper and calcium. These values were calculated using the values for all
the hi vols (5 values) except that for "Unmodified Hi Vol No. 1." The
data indicates that the daily values of "Unmodified Hi Vol No. 1" for copper
are far outside two standard deviations from the mean, while those for cal-
cium are well within this range. Thus, it is reasonable to assume that the
copper concentration in the ambient TSP was the same for all 6 hi vols on
any given day, and it is evident that the variable copper noted in unmodified
hi vol No. 1 came from the hi vol motor. The scope of the experiment, however,
does not permit determining unequivocally to what extent the modifications
may have reduced the copper on the filter to true ambient levels.
The copper levels found are somewhat below the value of 72 ng/m3 we
previously found for suburban locations (ref. 7) -- our test site, however,
is better described as rural rather than suburban. Although the brushes in
the hi vols we used were not new, they had run only a few hours and should
have been well seated. There was nothing in the hi vol operation to indicate
that any were running abnormally, although the data suggests that at least
one of them suddenly changed its copper emission rate. The low values of
the other hi vol in the unmodified set indicated that hi vols can run with
-5-
low copper emission. Visual observation of the arcing of the brushes for
these two motors was not rewarding - they both arced about the same. It
appears then that if one wishes to make a reliable determination of the
copper content of the total suspended particulate in ambient air, the ex-
haust from the hi vol motor should be discharged at a distance preferably
downwind from the hi vol.
REFERENCES
1. Hoffman, Gerald L.; and Duce, Robert A.: Copper Contamination of
Atmospheric Particulate Samples Collected with Gelman Hurricane
Samplers. Envir. Sci. & Tech., vol. 5, no. 11, Nov. 1971,
pp. 1134-1136.
2. Winchester, John W.: Trace Metal Associations in Urban Airborne
Particulates. Amer. Meteor. Soc. Bulletin, vol. 54, no. 2,
Feb. 1973, pp. 94-97.
3. Local Climatological Data, Sept. and Oct. 1974, Cleveland, Ohio.
National Oceanic and Atmospheric Administration, 1974.
4. King, Robert B.; and Fordyce, J. Stuart: Note on a Filter Holder
for High Volume Sampling of Airborne Particulates. J. Air Poll.
Contr. Assoc., vol. 21, no. 11, Nov. 1971, p. 720.
5. Neustadter, Harold E.; Sidik, Steven M.; King, Robert B.;
Fordyce, J. Stuart; and Burr, John C.: Use of Whatman-41 Filters
in Air Quality Sampling Networks (with Applications to Elemental
Analysis). NASA TN D-7595, 1974.
6. Dzubay, T. G.; and Stevens, R. K.: Applications of X-Ray Fluores-
cence to Particulate Measurements. In Proceedings of the Second
Joint Conference on Sensing of Environmental Pollutants, Washington,
D.C., Dec. 10-12,-1973, pp. 211-216.
7. King, Robert B.; Fordyce, J. Stuart; Antoine, Albert C.; Leibecki,
Harold F.; Neustadter, Harold E.; Sidik, Steven M.; Burr, John C.;
Craig, George T.; and Cornett, C. Lawrence: Preliminary Analysis of
an Extensive One Year Survey of Trace Elements and Compounds in the
Suspended Particulate Matter in Cleveland, Ohio. NASA TM X-71586, 1974.
-6-
TABLE I. - COPPER AND CALCIUM LEVELS, ng/m3
Date Piped and Gasketed Unmodified
Gasketed Hi Vol Hi Vol Hi Vol
1 2 Ave 1 2 Ave 1 2 Ave
9/25 Cu 26.5 22.7 24.6 67.5 82.0 74.8 17.0 21.2 19.1
Ca 2830 2740 2785 2580 2720 2650 <291* 2350 <1320
9/26 Cu 37.2 24.6 30.8 120 106 113 518 65.0
3460 2600 3030 3280 2960 3170 2600 2890 2745
9/30 Cu 24.6 <8.0*<16.4 48.5 106 72.2 378 24.0
Ca 1850 1620 1735 1480 2200 1840 1320 1510 1415
10/1 Cu 14.5 <6.9*<10.7 32.8 37.2 35.3 368 20.8
Ca 1070 700 885 575 775 675 788 544 666
10/3 Cu 50.5 19.0 35.3 74.4 105 89.5 584 57.4
Ca 1930 1500 1715 1970 1630 1800 1750 1670 1710
*Below detection limit
TABLE II. - STATISTICAL COMPARISON OF COPPER AND CALCIUM VALUES
Standard Unmodified
Mean Deviation Hi Vol
Date (P) a No. 1 i + 2a p - 20
9/25 Cu 44 29 17 102 0
Ca 2644 187 <291 3018 2270
9/26 Cu 71 42 518 155 0
Ca 3038 338 2600 3714 2362
9/30 Cu 42 38 378 118 0
Ca 1732 299 1320 2330 1134
10/1 Cu 23 13 368 49 0
Ca 733 210 788 1152 313
10/3 Cu 61 32 584 125 0
Ca 1740 202 1750 2144 1336
00
Ist
Figure 1. -Piped and gasketed hi -vol sampler.


Copper emissions from a high volume air sampler

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