Related Experiment Video
Updated: Apr 3, 2026

Experimental Protocol to Investigate Particle Aerosolization of a Product Under Abrasion and Under Environmental Weathering
Published on: September 16, 2016
Structural Change of Aerosol Particle Aggregates with Exposure to Elevated Relative Humidity
James F Montgomery1, Steven N Rogak1, Sheldon I Green1
1Department of Mechanical Engineering, The University of British Columbia , Vancouver, Canada V6T 1Z4.
Abstract:
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.
Related Concept Videos
Unsoundness of Aggregate due to Volume Change
The Colloidal State
Precipitate Formation and Particle Size Control
The obtained precipitate should be either a pure substance of known composition or easily converted to one by a simple process, such as ignition or drying. In addition, the precipitate should be insoluble and easily filterable. In general, filterability...
Porosity and Absorption of Aggregate
When all pores in an aggregate are filled with water, the aggregate is considered saturated and surface-dry. If left in dry air, water will evaporate until the...
Moisture Content and Bulking of Aggregate
When aggregates are exposed to rain or sit in stockpiles, they absorb moisture, which must be...
Colloidal precipitates

