A cartridge for use in an aerosol-generating system, the cartridge comprising: a first compartment having a first air inlet and a first air outlet, the first compartment containing a nicotine source; and a second compartment having a second air inlet and a second air outlet, the second compartment containing an acid source; wherein the first compartment comprises a first air flow channel extending from the first air inlet, or the first air outlet, longitudinally along at least a portion of the first compartment, wherein the first air flow channel is adjacent to and in fluid communication with the nicotine source; or wherein the second compartment comprises a second airflow channel extending from the second air inlet, or the second air outlet, longitudinally along at least a portion of the second compartment, wherein the second air flow channel is adjacent to and in fluid communication with the acid source; or wherein the first compartment comprises a first air flow channel extending from the first air inlet, or the first air outlet, longitudinally along at least a portion of the first compartment, wherein the first air flow channel is adjacent to and in fluid communication with the nicotine source; and the second compartment comprises a second air flow channel extending from the second air inlet, or the second air outlet, longitudinally along at least a portion of the second compartment, wherein the second air flow channel is adjacent to and in fluid communication with the acid source, wherein at least one of the first air flow channel and the second air flow channel is at least partially defined by one or more protrusions extending from an interior wall of the respective first compartment or second compartment, and wherein the one or more protrusions are configured to provide support for the nicotine source or the acid source. a first compartment having a first air inlet and a first air outlet, the first compartment containing a nicotine source; and a second compartment having a second air inlet and a second air outlet, the second compartment containing an acid source; wherein the first compartment comprises a first air flow channel extending from the first air inlet, or the first air outlet, longitudinally along at least a portion of the first compartment, wherein the first air flow channel is adjacent to and in fluid communication with the nicotine source; or wherein the second compartment comprises a second airflow channel extending from the second air inlet, or the second air outlet, longitudinally along at least a portion of the second compartment, wherein the second air flow channel is adjacent to and in fluid communication with the acid source; or wherein the first compartment comprises a first air flow channel extending from the first air inlet, or the first air outlet, longitudinally along at least a portion of the first compartment, wherein the first air flow channel is adjacent to and in fluid communication with the nicotine source; and the second compartment comprises a second air flow channel extending from the second air inlet, or the second air outlet, longitudinally along at least a portion of the second compartment, wherein the second air flow channel is adjacent to and in fluid communication with the acid source, wherein at least one of the first air flow channel and the second air flow channel is at least partially defined by one or more protrusions extending from an interior wall of the respective first compartment or second compartment, and wherein the one or more protrusions are configured to provide support for the nicotine source or the acid source.