The particle size distribution and concentration were measured in real time by means of an electrical low pressure impactor (ELPI, Dekati Ltd., Finland). There are 13 stages (12 channels), and the measurement size range is 0.023–9.314 lm aerodynamic diameter.
The cut-off diameter of each stage and median diameter of each channel are shown in Table 1. The Dp using in the following figures is the median diameter, which divides the cumulative number concentration distribution in half, fifty percent of the particle
number has particles with a larger diameter, and fifty percent of the particle number has particles with a smaller diameter. A Sogevac model SV25 vacuum pump was operated at a pressure drop of 100 mbar across the ELPI, resulting in an air flow rate of 10 L/min through the impactor.