An aerosol delivery unit for selectively delivering a dose of aerosolized matter, the aerosol delivery unit comprising: a base housing ; a canister at least partially received in the base housing , the canister containing matter to be aerosolized and including a valve stem that defines a portion of a discharge passageway extending from a discharge valve outlet of the canister to an inhalation passageway provided within the base housing ; a mouthpiece aperture in fluid communication with the inhalation passageway through which the aerosolized matter is discharged during an inhalation event; characterized in that , the aerosol delivery unit further comprises: a desiccant chamber containing a desiccant material, the desiccant chamber being in fluid communication with the discharge passageway at least when the aerosol delivery unit is in a storage configuration; and a seal member movable between a closed position, in which the seal member covers a discharge outlet of the discharge passageway to isolate the discharge passageway from the inhalation passageway , and an open position, in which the discharge outlet is in fluid communication with the inhalation passageway to allow the aerosolized matter to pass from the discharge passageway into the inhalation passageway for delivery to a user through the mouthpiece aperture . a base housing ; a canister at least partially received in the base housing , the canister containing matter to be aerosolized and including a valve stem that defines a portion of a discharge passageway extending from a discharge valve outlet of the canister to an inhalation passageway provided within the base housing ; a mouthpiece aperture in fluid communication with the inhalation passageway through which the aerosolized matter is discharged during an inhalation event; characterized in that , the aerosol delivery unit further comprises: a desiccant chamber containing a desiccant material, the desiccant chamber being in fluid communication with the discharge passageway at least when the aerosol delivery unit is in a storage configuration; and a seal member movable between a closed position, in which the seal member covers a discharge outlet of the discharge passageway to isolate the discharge passageway from the inhalation passageway , and an open position, in which the discharge outlet is in fluid communication with the inhalation passageway to allow the aerosolized matter to pass from the discharge passageway into the inhalation passageway for delivery to a user through the mouthpiece aperture . a desiccant chamber containing a desiccant material, the desiccant chamber being in fluid communication with the discharge passageway at least when the aerosol delivery unit is in a storage configuration; and a seal member movable between a closed position, in which the seal member covers a discharge outlet of the discharge passageway to isolate the discharge passageway from the inhalation passageway , and an open position, in which the discharge outlet is in fluid communication with the inhalation passageway to allow the aerosolized matter to pass from the discharge passageway into the inhalation passageway for delivery to a user through the mouthpiece aperture . <EOS>