shipping and drilling activities. Considering the high methane concentrations which can occur naturally, the CFC4 saturated hydrocarbons should be the best indicators of any future petrogenic inputs to this region. The unsaturated hydrocarbons, ethylene and propylene, do not occur in as high concentrations as have been reported for many other oceanic locations ( 4 ) which tends to support the view that biological productivity was low during the month of August for both years. I t must be kept in mind that sampling has been restricted to only a one-month period for two consecutive years. Nothing is known about the abundance of LMW-HC in this region prior to breakup of the ice or when the Mackenzie is in full flood. Acknowledgment I thank K. Kremling, E. Matsumoto, and P. Christensen for their critical evaluation of the manuscript.
Literature Cited (1) Swinnerton, J. W., Linnenbom, V. J.,J . Gas Chrornatogr., 5,570
(1967). (2) Brooks, J. M., Sackett, W. M., J . Geophys. Res., 78, 5248 (1973). (3) Brooks, J. M., Fredericks, A. D., Sackett, W. M., Swinnerton, J. W., Environ. Sei. Technol., 7,639 (1973). (4) Swinnerton, J. W., Lamontagne, R. A,, ibid., 8,657 (1974). (5) WEBSEC 71-72, Oceanographic Report No. CG 373-64, p 1, 1972.
(GYCirk, R. C., Blumer, M., Raymond, S.O., Deep Sea Res., 14,125 (1967). (7)-Yamamoto, S., Alcauskas, J. B., Crozier, T. E., J . Chern. Eng. Data, 21,78 (1976). (8)Lamontagne, R. A., Swinnerton, J. W., Linenbom, V. J., J . Geophys. Res., 76, 5117 (1971). (9) Matsumoto, E., personal communication. (10) Wilson, D. F., Swinnerton, J. W., Lamontagne. R. A., Science, 168,1577 (1970).
Received for review January 14, 1976. Accepted June 14, 1976.
Quenching Effects in SO2 Fluorescence Monitoring Instruments James A. Jahnke”, James L. Cheney, and James B. Homolya Stationary Source Emissions Research Branch, Emissions Measurement and Characterization Division, Environmental Sciences Research Laboratory, Environmental Protection Agency, Environmental Research Center, Research Triangle Park, N.C. 277 11 H An evaluation of the technique of determining SO2 concentrations by measuring the SO2 fluorescence excited a t the 2100 A region of the SO2 UV spectrum was performed. The
quenching effects resulting from 0 2 concentrations below and COS concentrations above ambient levels gave SO2 concentration measurements on the order of 5-10% higher than the reference values. Spanning the instrument with an SO2 in nitrogen span gas resulted in giving readings 30% lower than true values. Fluorescence excited a t the 1900-2300 8, region of the SO2 UV spectrum has recently been applied for use in commercial ambient and stationary source pollution monitors (1-4). In the application of this technique, several questions have arisen as to the effect of quenching of the 2138 8,-excited SO2 by gases present in stationary sources and of the effect of interferences by combustion gases absorbing in the wavelength region covered by the fluorescence detector (5, 6). Since quenching efficiencies for 0 2 , N2, and COShave not been determined for the fluorescence excited from the 1900-2300 8, region, it has not been possible to estimate the importance of this effect for varying gas concentrations. In an effort to evaluate the response of the fluorescence technique under field conditions, a series of experiments has been performed with a commercial instrument a t the EPA Simulated Stationary Source Facility (SSSF) operated for the Stationary Source Emissions Research Branch (7). Through this experimental program, we have found that quenching effects can be significant, but that with some caution these instruments can adequately monitor SO2 emissions from combustion sources. Fluorescence Method The absorption spectrum for SO2 in the region from 2000 to 4000 8, is shown in Figure 1 (8).The fluorescence spectrum 1246
Environmental Science & Technology
resulting from absorption a t the singlet excited state near 2100
A observed by Okabe et al. ( 1 )is also shown in Figure 1. The
fluorescence lifetime from this state due to predissociation was found by Okabe to be short enough relative to the quenching rate to produce an observable signal for SO2 in air a t 1 atm. This, coupled with the observation that the intensity is proportional to the SOP concentration, provided the basis for the development of the fluorescence monitor ( I ) . The effect of quenching on the fluorescence from this region has not been thoroughly studied, although Schwarz et al. (9) have obtained a value of 5.2 f 2.6 X lo6 s-l torrw1 for quenching by water a t the 2288 A excitation. A t the 2138 A excitation where the fluorescence decay rate, k j , is faster ( 5 X 108 vs. 3 X 10’ s-l a t 2228 A), a t 50% relative humidity, water quenched the fluorescence signal from only 0 to 5% vs. 20% quenching at 2288 8, (9).Also, Okabe found a quenching rate of 1.8 X lo6 s-l torr-l for argon a t the 2210 A band (10). With the removal of water vapor, quenching problems may not be serious in the case of the ambient air monitors since the relative concentrations of the constituents of an air mixture remain constant. Emissions from combustion sources, however, may vary widely in pepcentage amounts of 0 2 and COY, and the relative quenching effects of these gases become serious and need to be investigated. From the general form for the fluorescence intensity, Equation 1 ( I ) : IOII =
Z k q , ~+ , kf
+~ S O k s o g s o Z+ k j
~ S O ~
(1)
where I, is the intensity without quenching, I is the intensity with quenching, kSo2 is the self-quenching rate, K,, is the quenching rate for species i, and pLis the partial pressure of the species, the measured intensity, I , may be considerably affected by the values of kqL.To determine the importance of this effect, we have used a commercially available SO2 fluorescence monitor and have varied the composition of the sample gas in the test section of the SSSF.
Analyzer and Experimental Method
Analyzer. A commercial instrument described by Zolner et al. (Thermo Electric Corp., TECO Model 40) (2) was used in the present study. Wolfe and Giever (3) recently described a similar instrument. Basically, the analysis method consists of excitidg a conditioned SO2 sample in a flow-through chamber with a UV light source filtered with a bandpass filter centered a t 2100 8, with a 150 8, width. The fluorescent radiation filtered in the region 3200-3800 8, is then detected by a photomultiplier tube (Figure 1).Since the fluorescence intensity is only linear to levels up to 500 ppm S02, the signal is electronically linearized a t higher levels and is then displayed. The sample is preconditioned by water removal before reaching th,e fluorescence chamber by the use of a permeation tube dryer. An internal pump and pressure system provides a controlled rate of sample flow through the chamber. The method is nondestructive, and the sample may be recovered a t the exit port. In operation the instrument is zeroed with air and spanned with a reference SO2 in air mixture as suggested by the manufacturer. Excluding the possible effects of quenching, then, the accuracy of the instrument is ultimately dependent upon the degree of accuracy to which the span gas concentration is known. EPA Simulated Stationary Source Facility. The experiments were performed at the EPA Source Simulator Facility (7). The simulator itself is essentially a closed-loop wind tunnel (Figure 2), approximately rectangular with dimensions of 12 by 18 m with a volume of 76 m3 (Figure 2). The tunnel is constructed of stainless steel and has four 3-m-long test sections (0.6 by 0.9 m in cross section), each having optical ports and fittings for extractive systems. Special features built into the tunnel for stack simulation are as follows: a combustion products injection system using a propane gas boiler for the addition of CO2, CO, and water vapor; a velocity control system providing a maximum flow rate of 480 standard m3/ min with a velocity of 20 m/s in the test section; a particulate
I
DUPONT 128W I 1
BANOPASS
FLUORESCENCE
4
2000
2500
3000
a000
3500
a Figure 1. Spectral parameters for SO2 UV monitors WAYELEMGTH
16
cE.ll
SPAN A N D I N L E T GASCYLINDER RACK
- - - -1
FAN
L---'=--==~_----='-__
- - - - --j
Figure 2. Simulated Stationary Source Facility
generator for injecting fly ash or other particulate matter upstream of the test section; a gas handling system for injecting pollutant gases into the tunnel; and a computer control system programmed to monitor and control gas levels and to record and average up to 40 tunnel parameters. The source simulator has the capability of reproducing many of the characteristics of a combustion source stack. This, combined with the control system facility, gives the SSSF the attributes of a system with features between those of a controlled laboratory system and an actual stack. The simulator is not a large test cell in the sense that the concentrations of pollutants may be determined by the amount of pollutant injected. The tunnel parameters have not yet been well enough determined for this type of calculation to be relied on; therefore, the tunnel gas concentrations and other parameters are measured by specific instruments or by manual sampling methods. Experimental Methods. The monitor was attached to an extractive sampling pump which extracts a continuous sample from Test Section No. 1 and pushes it a t positive pressure through a Hankinson chiller and then to the extractive manifold (Figure 2). A Model 411 Du Pont UV SO2 analyzer (absorption a t 2800 A) served as a continuous monitor on the extractive system of the tunnel. SO2 concentrations were also determined in the test section by an in situ CEA UV Mark IV correlation spectrometer, placed in Port No. 4 and by EPA manual Method 6 (11)samples drawn from Test Section No. 3. Oxygen concentrations were measured by a Taylor-Servomex paramagnetic 0 2 analyzer, a Beckman electrochemical 0 2 analyzer, and by EPA Method 3 samples (ORSAT analysis) (11) drawn from Test Section 3. Carbon dioxide concentrations were determined by a Beckman NDIR COSanalyzer and also by EPA Method 3. A TECO chemiluminescent NO, analyzer was used to determine NO and NO2 concentrations, along with EPA Method 7 ( I 1 ) samples for NO, taken from section 3. Three different span gases were used to calibrate the SO2 instruments during the course of this work. The SOL,concentrations were determined by the barium perchlorate method (EPA Method 6) ( I I ) , giving values of 770 and 851 ppm, respectively, for two SO2-air mixtures (manufacturer's values given at 900 ppm) and 376 ppm for an Son-nitrogen mixture (376 ppm, manufacturer's value). All three span gases cross-correlated on the Du Pont 411 analyzer, while only the two SO2-air mixtures cross-correlated on the fluorescence analyzer. The CEA instrument was calibrated on the tunnel at a temperature of 38 "C and at SO2 step levels determined by the Du Pont 411 analyzer calibrated with the 770 ppm span gas. The following experiments were performed a t the facility: Calibration R u n s . These experiments were designed primarily to cross-check and calibrate the various instruments under ideal conditions prior to the variation of a tunnel parameter. In this experiment, as in the others, the Du Pont 411 analyzer determined relative SO2 values in a feedback loop, with the computer automatically activating a solenoid to add gas to maintain a constant SO2 level. Calibration runs were usually performed at SO2 levels of 200,400,600,800, and 1000 ppm in air (21% 0 2 ) at a temperature of 38 "C. The tunnel velocity was maintained at 1 2 m/s during the experiments to reduce the effect of sampling differences along the length of the test section. Boiler R u n ( C o n s t a n t Reduced 0 2 Concentration). The propane boiler was operated to reduce 0 2 levels in the tunnel. It,was possible to attain a stable 0 2 concentration as low as 5 f 1%.At a given 0 2 level, the SO2 concentration would then be varied stepwise and monitored by the tunnel instrumentation. Volume 10, Number 13, December 1976
1247
Boiler R u n ( C o n s t a n t SO2 Concentration-Varying 0 2 Concentrations). In these experifnents, a constant SO2 con-
centration was maintained in the tunnel while the 02 concentration was continuously varied. In a typical run, an SO2 level would first be maintained a t a 21% 0 2 concentration as a calibration check, the tunnel then purged, and the 0 2 concentration reduced to 5%. The SO2 level would then be brought up and stabilized a t the 5% 0 2 concentration, the boiler turned off, and the oxygen concentration allowed to increase continuously up t o 21% as the SO2 level was held constant. Readings given by the fluorescence monitor would then be compared to those of other methods of detection. Nitrogen R u n (Constant Reduced 02 Concentration). This experiment was similar to that of the boiler run with constant reduced 0 2 concentration, except that instead of the boiler, liquid nitrogen vaporized from two 160-1.storage tanks supplied the makeup gas to effect the reduced concentrations. Figure 3 shows schematically the course of this run as an example of a typical source simulator experiment. NO2 Interference S t u d y . Since NO:! absorbs in the UV region at which the SO2 fluorescence emission is detected (12), an interference study was performed to estimate the importance of this overlap in the SO2 measurements. In the study, a constant SO2 concentration of 500 ppm was first maintained in the tunnel (at 21% 0 2 concentration). NO:! was then added to obtain constant levels as determined by the TECO chemiluminescent NO, analyzer. The NO2 concentration was increased stepwise to a maximum level of 250 ppm.
When the SO*concentration was maintained a t a level of 1100 ppm, the fluorescence analyzer values were 10%higher than the reference value a t 11.5%02-88.5% N:! concentration. As the 0 2 concentration was increased to 2196, this difference decreased linearly (Figure 7 ) . From Figure 6, a t a given reduced oxygen concentration, the fluorescence analyzer values show increased deviations from the reference values a t increased SO2 levels. To obtain a sample more representative of combustion sources, the exhaust from the propane boiler supplied makeup air to the tunnel to reduce the oxygen concentration down to
TIME
-
Figure 3. Trace of source simulator experiment
1400
I
I
I
I
1
I
/' I/
Results
Since the SO2 analyzers used in this study were calibrated with reference to EPA Method 6, independent Method 6 samples were taken from the tunnel throughout the experiments. Although, a t best, the degree of precision inherent in the manual method was from 4 to 5%, the method was believed to be adequate to give absolute reference values for the simulator experiments. Consequently, the Method 6 values obtained were used to evaluate the corresponding instrumental results. Figure 4 shows the results of two calibration runs, with the tunnel O2 concentration held constant a t 21%. The instruments were spanned with the 770 ppm SO:!-air mixture and showed a better than lG??agreement with the Method 6 values obtained from the tunnel. The very good agreement between the instrumental results within each experiment should be noted. The differences between these values and the Method 6 values can be attributed to the errors inherent in sample extraction and manual method determinations and to span and drift problems in the instrumentation. Since the operating procedures of the fluorescence analyzer specify that the instrument be spanned with an SO*-air mixture, a preliminary experiment was performed to examine the extent of the quenching problem by deliberately spanning the instrument on an S02-nitrogen span gas. Figure 5 shows that the result of this type of miscalibration is to give values of approximately 30% lower than those obtained by the reference method. The converse question thus arises from these results as to the effect reduced oxygen concentrations in the sample gas will have on the instrument calibrated with an SO*-air span gas. The oxygen concentrations were first reduced by replacing the tunnel air with nitrogen gas as described in Section (2-4. Two types of data were obtained from the experiment: a plot of instrumentally determined SO:! values vs. Method 6 values a t a given 0 2 concentration (Figure 6), and a plot of instrument SO2 values vs. a changing 0 2 concentration with the tunnel SO:! concentration being held constant (by the Du Pont 411-computer feedback loop) as shown in Figure 7 . The fluorescence analyzer showed significant differences from the reference values a t the reduced 0 2 concentration of 12.5%. 1248
Environmental Science & Technology
200
/-
op 0
1
I
400
200
I
600
I
800
1
1000
I
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I
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EPA METHOD 6 -- SOz,ppm
Figure 4. Analyzer signal as function of SOz concentration in 21 % O2/NZmixture in source simulator. Instruments spanned with 770 ppm SOz in air span gas
n
800
-
(371pprn SO2 I N Nz)
8 w (3
r_
A FLUORESCENT ANALYZER .PHOTOMETRIC ANALYZER IN SITU MONITOR SPAN GAS
./
600-
9
/
+ 400-
3
3 zc-
/' 200 -
0
200
400
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800
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EPA METHOD 6 -- S02. ppm
Figure 5. Fluorescence signal as function of SO2 concentration in 21 % mixture in source simulator. Fluorescence analyzer spanned with 371 ppm SO2 in N2 span gas 02/N2
levels as low as 5% with a corresponding rise of the COS concentration to 10%. The experiments performed were similar to the N2 gas dilution experiment. In two experiments the SO2 concentration was held constant a t levels of 975 and 1375 ppm, respectively, and the oxygen concentration was allowed to vary from 5 to 21% as the COn concentration decreased from 10% to ambient with the addition of room air to the tunnel. In two other experiments the tunnel oxygen concentration was held a t 5.9% (Con = 8%) and 12.5% (COz = 6%), while the SO2 concentration was allowed to increase continuously to levels greater than 1000 ppm. Method 6 determinations were not made during the latter experiments because of the relatively rapid change of the tunnel SO2 concentration. The boiler experiments in which the oxygen concentration was varied gave results similar to the Nz dilution experiment, except that the rate of change of the fluorescence analyzer
1400
7 AFLUORESCENT ANALYZER OPHOTOMETR IC A N A L Y Z E R
1200
12.55 2% 0 2
D
p
readings with reduced 0 2 concentration was not as great with COz as a diluent as with N2.At SO2 levels of about 1000 ppm, with 0 2 = 5% and COz = lo%, the fluorescence analyzer readings were approximately 5% higher than the reference values. In the NO:! interference studies, no decrease in the fluorescence values relative to the reference and monitor values was observed for NO2 concentrations up to 250 ppm, while the SO2 level was maintained a t 500 ppm. A problem of considerable significance was encountered in spanning the fluorescence analyzer used in this investigation. In spanning the instrument the span value would drift upward for approximately one-half hour until a stable value would be attained. A typical drift over this period was from an initial value of 920 ppm upward to 1000 ppm. The problem then arose in setting the correct span value to obtain accurate calibration over the instrument measuring range. This problem was believed to be due to the adsorption of SO2 on the PVC walls of the reaction chamber. Consequently, we “conditioned” the chamber before an experiment by inletting span gas and sealing off the chamber several hours prior to the experiment. After this period the span value would remain relatively constant, and the instrument would give consistent and reproducible results as seen from Figure 4.This procedure, however, is somewhat inconvenient and requires that a sample free of SOs not be drawn through it once the chamber is conditioned, or the conditioning will be lost. These difficulties were felt to account for the lack of agreement between the fluorescence analyzer and monitoring method values in the dilution experiments (Figure 7 ) when extrapolated to 21%
800
n 600
z u z
02.
400 v1
0
200
0
400
600
1000
800
E P A METHOD 6 --
1200
SOZ.ppm
Figure 6. Fluorescence signal as function of SOz concentration in 12.5 i 2 % 02/Nzmixture
Discussion From the above results, the fluorescence analyzer SO:! readings are apparently dependent upon the composition of the combustion gas as well as the SO2 concentration. We interpret this dependence as the result of the relative quenching effects of 0 2 , NP,and COz on the SO:! fluorescence. Due to the lack of any published data on quenching effects of these gases, we have attempted to obtain approximate values of the quenching coefficients for 0 2 , N2,and COz by using the results of Figure 7 . Equation 1 may be modified in terms of the present evaluation to have the form:
c o 2 DILUTION
a
-
.
:
.* - 0
* . 0 *
AFLUORESCENTANALYLER .PHOTOMETRIC ANALYZER OEPIMETHODS
i
N2 DILUTION
”OD
t J
5
9-&-5-*-CO2 DILUTION
6
I
8
-1
9 10 11 12 13 14 15 16 17 18 19 20 21 PERCENT. 0 2
Figure 7. Measurements of SOz concentrations in source simulator as function of oxygen concentration Experiment with SO2 level set at 1375 pprn diluted with change of C o p concentration from 8 to 0 % . Experiment with SOp level set at 1100 ppm diluted with N p concentration changed from 88.5 to 79%. Experiment with SOn level set at 975 ppm diluted with change of C 0 2 concentration from 10 to 0%
where I,, is the ppm SO? reference value assuming 21% 0 2 concentration and 79% N2, and Z is the ppm SO:! reading of the fluorescence analyzer at the actual gas composition. The terms p i of Equation 1 are replaced here by terms ( p , - uLZ,,/I), where a, is the concentration of gas i in torr, to account for the fact that values of Z, were obtained a t an Nz concentration of ’79% (600 torr) and 0 2 concentration of 21% (160 torr) by the fluorescence analyzer used in the experiments. Values of k , = 1.1X lo8s-l and k S O a = 5 X 10‘ s-l torr-] were taken from Hui and Rice (13)with the assumption that the fluorescence excitation is principally that a t 2138 8. The results of this calculation showed qualitatively, that k o 2 > kco, > k y L .It was felt that the experimentally determined partial pressure values were not sufficiently accurate to give reliable quantitative estimates of the quenching coefficients. The magnitudes of these calculated coefficients, however, were qualitatively consistent in the calculations from each of the three data sets obtained from Figure 7. We summarize these results as follows: Oxygen quenches the 2138 A-excited SO2 fluorescence more than nitrogen. This is particularly significant if an SO2-niVolume 10, Number 13, December 1976
1249
trogen gas mixture instead of an SO?-air mixture is used to span the fluorescence instrument. As stated earlier and from Figure 5, use of an SOz-nitrogen span gas results in errors on the order of 30%. Carbon dioxide quenches the fluorescence to a lesser degree than oxygen, but by about the same order of magnitude. This is particularly important when the method is applied to combustion sources. Since the reduction of 0 2 levels in combustion sources is accompanied by a corresponding increase in COz levels, the net result is a minimizing of the quenching effect due to decreasing 0 2 levels. In fact, the spanning errors encountered with the analyzer used in this study could contribute a greater error than that resulting from any quenching effects. The fluorescence method for detecting SO2 emissions from combustion sources was thus adequate to monitor those emissions. Ideally, as has previously been noted ( 3 ) , the greatest accuracy can be obtained if the span gas consists of SO2 in a gas mixture characteristic of the source to be monitored. It has not been shown, however, that such SO2 mixtures remain stable over extended periods of time; therefore, care should be taken in using this procedure as a solution to the quenching problem. The introduction of NO2 a t levels found within a typical combustion source did not interfere significantly with the SOP measurements. The problem of arriving at a stable span value was the most serious drawback encountered in the present work. This, however, does not bear upon the fluorescence method and should be easily solved with a few instrumental modifications.
Acknowledgment
We thank Nancy Reierson of EPA for performing the Method 6 analyses and Mike Moran and his staff of Northrop Services, Inc., for their operation of the SSSF for these experiments. Literature Cited (1) Okabe, H., Splitstone, P. L., Ball, J . J., J . Air Pollut. Control
Assoc., 23,514 (1973). (2) Zolner, W., Cieplinski, E., Helm, D., Thermo Electron Corp., TECO 40 Manual-Appendix A. (3) Wolfe, C. L., Giever, P. M., "Design, Fabrication and Evaluation of a Fluorescence Sulfur Dioxide Monitor", Research Appliance Co. and Stanford Research Institute, presented at APCA Meeting 68, June 15,1975. (4) International Biophysics Corp., Celesco Industries, private communication. ( 5 ) Homolya, J. B., J . Air Pollut. Control Assoc., 25,809 (1975). (6) Byerly, R., IEEE Trans. Nucl. Sci., NS-22,856 (1975). (7) Moran, M. J., "Simulated Stationary Source Facility Users Handbook", TN-262-1535, Northrop Services, Inc., Huntsville, Ala. (8) Strickler, S. J., Howell, D. B., J . Chem. Phys., 49, 1947 (1968). (9) Schwarz, F. P., Okabe, H., Whittaker, J. K., Anal. Chem., 46,1024 (1974). (10) Okabe, H., J. Am. Chem. SOC.,93,7095 (1971). (11) Fed. Regist., 36 (1591, 15704 (1971). (12) Hall, J.C., Jr., Blacet, F. E., J . Chem. Phys., 20, 1745 (1952). (13) Hui, M.-H., Rice,'S. A., Chem. Phys. Lett., 17,474 (1972). Receiued for review February 2, 1976. Accepted June 14, 1976. Mention o f trade names or commercial products does not constitute endorsement or recommendation for use by EPA.
Jet-Cone Impactors as Aerosol Particle Separators Jeffrey H. Schott and William E. R a m * Department of Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, Minn. 55455
A jet-cone impactor, designed to eliminate particle bounce and reentrainment of collected aerosol material and to collect larger samples for analysis by removing impacted material to a secondary collection region with a portion of the gas flow, was calibrated experimentally for impaction surface angles of 45" and 60". Collection efficiencies were also calculated for a model impactor flow to determine effects of changing the impaction surface angle and jet Reynolds number. Sharpness of separation increased with increasing impaction surface angle, and impactor cut size decreased with increasing impaction surface angle. Variation of jet Reynolds number over a tenfold range had little effect on collection efficiency. Since agreement between experiment and theory was quite good, calculated collection efficiencies are recommended as a standard for this type of impactor.
To increase design possibilities and capabilities of impactors, this work considers the effects of Reynolds number, impaction surface angle, and split flow on collection efficiency of jet impactors with conical impaction surfaces. Effects of these quantities on collection efficiency were measured experimentally. Theoretical estimates of these effects were also obtained by observing the behavior of a mathematical model of the same impactors. 1250
Environmental Science & Technology
Experimental values of collection efficiencies were measured for conical impact surfaces with cone angles of 60" and 45". Split flow values were 0 and 10%. Jet Reynolds number was varied over a range from 1000-10 000. Effects on collection efficiency of two modifications were also studied. These modifications were holes in a plate separating a collecting and noncollecting region and a skimmer ring on the impact cone which changed the flow path of collected aerosol liquid. Collection efficiency was measured, with holes in the separating plate, for cone angles of 60" and 45' and split flows of 0 and 10%.The skimmer ring was used only for measurements with a cone angle of 45" and split flow of 10%. Theoretical collection efficiency curves were obtained from numerical solutions of the equations of motion of a model flow field. Computer programs developed by Marple ( I ) were used to construct solutions. Collection efficiency curves for impaction surface angles of go", 60°, and 45", jet Reynolds numbers of 1000, 3000,lO 000, and split flows of 0 and 10% were calculated. The effect of spacing ratio, N,, on collection efficiency has been studied both theoretically and experimentally. Investigations by Mercer and Stafford (2) and Marple ( I ) considered values of N , in a range from 0.125 to 10.0. For values of N , less than 1,decreasing N , increases the sharpness of separation and shifts the collection efficiency curve to lower values of N,+. However, position of the curve is very sensitive to small
