Response characteristics of PMP compliant condensation particle counters toward various calibration aerosols

Within the European legislation, a new limit for particle emissions of light and heavy duty engines based on the particle number (PN) was established in 2011. For PN determination, solid exhaust particles are quantified by means of a condensation particle counter (CPC). In literature, deviations in PN of up to 30% are reported for a comparison of different measurement set-ups. Among others variations in the counting efficiency (CE) of different CPCs have to be considered as possible error sources that contribute to the overall deviation in PN. Thereby the uncertainties in CE may result from variations in the calibration procedure of different manufacturers (e.g., calibration aerosol). To investigate this circumstance, devices from three different manufacturers were directly compared according to their CE for model aerosols. The subject CPCs exhibited differences of up to 17% (23 nm particles) in the counting efficiency when measuring simultaneously the same test aerosol. Depending on the PN size distribution in real exhaust, this might result in an error (∼9%) in the finally determined PN. Additionally, the CPC response for selected volatile exhaust components was investigated. In this way, we found out that the fraction of detected nucleation mode particles increases approximately by factor 3 in case particles consist of or contain volatile material (e.g., sulfuric acid).