Measurement of particle density by inertial classification of differential mobility analyzer–generated monodisperse aerosols

A density measurement technique based on the selection of a monodisperse aerosol with a differential mobility analyzer followed by classification according to aerodynamic diameter with an impactor has been designed and tested. Experimental results were obtained for several laboratory aerosols (dioctyl phthalate, (NH₄)₂SO₄NaCl, and H₂SO₄ at a range of humidities) by using four different microorifice uniform deposit impactor stages with aerodynamic diameter cut-offs of 0.12–0.56 Jim. The average error in measured particle densities is 4% and a maximum error of 8% is observed for all of the materials tested except NaCl, for which the measured effective density is 14% smaller than the true density. The discrepancy for NaCl is attributed to nonspherical particle shape. The system will be applied in the future to measure the densities of submicrometer atmospheric particles.