脉动相对湿度方法观测由体相及界面控制的气溶胶传质过程

设计搭建了可以控制样品室内相对湿度发生脉动式变化的压力控制装置。将这种装置与真空红外快速扫描技术联用，采集的时间分辨傅里叶变换红外光谱可以提供在亚秒时间尺度内，脉动相对湿度的准确数值以及湿度变化过程中气溶胶颗粒的含水量。分析这些数据可以了解相对湿度脉动变化过程中气溶胶的动态吸湿特性。选择硝酸钠，硫酸镁和硝酸镁三种无机盐气溶胶为研究对象，比较了他们在相对湿度发生脉动变化和准稳态变化条件下的吸湿特性。结果发现，实验0.12 s的时间分辨率下不足以观察到水在硝酸钠气溶胶和环境之间的传质受阻过程。而对于老化的硫酸镁气溶胶颗粒，胶态的形成减缓了水的扩散速率，体相传质成为速控步骤。对于老化的硝酸镁气溶胶颗粒，由于在颗粒表面难溶物的生成和富集，使得界面水的传质速率成为气溶胶与环境发生传质的决定性因素。这证明脉动压力变化装置与快速扫描真空红外联用可以有效便捷地观测区分体相和界面控制的气溶胶传质过程。

A Relative Humidity Pulse Approach to Observe Mass Transfer Processes Controlled by Bulk and Surface for Aerosols

With combination of a pulse relative humidity (RH) controlling system and rapid scan vacuum FTIR technique, dynamic hygroscopicity of aerosol can be studied during pulse RH process. The time-resolved FTIR spectra can provide both water content of aerosols and water vapor amount of the aerosol ambient in sub-second time resolution. Experiments were performed on sodium nitrate, magnesium sulfate and magnesium nitrate aerosols. By comparing their hygroscopicity in pulse RH process and quasi-equilibrium state, for sodium nitrate aerosols, under time resolution of 0.12 s, we didn’t see water transfer delay between aerosols and ambient environment. For magnesium sulfate aerosols, after gel formation, the water transfer speed is limited by the aerosol bulk phase. While for aged magnesium nitrate aerosols, non-soluble species generated and formed a film on the surface of aerosol particles, which slow down the water exchange rate between aerosols and ambient environment. This method turned out to be an efficient and convenient tool to elucidate the water transfer process controlled by bulk and surface for aerosols.