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[Display omitted] • Operando observation system is constructed to make in situ test on lab-on-a-chip. • Image processing method is developed based on automatic object detection. • It is first-time visualization of dynamic deposition process of submicron particle. • The growth site and direction of particle chain are investigated systematically. • This work confirms the effect of drag force on ultimate height of particle chain. Submicron particle is a harmful air pollutant due to size effect, gathering characteristic and biological activity, which not only causes a serious threat to human health and public sanitary security, but also is difficult to capture with lowest removal efficiency. Here, Operando investigation system is constructed to explore deposition characteristics of submicron particles in electric-flow coupled fields through combining microfluidic technology for forming micro electric field on the lab-on-a-chip with micro-visualization technology for capturing dynamic deposition process. Besides, based on object detection and deep learning, an image processing method is developed which can realize automatic object detection and rapid extraction of required information. Results show that particle chain grows preferentially from the convex position to prove the influence of electrode surface roughness on the growth site. The global electric field has a positive effect on keeping particle chain growing up at upright direction, and the growth process of particle chain is proposed: forming growth site stage, grow fast stage and fluctuation stage. Particle velocity in the airflow direction presents a decrease trend during the process particle migrates towards to electrode surface, which proves the direct influence of boundary layer effect on the ultimate height of particle chain. [ABSTRACT FROM AUTHOR]