bodies even though they are supplied by different sources. More than 60% of the Kishon reservoir waters are pumped from Lake Kinneret. The rest is contributed by winter floods from the watershed. In addition, some sewage from two neighboring small towns is also emptied into the Kishon reservoir. On the other hand, the Gevat reservoir gets its water only from the drainage of neighboring rural areas and from winter floods. A possible explanation for the observed similarity in the pesticide concentrations in the two reservoirs is the buffering capacity of the bottom sediment. Indeed preliminary study has shown that BHC, DDT, endrin, and dieldrin were found in the bottom sediment in concentrations on the order of several hundred nanograms per kg.
Literature Cited
(1) Hindin, B., “Pesticides, Plant Growth Regulators and Food
Ackno~cledgment
Additives,” Gunter Zweig, Ed., Academic Press, New York and London, 1967. (2) Berginsky, H., “Survey of Pesticides in Selected Water Sources in Israel,” Continuation of Hindin’s Survey, Mekorot Water Co. Ltd. (in Hebrew), 1969. (3) Hindin, E., “Chlorinated Hydrocarbon Pesticides in Selected Water Sources in Israel, a Preliminary Study,” Mekorot Water Co. Ltd., Water Quality Department, 1967. (4) Law, L. M . , Goerlitz, D. F., J . AOAC, 53, 1276-86 (1969). (5) Ettinger, M . B., Mount, D. I., Enciron. Sci. Technol., 1, 203-5 (1967). (6) Nicholson, H . P., Proc. Wash. Acad. Sci., 59, 77-89 (1969). ( 7 ) King, P. H.. Yeh, H . H . , Warren, P . S., Randall, C. W., J . Amer. Water Works Ass., 61,483-6 (1969). ( 8 ) Pionke, H. B.. Chesters, G., J . Enuiron. Qual., 2, 29-45 (1973).
We thank S. Milchen and H . Popisky for their help in the analyses of the water samples.
Received for recieu August 13, 1973. Accepted April 4, 1974. ,stud? u a s financed by Tohal, Water Pianningfor Israel Ltd.
This
Personal and High-Volume Air-Sampling Correlation Particulates Phillip M. Duvall and Richard C. Bourke” Detroit Diesel Allison Division, General Motors Corp., Indianapolis, Ind. 46206
Airborne particulate measurements are required both outside and inside an industrial plant to determine compliance with existing control regulations. The Environmental Protection Agency (EPA) specifies a high-volume sampling method for outside ambient air while Occupational Safety and Health Administration (OSHA) personnel generally use personal monitoring for determining particulate levels inside a plant. A personal monitoring method was developed by Detroit Diesel Allison which correlates with the EPA reference method in three types of ambient atmospheres: a “clean” laboratory area, outside ambient air in an industrial location, and inside an industrial plant in an area where oil mist is the predominant contaminant. Good agreement was obtained in all three cases after compensation was made for the effects of adsorbed moisture.
The need for reliable measurements of particulate concentrations in ambient air both outside and inside an industrial plant is well known. However, two different methods are used in these two areas where permissible limits are set by two different federal agencies-EPA and OSHA. In the industrial organization, however, both types of measurements generally are made by the same personnel and, for the sake of reliability in measurements and economy, a need for correlation is apparent. Ideally, the same instrument could be used in both cases or, at least, the monitors should be interchangeable so that the number required is reduced. Since both methods are gravimetric determinations of particulate concentrations, they should agree and correlation would mean a higher degree of confidence in both sets of data, Particulate concentrations in outside ambient air are generally measured by a high-volume reference technique
specified in detail by the EPA ( I ) . High-volume sampling has been used for some time and, if the recommended procedure is carefully followed, the obtained data have been found to be quite reliable. N o similar procedure has been established by OSHA, although samples are generally collected on membrane filters by means of personal monitors and general-area samplers ( 2 ) . The airflow of these monitors is approximately one thousandth of that of a high-volume sampler. Also, the filter material used iic the high-volume sampler is usually glass fiber purportedly capable of collecting particles greater than approximately 0.3 p in diameter, while the personal samplers use a variety of membrane filters of different pore-size diameters. In this study, filters with an average 0.8-p diameter pore size were used because of their general usage and availability. Differences also occur in the positioning of the impingement surfaces of the two different types of filters. The surface of the high-volume filter is facing upward toward an approximately vertical downward airflow, while the membrane filter surface is usually facing downward at approximately 45” to the horizontal, toward an upward airflow to simulate personnel breathing-zone conditions as closely as possible. In spite of the differences between the two methods, if any reliance is to be placed in the data obtained by either technique, a correlation between the two must be established. The purpose of this Kote is to describe the development of a membrane-filter, personal-monitoring technique that correlates with the high-volume air sampling reference method of the EPA in three different types of atmospheres-a clean laboratory area, outside ambient air in an industrial location. and inside an industrial plant where oil mist is the predominant contaminant. Selection of these three atmospheres permits comparison of the collection efficiencies of the two methods for particulates of widely varying size, chemical composition, and ambient air concentrations. For example, from optical and scanVolume 8 , Number 8, August 1974
765
/a- , , Figure
1.
High-volumeand pe rsonal air SamDlers
Lyt,=>
high-volume glass fiber filters
"I
pa","",aL""
YII
(165X)
ning-elecmm m ~ ~ u a c u parudies, y the laboratory samples consisted generally of small-diameter (0.1-1 p ) soot and dust particles and were obtained in an area where air con. centration generally averages 0.04-0.06 mg/md. The outside ambient air samples usually contained products of combustion, sand, and naturally occurring particulates, and the average particle size was in the 0.1-50-p range with concentrations ranging from 0.06-0.10 mg/m3. The in-plant samples consisted of 70-80% oil mist and the concentrations usually averaged 0.70 mg/m3 in the chosen area. ~~
~~
Experimentation, Data, and Discussion In all comparative sampling, both air samplers were operated adjacent to each other over exactly the same time period to minimize the effects of varying particulate concentrations in the ambient air. As shown in Figure 1, the membrane filter holder was connected to the top of the high-volume air sampler a t the air intake level. For accuracy in weighing in the low concentration areas, it was necessary to sample a t least 24 hr to obtain a sample of adequate weight. Since the nickel-cadmium batteries in the personal monitors are capable of operating 10-12 hr, it was necessary to operate the monitors from a parallel bank of a t least two batteries. In weighing the filters from the high-volume sampler, the procedures specified by the EPA ( I ) were used. The filters were equilibrated to a controlled humidity chamber before and after collection and then weighed on an analytical balance modified to accept the flat 8 x 10 in. glass fiber filters. However, because of the small size and mass of the membrane filters and samples, a more sensitive microbalance was used to compensate for moisture adsorption. Figure 2 shows the microbalance used which, because of its weighing chamber configuration, is well suited for weighing samples in a controlled humidity atmosphere independent of the ambient humidity. A small container of silica gel drying agent was placed in the chamber during weighing. A radioactive ionizing strip was placed under the filter and pan to minimize the effects of static charges on the filter weight in the dry atmosphere. To compensate for moisture adsorption on both the filter plgure 4, welgn[ loss
curves ,or ["ree Types ples obtained by personal monitoring 766
Environmental Science &Technology
0, par[,CU,a[eSam.
anrl "LA"
i" hIo.* nnllantnrl ~ " . I ~ ~ . Y I
n a r + i n , ~ l o + n rtho . x i a i n h + o
p.u'"'""'Y"-=,
"
1111
" * " ' 6 L ' * "
..m-~. *.-Ab
mnnitn-srl ll."l.ll"lr"
before and after collection until constant equilibrium
Table I. High-Volume and Personal Sampling Correlation Particulate concentration, mg/m3
Clean laboratory Sample 1 Sample 2 Sample 3 Outside industrial Sample 1 Sample 2 Inside industrial Sample 1 Sample 2 Sample 3
High-volume sampler
Personal monitor
0.051 0.050 0.037
0.049 0.038 0.032
0.073 0.079
0.076 0.089
0.80 0.55 0.43
0.77 0.57 0.42
-
values were obtained. It was these “dry” weights that were then used to calculate the particulate concentrations. Weight loss curves for several membrane filters prior to sampling are shown in Figure 3. Different percentage weight losses for the same area are illustrated because of differences in humidity in the area where the membranes were stored prior to use. After sampling, the particulate samples lose moisture in the dry weighing chamber depending on their average particle sizes and chemical nature. Figure 4 shows the weight loss curves for the three types of samples-those taken in a clean laboratory area, outside air in an industrial area, and inside an industrial plant where oil mist is the predominant contaminant. As might be expected, the sample having the smallest average particle size desorbed the highest weight percent of moisture. The clean atmosphere sample was composed of small (0.1-1 p ) dust and soot particles and lost almost 70% of its original weight. The samples taken inside an industrial plant, however, were composed of $O-80% oil mist which appeared to be hydrophobic, permitting the adsorption of only 20-3070 moisture. The samples taken outside an industrial plant were generally larger in particle size (0.1-30 p ) and, therefore,
intermediate in their water adsorption capabilities, desorbing 35-45% of their total weight. Figure 5 is a compilation of photomicrographs showing typical particulate samples taken in the three areas on the high-volume glass fiber filters. As can be seen, the particle size of the clean laboratory sample is very small. In comparison, the inside industrial sample looks fairly clean, although it is approximately ten times the weight of the clean sample because of the difficulty in distinguishing the oil film on the industrial-sample filter. Table I shows typical particulate concentrations that have been obtained in the three areas by the two methods-high-volume sampling and personal monitoring. Correlation between the two sampling methods is generally good for the types of atmospheres studied. Experience has shown that the degree of correlation appears to depend on proper compensation for moisture adsorption on and the care in handling of the membrane filters where very small weight gains (0.1-3 mg) are involved and large errors can occur. The possibility exists that certain atmospheres could cause noncorrelation between the two sampling methods. However, correlation has continually been good for those atmospheres of interest. Conclusions Correlation between the two methods of particulate sampling, high volume and personal monitoring, for the types of atmospheres sampled can be obtained if proper techniques are used. Compensation for moisture adsorption on personal samples and care in handling the small membrane filters appear to be the two main correlation determining factors. Literature Cited (11Environmental Protection Agency, Fed. Regist., 36 (84) (April 30, 1971). (21 U.S. Department of Health, Education and Welfare, National Institute of Occupational Safety and Health, “Industrial Hygiene Measurements Course Manual,” Course No. 550. Cincinnati, Ohio, February 1973.
Receiced f o r reaieu: S e p t e m b e r 14, 1973. Accepted May 2,1973
CORRESPONDENCE
Capture of Aerosol Particles by Spherical Collectors SIR: We were interested in the calculations by H . F . George and G. W. Poehlein [Enczron Scz Techno!, 8 (1). 4&9 (1974)] on the combined influence of inertial and electrostatic forces on the collection efficiencies of aerosol particles on spherical collectors, since we have recently completed similar computations ( 1 ) . Our results do not agree in detail with those presented in Figures 4 and 5 of George and Poehlein’s paper, however, and we have examined George’s thesis (2) to determine the possible reasons for the disagreements. We have used the letter “a” to differentiate our same numbered figures from those of George and Poehlein. First, examination of the computer program used by George reveals that, in our judgment. inadequate criteria were used for terminating calculations of particle trajectories in the electrostatic force case. leading to incorrect
evaluation of the limiting trajectory for collection. In the logic used, if the particle crosses the centerline (due to inertia) on the downstream side of the collector, it is considered that the particle will ultimately be collected and the numerical integration is stopped. Also. if the particle reaches a distance of 0.75 collector diameters ( D ,) beyond the center of the collector without having crossed the centerline, it is considered that the particle will never be collected and the integration is stopped. That these criteria are inadequate can readily be seen from the two trajectories computed by Nielsen using the potential fluid flow model and shown in Figure l a . In one case the particle crosses the downstream centerline without being collected, and in the other the particle reaches a distance of 0.75 I), beyond the center of the collector without having yet crossed the centerline and is collected. For the case in Volume 8 , Number 8 , August 1974
767
