The goal is to develop an aerosol charger based on a corona discharge for atmospheric concentration measurements (103-105 cm-3) within a response time of 100 ms.
Two ion sources, point-to-hole and wire-to-slit have been characterized. The increase of the ion flow in the post-discharge by EHD ion confinement in both the discharge gap and the hole has been shown.
At first, using an experimental survey driven in two mixing configurations, concentric and face-to-face, we have confirmed the aerosol diffusion charging law which depends on aerosol diameter and Ni.t product, with Ni, the ions concentration and t, the charging time. Thus, the originality of this charger relies on the very high heterogeneity of unipolar ion densities (Ni0 >109 cm-3) required to compensate the charging time of 50 ms. In these conditions, we have shown that aerosol diameter and the charging dynamic (which depends also on the diameter) control the aerosol trajectory.
The chargers have, next, been compared in different operating conditions, mainly in terms of the maximal charging and the minimal losses. In the chosen charger (point-to-hole ion source and concentric mixing), the relations charge/mobility and losses according to diameter have been characterized. We have also shown the linearity of the charged particles current with the aerosol concentration which allows the current-concentration data inversion.
The preliminary measurement system composed by the charger, the separator and the particle current measurements, satisfies the objectives of the study in terms of the concentration detection limit (103 cm-3) and the response time (100 ms).
We have thus shown the feasibility of an atmospheric aerosol concentration measurement system at 10 Hz using a corona discharge charger provided that the separation power is improved. Furthermore, knowing that aerosol losses are negligible and the lower limit of the partial charging, the developed charger is adaptable with other application.