Season linked responses to fine and quasi-ultrafine Milan PM in cultured cells

► In vitro biological effects of Milan summer and winter PMs. ► PM0.4 and PM1 biological effects and morphological features are partly similar. ► Winter PMs induce ROS and γH2AX in relation to the organic content. ► Endotoxins and metals enriched summer PM10 induces pro-inflammatory response. ► Chemical composition of particles determines the biological responses elicited.