Department of Mechanical Engineering, The University of British Columbia , Vancouver, Canada V6T 1Z4.
Department of Chemistry, The University of British Columbia , Vancouver, Canada V6T 1Z1.
Environ Sci Technol. 2015 Oct 20;49(20):12054-61. doi: 10.1021/acs.est.5b03157. Epub 2015 Oct 2.
Structural changes of aggregates composed of inorganic salts exposed to relative humidity (RH) between 0 and 80% after formation at selected RH between 0 and 60% were investigated using a tandem differential mobility analyzer (TDMA) and fluorescence microscopy. The TDMA was used to measure a shift in peak mobility diameter for 100-700 nm aggregates of hygroscopic aerosol particles composed of NaCl, Na2SO4, (NH4)2SO4, and nonhygroscopic Al2O3 as the RH was increased. Aggregates of hygroscopic particles were found to shrink when exposed to RH greater than that during the aggregation process. The degree of aggregate restructuring is greater for larger aggregates and greater increases in RH. Growth factors (GF) calculated from mobility diameter measurements as low as 0.77 were seen for NaCl before deliquescence. The GF subsequently increased to 1.23 at 80% RH, indicating growth after deliquescence. Exposure to RH lower than that experienced during aggregation did not result in structural changes. Fluorescent microscopy confirmed that aggregates formed on wire surfaces undergo an irreversible change in structure when exposed to elevated RH. Analysis of 2D movement of aggregates shows a displacement of 5-13% compared to projected length of initial aggregate from a wire surface. Surface tension due to water adsorption within the aggregate structure is a potential cause of the structural changes.
采用串联式差分迁移率分析仪（TDMA）和荧光显微镜研究了在 0 至 60%之间的选定相对湿度（RH）下形成后，暴露在 0 至 80%RH 之间的无机盐聚集物的结构变化。TDMA 用于测量由 NaCl、Na2SO4、（NH4）2SO4 和非吸湿性 Al2O3 组成的吸湿气溶胶颗粒的 100-700nm 聚集物的峰值迁移率直径随 RH 增加而发生的偏移。当暴露于高于聚集过程中 RH 的 RH 时，吸湿颗粒的聚集物被发现收缩。对于较大的聚集物和较大的 RH 增加，聚集重构的程度更大。在潮解之前，从迁移率直径测量计算出的生长因子（GF）低至 0.77 就可观察到 NaCl 的 GF。随后在 80%RH 时增加到 1.23，表明潮解后发生了增长。暴露于低于聚集过程中经历的 RH 不会导致结构变化。荧光显微镜证实，暴露在升高的 RH 下，在金属丝表面形成的聚集物会发生结构不可逆的变化。对聚集物二维运动的分析表明，与从金属丝表面初始聚集物的投影长度相比，有 5-13%的位移。由于水在聚集结构内的吸附引起的表面张力是结构变化的潜在原因。
