Table I. Yields of Peroxyacyl Nitrates Figure
Identifying peak, crn-I Absorption, (IJI) Infrared absorptivities, ppm-’ M-’ * ( 8 ) Ppm formed Ppm initial aldehyde Yield
PAN 1
PPN 2
PBzN 3
930
1050
1810
26.5112 1.8 x 10-4
23.513.8 5.3 x 10-4
27.8/1.8 6.9 x 10-4
3.8 4.0 95
3.0 3.0 100%
3.4 3.0 1130/oa
a H i g h yield may be due to inaccuracy of benzaldehyde
measurement.
ide were photolyzed, only 0.15 ppm of P A N formed after 120 min of irradiation. With the addition of 0.8 ppm chlorine to the system, the P A N concentration increased from 0.15-1.55 ppm after only 4 min of irradiation. For the formation of peroxypropionyl nitrate, 3 ppm of propionaldehyde were reacted with 3.1 ppm of nitrogen dioxide and 1.6 ppm of molecular chlorine in air. T h e reactant and product spectra are shown in Figure 2 . Peroxybenzoyl nitrate was formed in like manner from 3 p p m of benzaldehyde, 3.4 pprn of nitrogen dioxide, and 1.8 pprn of chlorine. This case is recorded in Figure 3. Peroxyformyl nitrate ( P F N ) , the simplest homolog of the series and never before been synthesized, was apparently formed in the irradiation of formaldehyde, nitrogen dioxide, and chlorine in air, as indicated by a characteristic PAN-type bands a t 800, 1300, 1400, and 1740 cm-’. I t is under further study. Figure 4 shows the P F N spectrum from the irradiation of 20 ppm of formaldehyde, 20 ppm of nitrogen dioxide, and 30 ppm of chlorine in a n atmosphere of oxygen.
Since yields are very high (Table I), known concentrations of PANS can be prepared by this method without the use of infrared equipment. One prepares a known concentration of aldehyde with a slight excess of nitrogen dioxide and chlorine, photolyzes the mixture, and assumes the corresponding P A N member forms in stoichiometric yields. T h e chlorine-aldehyde-NO2 method of P A N preparation appears to be general in its application. I t produces high yields of PANS relatively free from organic side products, and it gives further confirmation to the generally accepted molecular structure of the PANs.
Literature Cited (1) Taylor, 0 . C., J . Air Pollut. Control Assoc., 19,347 (1969). (2) Heuss, J. M., Glasson, W. A,, Enuiron. Sci. Technol., 2, 1109
(1968). (3) Stephens, E. R., Hanst, P. L., Doerr, R. C., Scott, W. E., Ind. Eng. Chem., 48,1998 (1956). (4) Stephens, E. R., Scott, W. E., Hanst, P. L., Deorr, R. C., J . Air Pollut. Control Assoc., 6, 159 (1956). (5) Stephens, E. R., Hanst, P . L., Doerr, R. C., Scott, W. E., ibid., 8,333 (1959). (6) Scott, W. E., Stephens, E. R., Hanst, P. L., Doerr, R. C., Proc. Am. Petrol. Inst. (III), 171 (1957). ( 7 ) Stephens, E. R., Darley, E. F., Taylor, 0. C., Scott, W. E., I n tern. J . Air Water Pollut., 4, 79 (1961). (8) Stephens, E. R., “The Formation, Reactions, and Properties of Peroxy Acyl Nitrates (PANs) in Photochemical Air Pollution” in “Advances in Environmental Science and Technology,” Vol. 1. J. N. Pitts. and R. L. Metcalf. Eds.. DD 119-46. Wilev Interscience, New York, N.Y., 1969, (9) Tuesday, C. S., “The Atmospheric Photooxidation of Trans2-butene and Nitric Oxide.” in “Chemical Reactions in the Lower and Upper Atmosphere,” pp 1-49, Interscience, New York, N.Y., 1961. (10) Stephens, E. R., Burleson, F. R., Cardiff, E. A , , J Air Pollut Control Assoc , 15,87 (1965). (11) Hanst, P. L., Lefohn, A. S., Gay, B. W. Jr., Appl. Spectros, 27, 188 (1973). Received f o r reuiew March 3, 1975. Accepted August 11, 1975.
Means to Evaluate Performance of Stationary Source Test Methods William J. Mitchell and M. Rodney Midgett Quality Assurance Branch, Environmental Monitoring and Support Laboratory, Office of Research and Development, U.S. Environmental Protection Agency, Research Triangle Park, N.C. 277 1 1 Described are two sampling arrangements t h a t allow four independent stationary source sampling trains to sample simultaneously a t essentially the same point in the stack. Presented are the results obtained with these sampling arrangements during field tests using the E P A particulate sampling train.
Spatial and temporal variations in the velocity profile ( t h e distribution of the flow across the stack) and in the pollutant profile (the distribution of the pollutant concentration across the stack) frequently occur in the stacks of stationary sources. Since a shift in the velocity profile does not always produce an identical shift in the pollutant profile, the effect of these spatial and temporal variations on the sampling results must be minimized when sampling stationary sources. T o minimize the occurrence of temporal variations, the source is generally required t o operate at maximum rated capacity while it is being sampled. T h e
spatial variation is generally handled by dividing the stack into sections of equal area and sampling each area for an equal period of time (traversing). Traditionally, the within-laboratory and between-laboratory precision of test methods is determined through collaborative testing (round-robin testing). T h e collaborative test is designed so that the participants (collaborators) each make one or more measurements on identical samples using the same test method. Then, from a statistical analysis of the results, a n estimate is made of the within-laboratory and between-laboratory precision of the test method. This general technique has been used very widely for the validation of methods for the analysis of such items as water, drugs, food and agricultural products, fertilizers, coal, and ores. When a stationary source test method is collaboratively tested, the sampling, as well as the analytical aspects of the method, must be evaluated. However, the need t o traverse the stack while sampling creates a series of complex problems with no easy solutions. Paramount among these beVolume IO, Number l , January 1976
85
comes the problem of the simultaneous extraction of representative samples from the stack by each of the collaborative test teams. For circular stacks, this automatically limits participation to four test teams, each sampling independently through one of the 90' ports, and each rotating to the next port on a signal from the test coordinator. This means that a t least nine people (two persons per team, plus a test coordinator) must often be on the stack a t the same time. Also, extensive modifications of the sampling platform priorsto the collaborative test may be necessary to accommodate the sampling teams and their equipment. Add to this the cost of maintaining nine people in the field for the two to three weeks required to gather sufficient data for a statistically valid collaborative test, and it becomes apparent that collaborative testing of source emission methods can be extremely expensive. Our experience has shown that before a stationary source test method can be successfully collaboratively tested, it must be described in enough detail to ensure t h a t each collaborator uses exactly the same sampling and analysis procedures, and further, it must give repeatable results when one laboratory analyzes the same sample several times. However, laboratory investigations by themselves are insufficient for determining the performance of source test methods under actual field conditions, and also are insufficient for identifying those methods worthy of collaborative testing. Similarly, because of the effects of spatial and temporal concentration variations in the stack, it is difficult to draw conclusions on method variability from consecutive samples gathered from a stack by a single train.
For these reasons, a new evaluation technique was sought to bridge the gap between the single-train, singlelaboratory method evaluation and the interlaboratory collaborative testing. The result was two sampling train arrangements that allow four independent trains to sample simultaneously a t essentially the same point in the stack. Field tests have shown that these sampling arrangements can be used to evaluate the reliability of stationary source test methods to see if they warrant being collaboratively tested. Because elaborate, pretest site preparations are not required, and only one man is necessary for each sampling train, the cost per sample is only a fraction of the cost per sampled that would be expended for a full-scale, collaborative test of the method. These two sampling train arrangements allow an estimate to be made of the between-laboratory agreement that would be expected from two identical or different sampling trains that had simultaneously sampled the same source such that spatial and temporal variations did not affect the results. The usefulness of these sampling arrangements was evaluated using the EPA particulate sampling method ( 1 ) (Method 5 ) . T h e particulate train was selected as the vehicle to test the usefulness of these arrangements because it requires the most careful attention to detail and it is the stationary source test method that would be most affected by spatial and temporal variations in the source. Thus, if replicate particulate samples could be obtained with the sampling arrangements described here, then we could reasonably expect that these sampling arrangements would be applicable to most other stationary source test methods.
n 9 cn
I I L
u
UL
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(&
"S" TYPE PITOT TUBE
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Figure 1. Single-pitot sampling arrangement
Figure 2 Double-pitot sampling arrangement
Top, side view, bottom, upstream view
Top, side view: bottom, upstream view
86
Environmental Science & Technology
1.0 in,
i
the nozzles and the pitot tube(s) was held constant by stainless steel clamps mounted on the probes. The probe liners were maintained a t the same temperature ( 1 2 l O C ) by connecting each probe’s heating wire to the same electrical outlet strip. All the filter holders were placed in the same heated box and all the impingers were placed in one box that contained a mixture of ice in water. T o facilitate movement of the probes into and out of the stack, all the sampling equipment, with the exception of the meter boxes, was mounted on one lab cart. A t each site, a sampling point was selected a t which the velocity profile measured by an s-type pitot tube varied by less than 2% of the average velocity across the area that would be occupied by the four nozzles and the pitot tube(s). Within a test, all sampling runs were done a t the same selected sampling point. When a single-pitot sampling arrangement was being used, the pitot tube was attached to the control box of train 1. The operator of this train determined the velocity head ( I p ) a t 5-min intervals, and then each train operator used this I p to obtain an isokinetic sampling rate in his train. When the double-pitot sampling arrangement was being used, one of the pitot tubes was attached to the control box of train 1, and the other pitot tube was attached to the control box of train 3. The operator of train 1 determined the I p a t 5-min intervals, and then he and the operator of train 2 used this I p to obtain an isokinetic sampling rate in their respective trains. At the same time, the operator of train 3 also determined the I p using the other pitot tube. Then both he and the operator of train 4 used this A p to obtain an isokinetic sampling rate in their respective trains. In the 16 sampling runs accomplished, all the trains were able to operate within 10%of the isokinetic sampling ratethe allowable range for a Method 5 determination ( I ). A t the end of each sampling run, the particulate material collected from the nozzle up to and including the filter was recovered from the trains. The particulate material caught in the nozzle, probe, and filter holder was removed by washing these train components first with distilled water and then with acetone while scrubbing them with a nylon brush. The glass fiber filters, tared prior to the test, were removed from the filter holder with a pair of tweezers, placed in a culture dish, and then were returned to the laboratory for a weight gain determination.
Experimental Design and construction specifications for the EPA Method 5 ( 1 ) sampling train have been described by Martin ( 2 ) . A description of the operating principles of the train has been presented by Rom ( 3 ) .Basically, the train is operated as follows: a pitot tube (a velocity measuring device) is used in conjunction with an orifice and a vacuum pump to sample for the particulate a t the same velocity that it is moving in the stack (isokinetic sampling). At the end of each sampling run, the particulate that has been collected in the train is recovered and weighed. The particulate concentration in the stack, which is usually referred to as the particulate loading, is then obtained by dividing the total volume of stack gas sampled (corrected to the reference conditions of 2 1 O C and 1 atmosphere pressure) into the weight of particulate collected in the train. T h e two sampling probe/pitot tube arrangements developed and tested are shown in Figures 1 and 2. In the sampling arrangement in Figure 1, the four sampling nozzles are symmetrically located about a type-s pitot tube by placing one nozzle a t each corner of a 6-cm square and placing the pitot tube a t the center of the square. In the sampling arrangement in Figure 2, each nozzle is located a t a corner of a 3.5-cm square and the two pitot tubes used are placed on either side of the square. This last sampling arrangement was developed to see if decreasing the distance between the sampling nozzles would improve the withinrun standard deviation. Except for the differences between the two nozzle/pitot tube arrangements mentioned above, the sampling trains used in all three studies were identical in design and construction. These sampling arrangements have been field tested on three occasions. Two of the field tests described here (tests 2 and 3) were done a t the same municipal incinerator, but a t different times of the year. The other test was done a t a large coal-fired power plant. The sampling procedure used was similar to that specified in the Federal Register ( I ) except that: (1) fixed-point sampling rather than multiplepoint sampling (traversing) was used; and (2) for some sampling runs, the sampling time was less than the 2 hr specified in the Federal Register. (The sampling time was varied to see if the within-run standard deviation was sensitive to the total weight of particulate collected.) During each sampling run, the relative distance between M
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Volume 10, Number 1, January 1976
87
___-_
Table I. Within Run Variations in Particulate Loading Mg/std. m3,dry basis Run Test time, no. Run min
1
2
3
1 2 3 4 5 6 7 8 9 10 11.1 12a 13a 14a 15 16
205 190 207 155 60.4 57.1 62.5 54.2 51.0 56.3 140 113 114 126 153 103
202 196 240 150 61.9 62.2 61.3 51.8 50.5 59.9 143 107 234b 123 141 106
204 222 222 188 63.2 64.1 58.2 49.6 50.5 62.4 131 125 200b 134 161 104
1
2
3
90 30 30 30 120 120 150 120 55 55 120 90 120 90 120 90
Train
4
Mean %C.V.
221 208 4.2 185 198 8.3 199 217 8.3 141 159 13.0 64.6 62.5 2.8 62.5 61.5 4.9 56.9 59.7 4.4 45.3 50.2 7.5 46.1 49.5 4.6 51.9 57.6 7.9 133 137 4.4 128 118 8.6 114 166 37.0 144 132 7.0 139 148 6.7 103 104 1.3
a D o u b l e - p i t o t s a m p l i n g a r r a n g e m e n t used in t h i s r u n . T r a i n n o z zle b r u s h e d t h e w a l l of t h e stack as it was b e i n g inserted i n t o t h e stack.
Results a n d Discussion of Results Table I presents the particulate results from each sampling run and also presents the within-run percent coefficients of variation (% C.V.). This percent coefficient of variation, calculated using Equation 1, is a statistical measure that expresses the standard deviation as a percentage of the mean. This technique was used to facilitate interpreting the results because the mean particulate loading varied between runs and between tests.
magnitude of the mean particulate concentration measured. From the plot, it is apparent t h a t the two-pitot arrangement gave results comparable to the single-pitot arrangement. A similar linear regression analysis (not presented) that compared the within-run standard deviation for each sampling run with the sampling time for that run, determined that the variation in the within-run standard deviation was not caused by changes in the run sampling time. Consequently, there is no reason to believe that the total weight of the particulate collected or the total volume of stack gas sampled affected the within-run standard deviations. An examination of the individual train results in Table I shows that no train was consistently high or consistently low and that considering the large number of errors t h a t can occur in a stationary source test, the agreement between the trains in any one run is quite good. Conclusion From the results reported here, it is concluded that either of the four-train sampling arrangements can be a useful means to determine the agreement that might be expected between similar stationary source sampling trains under controlled conditions prior to subjecting the stationary source test method to a collaborative test. Further, these sampling probe arrangements might be a noncontroversial means to evaluate the relative performance capabilities of dissimilar stationary source test methods or sampling trains applicable to measuring the same pollutant. They should also be useful for determining the effect that changing such things as sampling rate, probe or filter temperature, type of probe material, or number of or location of impingers or filters might have on the performance of a certain sampling train. Literature Cited (1) Environmental Protection Agency, “Standards of Performance
within-run standard deviation x 100 % C.V. = run mean particulate concentration Figure 3 presents the results of a linear regression analysis that compared the standard deviation for a run with the corresponding mean particulate loading determined by the four trains in that run. This linear regression analysis determined that 73% of the change in the within-run standard deviations was associated with the changes in the
88
Environmental Science & Technology
for New Stationary Sources,” Fed. Regist., 36, 24876-90 (December 23, 1971). ( 2 ) Martin, R. M., “Construction Details of Isokinetic SourceSampling Equipment,” Environmental Protection Agency, Air Pollution Technical Information Center, Publication APTD 0581. (3) Rom, J. J., “Maintenance, Calibration, and Operator of Isokinetic Source Sampling Equipment,” ibid., Publication APTD 0576. Received for reuieu A u g u s t 26, 1974. Accepted A u g u s t 18, 1975.
