Mobility Particle Size Spectrometers: Calibration Procedures And Measurement Uncertainties

Abstract

Mobility particle size spectrometers (MPSS) belong to the essential instruments in aerosol science that<br> determine the particle number size distribution (PNSD) in the submicrometer size range. Following<br> calibration procedures and target uncertainties against standards and reference instruments are<br> suggested for a complete MPSS quality assurance program: (a) calibration of the CPC counting efficiency<br> curve (within 5% for the plateau counting efficiency; within 1 nm for the 50% detection efficiency<br> diameter), (b) sizing calibration of the MPSS, using a certified polystyrene latex (PSL) particle size<br> standard at 203 nm (within 3%), (c) intercomparison of the PNSD of the MPSS (within 10% and 20% of<br> the dN/dlogDP concentration for the particle size range 20–200 and 200–800 nm, respectively), and (d)<br> intercomparison of the integral PNC of the MPSS (within 10%). Furthermore, following measurement<br> uncertainties have been investigated: (a) PSL particle size standards in the range from 100 to 500 nm<br> match within 1% after sizing calibration at 203 nm. (b) Bipolar diffusion chargers based on<br> the radioactive nuclides Kr85, Am241, and Ni63 and a new ionizer based on corona discharge follow the<br> recommended bipolar charge distribution, while soft X-ray-based charges may alter faster than<br> expected. (c) The use of a positive high voltage supply show a 10% better performance than a negative<br> one. (d) The intercomparison of the integral PNC of an MPSS against the total number concentration is<br> still within the target uncertainty at an ambient pressure of approximately 500 hPa.