Design and evaluation of a calibration system for portable motor vehicle emission particle number detectors

The supervision of the number concentration of particles emitted from motor vehicles is becoming increasingly strict. The regular calibration of portable particle number (PN) detectors is a prerequisite to ensure the effective supervision of PN. At present, the calibration of PN detectors is mostly completed in the laboratory. However, due to the complexity and poor portability of the laboratory calibration system, it is difficult to use this system for the on-site calibration of PN detectors. To this end, a portable motor vehicle emission PN detector calibration system based on the principles of negative pressure siphon atomization, differential electrical mobility classifier, and fA-level weak current measurement was developed, which could quickly and accurately calibrate the PN detector on-site. The system consists of three parts: an atomizer generator, a plate differential mobility analyzer (PDMA), and an aerosol electrometer. The atomizer generator produces NaCl particles with a median particle size of 70 nm and fluctuation of <10%. The particle size classification deviation of the PDMA is <3.7% and the counting error of the aerosol electrometer is <10%. The On-board Emissions Measurement System was calibrated as a PN detector on a self-developed portable calibration system as well as on a laboratory calibration system. The comparison results showed that the measurement results of the portable calibration system were closer to the instrument factory report certificate results, and the maximum error did not exceed 6.72%.