High-resolution low-pressure cascade impactor

• The study introduces a new high-resolution low-pressure cascade impactor (HRLPI).
• It uses the electrical detection of particles and stages that have sharp cut-curves.
• Measurement size range is from 5 to 200 nm (10 impactor stages + filter stage).
• The HRLPI was compared with five other instruments in the laboratory tests.
• Only the HRLPI and SMPS performed from the bimodal test case (GMDs 15 and 30 nm).

This study introduces the calibration and performance evaluation of a new high-resolution low-pressure cascade impactor (HRLPI). It is a 10-stage cascade impactor designed to be used with the electrical detection of aerosol particles. The particle size range with the filter stage is approximately from 5 nm to 200 nm, and the flow rate is 1.2 lpm. The cutpoint of the first stage is 7.7 nm, which is so far the lowest cutpoint introduced for cascade impactors. The HRLPI stages have sharp cut-curves, which improve the performance significantly when the cutpoints are brought as close to each other as in the HRLPI. The HRLPI was calibrated with monodisperse dioctylsebacate particles. The average cut-curve steepness parameter was 9.9, and for the ELPI+ the corresponding value was 3.5. The HRLPI was tested in laboratory measurements together with five other commercial instruments. The HRLPI could resolve the location of the size distribution mode down to 10 nm, whereas for the ELPI with an additional low cutpoint stage, the minimum size was around 24 nm. Measurements also showed that the HRLPI and SMPSs were the only instruments of the tested five size-distribution measurement instruments that could resolve a bimodal distribution in which the geometric mean diameters of the modes were around 15 nm and 30 nm.