Abstract:
A convenient apparatus and method for inserting surrogate metal-entraining aerosols into exhaust stacks for the purpose of realistic dynamic testing of an emissions monitor. The aerosols contain elements required to be detected by the monitor. The 14 metals regulated by the EPA as hazardous air pollutants are of particular interest. The method requires less time and fewer skilled technicians than conventional testing methods. In a preferred embodiment of the present invention, a burner (e.g., propane or kerosene) is combined with a combustion chamber, a fan, an air compressor, at least one peristaltic pump, at least one surrogate reservoir, and the necessary ductwork for connection to an exhaust stack. The amount of surrogate aerosol to be introduced to the stack is adjusted at the peristaltic pump. After heating by the burner and subsequent introduction into the hot stack, the surrogate homogeneously mixes with the exhaust stream and is presented to the sensor as a dry gas component of the exhaust stream. Other applications include use as an exhaust stack simulator and as a standardized source of aerosols containing hazardous air pollutants, in particular metal-entraining aerosols.

Description:
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     The invention described herein may be manufactured and used by or for the government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor. 
     FIELD OF THE INVENTION 
     The present invention pertains to an aid for performance testing a sensor. In particular, a preferred embodiment is a dry-gas-from-aerosol generator for testing an emissions monitor, more particularly an airborne pollutant emissions monitor capable of detecting metal emissions. In addition, an embodiment can be employed as a simulator, e.g., simulating a large-scale boiler&#39;s exhaust stack. A third application is a standardized source of hazardous air pollutants provided as a dry aerosol, in particular metal-entrained dry aerosols. 
     BACKGROUND 
     The United States Environmental Protection Agency (EPA) recognizes 14 metals as air pollutants when emitted in exhaust emissions from sources such as the stacks of industrial incinerators, furnaces, and boilers. Conventionally, these sources are monitored for compliance with EPA regulations through a series of manual test methods. These methods require extraction of large volumes of exhaust gases from an exhaust stream over a period of one to three hours. The targeted emissions, e.g., metal aerosols, vapors, and particulates are collected in filters and typically are analyzed offsite. Recent technology now provides the capability to analyze emissions nearly continuously via robust in-stack sensors connected to onsite monitors. See U.S. Pat. No. 5,596,405 , Method and Apparatus for the Continuous Emissions Monitoring of Toxic Airborne Metals , issued to Seltzer et al, Jan. 21, 1997. Historically, as the technology becomes available, EPA modifies regulations to take advantage of the improved capability. In this case, the regulations are re-written to include compliance criteria based on availability of “continuous emission” monitors that can readily provide emissions criteria over both short (e.g., one hour) and long (e.g., 24 hours) time intervals. Further, the new robust sensor/onsite monitor provides the inherent capability to time-resolve measurements and assure interim compliance in real time, heretofore unavailable using manual methods or low cost automated methods. 
     The majority of exhaust gas pollution emission analyzers use the detected species in the gaseous state. Among these are analyzers for detecting carbon monoxide (CO), nitrogen oxides (NO x ), and sulfur oxides (SO x ). Commercially prepared and certified gas mixtures are available as aerosols for use in evaluating emission analyzers. The same gas source can be introduced into the candidate analyzer and the reference analyzer, permitting a side-by-side comparison. Similarly, a specific gas mixture can be inserted into an exhaust gas stream to permit comparative measurements of in-stack sensors/monitors using both a candidate test method, e.g., a preferred embodiment of the present invention, and a reference test method, e.g., an EPA-approved manual method. 
     A significant factor in achieving EPA acceptance of the new generation of “in-stack” sensor/monitors is the ability to test them in the same “real time” that they are designed to operate. Further, the chosen test method should be efficient, accurate, and reliable for a wide range of exhaust streams and operational environments. Specific requirements include the ability to compare performance of the new monitoring technology to the EPA-approved reference methods for determining compliance, i.e., manually derived testing. One of the most basic problems to overcome in this comparison is providing representative exhaust streams composed of a known and relatively constant multi-element (metal) constituent for a given time period. Consider that the constituent need be both temporally consistent, i.e., be held constant, and offer a wide range of representative metals, including weight percentage levels, in the exhaust stream. That is, the concentrations of the various metals and the timeline for insertion in the exhaust stream should be known a priori and able to be controlled accurately over time. 
     Rarely does an unmodified exhaust stream exhibit metal emissions of the necessary elemental diversity and compositional and temporal stability to enable efficient, yet accurate and reliable, comparative testing. Metal emissions within a typical actual exhaust stream are sporadic, short-lived, and limited in elemental composition by the specific fuel or waste feed used as input. For example, inserting enough metal in the original fuel of a combustor (as metal oxides or salts, for example) to achieve emissions levels necessary to test the competing emissions sensors/monitors weld most likely violate the EPA&#39;s regulations for control of hazardous pollutants! Also, because the combustor is equipped with scrubbers and other emissions control devices to prevent excess emissions, providing enough excess metals at the input, i.e., in the fuel, may not be possible to attain the required levels for testing the sensors/monitors at the output, i.e., the exhaust stack. 
     Another method tried with little success is the insertion into the exhaust stream of metals via nebulization, i.e., spraying an aqueous metal solution. The theory is that given the high heat of the exhaust stream there will be sufficient latent heat to evaporate the water vapor in the nebulized metal solution, leaving a dry aerosol with entrained metals. However, experience with such methods has shown that in typical exhaust streams, the gases lack capacity to absorb additional moisture. This results in incomplete evaporation and water droplets containing entrained metals transit the exhaust stack. These droplets are deposited on the hardware used for manual extraction where they then quickly evaporate on the hot surface of the hardware and deposit metal for subsequent analysis. Thus, there is a dramatic difference between the results obtained with the candidate in-stack sensor/monitor and the EPA-approved manual method. The manual method can recover the evaporated metals on the hardware surface since the extraction hardware is washed and the metals recovered. No such provision is available for the “real time” in stack sensor/monitor. 
     Yet another approach is the generation and insertion of organic vapors with entrained metals. This is accomplished by chemically reacting two substances intentionally inserted and brought into close contact in the exhaust stream. A major disadvantage of this method is the toxicity of the substances needed to carry out the reaction. Further, even considering the handling difficulties of candidate substances, this method still does not provide the necessary aerosol needed to insure a valid test comparison. A viable solution need provide a source of: 
     dry, multi-element aerosol with entrained metals of interest, 
     dry aerosol-entrained metals independent of fuel or waste feed, and 
     dry aerosol-entrained metals independent of temperature and moisture content, that ideally is compact, lightweight, easy to use, reliable, and provides a reproducible output. 
     Certified sources of metal air pollutants, similar to the commercially prepared gas mixtures noted above, are not presently available. Actual exhaust streams having entrained metals are primarily aerosols and particulates. Rarely do they consist of vapors. It is not practical, assuming physical possibility, to commercially prepare a homogenous mixture of targeted species (i.e., EPA-defined hazardous metals), contain it in a pressurized bottle, and be able to insert amounts of this mixture on a reproducible basis into a “front-end” of a sensor/monitor. 
     A solution to this testing problem is a system and method for introducing a dry gas mixture of known metal composition into the exhaust stream at known times and for known time intervals. It is not even critical at this juncture that the concentration of the gas/metal mixture be precisely known at input. So long as the mixture is inserted at a constant rate in the exhaust stream for consequent measurement using the manual EPA-approved method and the sensor/monitor to be tested, the system and method provide an efficient, reliable and accurate, solution. Insertion of the surrogate mix at or near the input end of the exhaust stream insures a homogenous mixture of existing exhaust gases and the surrogate mix by the time the exhaust stream reaches the sensor/monitor positioned near the output of the exhaust stream. Thus, a reliable alternate means for providing the necessary variety and levels of hazardous element emissions at the sensor/monitor, at a relatively constant level held relatively constant over a given time period, is provided as a preferred embodiment of the present invention. 
     SUMMARY OF THE INVENTION 
     A preferred embodiment of the present invention provides a method and apparatus for generating dry metal-containing aerosols, of known composition and concentration, and inserting same into an exhaust stream of a combustor. These dry aerosols simulate the entrained metal in hot exhaust gas that may be present in an exhaust stream from an industrial boiler, for example. They are inserted at a constant rate in order to support performance evaluation of multiple emission monitors as compared to a reference method such as EPA Method 29. Further, since the invention emits CO 2  and moisture, and these, elements are also present in the exhaust streams of actual combustors, an embodiment could serve as a “stand-alone” simulator to optimize design of emissions monitors and related systems associated with exhaust stacks. 
     A preferred embodiment of the present invention comprises: 
     a combustion chamber 
     a fuel tank, 
     a container for aqueous-entrained hazardous elements, e.g., metal salts 
     a forced-air draft fan, 
     a pump, 
     a nebulizer, 
     an air compressor, and 
     metal ducting. 
     The combustion chamber may be of approximately 35-50,000 BTU capacity, although it is not limited to this range, but depends on the test setup. It can be fueled by kerosene, propane or other appropriate fuel, and be one of a number of commercially available small-scale industrial fan-forced heaters. The fuel tank may be integral with the apparatus encompassing the combustor. The forced-air draft fan also may be integral with the apparatus encompassing the combustor and is capable of providing approximately 100-200 ft 3 /min to the combustion chamber. The fan is also of sufficient capacity to overcome effects of static pressure and fluctuations resulting from contact of the inserted mixture with the hot gases of the exhaust stream. 
     The pump can be a peristaltic or other type of pump able to provide the aqueous stream from the container of metal salts to the nebulizer at a fixed constant rate. The nebulizer, powered by the air compressor, is capable of generating a fine liquid aerosol from the aqueous stream provided from the container. The metal ducting connects the output of the nebulizer to the exhaust stack confining the exhaust stream. 
     As the fine aerosol stream is inserted into the hot combustion chamber, some of the metal salts are thermally decomposed, resulting in combustion and subsequent oxidation of the metal constituents. The metal salt and metal oxide aerosols are then entrained in the fan-forced draft, transit the ductwork, and enter the exhaust stream as a dry aerosol. The fan-forced draft is adjustable to insure proper aspiration and optimal pressure in the combustion chamber of the heater. 
     To ensure test reproducibility, an aqueous solution of metal salts of known composition and concentration is made available. A peristaltic pump incorporating a variable and controllable rate, withdraws the metal-entrained liquid from its container and delivers it to a nebulizer at a constant rate. Given a priori knowledge of the solution makeup, i.e., number of mg/l of each metal in solution, and the pump&#39;s delivery rate, i.e., 1/min, then the rate and composition of metals inserted into the exhaust stream can be determined. 
     Also knowing a priori the exhaust stream flow rate, and assuming that 100% of the metal-entrained aerosol is inserted, entrained in the exhaust stream, and homogeneously mixed prior to receipt at the sensor/monitor, an exhaust gas metal concentration can be approximated. This provides a theoretical maximum concentration, or upper bound, on the metal concentration to be expected at the sensor/monitor. It also provides equal amounts of a dry gas, homogeneously mixed in the exhaust stream, to the candidate sensor/monitor and the hardware inserted for manually taking data using EPA-approved methods for comparison and performance evaluation. 
     The hardware setup and attendant method of a preferred embodiment of the present invention is applicable to any metal that exists as a water-soluble salt, and to any element, inorganic or organic, that one wishes to investigate, not just the 14 metals currently on the EPA list of hazardous metal air pollutants. 
     In another preferred embodiment of the present invention, an incinerator simulator is envisioned. Since the combustion chamber generates by-products of combustion, e.g., CO 2  and H 2 O, that closely simulates that of an industrial boiler, for example, it may be used as a simulator of the boiler. Thus, a preferred embodiment of the present invention can be set up for use in factory or customer testing of emissions monitors prior to installation in large stacks. It can also be used for research and development where optimization of design is the goal. For example, dilution of combustor exhaust using ambient air reduces exhaust gas temperatures to values approximating actual exhaust streams of large-scale industrial combustors. The combustor is configured in much the same way as above except that it is connected to a “mini-stack” for simulation of an actual large-scale exhaust stack. Note that regulatory permits may be required for operation of the simulator since it will be exhausted to the atmosphere in the typical test. 
     A third embodiment of the present invention is as a standard source for surrogate metal-entrained atmospheric emissions. The benefit of using this embodiment for such a source is the precise control of all parameters that is possible using such an embodiment. For example, in a typical application strict control of the aqueous metal solution inserted into an entraining airflow is possible for establishing the required accurate reproducibility. Also, this application requires an embodiment of the present invention to undergo rigorous validation tests and certification procedures and since it uses essentially commercial off-the-shelf (COTS) components, the certification also should be straightforward. At present, there are no standardized sources of metal-entrained aerosols, thus this embodiment has high value to the environmental community for direct testing of emissions monitoring systems and methods. 
     Advantages of preferred embodiments of the present invention, as compared to conventional systems, include permitting: 
     simplified test systems using COTS hardware; 
     use of reconfigurable pumps; 
     simplified design of alternate configurations; 
     inexpensive fabrication; 
     reduced man-hours for operation; 
     reduced system complexity; 
     reduced system capital costs; 
     improved test robustness; 
     low maintenance costs; 
     increased flexibility in test conduct; 
     fewer tests or higher duty factor per test or both; 
     high reliability; and 
     ready upgradability. 
     Embodiments of the present invention can be applied to testing and optimization of hazardous air pollutant emissions monitors of all method types including: plasma emission-based, laser-based, electric spark, X-ray fluorescence, and manual methods involving, for example, filter capture of metal aerosols for later analysis. This saves capital equipment, as well as training and maintenance, costs. Further, a preferred embodiment of the present invention may be used in simulators or standardized sources that will cost less and provide more accurate and easily interpreted data for training and updating operators and maintenance technicians. 
     Preferred embodiments are fully disclosed below, albeit without placing limitations thereon. 
    
    
     BRIEF DESCRIPTION OF DRAWINGS 
     FIG. 1 depicts relative positions of components in a preferred embodiment of the present invention as installed proximate an actual exhaust stack. 
     FIG. 2 represents a preferred embodiment of the present invention used as a simulator. 
     FIG. 3 represents an alternative configuration to the nebulizer depicted in FIG.  1 . 
    
    
     DETAILED DESCRIPTION 
     A preferred embodiment of the present invention, the apparatus  100  of FIG. 1, incorporates: 
     a fan-forced heater  101  sized from 35-50,000 BTU; 
     a fuel source  102  such as a propane tank; 
     a forced-air draft fan  103  that may be integral to the heater  101 ; 
     a nebulizer  104  that consists essentially of a tube for intaking a fluid and compressed air and outputting a fine spray, i.e., a “wet” aerosol; 
     a pump  105  such-as a peristaltic pump, for providing a constant rate of fluid to the nebulizer  104 ; 
     a regulated source of compressed aid  106 , such as a regulated air compressor; 
     a container of metal-entrained aqueous solution(s)  107  of known concentration and composition; and 
     ductwork  108  connecting the output of the combustion chamber  101 A of the heater  101  to an exhaust stack  109 . 
     The-combustion chamber  101 A of a small-scale industrial fan-forced propane or kerosene heater  101  suffices for heating the fine spray  104 A of the nebulizer  104 , thus drying it sufficiently to mix homogeneously as a “dry” aerosol when inserted into the exhaust stack  109 . The draft fan nominally provides an airflow of 100-200 ft 3 /min to overcome the effects of static pressure and pressure fluctuations arising from contact with the hot stack gases. 
     The COTS heater  101  is modified as follows to optimize operation of this embodiment of the present invention: 
     a. A pneumatic nebulizer  104  such as concentric glass nebulizer or V-groove type, is mounted behind e rear partition (not separately shown) of the combustion chamber  101 A. The nebulizer&#39;s outlet orifice (not separately shown) is oriented such that a conical spray pattern  104 A is directed through a hole in the partition at the rear of the combustion chamber  101 A toward the flame zone  101 B of the combustion chamber  101 A so that maximum interaction between the spray and the flame is achieved. Temperatures within the chamber  101 A typically exceed 500° C. This provides sufficient latent heat to completely evaporate the moisture within the spray  104 A, yielding a dry aerosol (not separately shown) having entrained metals of the initial solution. A glass nebulizer  104  must be recessed sufficiently to avoid damage from the flame. 
     b. At the high temperatures of the combustion chamber  101 A, some of the metal salts thermally decompose, combust, and oxidize the metal constituent. The remaining metal salts, together with the oxidized metal, are entrained in the fan-force draft air and inserted via the ductwork  108  into the stack  109 . 
     c. The forced-air fan is provided with a means to adjust the flow of forced air to the combustion chamber, such as a rheostat (not separately shown) for controlling fan speed or a movable baffle (not separately shown) in the input air duct to manually reduce air flow as needed. 
     To ensure that the surrogate metal-entrained gases are generated at a constant rate that is reproducible, a container  107  of a solution, such as an aqueous solution, of dissolved metals of known composition and concentration is provided. A peristaltic pump  105 , incorporating a speed control, withdraws fluid from the container  107  and delivers it to the nebulizer  104  at a given constant rate. 
     Note that if the concentration of the individual metal(s) in the solution(s) in mg/l and the pump&#39;s delivery rate in 1/min are known, then the rate of insertion of the surrogate into the stack  109  can be readily determined. For example, a solution containing 1000 mg/l of Chromium (Cr) introduced to the nebulizer  104  at 0.010 l/min, provides a surrogate sample of Cr at 10 mg/min (10,000 μg/min) to the stack  109 . Assuming that the exhaust stream flow rate is known and that 100% of the metal-entrained aerosols are inserted into the stack  109 , entrained in the hot exhaust stream, and homogeneously mixed therein, an approximation of the metal content of the exhaust gas can be made. For example, if our Cr sample above were introduced into an exhaust stream flow of 100 m 3 /min, a concentration of 100 μg/m 3  is expected to be the upper bound Cr concentration within the exhaust stream, assuming that the original (unsupplemented) exhaust stream contained negligible Cr. 
     Also, note that this method is not intended to provide exhaust stream concentrations of an exact value since insufficient data exist on the actual transport mechanism of the surrogate aerosol as it mixes in the exhaust stream. Rather, the above process provides an upper bound, a theoretical maximum concentration. The reference test hardware and EPA-approved manual data analysis method can provide a near approximation of the actual emissions that the candidate emissions sensor/monitor is to quantify. 
     The above described example method is applicable to any salt dissolvable in water. In the case of mercury (Hg), for,example, insertion of aqueous aerosols of mercuric nitrate (HgNO 3 ) or other Hg salt, into the combustion chamber  101 A results in the generation of a large fraction of Hg vapor, since Hg salts have a low decomposition temperature and Hg metal has a low boiling point. It is possible that other metals will vaporize similarly but oxidize downstream upon a reduction in gas temperature within the stack  109  relative to the temperature in the combustion chamber  101 A. 
     An additional advantage of the “real time” evaluation of emissions sensor/monitors afforded by a preferred embodiment of the present invention involves determining the response time of the sensor/monitor. By abruptly terminating the introduction of the surrogate solution to the burner, the amount of time required for the emissions sensor/monitor to recognize the reduction in emissions can be measured. A typical standard for response time is the time it takes for the sensor/monitor to recognize a falloff of 90% in emission level when a step change to zero in surrogate introduction is effected. Using a preferred embodiment of the present invention, this procedure can be conducted and evaluated during actual testing. 
     In another preferred embodiment of the present invention, an apparatus very similar to the above described is used as a portable simulator of a large-scale exhaust stack such as may be used with an industrial boiler. Referring to FIG. 2, the same burner arrangement is used, however, FIG. 2 shows only the heater  101  and ductwork  108  for simplicity. Since the heater  101  generates byproducts similar to a large industrial boiler, for example, CO 2  and H 2 O as vapor, it is feasible to deploy a portable apparatus such as described above for research and development or on-site testing of emissions sensors/monitors at a manufacturer&#39;s facility. There would be no need to seek out an actual large scale combustor to conduct these basic tests and design investigations. Dilution of the heater&#39;s exhaust using ambient air would provide a surrogate exhaust stream closely resembling that of an actual industrial combustor. 
     Specifically, the configuration of FIG. 1 may be assembled as follows: 
     a. the propane (or kerosene) fan-forced heater  101  is connected to a fuel tank  102 , such as a pressurized liquid propane tank. A COTS heater  101  is most desirable since provisions exist for fuel connection, storage, delivery, and regulation. 
     b. the heater  101  is connected via ductwork  108  to an inlet port (not separately shown) of the exhaust stack  109 . The ductwork  108  is of sufficient diameter to eliminate excess backpressure on the heater  101  from the hot exhaust stream. A minimum inside diameter of 4 inches for ductwork  108  no longer than 4 feet is optimum for connecting the end of the conical ductwork  108  to the port of the stack  109 . The ductwork  108  is flexible metal curved upward from the heater  101  to facilitate aspiration and entrainment of the inserted hazardous element, e.g., EPA-hazardous metals, aerosols, while minimizing static pressure on the heater  101 . 
     c. a source of regulated compressed air  106 , such as a regulated air compressor, is connected to the nebulizer  104  and adjusted to approximately 30 psi. 
     d. the inlet of the regulated pump  105 , such as a peristaltic pump, is attached to a length of plastic tubing (not separately shown) and the other end of the plastic tubing is attached to an outlet of the container of metal salt solution(s)  107 . 
     e. the outlet of the pump  105  is attached to the inlet of the nebulizer  104  using a second length of plastic tubing (not separately shown). 
     f. the heater  101  is ignited and the flame allowed to stabilize. 
     g. the pump  105  is started, providing a constant flow of aqueous metal solution to the nebulizer  104  and simultaneously the air compressor  106  is started, providing necessary pressure to generate a fine spray (“wet aerosol”)  101 A from the solution inserted by the pump  105  at the input of the nebulizer  104  prior to output from the nebulizer  104  to the combustion chamber  101 A. 
     h. the spray of the nebulizer  104 A is directed into the flame zone  101 B of the combustion chamber  101 A where the water component is evaporated, yielding a dry metal salt entrained in an aerosol. Depending on the thermal and chemical characteristics of the metal salt, it may thermally decompose, resulting in atomization of the metal constituent. Thus, the atomized metal will oxidize in the flame  101 B and exit the combustion chamber  101 A as a solid particle. The metal salts that resist decomposition will exit as a “dry” metal-entraining aerosol. For highly volatile metals, such as Hg, the metal may exit the combustion chamber  101 A as a metallic vapor. 
     i. varying the chemical composition of the aqueous solution, e.g., nitrates, chlorides, phosphates, etc., it is possible to affect the chemical form of the combustion product exiting the combustion chamber  101 A. 
     j. multi-element solutions are possible so long as the individual constituents are chemically compatible in solution. For example, cobalt chloride (CoCl 2 ) and silver nitrate (AgNO 3 ) are incompatible, causing the precipitation of the insoluble precipitate silver chloride (AgCl). Thus, to accommodate metal compounds that are otherwise incompatible in a single aqueous solution, multiple solutions can be prepared and stored in separate containers with multiple lines to multiple pumps or a multi-channel pump  105  and a separate dedicated nebulizer  104  for each solution, given that “time multiplexing” is not desired. 
     In FIG. 2, the entire apparatus is partially represented as the modified heater  101  and ductwork,  108  and it is understood that the missing components of FIG. 1 are also a part of this configuration but omitted from FIG. 2 for simplicity. The heater  101  heats the surrogate mixture and inserts it into the ductwork  108  in the same fashion as for the first embodiment above. However, the stack into which the surrogate is inserted is a “mini-stack”  201 . This mini-stack  201  has no intrinsic flow of “real” exhaust gases. Rather, it is a simulation of an actual stack, and actual stack gases are simulated by the provision of ambient air via a variable speed draft blower  202  at the bottom of the mini-stack. The speed of the blower  202  can be varied electronically, or operated at maximum speed and airflow controlled via flow dampers in the ducting. By adjusting the flow of ambient air, the concentration of CO 2 , H 2 O, and surrogate metals can be varied to meet test requirements. Since the exhaust from this “simulator” must be vented to atmosphere, an operating permit may have to be obtained from state and local regulators. A sampling probe  203 , representing the in-stack sensor is placed near the mini-stack&#39;s exit to simulate the position of a candidate emission&#39;s sensor. The output of the sensor is then sent to an appropriate monitor (not separately shown) for display and subsequent evaluation. 
     Referring to FIG. 3, an alternate burner configuration  300  is depicted. The burner (not separately shown) is termed a “total consumption burner.” The total consumption burner eliminates the need for a nebulizer  104  by providing a feed path  301  for the surrogate solution from the source  107  through an orifice (not separately shown) directly to the combustion zone  101 B of the burner. A preferred fuel for the total consumption burner is hydrogen gas mixed with oxygen gas or air. This feed path  301  is provided concentric with and through the fuel feed path  304 . Note that the stream  303  provided to the combustion zone  101 B is still a fluid aerosol spray. An air intake  302  is provided to help draw the surrogate solution directly from the source  107  by the pressure difference between the pressure within the combustion chamber and ambient air. The inherent value of this configuration is that there is some assurance that 100% of the surrogate solution is getting to the combustion zone, thus 100% of the dissolved surrogate will interact with the flame. In this way, an investigator is able to quantify the amount of surrogate fed to the combustion zone. The nebulized aerosol spray could possibly divert some of the surrogate to the side of the combustion chamber and not react all of the surrogate with the flame. 
     A third application for a preferred embodiment of the present invention is that of a standardized source of metal-entrained aerosols. This application may well be suited to the use of the total consumption burner as described above. A standardized source requires precise control of operating parameters. Since the material and components used in the above described embodiment of the present invention can be COTS hardware, including the total consumption burner, and the process for implementing the method of the present invention is straightforward, the precise control needed for a “standard” source is achievable. For example, strict control of aqueous metal introduction and air flow are two primary requirements that have been detailed above in relation to the peristaltic pump, the regulated air compressor, and even the blower used on the simulator version. 
     The above descriptions should not be construed as limiting the scope of the invention but as mere illustrations of preferred embodiments. For example, although examples discussed hazardous metal constituents at length, the method and apparatus is applicable to any surrogate, hazardous or not, organic or inorganic, that a user may need to introduce into an exhaust stream. The scope shall be determined by appended claims as interpreted in light of the above specification.