A method for creating a negative bias pressure within a sealed reservoir (186, 220) for aerosolizing liquid drug, the method comprising: providing a liquid reservoir (186, 220, 410, 510) coupled with an aerosol generator, the aerosol generator comprising an aperture plate, the aperture plate having a liquid side and an air side; storing a liquid in the liquid reservoir (186, 220, 410, 510), the liquid reservoir (186, 220, 410, 510) having a headspace (130, 184) filled with air; providing a reservoir cap (150, 180, 230, 450, 530) for the liquid reservoir (186, 220, 410, 510), the cap comprising: means that permit air to exit the headspace (130, 184) through the reservoir cap (150, 180, 230, 450, 530) during sealing but that do not permit air to exit the headspace (130, 184) following sealing; and an O-ring (235, 420, 520) that maintains a seal between the reservoir cap (150, 180, 230, 450, 530) and an inner edge of the liquid reservoir; the method further comprising sealing the liquid reservoir (186, 220, 410, 510) to create the sealed reservoir via the reservoir cap (150, 180, 230, 450, 530) to fill a portion of the headspace and release air from the headspace of the liquid reservoir (186, 220, 410, 510) by the air exiting the headspace via the means permitting air to exit the headspace as the liquid reservoir (186, 220, 410, 510) is sealed using the reservoir cap (150, 180, 230, 450, 530) and passing to outside of the O-ring (235, 420, 520), and creating an airtight seal; maintaining an ambient pressure by allowing air to escape from the headspace of the liquid reservoir (186, 220, 410, 510) via the means permitting air to exit the headspace (130, 184) through the reservoir cap while the liquid reservoir (186, 220, 410, 510) is being sealed using the reservoir cap (150, 180, 230, 450, 530); maintaining the ambient pressure in the sealed liquid reservoir (186, 220, 410, 510) until a portion of the liquid is dispensed; vibrating the aperture plate to dispense a portion of the liquid thereby decreasing the amount of the liquid in the sealed reservoir and creating a negative bias pressure between the air side and the liquid side of the aperture plate. providing a liquid reservoir (186, 220, 410, 510) coupled with an aerosol generator, the aerosol generator comprising an aperture plate, the aperture plate having a liquid side and an air side; storing a liquid in the liquid reservoir (186, 220, 410, 510), the liquid reservoir (186, 220, 410, 510) having a headspace (130, 184) filled with air; providing a reservoir cap (150, 180, 230, 450, 530) for the liquid reservoir (186, 220, 410, 510), the cap comprising: means that permit air to exit the headspace (130, 184) through the reservoir cap (150, 180, 230, 450, 530) during sealing but that do not permit air to exit the headspace (130, 184) following sealing; and an O-ring (235, 420, 520) that maintains a seal between the reservoir cap (150, 180, 230, 450, 530) and an inner edge of the liquid reservoir; the method further comprising sealing the liquid reservoir (186, 220, 410, 510) to create the sealed reservoir via the reservoir cap (150, 180, 230, 450, 530) to fill a portion of the headspace and release air from the headspace of the liquid reservoir (186, 220, 410, 510) by the air exiting the headspace via the means permitting air to exit the headspace as the liquid reservoir (186, 220, 410, 510) is sealed using the reservoir cap (150, 180, 230, 450, 530) and passing to outside of the O-ring (235, 420, 520), and creating an airtight seal; means that permit air to exit the headspace (130, 184) through the reservoir cap (150, 180, 230, 450, 530) during sealing but that do not permit air to exit the headspace (130, 184) following sealing; and an O-ring (235, 420, 520) that maintains a seal between the reservoir cap (150, 180, 230, 450, 530) and an inner edge of the liquid reservoir; the method further comprising sealing the liquid reservoir (186, 220, 410, 510) to create the sealed reservoir via the reservoir cap (150, 180, 230, 450, 530) to fill a portion of the headspace and release air from the headspace of the liquid reservoir (186, 220, 410, 510) by the air exiting the headspace via the means permitting air to exit the headspace as the liquid reservoir (186, 220, 410, 510) is sealed using the reservoir cap (150, 180, 230, 450, 530) and passing to outside of the O-ring (235, 420, 520), and creating an airtight seal; maintaining an ambient pressure by allowing air to escape from the headspace of the liquid reservoir (186, 220, 410, 510) via the means permitting air to exit the headspace (130, 184) through the reservoir cap while the liquid reservoir (186, 220, 410, 510) is being sealed using the reservoir cap (150, 180, 230, 450, 530); maintaining the ambient pressure in the sealed liquid reservoir (186, 220, 410, 510) until a portion of the liquid is dispensed; vibrating the aperture plate to dispense a portion of the liquid thereby decreasing the amount of the liquid in the sealed reservoir and creating a negative bias pressure between the air side and the liquid side of the aperture plate.