Performance evaluation of the HR-ELPI + inversion

Data inversion methods used in aerosol measurement instruments have significant influence on the resolution and quality of the result. A freshly launched new electrical low pressure impactor (ELPI) instrument version, high resolution ELPI+ (HR-ELPI+, Dekati Ltd.), uses an iterative inversion calculation method to improve particle size resolution, concentration, and data analysis quality. In this article, the performance of the HR-ELPI + is critically analyzed by simulations and experiments in laboratory and field conditions, and the results are compared with a conventional inversion data analysis method (cut-point diameter concept) and with common reference instruments (e.g., SMPS and EEPS). The results showed that the HR-ELPI + inversion has limited performance at the lower and upper limits of the instrument’s size range, and can suffer if the raw currents have signal dependent noise more than 50% or electric noise more than 1%. However, the HR-ELPI + clearly provide remarkably better resolution and quality with low oscillation risk compared to the conventional cut-point diameter concept of the ELPI. The HR-ELPI + also showed generally very similar size distributions and number concentrations compared to the reference instruments.