The present disclosure relates to an humidification attachment module (66) arranged to be coupled with an air treatment apparatus (10), the module comprising a fluid dispensing unit (88) for a humidification fluid that is supplied by a fluid reservoir (86), a flow inlet (74) for an inlet air flow (120), a first flow path defined between the flow inlet (74) and a first flow outlet (76), a second flow path defined between the flow inlet (74) and a second flow outlet (78), and a flow dividing unit (100), wherein the first flow path bypasses the fluid dispensing unit (88), wherein the second flow path passes through the fluid dispensing unit (88), and wherein the flow dividing unit (100) is operable to divide an overall flow through the humidification module into a first flow path component (122) and a second flow path component (124). The present disclosure further relates to air treatment apparatus (10) and to a method of augmenting an air treatment apparatus (10).