A cartridge 100 is provided for use in an aerosol-generating system 10 for the generation of an aerosol comprising nicotine salt particles. The cartridge 100 comprises a first compartment 110 comprising a nicotine source 210 comprising a first carrier material 211 impregnated with nicotine, the first compartment 110 being a first air inlet (132) and a first air outlet (133). The first compartment 110 is a first air flow path 217 extending over the first surface 213 of the first carrier material 211 between the first air inlet 132 and the first air outlet 133 Is defined. The cartridge 100 also includes a second compartment 120 comprising an acid source 220 comprising a second carrier material 221 impregnated with acid, and the second compartment 220 It has an inlet port 134 and a second air outlet port 135. The second compartment 220 is a second airflow path 227 extending over the first surface 223 of the second carrier material 221 between the second air inlet 134 and the second air outlet 135 Is defined. The first partition 110 and the second partition 220 are arranged in parallel in the cartridge 100. The thickness of at least one of the first carrier material 211 and the second carrier material 221 is respectively changed in a direction along the first airflow path 217 or the second airflow path 227, respectively.