Highly accurate calibration of particle number portable emissions measurement systems (PN-PEMS) via actual soot charging probability correction

Abstract

The upcoming Euro 7 vehicle emissions regulation sets new requirements for calibrating PN-PEMS. In current PN concentration calibration methods, arbitrary selection of aerosol materials and incorrect estimation of multiply-charged particles lead to calibration deviation. This study proposes a novel, accurate calibration method based on the calibration and correction of the actual charging probability of soot for calibrating PN-PEMS. The accurate calibration results of a PN-PEMS show a maximum reduction of 7.65 % in the +1-charging probability deviation and of 3.15 % in the counting efficiency deviation. The calibration of the actual charging probability of soot introduces a calibration uncertainty increment of 0.09 %-2.71 %, and the overall uncertainty is < 4.76 %, which makes the calibration results more credible. The interaction of calibration aerosols of different physicochemical properties with the condensation particle counter working fluid and catalytic stripper device is the main reason for the different PN-PEMS calibration results. The calibration of the actual charging probability of particles is the fundamental method to eliminate the calibration deviation caused by the estimation and correction of multiply-charged particles.