A purification method comprises providing a purification device comprising at least one exhaust gas purification member having an upstream surface through which the exhaust gas enters the purification member and a downstream surface through which the exhaust gases exit the purification member. The method further includes, in the absence of forced circulation of the exhaust gas through the purification member by an engine of the vehicle, heating radiatively at least either the upstream zone or the downstream zone, for example before starting the engine of the vehicle.