(36)

the following points 8.1.13 to 8.1.13.2.5 are inserted: ‘8.1.13. PM measurements 8.1.13.1. PM balance verifications and weighing process verification 8.1.13.1.1. Scope and frequency This section describes three verifications. (a) Independent verification of PM balance performance within 370 days prior to weighing any filter; (b) Zero and span of the balance within 12 h prior to weighing any filter; (c) Verification that the mass determination of reference filters before and after a filter weighing session be less than a specified tolerance. 8.1.13.1.2. Independent verification The balance manufacturer (or a representative approved by the balance manufacturer) shall verify the balance performance within 370 days of testing in accordance with internal audit procedures. 8.1.13.1.3. Zeroing and spanning Balance performance shall be verified by zeroing and spanning it with at least one calibration weight, and any weights that are used shall meet the specifications in point 9.5.2 to perform that verification. A manual or automated procedure shall be used: (a) A manual procedure requires that the balance shall be used in which the balance shall be zeroed and spanned with at least one calibration weight. If normally mean values are obtained by repeating the weighing process to improve the accuracy and precision of PM measurements, the same process shall be used to verify balance performance; (b) An automated procedure is carried out with internal calibration weights that are used automatically to verify balance performance. These internal calibration weights shall meet the specifications in point 9.5.2 to perform that verification. 8.1.13.1.4. Reference sample weighing All mass readings during a weighing session shall be verified by weighing reference PM sample media (e.g. filters) before and after a weighing session. A weighing session may be as short as desired, but no longer than 80 hours, and may include both pre- and post-test mass readings. Successive mass determinations of each reference PM sample media shall return the same value within ± 10 μg or ± 10 % of the expected total PM mass, whichever is higher. Should successive PM sample filter weighing events fail that criterion, all individual test filter mass readings mass readings occurring between the successive reference filter mass determinations shall be invalidated. These filters may be re-weighed in another weighing session. Should a post-test filter be invalidated then the test interval is void. That verification shall be performed as follows: (a) At least two samples of unused PM sample media shall be kept in the PM-stabilization environment. These shall be used as references. Unused filters of the same material and size shall be selected for use as references; (b) References shall be stabilized in the PM stabilization environment. References shall be considered stabilized if they have been in the PM-stabilization environment for a minimum of 30 min, and the PM-stabilization environment has been within the specifications of point 9.3.4.4 for at least the preceding 60 min; (c) The balance shall be exercised several times with a reference sample without recording the values; (d) The balance shall be zeroed and spanned. A test mass shall be placed on the balance (e.g. calibration weight) and then removed ensuring that the balance returns to an acceptable zero reading within the normal stabilization time; (e) Each of the reference media (e.g. filters) shall be weighed and their masses recorded. If normally mean values are obtained by repeating the weighing process to improve the accuracy and precision of reference media (e.g. filters) masses, the same process shall be used to measure mean values of sample media (e.g. filters) masses; (f) The balance environment dew point, ambient temperature, and atmospheric pressure shall be recorded; (g) The recorded ambient conditions shall be used to correct results for buoyancy as described in point 8.1.13.2. The buoyancy-corrected mass of each of the references shall be recorded; (h) Each of the reference media's (e.g. filter's) buoyancy-corrected reference mass shall be subtracted from its previously measured and recorded buoyancy-corrected mass; (i) If any of the reference filters' observed mass changes by more than that allowed under this section, all PM mass determinations made since the last successful reference media (e.g. filter) mass validation shall be invalidated. Reference PM filters may be discarded if only one of the filters mass has changed by more than the allowable amount and a special cause for that filter's mass change can be positively identified which would not have affected other in-process filters. Thus the validation can be considered a success. In that case, the contaminated reference media shall not be included when determining compliance with paragraph (j) of this point, but the affected reference filter shall be discarded and replaced; (j) If any of the reference masses change by more than that allowed under point 8.1.13.1.4, all PM results that were determined between the two times that the reference masses were determined shall be invalidated. If reference PM sample media is discarded in accordance with point (i), at least one reference mass difference that meets the criteria set out in point 8.1.13.1.4 shall be available. Otherwise, all PM results that were determined between the two times that the reference media (e.g. filters) masses were determined shall be invalidated. 8.1.13.2. PM sample filter buoyancy correction 8.1.13.2.1. General PM sample filter shall be corrected for their buoyancy in air. The buoyancy correction depends on the sample media density, the density of air, and the density of the calibration weight used to calibrate the balance. The buoyancy correction does not account for the buoyancy of the PM itself, because the mass of PM typically accounts for only (0,01 to 0,10) % of the total weight. A correction to this small fraction of mass would be at the most 0,010 %. The buoyancy-corrected values are the tare masses of the PM samples. These buoyancy-corrected values of the pre-test filter weighing are subsequently subtracted from the buoyancy-corrected values of the post-test weighing of the corresponding filter to determine the mass of PM emitted during the test. 8.1.13.2.2. PM sample filter density Different PM sample filter have different densities. The known density of the sample media shall be used, or one of the densities for some common sampling media shall be used, as follows: (a) For PTFE-coated borosilicate glass, a sample media density of 2 300 kg/m3 shall be used; (b) For PTFE membrane (film) media with an integral support ring of polymethylpentene that accounts for 95 % of the media mass, a sample media density of 920 kg/m3 shall be used; (c) For PTFE membrane (film) media with an integral support ring of PTFE, a sample media density of 2 144 kg/m3 shall be used. 8.1.13.2.3. Air density Because a PM balance environment shall be tightly controlled to an ambient temperature of 295 ± 1 K (22 ± 1 °C) and a dew point of 282,5 ± 1 K (9,5 ± 1 °C), air density is primarily function of atmospheric pressure. Therefore a buoyancy correction is specified that is only a function of atmospheric pressure. 8.1.13.2.4. Calibration weight density The stated density of the material of the metal calibration weight shall be used. 8.1.13.2.5. Correction calculation The PM sample filter shall be corrected for buoyancy by means of equation (6-27): (6-27) Where: m cor is the PM sample filter mass corrected for buoyancy m uncor is the PM sample filter mass uncorrected for buoyancy ρ air is the density of air in balance environment ρ weight is the density of calibration weight used to span balance ρ media is the density of PM sample filter with (6-28) Where: p abs is the absolute pressure in balance environment M mix is the molar mass of air in balance environment R is the molar gas constant. T amb is the absolute ambient temperature of balance environment’;