A conceptual diagram for the seasonal variation of the photochemistry and a new O₃ pollution control strategy. (A) From a phenomenon perspective, high and conserved total oxidants were observed from hot to cool seasons in Eastern Chinese conurbations despite a decrease of temperature and solar radiation and increase of NO₂ concentrations. In the framework of the new control strategy, the photochemical O₃ production is split into two components: primary RO_x production and the amplification factor during the OH-HO₂-RO₂ radical cycling (often noted as ChL). In the cool seasons, it is in fact the radical precursors, in addition to the widely regulated species—NO_x and VOCs, that are worth considering as mitigation subjects for the control of primary RO_x production. (B), (C) O₃ relative incremental reactivity of NO_x, VOCs and primary RO_x productions during warm and cool seasons.