Reference Method for the Determination of Coarse Particulate Matter as PM 10-2.5 in the Atmosphere

1.0 Applicability and Definition 1.1 This method provides for the measurement of the mass concentration of coarse particulate matter (PM 10-2.5 ) in ambient air over a 24-hour period. In conjunction with additional analysis, this method may be used to develop speciated data. 1.2 For the purpose of this method, PM 10-2.5 is defined as particulate matter having an aerodynamic diameter in the nominal range of 2.5 to 10 micrometers, inclusive. 1.3 For this reference method, PM 10-2.5 concentrations shall be measured as the arithmetic difference between separate but concurrent, collocated measurements of PM 10 and PM 2.5 , where the PM 10 measurements are obtained with a specially approved sampler, identified as a “PM 10c sampler,” that meets more demanding performance requirements than conventional PM 10 samplers described in appendix J of this part. Measurements obtained with a PM 10c sampler are identified as “PM 10c measurements” to distinguish them from conventional PM 10 measurements obtained with conventional PM 10 samplers. Thus, PM 10-2.5 = PM 10c − PM 2.5 . 1.4 The PM 10c and PM 2.5 gravimetric measurement processes are considered to be nondestructive, and the PM 10c and PM 2.5 samples obtained in the PM 10-2.5 measurement process can be subjected to subsequent physical or chemical analyses. 1.5 Quality assessment procedures are provided in part 58, appendix A of this chapter. The quality assurance procedures and guidance provided in reference 1 in section 13 of this appendix, although written specifically for PM 2.5 , are generally applicable for PM 10c , and, hence, PM 10-2.5 measurements under this method, as well. 1.6 A method based on specific model PM 10c and PM 2.5 samplers will be considered a reference method for purposes of part 58 of this chapter only if: (a) The PM 10c and PM 2.5 samplers and the associated operational procedures meet the requirements specified in this appendix and all applicable requirements in part 53 of this chapter, and (b) The method based on the specific samplers and associated operational procedures have been designated as a reference method in accordance with part 53 of this chapter. 1.7 PM 10-2.5 methods based on samplers that meet nearly all specifications set forth in this method but have one or more significant but minor deviations or modifications from those specifications may be designated as “Class I” equivalent methods for PM 10-2.5 in accordance with part 53 of this chapter. 1.8 PM 2.5 measurements obtained incidental to the PM 10-2.5 measurements by this method shall be considered to have been obtained with a reference method for PM 2.5 in accordance with appendix L of this part. 1.9 PM 10c measurements obtained incidental to the PM 10-2.5 measurements by this method shall be considered to have been obtained with a reference method for PM 10 in accordance with appendix J of this part, provided that: (a) The PM 10c measurements are adjusted to EPA reference conditions (25 °C and 760 millimeters of mercury), and (b) Such PM 10c measurements are appropriately identified to differentiate them from PM 10 measurements obtained with other (conventional) methods for PM 10 designated in accordance with part 53 of this chapter as reference or equivalent methods for PM 10 . 2.0 Principle 2.1 Separate, collocated, electrically powered air samplers for PM 10c and PM 2.5 concurrently draw ambient air at identical, constant volumetric flow rates into specially shaped inlets and through one or more inertial particle size separators where the suspended particulate matter in the PM 10 or PM 2.5 size range, as applicable, is separated for collection on a polytetrafluoroethylene (PTFE) filter over the specified sampling period. The air samplers and other aspects of this PM 10-2.5 reference method are specified either explicitly in this appendix or by reference to other applicable regulations or quality assurance guidance. 2.2 Each PM 10c and PM 2.5 sample collection filter is weighed (after moisture and temperature conditioning) before and after sample collection to determine the net weight (mass) gain due to collected PM 10c or PM 2.5 . The total volume of air sampled by each sampler is determined by the sampler from the measured flow rate at local ambient temperature and pressure and the sampling time. The mass concentrations of both PM 10c and PM 2.5 in the ambient air are computed as the total mass of collected particles in the PM 10 or PM 2.5 size range, as appropriate, divided by the total volume of air sampled by the respective samplers, and expressed in micrograms per cubic meter (µg/m 3 )at local temperature and pressure conditions. The mass concentration of PM 10-2.5 is determined as the PM 10c concentration value less the corresponding, concurrently measured PM 2.5 concentration value. 2.3 Most requirements for PM 10-2.5 reference methods are similar or identical to the requirements for PM 2.5 reference methods as set forth in appendix L to this part. To insure uniformity, applicable appendix L requirements are incorporated herein by reference in the sections where indicated rather than repeated in this appendix. 3.0 PM 10-2.5 Measurement Range 3.1 Lower concentration limit. The lower detection limit of the mass concentration measurement range is estimated to be approximately 3 µg/m 3 , based on the observed precision of PM 2.5 measurements in the national PM 2.5 monitoring network, the probable similar level of precision for the matched PM 10c measurements, and the additional variability arising from the differential nature of the measurement process. This value is provided merely as a guide to the significance of low PM 10-2.5 concentration measurements. 3.2 Upper concentration limit. The upper limit of the mass concentration range is determined principally by the PM 10c filter mass loading beyond which the sampler can no longer maintain the operating flow rate within specified limits due to increased pressure drop across the loaded filter. This upper limit cannot be specified precisely because it is a complex function of the ambient particle size distribution and type, humidity, the individual filter used, the capacity of the sampler flow rate control system, and perhaps other factors. All PM 10c samplers are estimated to be capable of measuring 24-hour mass concentrations of at least 200 µg/m 3 while maintaining the operating flow rate within the specified limits. The upper limit for the PM 10-2.5 measurement is likely to be somewhat lower because the PM 10-2.5 concentration represents only a fraction of the PM 10 concentration. 3.3 Sample period. The required sample period for PM 10-2.5 concentration measurements by this method shall be at least 1,380 minutes but not more than 1,500 minutes (23 to 25 hours), and the start times of the PM 2.5 and PM 10c samples are within 10 minutes and the stop times of the samples are also within 10 minutes (see section 10.4 of this appendix). 4.0 Accuracy (bias) 4.1 Because the size, density, and volatility of the particles making up ambient particulate matter vary over wide ranges and the mass concentration of particles varies with particle size, it is difficult to define the accuracy of PM 10-2.5 measurements in an absolute sense. Furthermore, generation of credible PM 10-2.5 concentration standards at field monitoring sites and presenting or introducing such standards reliably to samplers or monitors to assess accuracy is still generally impractical. The accuracy of PM 10-2.5 measurements is therefore defined in a relative sense as bias, referenced to measurements provided by other reference method samplers or based on flow rate verification audits or checks, or on other performance evaluation procedures. 4.2 Measurement system bias for monitoring data is assessed according to the procedures and schedule set forth in part 58, appendix A of this chapter. The goal for the measurement uncertainty (as bias) for monitoring data is defined in part 58, appendix A of this chapter as an upper 95 percent confidence limit for the absolute bias of 15 percent. Reference 1 in section 13 of this appendix provides additional information and guidance on flow rate accuracy audits and assessment of bias. 5.0 Precision 5.1 Tests to establish initial measurement precision for each sampler of the reference method sampler pair are specified as a part of the requirements for designation as a reference method under part 53 of this chapter. 5.2 Measurement system precision is assessed according to the procedures and schedule set forth in appendix A to part 58 of this chapter. The goal for acceptable measurement uncertainty, as precision, of monitoring data is defined in part 58, appendix A of this chapter as an upper 95 percent confidence limit for the coefficient of variation (CV) of 15 percent. Reference 1 in section 13 of this appendix provides additional information and guidance on this requirement. 6.0 Filters for PM 10c and PM 2.5 Sample Collection. Sample collection filters for both PM 10c and PM 2.5 measurements shall be identical and as specified in section 6 of appendix L to this part. 7.0 Sampler. The PM 10-2.5 sampler shall consist of a PM 10c sampler and a PM 2.5 sampler, as follows: 7.1 The PM 2.5 sampler shall be as specified in section 7 of appendix L to this part. 7.2 The PM 10c sampler shall be of like manufacturer, design, configuration, and fabrication to that of the PM 2.5 sampler and as specified in section 7 of appendix L to this part, except as follows: 7.2.1 The particle size separator specified in section 7.3.4 of appendix L to this part shall be eliminated and replaced by a downtube extension fabricated as specified in Figure O-1 of this appendix. 7.2.2 The sampler shall be identified as a PM 10c sampler on its identification label required under § 53.9(d) of this chapter. 7.2.3 The average temperature and average barometric pressure measured by the sampler during the sample period, as described in Table L-1 of appendix L to this part, need not be reported to EPA's AQS data base, as required by section 7.4.19 and Table L-1 of appendix L to this part, provided such measurements for the sample period determined by the associated PM 2.5 sampler are reported as required. 7.3 In addition to the operation/instruction manual required by section 7.4.18 of appendix L to this part for each sampler, supplemental operational instructions shall be provided for the simultaneous operation of the samplers as a pair to collect concurrent PM 10c and PM 2.5 samples. The supplemental instructions shall cover any special procedures or guidance for installation and setup of the samplers for PM 10-2.5 measurements, such as synchronization of the samplers' clocks or timers, proper programming for collection of concurrent samples, and any other pertinent issues related to the simultaneous, coordinated operation of the two samplers. 7.4 Capability for electrical interconnection of the samplers to simplify sample period programming and further ensure simultaneous operation is encouraged but not required. Any such capability for interconnection shall not supplant each sampler's capability to operate independently, as required by section 7 of appendix L of this part. 8.0 Filter Weighing 8.1 Conditioning and weighing for both PM 10c and PM 2.5 sample filters shall be as specified in section 8 of appendix L to this part. See reference 1 of section 13 of this appendix for additional, more detailed guidance. 8.2 Handling, conditioning, and weighing for both PM 10c and PM 2.5 sample filters shall be matched such that the corresponding PM 10c and PM 2.5 filters of each filter pair receive uniform treatment. The PM 10c and PM 2.5 sample filters should be weighed on the same balance, preferably in the same weighing session and by the same analyst. 8.3 Due care shall be exercised to accurately maintain the paired relationship of each set of concurrently collected PM 10 c and PM 2.5 sample filters and their net weight gain data and to avoid misidentification or reversal of the filter samples or weight data. See Reference 1 of section 13 of this appendix for additional guidance. 9.0 Calibration. Calibration of the flow rate, temperature measurement, and pressure measurement systems for both the PM 10c and PM 2.5 samplers shall be as specified in section 9 of appendix L to this part. 10.0 PM 10-2.5 Measurement Procedure 10.1 The PM 10c and PM 2.5 samplers shall be installed at the monitoring site such that their ambient air inlets differ in vertical height by not more than 0.2 meter, if possible, but in any case not more than 1 meter, and the vertical axes of their inlets are separated by at least 1 meter but not more than 4 meters, horizontally. 10.2 The measurement procedure for PM 10c shall be as specified in section 10 of appendix L to this part, with “PM 10c ” substituted for “PM 2.5 ” wherever it occurs in that section. 10.3 The measurement procedure for PM 2.5 shall be as specified in section 10 of appendix L to this part. 10.4 For the PM 10-2.5 measurement, the PM 10c and PM 2.5 samplers shall be programmed to operate on the same schedule and such that the sample period start times are within 5 minutes and the sample duration times are within 5 minutes. 10.5 Retrieval, transport, and storage of each PM 10c and PM 2.5 sample pair following sample collection shall be matched to the extent practical such that both samples experience uniform conditions. 11.0 Sampler Maintenance. Both PM 10c and PM 2.5 samplers shall be maintained as described in section 11 of appendix L to this part. 12.0 Calculations 12.1 Both concurrent PM 10c and PM 2.5 measurements must be available, valid, and meet the conditions of section 10.4 of this appendix to determine the PM 10-2.5 mass concentration. 12.2 The PM 10c mass concentration is calculated using equation 1 of this section: Where: PM 10c = mass concentration of PM 10c , µg/m 3 ; W f , W i = final and initial masses (weights), respectively, of the filter used to collect the PM 10c particle sample, µg; V a = total air volume sampled by the PM 10c sampler in actual volume units measured at local conditions of temperature and pressure, as provided by the sampler, m 3 . Note: Total sample time must be between 1,380 and 1,500 minutes (23 and 25 hrs) for a fully valid PM 10c sample; however, see also section 3.3 of this appendix. 12.3 The PM 2.5 mass concentration is calculated as specified in section 12 of appendix L to this part. 12.4 The PM 10−2.5 mass concentration, in µg/m 3 , is calculated using Equation 2 of this section: 13.0 Reference 1. Quality Assurance Guidance Document 2.12. Monitoring PM 2.5 in Ambient Air Using Designated Reference or Class I Equivalent Methods. Draft, November 1998 (or later version or supplement, if available). Available at: www.epa.gov/ttn/amtic/pgqa.html. 14.0 Figures Figure O-1 is included as part of this appendix O. [71 FR 61230, Oct. 17, 2006]