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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0.12s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。
The pressure control device is designed to control the pulsation of the relative humidity in the sample chamber. Combined with the rapid vacuum IR scanning technique, time-resolved Fourier transform infrared spectroscopy was acquired to provide accurate values of the relative humidity of the pulsation in the sub-second time scale and the moisture content of the aerosol particles during the humidity change. Analyzing these data will provide insight into the dynamic hygroscopic nature of aerosols during changes in relative humidity fluctuations. Three kinds of inorganic salt aerosols, sodium nitrate, magnesium sulfate and magnesium nitrate, were selected as the research objects to compare their hygroscopicity under fluctuating and quasi-steady-state changes of relative humidity. It was found that the time resolution of 0.12 s was not sufficient to observe the mass transfer of water between the sodium nitrate aerosol and the environment. For aged magnesium sulfate aerosol particles, the formation of colloids slowed down the diffusion rate of water, and mass transfer became a speed-controlled step. For aged magnesium nitrate aerosol particles, the mass transfer rate of interface water becomes the decisive factor of mass transfer between aerosol and environment due to the formation and enrichment of insoluble matter on the particle surface. This proves that the pulsating pressure changing device and the rapid scanning vacuum infrared can effectively and conveniently observe the mass transfer and the interface controlled aerosol mass transfer process.