利用一种自制的湿度调节设备与真空红外光谱仪相结合, 提出了一种研究醋酸镁气溶胶的吸湿性和传质动力学的新方法。 湿度调节装置通过改变纯水汽压力来调节样品室的相对湿度, 这样可以实现湿度以不同的速度发生变化。 与红外光谱手段相结合, 湿度缓慢变化, 让气溶胶时刻处于准稳态过程, 可以研究气溶胶在热力学稳态的吸湿性质。 湿度脉冲式改变, 可以研究气溶胶的动态吸湿性质以及传质动力学过程。 红外光谱的扫描方式随着湿度的改变速度进行调节。 由于实验中的相对湿度由纯水气提供, 因此通过对红外方光谱中纯水气的特征吸收峰面积的定量计算获得与光谱同步的相对湿度值。 研究发现, 当湿度稳定在一个高湿度时, 醋酸根和液态水的峰面积在持续下降。 并且首次发现经过一个准稳态的湿度循环后(1.05×104 s), 在80%RH条件下, 水峰面积由1.5降低至1.1。 通过改变实验方案并对其结果进行对比可知, 在高湿度条件下, 醋酸镁发生水解, 生成的醋酸由于样品室内的负压而挥发, 因此引起气溶胶含水量下降。 采用脉冲发式快速改变样品室的湿度, 一个湿度脉冲循环需要10 s。 计算脉冲循环过程中气溶胶的含水量发现, 在湿度高于70%RH时, 气溶胶含水量没有减少。 但是加湿过程的水传输比去湿过程的水传输快。 这些现象说明醋酸镁的水解速率小于湿度的脉冲改变速率。 在湿度快速变化的过程中, 气溶胶液滴表面难溶物的形成引起水传输发生受阻现象。

A combination of vacuum FTIR spectrometer (Vertex 80v, Bruker, German) and novel relative humidity (RH) adjusting equipment,which provides the pressure by pure water vapor, is used to study the hygroscopicity of magnesium acetate (Mg(CH3COO)2) aerosols. The RH can change not only rapidly but also slowly by the RH adjusting equipment.Because the RH is decided by the pure vapor, the real-time RH can be gained by calculating the integrated intensity of a feature band of vapor in an IR spectrum. Such the synchronism between FTIR spectrum and RH canbe ensured.The high-quality spectra of aerosols are obtained and the water peak and feature peaks of Mg(CH3COO)2 are analyzed during the slow and rapid RH changing process.The result shows that the areas of acetate ions and water decreases continuously at constant high RHs. After a slow cycle of RH (1.05×104 minutes), the water area decreases from 1.5 to 1.1, which means that the water content decreases after a cycle of RH. This phenomenon is reported at first up to date. The detailed analysis suggests that the hydrolysis of Mg(CH3COO)2 at high RH produces acetic acid, which was put out from the aerosols owing to the decrease of the pressure around the aerosols droplets. Furthermore, the dynamic hygroscopicity of Mg(CH3COO)2 aerosols is studied by changing RH as a pulse mode. It reveals that there is only water transfer hysteresis and no water loss after a pulse (10 seconds) when the RH is above 70%. Compared to slow process, it can be concluded that the hydrolysis reaction rate is slower than that of a pulse RH. The water transfer limited on rapid process should rise from some species on the surface of aerosols.