An experimental investigation into the atomization characteristics of an annular swirling sheet generated by an airassist atomizer is carried out. In this study, water and air are considered as the working fluid and assisting fluid in the atomization process respectively. A high-speed shadowgraphy technique is used to capture the instantaneous spray structure. The effects of various operating parameters such as central air/annular liquid mass flow rate and degree of liquid preheating are investigated on spray cone angle and the breakup length of the conical sheet and large-scale instabilities. We have found that breakup length variation is insensitive to the liquid preheating; however, spray cone angle is observed to increase with increasing temperature. At a given fluid pressure, increasing the central airflow rate shortens the breakup length of the spray. Besides it, Proper Orthogonal Decomposition (POD) analysis is carried out to understand the coherent spatial structures. © 2023, The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd.