Laboratory Studies of Contact Efflorescence

随着大气相对湿度的循环，盐水气溶胶以离子盐或离子水溶液的形式存在。过饱和和欠饱和相变通常表现出滞后行为作为相对湿度的函数。当相变从固体颗粒突然转变为饱和水溶液时的（增加的）RH是潮解相对湿度（DRH）。干燥的水滴在结晶之前保持过饱和溶胶状态的下降相对湿度，称为风化相对湿度（ERH）。风化可以基于成核机制而不同，通过与种子接触或将该种子浸入过饱和液滴中。一系列实验室调查的目的是进一步研究接触风化相比，浸泡风化的气溶胶类型和尺寸的大气颗粒的代表。在一个单一的液滴光学陷阱气溶胶相变将被用来系统地遵循风化机制。考虑气溶胶粒子相变的重要性包括对非均匀化学过程、光散射、云的形成和降水的影响。对均相（气相）化学和气候的直接影响也仍然不确定。

As atmospheric relative humidity cycles, saline aerosols exist either as ionic salts, or as aqueous ionic solution. Supersaturated and undersaturated phase change typically demonstrate hysteresis behavior as a function of relative humidity. The (increasing) RH at which the phase transition abruptly changes from solid particle to a saturated aqueous solution is the deliquescence relative humidity (DRH). The decreasing RH that drying aqueous droplets remain as supersaturated sols until crystallization, is the efflorescence relative humidity (ERH). Efflorescence may differ based on the nucleation mechanism, either by contact with a seed, or immersion of that seed into the supersaturated droplet. The objective of a series of laboratory investigations is to further study contact efflorescence compared to immersion efflorescence on aerosol types and sizes representative of atmospheric particles. Aerosol phase changes in a single droplet optical trap will be used to systematically follow efflorescence mechanisms. The importance of accounting for aerosol particle phase changes includes effects on heterogeneous chemical processes, light scattering, and cloud formation and precipitation. Direct effects on homogeneous (gas phase) chemistry and climate also remain uncertain.