Inter-Laboratory Comparison Exercise CPC CALIBRATION CALIBRATION AEROSOL AND LABORATORY SETUP Key Findings PMP Meeting 2018-11-07 Alexander Terres

Round Robin: Status All measurements and evaluation finished Report circulated to all participants for final comments Transfer of findings to CPC calibration sub-group Terres: CPC Calibration Round Robin | Key Findings, 47th PMP Meeting | 2018-05-16

Key Findings: Aerosol Generator Soot aerosol provided lower counting efficiencies than emery oil at 23nm (29% vs 49%) and at 41nm (78% vs. 91%) Soot-like generators offered a low uncertainty, even without standardization  Inter-laboratory standard deviation 2% - 3% for in-house CAST and Palas at 41nm and 70nm Inherently, soot has more degrees of freedom than electrospray + emery oil  Required: Proven setup, regular checks and standardization (e.g. fuel/air ratio, size distribution) Thermal treatment necessary for stability and universal application (mandatory for PCRF and PN-PEMS) Transfer function from soot-like to emery oil is possible (but was not part of the RR) To be checked: Can the CPC meet D50 and D90 with soot by changing temperatures? Using emery oil is a trade-off: Low uncertainty from a purpose-specific generator (only for CPC), but high uncertainty from overall procedure with various generators (Emery oil + soot + NaCl + …) Terres: CPC Calibration Round Robin | Key Findings, 47th PMP Meeting | 2018-05-16

Key Findings: CPC/Reference Repeatability Within 1 Laboratory Same reference CPC vs. same electrometer 1 year, 40 calibrations Standard deviation/range of valid measurements: @41nm: 1.5 / 90%-96% @70nm: 1.3 / 90%-95% Without calibration: 0.7 – 1.2 Blue/green: before/after calibration  variability within 1 laboratory Terres: CPC Calibration Round Robin | Key Findings, 47th PMP Meeting | 2018-05-16

Key Findings: Circulated CPC Notable deterioration between starting measurement and final measurement at manufacturer (w/ emery oil) At 23nm: 51%  46% At 41nm: 93%  88% At 55 nm: 96% 93% Sample flow was reduced but within tolerance (efficiency is flow corrected) In addition to laboratory facilities uncertainty, Circulated CPC seems to be a significant source of uncertainty between labs Normalization to cancel out reference counter did not improve comparability between labs CPC stability between labs hard to estimate (see above). Influence of transport, drying and contamination possible Emery oil calibrated CPCs require recalibration to meet legal targets at 23/41nm for soot-aerosol  validate! (not part of RR) Comparability between CPC models better when KF is always applied to calibration at 23/41nm  Some CPC models internally apply a KF all the time  Standardization necessary!

Key Findings: Procedure Plateau uncertainty: At 70 nm the CPC did not reach the plateau with soot (2-3 percentage points less) At 70 nm the std. deviation was 2-3 percentage points w/ miniCAST, PALAS (range: 90%-96%), Doubly charged correction at this size was 3% (Lab A) to 7% (Lab B) when using electrometer Plateau uncertainty is best indicator for improvement in calibration (biggest impact in the field – PMP use!) Implementation of ISO 27891 procedure + reference aerosol Open questions at 23nm where uncertainty is largest (not investigated in this RR): DMA calibration Thermal stability, soot morphology (miniCAST) (measurements from one lab showed an influence) CPC drift, contamination

Key Findings: Procedure/Documentation Calibration results should be shown in the form: ηCPC = 95% ±3% documentation of the uncertainty budget Example in ISO 17025 for calibration labs CPCs can deteriorate during one calibration interval (1 year) Important: quality check of calibration setup with shorter frequency (1-2 months) WLTP regulation includes these checks for test CPCs No calibration for the aerosol generator available Regular documentation of performance + operation points necessary Needed for complete traceability of PN calibration Terres: CPC Calibration Round Robin | Key Findings, 47th PMP Meeting | 2018-05-16

Key Findings: 10nm Only few measurements with 10nm Round Robin CPC (due to lack of suitable reference and/or lack of time) Impression: uncertainty at 10nm/15nm similar or better than engine exhaust CPC at 23nm Material influence at 10nm/15nm: seems smaller than for 23nm; few data  General points, calibration: Sub-10nm reference device needed: electrometer, ultrafine CPC (full flow!) Huge impact of diffusion losses: Residence times must be the same, mathematical correction significantly increases the uncertainty and can manipulate the results Generator: miniCAST able to produce 10nm particles, composition not investigated  concentration 1000-3000 1/cm³ Thermal stability at 10/15nm needs to be demonstrated DMA: Long-DMA suitable for 10/15nm ? Traceable DMA calibration unclear (typically extrapolation from 70nm/100nm PSL)

Key Findings: Conclusions Generator: soot-like provides low level of uncertainty; still more degrees of freedom than emery oil Reference Counter: influence relatively small, traceability needed, flow correction a must CPC: deterioration during 1 year Procedure: Implement common procedure following ISO 27891 + generator for PMP Documentation: for calibration lab – provide uncertainty budget + regular quality checks (e.g. monthly) 10nm: Soot generator needs further investigation, e.g. properties of CAST aerosol, concentration with PALAS DMA calibration needs further investigation Aerosol influence might be different than for 23nm CPCs Terres: CPC Calibration Round Robin | Key Findings, 47th PMP Meeting | 2018-05-16

Key Findings: Outlook Overall PN measurements uncertainty will be improved significantly if: A single standard aerosol is defined It is used for both stationary PMP-compliant devices and mobile PN-PEMS An agreement is made on K-factor application Traceability and ISO 27891 are implemented by all users These topics should be covered by calibration procedures for future post Euro 6 EU legislation. Terres: CPC Calibration Round Robin | Key Findings, 47th PMP Meeting | 2018-05-16

Thank you for your attention Terres: CPC Calibration Round Robin | Key Findings, 47th PMP Meeting | 2018-05-16