Comparability of mobility particle sizers and diffusion chargers

A large study on the comparability of various aerosol instruments was conducted. The study involved altogether 24 instruments, including eleven scanning, sequential and fast mobility particle sizers (five Grimm SMPS+C, three TSI SMPS and three FMPS) with different settings and differential mobility analyzers (DMAs), twelve instruments based on unipolar diffusion charging to determine size integrated concentrations and in some cases mean particle size (five miniDiSCs of the University of Applied Sciences and Arts Northwestern Switzerland, four Philips Aerasense nanoTracers, two TSI Nanoparticle Surface Area Monitors and one Grimm nanoCheck) and one TSI ultrafine condensation particle counter (UCPC). All instruments were simultaneously challenged with particles of various sizes, concentrations and morphologies. All measurement results were compared with those from a freshly calibrated SMPS for size distributions and the UCPC for number concentration. In general, all SMPSs showed good comparability with particularly the sizing agreeing to within a few percent. Differences in the determined number concentration were somewhat more pronounced, but the largest deviations could be tracked back to the use of an older software version. The comparability of the FMPSs was shown to be lower, with discrepancies on the order of ±25% for sizing and ±30% for total concentrations. The discrepancies between FMPSs and the internal reference SMPS seemed to be influenced by particle size and morphology. Total number and/or lung deposited surface area concentrations measured with unipolar diffusion charger based instruments generally agreed to within ±30% with the internal references (CPC for number concentrations; lung deposited surface area derived from SMPS measurements), as long as the particle size distributions of the test aerosols were within the specified limits for the instruments. When the upper size limit was exceeded, deviations of up to several hundred percent were detected.