An aerosol distributor and an arrangement for filter leakage detection in a gas filtration system comprising such aerosol distributor, the aerosol distributor being configured to be positioned in a gas stream upstream of a filter, said aerosol distributor comprising: a hollow housing having at least one aerosol inlet for admitting an aerosol from an aerosol source into a chamber inside said housing, and a plurality of aerosol outlet holes for releasing the aerosol from the chamber into a gas stream surrounding the housing, wherein said housing has a plate like shape having an upstream surface configured to face an incoming gas stream and a downstream surface configured to face a filter, wherein said housing comprises a plurality of channels extending between channel inlets at the upstream surface and channel outlets at the downstream surface of the housing, such that gas from the gas stream can pass through the housing.