As an important reactive trace gases in the troposphere, nitryl chloride (ClNO₂) has significant impacts on atmospheric oxidation capacity, the degradation of primary pollutants and the formation of secondary pollutants, and plays indispensable roles in global cycles of both nitrogen and chlorine. In this paper, we introduce basic properties of ClNO₂ as well as its formation and removal mechanisms in the troposphere, and describe in brief techniques currently used in laboratory and field work to measure ClNO₂. In addition, we review spatial and temporal distributions of tropospheric ClNO₂ over the globe as reported in the last 10~20 years, discuss in a systematical manner chemical mechanisms and environmental factors which determine its heterogeneous formation in the atmosphere via critical analysis of important results from laboratory studies and field measurements, and summarize impacts of ClNO₂ on chlorine radicals, atmospheric oxidation capacity as well as the formation of O₃ and nitrate aerosol. We emphasize that ClNO₂ couples gas phase chemistry and heterogeneous chemistry, and also couples nocturnal atmospheric chemistry with daytime photochemistry, thus very likely playing an important role in the formation of air pollution complex in China. Important questions which remain to be answered to better understand atmospheric chemistry of ClNO₂ are outlined at the end, and we also discuss in brief how these questions can be addressed in future work.