Ground-level ozone is a pervasive air pollutant, which could be formed from substantial flare emissions during chemical plant start-up operations, shutdown operations and emergency events. Especially in regions where chemical plants are concentrated, the regional air-quality might be aggravated by the simultaneous planned turnaround operations of multiple chemical plants and the synergies of multiple plant start-up. It is uncontroble and unpreditive for chemical plants to experience the emergency events (unplanned operations), which generate intensive and tremendous flare emissions in a very short time. So, both planned and unplanned operations can cause highly localized and transient air-quality impacts as well as negative social effects. Flare minimization is recognized as an effective strategy for chemical plants to reduce the negative air-quality impacts and save the raw materials. In this paper, a systematic methodology has been developed for air-quality conscious study for proactive emission control under chemical plant start-up, shutdown and emergency events. The multi-scale modeling is developed to integrate process knowledge of plant shutdown emissions together with regional air-quality modeling for quantitatively investigating the sensitivity of ground-level ozone change due to an ethylene plant shutdown. It couples dynamic process simulation for chemical plant operations with regional air-quality modeling and explores cost-effective and environmentally benign air-quality control strategies. This study can provide valuable and quantitative support for all relevant stakeholders, including environmental agencies, regional plants, and local communities.