Experimental and Theoretical Investigations of the Effect of the Calibration Aerosol Material on the Counting Efficiencies of TSI 3790 Condensation Particle Counters

Abstract

The counting efficiencies of two TSI 3790 Condensation Particle Counters (CPCs) were investigated experimentally for graphite, poly-(alpha)-olefin (PAO), tetradecane (C14), and hexadecane (C16) particles at saturator-to-condenser temperature differences spanning from 5.6• C to 11.3 • C. The efficiencies determined with PAO, C14, and C16 particles were broadly similar, while tests with graphite particles resulted in systematically lower counting efficiencies. The differences between PAO and graphite particles were reduced at elevated temperature differences, i.e., as the saturation ratios inside the condenser increased. The possibility to predict measured counting efficiencies by heterogeneous nucleation theory was also assessed. The results for PAO, C14, and C16 were representative of perfectly wettable particles, while graphite data could only be reproduced with a contact angle of 6-12• , for all temperatures examined. Line tension fits revealed a linear correlation with the graphite mobility diameter for all operating temperatures (5 × 10 −11 N at 15 nm to 4 × 10 −10 N at 70 nm). This could actually indicate that the mobility diameter underestimates the contact line for these complex geometry graphite aggregates. An examination of the calculated activation regions inside the condenser indicated that the upper part of the counting efficiency curve (>50%) is very sensitive to flow and temperature nonidealities. This observation is in quantitative agreement with systematic deviations observed between theoretical predictions and experimental data. Numerical calculations for a range of working fluids suggested that for a given Received 12 April 2012; accepted 10 July 2012. The authors would like to gratefully acknowledge Dominique Lesueur for his valuable contribution to the experimental work and Carsten Gruening and Sebastiao Martin Dos Santos for providing the nebulizer employed in the calibration of the DMAs. A. Mamakos and Y. Drossinos would like to thank Giorgio Martini, Panagiota Dilara, and Alois Krasenbrink for their support. INEOS Oligomers is also acknowledged for supplying the poly-(alpha)-olefin employed in the experiments. The authors would also like to thank TSI for supplying one of the TSI 3790 units employed in the study. The study was partially funded by the EMRP-ENV02 PartEmission project. The EMRP is jointly funded by the EMRP participating countries within EURAMET and the European Commission.Address correspondence to Yannis Drossinos, European Commission, Joint Research Centre, I-21027, Ispra, VA, Italy. E-mail: ioannis. drossinos@jrc.ec.europa.eu affinity of the calibration particle to the examined vapors (i.e., for a finite contact angle), the benefit from shifting to a fluid alternative to butanol is limited. Further investigations on the reduction of the material dependence should focus on the identification of working fluids exhibiting greater affinity for different particle materials (e.g., lower contact angle).

Characterization of Combustion Aerosol Produced by a Mini-CAST and Treated in a Catalytic Stripper

“…This evidence raises concerns regarding the traceability of CPC calibrations against combustion aerosol. On the other hand, the counting efficiencies for emery oil, while not representative of combustion soot, reproduced the manufacturer's certified values to within 4%, in good agreement with other published data (Giechaskiel and Bergmann 2011;Mamakos et al 2013).…”

“…The certification values by TSI, determined using emery oil, are also shown (crosses). primary particle sizes pointing towards a morphology effect on the activation energy barrier (i.e., affecting the contact line Mamakos et al 2013). Differences in the chemistry of the particle surface and/or adsorbed volatile material could also have contributed to the different affinity for butanol.…”

“…Appropriate selection of the calibration aerosol is of crucial importance, as the instrument response may strongly depend on particle chemistry and morphology (Biskos et al 2004;Mamakos et al 2013). Ideally, the calibration aerosol should resemble that of the emission source, but there is an inherent difficulty in identifying such a reference aerosol given the strong dependence of engine exhaust aerosol properties on the engine operating conditions (Mathis et al 2005;Olfert et al 2007), fuel (Tzamkiozis et al 2011) and engine types (Mathis et al 2004).…”

Evaluation of a 10 nm Particle Number Portable Emissions Measurement System (PEMS)

“…The different residence times, the different dilutions (10 versus 1000), and the different operating temperatures of the detectors (60 • C versus 25 • C) of the PEMS10 and TP10 respectively are also expected to have affected the size of these particles. It is also possible that the lower 23 nm measurements with the reference system at the tailpipe is linked to the lower affinity of these particle for butanol [59,60]. Table 1.…”

Dependence of CPC cut-off diameter on particle morphology and other factors

“…Several authors found a strong dependence on the chemical composition of the calibration material used for the 50% cutoff diameter determination (Wang et al 2010;Mamakos et al 2013). Furthermore, a degradation of the performance of the CPCs after extended use was noticed .…”