The retentions of gases upon freezing of water from available studies are conflicting. Using molecular dynamic simulations, we have revealed that the retention efficiency of NH3 upon freezing cloud is close to 0 rather than 1 during deep convection. Our results further provide theoretical framework to explain the first-ever satellite-observed high concentration of NH3 in the upper troposphere and lower stratosphere (UTLS). As NH3 emission continues to increase, this study calls upon the emergent need to assess the role of NH3 in UTLS chemistry especially in the deep convective regions. Methodologically, the molecular dynamics simulation is demonstrated as a tool for improving parameterization of interactions between trace gases and cloud (including ice) particles in global atmospheric models.