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Method 202 - Condensible Particulate Matter
FREQUENTLY ASKED QUESTIONS (FAQS) for Method 202
Does EPA Method 202 provide reproducible results?When conducted consistently and carefully, EPA Method 202 does provide acceptable precision for most emission sources. However, several options are allowed by the method to accommodate State/local test methods that existed at the time the method was proposed and promulgated in the Federal Register. Each of these opotions may change the mass that would be counted as condensable particulate matter. As a result, when the same source is tested using different options allowed by the method there may appear to be a large variation of the condensable particulate emissions. In addition, the flue gas characteristics may exacerbate the perception of the amount of variation that is introduced by the optional procedure. For example, under specified conditions, EPA Method 202 allows the one hour nitrogen purge to be replaced with air or not conducted when specified conditions exist. Each of these options results in more SO2 remaining dissolved in the impinger water. The dissolved SO2 slowly converts to SO3 and then to H2SO4. While the SO2 should not be counted as condensable particulate matter, both SO3 and H2SO4 form particulate matter. As a result, EPA Method 202 should not be considered to be a single standardized test method, but should be considered to be a collection of test methods. Therefore, when EPA Method 202 is specified as the applicable test method, any optional procedures should also be specified in order to achieve results that are more in agreement with the basis of the specified emission limitation.Some consultants control the variability of EPA Method 202 by using EPA Method 8 as an alternate test method. Can Method 8 be used as an alternative to EPA Method 202?EPA has not approved the use of Method 8 as an alternative for Method 202. There are several differences between Method 8 and Method 202 that would result in significant differences in the mass collected and analyzed. First, Method 8 has no extraction and analysis for the organic material. Second, in addition to missing any organic material, Method 8 would miss some of the inorganic particulate that was transferred from the first impinger to the second and third impinger. A lot of the water that shows up in the second (and third) impinger is mist created in the first impinger that is collected in the subsequent impingers. Also, impingers are not 99+% efficient at capturing particulate in the water. Analysis of only the first impinger would miss any particulate that would be in the second and third impingers. The amount of particulate missed by analyzing only the first impingers and the collection efficiency of the impingers with standard tips. Our guess is that the collection efficiency is less than 90%.Which of the several procedures mentioned in EPA Method 202 should be used to provide the best measurement of particulate matter emissions that would be created by dilution and cooling in the ambient air?To obtain the best measurement of particulate matter resulting from the dilution cooling of the sampled gas stream, the following procedures should be used:The one hour purge with dry nitrogen should be performed immediately following the final leak check of the system. Reducing purge duration, using air as a purge gas and eliminating the purge step of EPA Method 202 introduces a positive bias as a result of the conversion of SO2 to SO3 and then eventually to H2SO4. Even low concentrations of SO2 in the exhaust gas will dissolve into the impinger solution and if not removed by nitrogen purging will result in a positive bias. Use the alternative procedure describe in section 8.1 to neutralize the H2SO4. Neutralizing the inorganic portion to a PH of 7.0 determines the un-neutralized sulfuric acid content of the sample without over correcting the amount of neutralized sulfate in the inorganic portion. These neutralized sulfates (such as (NH4)2SO4 or NH4SO4) would be created in the exhaust gas upon dilution cooling in the ambient air and result in fine particulate formation. Ion chromatography, for SO4 measures both the amount of neutralized and un-neutralized SO4 contained in the impinger solution prior to the addition of NH4OH and therefore introduces a negative bias. Evaporate the last 1 ml of the inorganic fraction by air drying following evaporation of the bulk of the impinger water in a 105 degrees C oven as described in the first sentence of section 5.3.2.3. The presence of free ammonia and HCl in the exhaust gas will form Ammonium Chloride that produces fine particulate upon dilution and cooling in the ambient air. While the above procedures should arrive at the best measurement of the particulate matter emissions that are created by dilution and cooling in the ambient air, many State and local agencies have established applicable limits based upon the application of other options that are included in EPA Method 202. Because of the close connection between the applicable emission limits and the method used to demonstrate compliance, the above procedures may result in different values than would be achieved using other options in Method 202. In order to measure the emissions that are specified by the State requirements, the procedures specified in the State test method should be followed. I have heard of instances where EPA Method 202 does not provide reproducible results when the same procedures are used for all source tests. What are some of the reasons for this problem?During the evaluation of the method, we initially encountered excessive imprecision. However, by the use of improved preparation and clean up procedures, introduction of contaminants were reduced and precision improved to acceptable levels. Pre-test preparation of the glassware must be impeccable to remove inorganic and organic contaminants on the surfaces of the impingers, probe liners and sample recovery glassware. Source sampling contractors should select reagents and purge gas to minimize potential contamination and should evaluate the quality of these materials prior to field use. The recovery of the samples should be accomplished in a location where potential contaminants are minimized. It should be recognized that low sample weights may introduce the appearance of excessive imprecision that is the natural result of measurements near the limit of detection.Do I have to use Method 202 to measure emissions of condensable particulat?There may be some sources where the use of EPA Method 202 would not be required in order to measure the particulate matter that the method is intended to measure. While not stated within the method, the particulate matter measured by this method is intended to represent that material that would become solid or liquid at ambient conditions but passes through the filters maintained at elevated temperatures. Therefore, a process with an exhaust gas temperature that is at ambient conditions could use EPA Method 17 to represent total particulate matter or EPA Method 201A to represent particulate matter that is smaller than 10 uM in aerodynamic diameter.Depending on the exhaust gas moisture content, there may be some sources with elevated exhaust gas temperatures where modification and operation of the sampling train may allow the sampling gas to be cooled to essentially ambient temperatures and satisfy the intent of EPA Method 202. Although ambient temperatures can vary considerably, a temperature of 20 °C (68 °F) is a reasonable value for ambient temperature since that is the standard temperature to which source test methods are corrected. In addition, this temperature is consistent with the range of temperatures that would be considered to be "room temperature" and allowed by Method 202 for final evaporation of the inorganic and organic particulate matter portions. As with other source sampling methods, it is reasonable to include a range of allowable filtration temperature variations to accommodate difficulties in maintaining constant temperatures and preventing condensation of water vapors on the filter and internal surfaces of the probe. What is EPA doing to assess and reduce artifact formation in Method 202?EPA has performed at least two studies to assess artifact formation, is continuing some limited assessments, and is exploring improvements to Method 202. The paper, "Laboratory and Field Evaluation of the EPA Method 5 Impinger Catch for Measuring Condensible Matter from Stationary Sources" (Method 5 Paper) is a summary report of the results of this early study and was presented at an AWMA specialty conference. The second study was performed in 2005 by Battelle. The report, "Laboratory Evaluation of Method 202 to Determine Fate of SO2 in Impinger Water" (Battelle Paper) replicates some of the earlier work and addresses some additional areas. EPA was encouraged by a proposed minor modification to the glassware and beginning conditions of Method 202 that were presented in the proceedings of a November 2005 AWMA specialty conference. The paper, "Optimized Method 202 Sampling Train to Minimize the Biases Associated with Method 202 Measurement of Condensible Particulate Matter Emissions" (Minimizing Bias Paper) by Richards, Holder and Goshaw presents some background and results that were obtained using this minor modification. In July 2006 EPA obtained resources to investigate in more detail artifact formation in Method 202 and to explore improvements that may further reduce the artifacts. EPA engaged several industrial and State agency stakeholders to comment on EPA's laboratory test plan and to expand on the laboratory evaluations to address gas matrix conditions that were overlooked or other conditions that they believe should be addressed. On August 1, 2006, EPA held a workshop in Research Triangle Park, North Carolina, to present to the stakeholders the Agency plan for evaluating Method 202 and potential modifications that would reduce artifact formation. At the workshop, stakeholders made suggestions for improving and expanding the plan. In addition, several stakeholders volunteered to use the final protocols to conduct laboratory evaluations that replicated some of the Agency evaluations, as well as extending the evaluations to address other gas matrices that were of interest to them. The Agency will combine the data from its own evaluations and the stakeholders' laboratory experiments to evaluate the artifact formation associated with Method 202 and the modified methods. The EPA is also making the invitation request and the minutes of the workshop (Invitation and Minutes) available to keep interested parties informed of the ongoing activities to improve Method 202. The Agency is also soliciting additional stakeholders that would like to join the effort by following the protocol, replicating evaluations, expanding the matrices being evaluated, and sharing results with all stakeholders. If you are an interested stakeholder, contact Ron Myers at myers.ron@epa.gov .On September 27, 2006, Ron Myers e-mailed all of the stakeholders update information on the progress of the project. Included in this email were the results of EPA's laboratory results of the comparative sulfate analyses of the EPA Method 202 and the Dry Impinger Method. Also included in the e-mail were preliminary results provided by Jorge Marson of Environment Canada. Jorge provided data on dry impinger laboratory experiments and some additional issues related to obtaining consistent weighing results. On November 9, 2006, Ron Myers e-mailed all of the stakeholders the approved Quality Assurance Project Plan (QAPP) for the laboratory assessment of the proposed method for quantifying condensable particulate matter. The e-mail transmitting the QAPP to the stakeholders requested comments on the plan and requested that stakeholders who were interested in supplementing the EPA assessment submit their plans using a template that was included in EPA's QAPP document. The QAPP that was attached to the e-mail is available through this link. On January 18, 2007, a meeting of several experienced stack testing individuals and two local equipment vendors was held to discuss hardware issues associated with modifications of the sampling equipment and the glassware for the proposed condensable particulate matter test method. Minutes of the meeting are provided here. On January 5, 2007, Ron Myers e-mailed all of the stakeholders an announcement of a February 9, 2007 workshop to discuss our progress, the results of our laboratory study, and commitments to extend the investigation by stakeholders external to EPA. On February 8, 2007, all of the stakeholders were e-mailed a list of individuals that had indicated that they would attend the workshop or participate by phone. Attached to the e-mail was the preliminary agenda and presentations by EPA and several stakeholders. Minutes of the workshop were drafted and circulated to individuals that made presentations or made comments during the workshop. The revised minutes and the final presentation materials used at the workshop are available here. EPA has made an earlier draft version of the dry impinger test method available to stakeholders with the understanding that all parties (the owner of the source, the source test contractor and the regulatory authority) understood that it was a work in progress and agreed to its use. These stakeholders have provided feedback to EPA on the performance of the method, and EPA has assisted the stakeholders in resolving unexpected results. EPA has compiled stakeholder comments and recommendations, submitted up to April 17, 2007, on procedures that the stakeholders believe would improve the precision of condensable particulate matter source testing. In response to the comments and recommendations, EPA analyzed and recorded both the comments and evaluations in this document. In addition, the Alliance of Automotive Manufacturers (Alliance), a stakeholder in the study to improve the condensable particulate matter test method, conducted field testing to compare EPA Method 202 to the improved dry impinger test method. The stationary source chosen by the Alliance for comparison evaluation was a wet machining operation associated with an oil mist collector control device that serves an automotive machining process for transmission components. The source’s flue gas temperature was less than or equal to 85F. The study, conducted on March 29th and 30th, 2007, consisted of simultaneous testing of condensable particulates with Method 202 and with the dry impinger method evaluated by EPA in laboratory studies. One of the Alliance's conclusions is that there is no significant statistical difference between the improved method and traditional Method 202. The report submitted to EPA on 7-26-2007 is available here. Concurrent with these stakeholder efforts, EPA has revised the dry impinger test method to improve and, where needed, to clarify the required procedures. The revised dry impinger test method is available here for continued use by stakeholders as long as all parties understand that this method is a work in progress and agree to its use. EPA is making this version available to the entire stakeholder community for review and comment prior to posting this method to the "Other Test Methods" web page. We would appreciate any recommendations that stakeholders believe would make the method more precise and more consistent with quantifying primary particulate matter emissions (that is, those emissions formed near the stack exit as a result of condensation or chemical reaction with stack gases following cooling to ambient temperature and pressure). EPA will consider all comments received prior to October 26, 2007 for incorporation in the initial posting of the method to this web site. Comments, recommendations, and justifications should be submitted to Ron Myers at myers.ron@epa.gov . Since October 26, 2007, additional stakeholder sponsored laboratory studies were performed providing information justifying several minor modifications in the procedures of the draft dry impinger test method that was posted to this site. In addition, several stakeholders have provided recommendations for editorial and substantive changes in the posted method. We are now posting the dry impinger method to the “Other Test Methods” site as OTM 28. We have made every effort to insure that the method provides an accurate and precise measurement of condensable particulate matter emissions. As with the previous draft dry impinger test method, we are soliciting comments on the method as posted and will consider all comments received prior to June 27, 2008. Comments, recommendations, and justifications should be submitted to Ron Myers at myers.ron@epa.gov Concurrent with the posting of the dry impinger test method to the Other Test Methods web page, we are posting an updated filterable PM10 and PM2.5 test method OTM 27. OTM 27 is a reformatted and edited version of Conditional Test Method 40. As with OTM-28, we are soliciting comments on this method and will consider comments received by June 27, 2008. Update (August 19, 2008): Several comments on the conduct of the dry impinger test method for CPM were evaluated. We have revised the dry impinger test method to accommodate those comments. Most are changes in the method to correct typographical errors and to clarify some issues associated with the conduct of the method. In assessing and addressing the comments from stakeholders, we noticed that in Equation 1, the constant used for the correction of the addition of ammonia hydroxide was 18.03 when it should be 17.03. We have reposted OTM 28 to the Other Test Method web page with the revisions. Several comments were received on the conduct of OTM 27. OTM 27 uses a pair of cyclones to size the filterable material. Several of the comments were associated with the physical size of the combined PM10 and PM2.5 cyclones, and the ability to use these in exhaust systems that are typical for their industry. Some of these same commenters also requested modifications to address the potential for low sample weight collection. They indicated that the current method would require extending the sample time in order to collect a weighable mass for PM 10 and PM2.5. With existing particle sizing technology, reducing the size of the cyclones would require a substantial reduction in the flow rates of the sampler to achieve proper particle sizing. Reducing the flow rate would adversely impact the duration of the sampling campaign needed to collect weighable masses. As with OTM 28, there are corrections to address typographical mistakes. We have also made revisions to clarify the need to maintain the sampling conditions necessary to collect a good sample and address some of the size issues associated with the hardware. Here is the link the updated OTM 27. We have compiled a summary of the comments that we received, our responses to the comments, and copies of the comment letters or e-mails that we received here. OTM 27 and 28 will provide the template for future proposed revisions to EPA Test Methods 201A and 202. We do not expect that there will be any revisions to OTM 27 and 28 until we propose revisions to Methods 201A and 202. We recognize that several stakeholders are using these two test methods to characterize their emissions and prepare for future requirements. We are interested in information on the performance of the test methods and for suggested changes that would improve the reliability and precision of these methods. We are also interested in obtaining source test data using these methods so that the emission factors for the processes being tested can be evaluated for revision. In order to facilitate the ability to use these test data, we strongly encourage stakeholders to use the Electronic Reporting Tool, ERT, to document the conduct of the emissions test and the operation of the source. Still have questions on this method? Contact the EMC expert Ron Myers at myers.ron@epa.gov . |
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