EP A/600/A-96/062 Development of Calibration Procedures for Toxic Metal Aerosols for Continuous Emission Monitoring Systems Thomas J. Logan, National Exposure Research Laboratory, U. S. Environmental Protection Agency, Research Triangle Park, North Carolina 27711 James F. McGaughey and Raymond G. Merrill Radian Corporation, P, O. Box 13000, Research Triangle Park, North Carolina 27709 An aerosol generation system has been developed to calibrate die performance of continuous emissions monitoring systems (CEMS) for toxic metal aerosols. The U. S. Environmental Protection Agency Office of Solid Waste has proposed the use of metals monitoring as an approach to better assess die risk of incinerator emissions. Prior to the development of metals CEMS regulations, it is necessary to determine a method to evaluate die expected performance of CEMS. To measure the performance of CEMS, a dynamic calibration approach which can be used to evaluate monitor performance must be developed and tested. This calibration approach requires stable aerosol concentrations of the 16 toxic metals on a system that has a flow rate of 20 liters per minute for the air stream containing die metals aerosol. The concentration of the metals in die aerosol must be able to vary over the range - of 10 to 1000 micrograms per cubic meter, on an aerosol generating system that can operate in a stable mode for at least 30 minutes. The aerosol generation system that has been developed meets the above requirements, and has been tested in a laboratory environment. INTRODUCTION The Office of Solid Waste has proposed the use of metals monitoring as an approach to better assess the risk of incineration emissions. Preliminary to the development of metals CEMS regulation it is necessary to determine the expected performance of such CEM systems. In order to measure the performance of CEM systems, it will be necessary to develop and test a dynamic calibration approach which can be used to evaluate monitor performance. Several metals CEMS are currently under development which use various analytical techniques such as inductively coupled argon plasma spectroscopy 0CAPS) and laser spark spectroscopy (LASS). Each metals CEM uses a unique approach to sampling. To encompass these different techniques (which are still under development) under a single calibration system, specific requirements were imposed The requirements are as follows: 1. Develop stable aerosol concentrations of the 16 toxic metals; Antimony (Sb), Arsenic (As), Barium (Ba), Beryllium (Be), Cadmium (Cd), Chromium (Cr), Cobalt (Co), Copper (Cu), Lead (Pb), Manganese (Mn), Mercury (Hg), Nickel (Ni), Selenium (Sc), Silver (Ag), Thallium (Tl) and Zinc (Zn). 2. Develop a system that will have a flow rate of the air stream containing the metals aerosol of 20 liters per minute (LPM). 3. Vary the concentration of the metals in the aerosol over the range of 10 to 1000 micrograms per cubic meter (Hg/m3). 4. Operate the system in a stable mode for at least 30 minutes. In order to gain some insight into the work currently being performed by other researchers on the development of metals CEMS, Jim McGaughey of Radian Corporation and Tom Logan of the EPA visited the Sandia National Laboratory (SNL) and the Stanford Research Institute (SRI), both in California. Both organizations woe performing research with LASS vsing aerosol-generating systems available from commercial vendors. SNL was using a nebulizer that is commonly used with sample introduction in ICAPS systems, while SRI was using a nebulizer commonly used in the medical field for respiratory therapy. Considering the cost and availability of the two types of 1 ------- nebulizers, the first approach to the development of a dynamic calibration procedure was the use of medical nebulizers. NEBULIZER SELECTION Three nebulizers were evaluated in the Radian laboratory relative to such parameters as ease of operation and ability to be modified easily. The field was narrowed to a single device with a product name of "Acorn II # 124014." This unit was designed to provide a mean particle size of approximately 1.5 microns at an output (nebulization rate) of 0.31 mL per minute (mL/m) with an air supply flow rate of 8 LPM. PREPARATION OF SPIKING SOLUTION Aqueous solutions containing the 16 metals were prepared for charging the nebulizer. Due to the complexity of the solution, specific salts of each of the metals were selected based on their solubility in water and dilute nitric acid. The combination of certain compounds and the use of hydrochloric acid had to be avoided to minimize the precipitation of several of the metals, particularly silver. Three separate solutions were prepared. Each solution contained the 16 metals at concentrations of 15 parts per million (ppm), 30 ppm and 60 ppm respectively. The stock solution of the metals was prepared at a concentration of 60 ppm. All metals except chromium and antimony were made from commercially available solutions purchased at 1000 ppm each. A 1000 ppm chromium stock was made by dissolving 7.698 grams of chromium in one liter of water. A 1000 ppm antimony stock was made by dissolving 2.742 grams of ' antimony potassium tartrate in one liter of warm water. Twelve mL of each of the 16 stock solutions was added to a volumetric flask and diluted to 200 mL with 5% nitric acid. This 60 ppm solution was then used to prepare the 30 ppm and the IS ppm solutions by dilution with 5% nitric acid. INITIAL CONFIGURATION OF AEROSOL GENERATOR The initial configuration of the aerosol generation system is shown in Figure 1. The nebulizer was connected by a compression fitting to one end of a glass tube. The glass tube is approximately one half inch in diameter and in the shape of a "U." The length from the point where the nebulizer is attached to the bend is approximately 2 feet. The outlet is fitted with a ground glass socket joint that is used to connect to an EPA Method 5 glass filter holder. Just above the point where the nebulizer attaches to the glass tube is a port for the introduction of make-up air. Eight LPM of air is supplied to the nebulizer through rotameter A and 12 LPM of make up air is supplied through rotameter B for a total flow of 20 LPM. It should be noted that in this configuration the glass tube is in a vertical position. The use of glass fiber filters to collect the aerosol followed by analysis by ICAPS was selected as the approach to monitor the performance of the system during development. A glass fiber filter is not the best choice for the collection of some metals such as mercury. However, the collection efficiency for the majority of the metals of interest was sufficient to be able to evaluate the system performance. During initial experiments with this configuration using only the 8 LPM of air to operate the nebulizer, the recovery of the metals were within ±10% of the target value. However, when the make-up air was added the recoveries were reduced to approximately 60% of the target values. Observations made during the operation of the system with the make-up air flowing indicated that the make up air was cooling the aerosol sufficiently to cause condensation which was draining back into the nebulizer. This condensation was apparently diluting the spiking solution in the nebulizer and therefore reducing the concentration of the metals. This experiment was repeated with heat applied to the glass tube. The amount of condensation was reduced as evidenced by improved recoveries, but heating did not completely solve the recovery problem. The system was again modified by positioning the glass tube in a horizontal position as discussed below. FINAL CONFIGURATION OF AEROSOL GENERATOR The final configuration of the aerosol generation system is shown in Figure 2. In this configuration the glass tube is in a horizontal position with the nebulizer attached between the glass tube and the point where the make-up air enters the 2 ------- system. The advantage of this configuration is that the make-up air now sweeps the aerosol into the glass tube and prevents any condensed materials from entering the aerosol generator. In addition to the changes discussed above, the make-up air and the glass tube were preheated to approximately 60 °C. The combination of the heat and the horizontal configuration eliminated the problem of condensation. With the system in the horizontal configuration, samples were again collected for 10 minutes each using 15 ppm, 30 ppm and 60 ppm spiking solutions. The fluid reservoir of the nebulizer contains approximately 6 mL of spiking solution, enough for about 20-30 minutes of operation. The results are given in Tables 1 through 3. These results show that the recoveries of the metals contained in the aerosol are within ±10% of the theoretical value except for silver, lead, chromium, antimony, thallium, zinc and mercury. Silver recoveries are commonly lower than expected in many samples due to the presence of chloride which combines with silver to produce an insoluble salt Traces of chloride in the water used to make the solutions or introduced during sample collection could cause the lower recoveries. Chromium and antimony showed acceptable results for the 30 ppm and 60 ppm runs, but only about 85% recovery for the 15 ppm samples. This low recovery is most likely just an anomaly, as previous data sets have shown acceptable recoveries (±10% of theoretical value). Lead and thallium showed the same behavior. The recoveries for zinc were marginally outside of the 10% window on the high side due to zinc contamination in the laboratory which is a common occurrence. Mercury recoveries were poor, as expected, due to the inability of the filter to collect the more volatile mercury. The important observation made from reviewing the recovery data is that the aerosol generation system does produce stable aerosols of known concentration and that any results outside of the 10% window for recovery are the result of instrument variability, difficulties with precipitation of metals from the spiking solution or poor collection efficiency of the filter for certain metals. CONCLUSIONS AND RECOMMENDATIONS Based on the results discussed above, the following conclusions can be reached: 1. Stable aerosols containing metals of known concentration over the range of 10-1000 ng/m3 with a total flow of 20 LPM can be generated. 2. The aerosol generation system can operate in a stable mode for 30 minutes or more. Based on the information gained from the laboratory experiments the following recommendations can be made: 1 As the development of the metals CEMS progresses, the delivery system of the generator needs to be modified to accommodate the sampling approach of as many methods as possible. This modification may encompass increasing the scale of the system to provide a larger total air flow and consequently a largo* amount of the generated aerosol. 2 The use of electronic flow measuring devices for both air supplies needed for the system would provide the most accurate flow settings. These flow settings are critical for determining the metals concentration in jig/m3. 3 The solution containing the metals may need to be prepared in two or three separate solutions with fewer metals in each to minimi^ interactions and incompatibilities among the metal compounds. DISCLAIMER The information in this document has been funded wholly by the United States Environmental Protection Agency under contract 68-D4-0022 to Radian Corporation. It has been subjected to Agency review and approval for publication. Mention of trade names or commercial products does not constitute endorsement or recommendation for use. 3 ------- Table 1. Results for IS FPM Study ppm Metal Sim# Average Theoretical % Recovery % BSD1 A* Am Ba Be Cd Co Ct Cu Ma Ni Fb Sb Se T1 Zs H* 0.178 0.388 0.371 0.386 0.387 0.381 0.357 0.374 0.372 0.381 0.248 0.329 0.390 0.191 0.446 0.152 0.134 0.368 0.363 0.363 0.365 0.355 0.314 0.356 0.356 0.361 0.231 0.358 0.373 0.145 0.483 0.151 0.201 0.412 0.388 0.398 0.407 0.391 0.373 0.386 0.396 0.395 0.340 0.375 0.435 0.198 0.471 0.142 0.222 0.411 0.400 0.403 0.410 0.392 0.380 0.393 0.391 0.395 0.381 0.358 0.413 0.260 0.510 0.116 0.219 0.386 0.439 0.398 0.398 0.390 0.380 0.389 0.387 0.387 0.317 0.352 0.407 0.275 0.553 0.099 0.191 0.393 0.392 0.390 0.393 0.382 0.361 0.380 0.380 0.384 0.303 0.354 0.404 0.214 0.493 0.132 0.42 0.42 0.42 0.42 0.42 0.42 0.42 0.42 0.42 0.42 0.42 0.42 0.42 0.42 0.42 0.42 45.4 93.6 93.4 92.8 93.7 90.9 85.9 90.4 90.6 91.4 72.2 84.4 96.1 50.9 117.3 31.4 19.01 4.73 7.62 4.14 4.63 4.09 7.70 3.95 4.29 3.66 20.75 4.68 5.82 24.95 8.30 17.80 'Relative standard deviation: J4RSD ¦ SD mean x 100 Table 2. Results for 30 ppm Study PP" Run#1 Metal 1 2 5 Average Theoretical Recovery 1SD2 Ag 0.551 0.565 0.585 0.567 0.84 67.5 3.01 A* 0.878 0.860 0.745 0.828 0.84 98.5 8.72 Ba 0.795 0.786 0.696 0.759 0.84 90.4 7.21 Be 0.854 0.829 0.832 0.838 0.84 99.8 1.63 Cd 0.853 0.833 0.836 0.841 0.84 100.1 1.28 Co 0.835 0.811 0.820 0.822 0.84 97.9 1.48 Cr 0.812 0.782 0.791 0.795 0.84 94.6 1.94 Cu 0.823 0.790 0.796 0.803 0.84 95.6 2.19 Mn 0.825 0.801 0.811 0.812 0.84 96.7 1.48 Ni 0.831 0.808 0.811 0.817 0.84 97.2 1.53 Pb 0.716 0.681 0.706 0.701 0.84 83.5 2.57 Sb 0.804 0.786 0.660 0.750 0.84 89.3 10.46 Se 0.852 0.844 0.869 0.855 0.84 101.8 1.49 T1 0.562 0.583 0.632 0.592 0.84 70.5 6.06 ZB 0.957 0.941 0.909 0.936 0.84 111.4 2.61 n-Hf™ 0.410 0.355 0.300 0.355 0.84 42.3 1S.50 1Only three runs preset*. Run 3 wm» not spiked and Run 4 wm double tpiked. 2Relative standard deviation: %RSD * —— X 100 ------- Table 3. Results for 60 ppm Study PP*11 Run# Metal 1 2 3 4 5 Average Theoretical % Recovery ksd1 H 1.255 1.027 1.077 1.283 1.072 1.143 1.68 68.0 10.26 Am 1.752 1.729 1.699 1.784 1.751 1.743 1.68 103.8 1.80 m 1.599 1.473 1.496 1J72 1.517 1.531 1.68 91.2 3.44 Be 1.763 1.616 1.652 1.723 1.669 1.685 1.68 100.3 3.47 Cd 1.754 1.622 1.651 1.729 1.668 1.685 1.68 100.3 3.27 Co 1.722 1.589 1.620 1.695 1.633 1.652 1.68 98.3 3.33 Cr 1.674 1.446 1.476 1.658 1.477 1.546 1.68 92.0 7.13 Cu 1.673 1.514 1.550 1.649 1.571 1.591 1.68 94.7 4.23 Mn 1.691 1.568 1J93 1.657 1.606 1.623 1.68 96.6 3.08 Ni 1.712 1.595 1.623 1.687 1.626 1.649 1.68 98.1 2.96 Ffe 1.477 1.304 1.353 1589 1.335 1.412 1.68 84.0 8.43 Sb 1.611 1.493 1.516 1.630 1.500 1.550 1.68 92.3 4.21 S« 1.779 1.645 1.561 1.752 1.600 1.667 1.68 99.3 5.69 *n 1.282 1.150 1.180 1.329 1.166 1.221 1.68 72.7 6.49 Zn 1.871 1.753 1.744 1.845 1.769 1.796 1.68 106.9 3.21 He 0.722 0.784 0.773 0.591 0.972 0.768 1.68 45.7 17.90 SD 1 Relative «t*nd«n! deviation: %RSD = x 100 ------- Glass Tube Make Up Air Rotameters Cylinder Compressec Air } Fitter Spiking Solution Nebulization Air Nebulizer Figure 1. Initial Configuration Preheated Make Up Air Heated Glass Tube Spiking Solution Variac Nebulizer Nebulization Air Heater 5 Filter Cylinder Compressed Air Rotameters Figure 2. Modified Configuration ------- I TECHNICAL REPORT DATA 1. REPORT NO. 2. EPA/600/A-96/062 4. TITLE AND SUBTITLE Development of Calibration Procedures for Toxic Metal Aerosols for Continuous Emission Monitoring Systems S.REPORT DATE 6.PERFORMING ORGANIZATION CODE 7. AUTHORS) Thomas J. Logan, James F. McGaughey*, and Raymond G. Merrill* 8.PERFORMING ORGANIZATION REPORT NO. 9. PERFORMING ORGANIZATION NAME AND ADDRESS ~Radian Corporation P.O. Box 13000 RTP, NC 27709 10.PROG RAM ELEMENT NO. 11. CONTRACT/GRANT NO. 12. SPONSORING AGENCY NAME AND ADDRESS National Exposure Research Laboratory Office of Research and Development U.S. Environmental Protection Agency Research Triangle Park, NC 27711 13.TYPE OF REPORT AND PERIOD COVERED 14. SPONSORING AGENCY CODE 15. SUPPLEMENTARY NOTES 16. ABSTRACT An aerosol generation system has been developed to calibrate the performance of continuous emissions monitoring systems (CEMS) for toxic metal aerosols. The U.S. Environmental Protection Agency Office of Solid Waste has proposed the use of metals monitoring as an approach to better assess the risk of incinerator emissions. Prior to the development of metals CEMS regulations, it is necessary to determine a method to evaluate the expected performance of CEMS. To measure the performance of CEMS, a dynamic calibration approach which can be used to evaluate monitor performance must be developed and tested. This calibration approach requires stable aerosol concentrations of the 16 toxic metals on a system that has a flow rate of 20 liters per minute for the air stream containing the metals aerosol. The concentration of the metals in the aerosol must be able to vary over the range of 10 to 1000 micrograms per cubic meter, on an aerosol generating system that can operate in a stable mode for at least 30 minutes. The aerosol generation system that has been developed meets the above requirements, and has been tested in a laboratory environment. 17. KEY WORDS AND DOCUMENT ANALYSIS a. DESCRIPTORS b.IDENTIFIERS/ OPEN ENDED TERMS c.COSATI 18. DISTRIBUTION STATEMENT RELEASE TO PUBLIC 19. SECURITY CLASS (This Report) UNCLASSIFIED 21. NO. OF PAGES 20. SECURITY CLASS (Ihis Page) UNCLASSIFIED 22. PRICE ------- |