40 CFR Appendix O to Part 50, Reference Method for the Determination of Coarse Particulate Matter as PM10-2.5 in the Atmosphere
1.1 This method provides for the measurement of the mass concentration of coarse particulate matter (PM10-2.5) 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, PM10-2.5 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, PM10-2.5 concentrations shall be measured as the arithmetic difference between separate but concurrent, collocated measurements of PM10 and PM2.5, where the PM10 measurements are obtained with a specially approved sampler, identified as a “PM10c sampler,” that meets more demanding performance requirements than conventional PM10 samplers described in appendix J of this part. Measurements obtained with a PM10c sampler are identified as “PM10c measurements” to distinguish them from conventional PM10 measurements obtained with conventional PM10 samplers. Thus, PM10-2.5 = PM10c − PM2.5.
1.4 The PM10c and PM2.5 gravimetric measurement processes are considered to be nondestructive, and the PM10c and PM2.5 samples obtained in the PM10-2.5 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 PM2.5, are generally applicable for PM10c, and, hence, PM10-2.5 measurements under this method, as well.
1.6 A method based on specific model PM10c and PM2.5 samplers will be considered a reference method for purposes of part 58 of this chapter only if:
(a) The PM10c and PM2.5 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 PM10-2.5 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 PM10-2.5 in accordance with part 53 of this chapter.
1.8 PM2.5 measurements obtained incidental to the PM10-2.5 measurements by this method shall be considered to have been obtained with a reference method for PM2.5 in accordance with appendix L of this part.
1.9 PM10c measurements obtained incidental to the PM10-2.5 measurements by this method shall be considered to have been obtained with a reference method for PM10 in accordance with appendix J of this part, provided that:
(a) The PM10c measurements are adjusted to EPA reference conditions (25 °C and 760 millimeters of mercury), and
(b) Such PM10c measurements are appropriately identified to differentiate them from PM10 measurements obtained with other (conventional) methods for PM10 designated in accordance with part 53 of this chapter as reference or equivalent methods for PM10.
2.1 Separate, collocated, electrically powered air samplers for PM10c and PM2.5 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 PM10 or PM2.5 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 PM10-2.5 reference method are specified either explicitly in this appendix or by reference to other applicable regulations or quality assurance guidance.
2.2 Each PM10c and PM2.5 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 PM10c or PM2.5. 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 PM10c and PM2.5 in the ambient air are computed as the total mass of collected particles in the PM10 or PM2.5 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 PM10-2.5 is determined as the PM10c concentration value less the corresponding, concurrently measured PM2.5 concentration value.
2.3 Most requirements for PM10-2.5 reference methods are similar or identical to the requirements for PM2.5 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.
3.1 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 PM2.5 measurements in the national PM2.5 monitoring network, the probable similar level of precision for the matched PM10c 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 PM10-2.5 concentration measurements.
3.2 Upper concentration limit. The upper limit of the mass concentration range is determined principally by the PM10c 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 PM10c 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 PM10-2.5 measurement is likely to be somewhat lower because the PM10-2.5 concentration represents only a fraction of the PM10 concentration.
3.3 Sample period. The required sample period for PM10-2.5 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 PM2.5 and PM10c samples are within 10 minutes and the stop times of the samples are also within 10 minutes (see section 10.4 of this appendix).
4.1 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 PM10-2.5 measurements in an absolute sense. Furthermore, generation of credible PM10-2.5 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 PM10-2.5 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.
5.1 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 PM10cand PM2.5Sample Collection. Sample collection filters for both PM10c and PM2.5 measurements shall be identical and as specified in section 6 of appendix L to this part.
7.0 Sampler. The PM10-2.5 sampler shall consist of a PM10c sampler and a PM2.5 sampler, as follows:
7.1 The PM2.5 sampler shall be as specified in section 7 of appendix L to this part.
7.2 The PM10c sampler shall be of like manufacturer, design, configuration, and fabrication to that of the PM2.5 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 PM10c 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 PM2.5 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 PM10c and PM2.5 samples. The supplemental instructions shall cover any special procedures or guidance for installation and setup of the samplers for PM10-2.5 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.
8.1 Conditioning and weighing for both PM10c and PM2.5 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 PM10c and PM2.5 sample filters shall be matched such that the corresponding PM10c and PM2.5 filters of each filter pair receive uniform treatment. The PM10c and PM2.5 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 PM10c and PM2.5 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 PM10c and PM2.5 samplers shall be as specified in section 9 of appendix L to this part.
10.1 The PM10c and PM2.5 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 PM10c shall be as specified in section 10 of appendix L to this part, with “PM10c” substituted for “PM2.5” wherever it occurs in that section.
10.3 The measurement procedure for PM2.5 shall be as specified in section 10 of appendix L to this part.
10.4 For the PM10-2.5 measurement, the PM10c and PM2.5 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 PM10c and PM2.5 sample pair following sample collection shall be matched to the extent practical such that both samples experience uniform conditions.
11.0 Sampler Maintenance. Both PM10c and PM2.5 samplers shall be maintained as described in section 11 of appendix L to this part.
12.1 Both concurrent PM10c and PM2.5 measurements must be available, valid, and meet the conditions of section 10.4 of this appendix to determine the PM10-2.5 mass concentration.
12.2 The PM10c mass concentration is calculated using equation 1 of this section:
Total sample time must be between 1,380 and 1,500 minutes (23 and 25 hrs) for a fully valid PM10c sample; however, see also section 3.3 of this appendix.
12.3 The PM2.5 mass concentration is calculated as specified in section 12 of appendix L to this part.
12.4 The PM10−2.5 mass concentration, in µg/m 3, is calculated using Equation 2 of this section:
1. Quality Assurance Guidance Document 2.12. Monitoring PM2.5 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.
Figure O-1 is included as part of this appendix O.