Fine particle losses in electrical low-pressure impactor

The fine particle losses in the individual impactor stages of the electrical low-pressure impactor (ELPI) were studied. Three different loss mechanisms were considered: diffusion, space charge, and image charge deposition. Diffusion losses were determined experimentally in particle size range of 10– 400 nm . The measured values varied from 0.1 to 6% depending on particle size and impactor stage. In the measurement range of the instrument, i.e. above 30 nm , the losses were below 2%. Image charge losses exceeded the diffusion losses when particle size was larger than 200 nm , but even the combined loss in this size range was below 0.5%. Space charge losses were determined both experimentally and through calculations. The space-charge effect was found to be a dominant loss mechanism in ELPI when measured concentrations were high.