A method for collecting fine particles from flue gases onto selected collector surfaces includes leading the flue gases from a combustion chamber to a selected chamber that is part of a flow channel of the flue gasses. The selected channel is delimited by walls presenting the selected collector surfaces. Gas ions are formed with aid of a corona discharge of an ion source inside the selected chamber. The ion source includes a separate body relative to the selected chamber that is electrically passive and contains a corona electrode maintained at a high-voltage relative to the collector surfaces. The selected collector surfaces form a counter potential to the high voltage of the corona electrode. The gas ions are led to the selected chamber and mixed with the flue gases to charge the fine particles in the flue gas which are collected on the selected collector surfaces.