PM_2.5 and O₃ are two major air pollutants. Some mitigation strategies focusing on reducing PM_2.5 may lead to substantial increase in O₃. We use statistical emulation combined with atmospheric transport model to perform thousands of sensitivity numerical studies to identify the major sources of PM_2.5 and O₃ and to develop strategies targeted at both pollutants. Our scientific evidence suggests that regional coordinated emission control is required to mitigate PM_2.5 whilst preventing O₃ increase.