Effect of sampling in the evaluation of particle size distribution in nanoaerosols

The isokinetic sampling procedure is adopted to avoid errors in important parameters (particle concentration, collection efficiency, etc.) in aerosol studies. To attain isokinecity in a given sampling can be costly or difficult to control. This study aims at evaluating the behavior of nanometric particles in the laminar aerosol flow for various conditions of non-isokinetic sampling. Polydispersed sodium chloride (NaCl) particles dispersed in an extra pure air current were used as a test aerosol. The analysis was based on comparisons of size distribution measurements of the particles collected using different sampling nozzles and v1/v2 ratios (i.e. between the velocity in the main duct, v1, and at the nozzle, v2). The results show that the size distribution was an independent ratio, for a given sampling nozzle. Also, the sampling size distribution did not depend on the ratio between the diameter of the sampling nozzle and that of the main flow duct in the system. Based on these findings, it can be concluded that, within the particle size range of 12.0–130.0 nm, duct Re < 600, duct/sampling velocity ratio (v1/v2) ranging from 0.28 to 6.25 and small particle Stokes number (St') ranging from 2.7 × 10−7 to 1.1 × 10−5, the effects of non-isokinetic sampling at the particle size distribution are negligible.

With polydispersed NaCl particles used as test aerosol, isokinetic and non-isokinetic sampling tests were performed in a circular duct. Different sampling nozzles and v1/v2 ratios (i.e. between the velocity in the main duct, v1, and at the nozzle, v2) were tested. The results show that, within the particle size range of 12.0–130.0 nm, duct Re < 600, duct/sampling velocity ratio (v1/v2) ranging from 0.28 to 6.25 and small particle Stokes number (St') ranging from 2.7 × 10−7 to 1.1 × 10−5, the effects of non-isokinetic sampling at the particle size distribution are negligible.Figure optionsDownload as PowerPoint slide