The contact electrification of aerosolized micron-scale oxide particles has been investigated experimentally and the size and composition dependence determined. The net charge acquired by particles contacting the aerosolizer was seen to increase linearly with their surface area. A physically meaningful model based upon electron transfer has been applied leading to a predictive expression for the total particle surface charge concentration generated (a) dependent on the absolute generalized relative electronegativity (chi(AGR)); sigma = a chi(AGR) - b, where a = 4.7 e/mu m(2)/V, b = -27 e/mu m(2) and chi(AGR) is obtained by knowing the composition of the two contacting surfaces. The influence of relative humidity and particle cohesion on the contact electrification process was investigated. A maximum surface charge concentration of around 100 e/mu m(2) was found, in agreement with previous work. (C) 2018 The Authors. Published by Elsevier B.V.