FTIR-ATR (Attenuated Total Reflection) and microscopic imaging technique were used to observe the crystallization kinetics of NaNO3 aerosol through stepwise changes of ambient humidity. The repeated experiments showed that NaNO3 droplets have subsequently effloresced post the saturation point of RH 74. 5%. Furthermore, the crystallization rate obviously increases after the environmental RH reaching the efflorescence point. However, the NaNO3 crystallization rate is not accelerated by the humidity decreases. Instead, it is related to the varying rate of RHs. Non-linear fitting of experimental results reveals that there lies in an exponential relationship for the crystallization rate during RH reduction, while linear fitting takes place when the RH is maintained stable. Through the microscopy, bigger droplets were observed to crystallize faster than smaller droplets at higher RH despite the same order of magnitude of the droplets.%阶梯状改变环境湿度,利用FTIR-ATR(Attenuated Total Reflection)技术以及显微成像技术观察NaNO3气溶胶微粒的结晶动力学.多次实验证实NaNO3液滴在饱和点74.5％RH之后开始陆续风化,至风化点53％RH之后结晶速率明显增快,但并不是相对湿度越低,结晶速率越快,而是相对湿度的变化率越大,结晶速率越快.对数据进行非线性拟合发现在湿度下降处结晶速率呈指数关系,在湿度稳定時结晶速率呈线性关系.并且通过显微镜观察到尽管样品NaNO3液滴的直径在同一个数量级上,仍能看出结晶速率与液滴半径关系紧密,半径越大越易结晶,结晶的相对湿度越高.
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