A kit of parts for assembly into an impactor for aerosol component collection, such as for exhaled breath, the kit comprising: a housing configured to define an aerosol inlet for receiving an aerosol sample in use and, when the kit of parts is assembled into the impactor, to define at least in part an aerosol flow path from the aerosol inlet through the impactor; an impactor component receivable into an assembly providing the impactor, the assembly comprising at least the housing, and the impactor component having an impaction surface onto which one or more aerosol components from the aerosol sample are to be deposited in use; and a sealing component for sealing around the impaction surface of the impactor component, the sealing component being changeable from a sample collection configuration in which the impaction surface is exposed for aerosol component collection to a sample containment configuration in which the impaction surface is isolated from the external environment; the kit of parts being configured such that: the impactor component is receivable into the assembly such that, when the sealing component is in the sample collection configuration and an aerosol sample is being received at the aerosol inlet in use, the aerosol flow path of the aerosol sample is directed onto the impaction surface to promote aerosol deposition thereon; and characterized in that the kit of parts is further configured such that the sealing component is changeable in the assembly into the sample containment configuration before removal of the impactor component from the assembly, so as to retain any aerosol components deposited on the impaction surface. a housing configured to define an aerosol inlet for receiving an aerosol sample in use and, when the kit of parts is assembled into the impactor, to define at least in part an aerosol flow path from the aerosol inlet through the impactor; an impactor component receivable into an assembly providing the impactor, the assembly comprising at least the housing, and the impactor component having an impaction surface onto which one or more aerosol components from the aerosol sample are to be deposited in use; and a sealing component for sealing around the impaction surface of the impactor component, the sealing component being changeable from a sample collection configuration in which the impaction surface is exposed for aerosol component collection to a sample containment configuration in which the impaction surface is isolated from the external environment; the kit of parts being configured such that: the impactor component is receivable into the assembly such that, when the sealing component is in the sample collection configuration and an aerosol sample is being received at the aerosol inlet in use, the aerosol flow path of the aerosol sample is directed onto the impaction surface to promote aerosol deposition thereon; and characterized in that the kit of parts is further configured such that the sealing component is changeable in the assembly into the sample containment configuration before removal of the impactor component from the assembly, so as to retain any aerosol components deposited on the impaction surface. the impactor component is receivable into the assembly such that, when the sealing component is in the sample collection configuration and an aerosol sample is being received at the aerosol inlet in use, the aerosol flow path of the aerosol sample is directed onto the impaction surface to promote aerosol deposition thereon; and characterized in that the kit of parts is further configured such that the sealing component is changeable in the assembly into the sample containment configuration before removal of the impactor component from the assembly, so as to retain any aerosol components deposited on the impaction surface.