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In the last three decades,huge efforts have been taken to improve understanding of the relationship between ambient nucleation of new particles and its impact on the climate in marine boundary layer (MBL),e.g.,CLAW hypothesis and studies related.However,only >40-50 nm new particles could be activated as cloud condensation nuclei (CCN) under typical range of water supersatuations occurring in MBL.The knowledge gap still existed,i.e.,which chemicals are critical factors in growing nucleated particles to CCN size in MBL.In this study,we found that nucleated particles in MBL cannot grow over 40 nm in absence of strong formation of NH4NO3.However,the strong formation of NH4NO3 together with organics can grow nucleated particles close to or over 50 nm in MBL.These indicate that the strong formation of NH4NO3 is a critical factor to grow nucleated particles to CCN size in MBL.However,the strong formation of NH4NO3 occurred only in polluted air mass in MBL.Thus,ambient nucleation of new particles in clear and remote MBL is probably not a source of CCN due to lack of a strong formation of NH4NO3 and the nucleation may have no impact on the climate.