Charged nanoparticle formation from humidified gases with and without dilute benzene under electron beam irradiation

The nucleation of aerosols in a field of high-density free radicals, ions, and secondary thermalized electrons was studied by irradiating air, N-2, O-2, and Ar containing different water contents with electron beams. The charged nanoparticles in the irradiating gases were analyzed by a cluster differential mobility analyzer equipped with a Faraday cup electrometer. All experiments with humidified gases formed both positively and negatively charged particles with mean mobil. equiv. diameters (D-m) range of 7-10 nm and with the same number concentration (N) as well as water ion clusters with D-m range of 1.0-1.1 nm. The N of these large particles increased with water content and absorbed dose. The experimental result showed that hydrogen peroxide was contained in these large charged particles as its part. In the presence of ppbv-level benzene, the D-m and N of large charged particles increased with benzene concentration, although their D-m were constant at different doses. (C) 2003 Elsevier Ltd. All rights reserved.