Abstract
Sampling on different substrates is commonly used in laboratory and field studies to investigate the morphology and mixing state of aerosol particles. Our focus was on the transformations that can occur to the collected particles during storage, handling, and analysis. Particle samples were prepared by electrostatic deposition of size-classified sodium chloride, sulfuric acid, and coated soot aerosols on different substrates. The samples were inspected by electron microscopy before and after exposure to various environments. For coated soot, the imaging results were compared against mass-mobility measurements of airborne particles that underwent similar treatments. The extent of sample alteration ranged from negligible to major, depending on the environment, substrate, and particle composition. We discussed the implications of our findings for cases where morphology and the mixing state of particles must be preserved, and cases where particle transformations are desirable.
Highlights
Atmospheric aerosols play a major role in regional air quality and global climate [1,2,3,4]
We examined aerosol particles composed of sodium chloride, sulfuric acid, untreated soot, and sulfuric acid-coated soot
The untreated particles appeared as cubes with well-defined edges (Figure 2a) because the expected, the untreated particles appeared as cubes with well-defined edges (Figure 2a) because the highest relative humidity (RH) experienced by these particles during sample manipulation never exceeded 50%, which is highest RH experienced by these particles during sample manipulation never exceeded 50%, which well below the 75% deliquescence RH of sodium chloride
Summary
Atmospheric aerosols play a major role in regional air quality and global climate [1,2,3,4]. The effects of aerosols are highly dependent on the particle number concentration, and on the particle size, composition, mixing state, phase state, and morphology. The knowledge of these properties is crucial for an accurate prediction of the environmental impacts of aerosols. The samples are stored for hours, days, or even months, before being transported to the analysis facility, either by the researcher or over a commercial carrier. The samples are analyzed by the researcher or by the facility staff. Electron microscopy (EM) is a widely used off-line technique for particle analysis because it can provide a direct evaluation of the particle size and Atmosphere 2017, 8, 162; doi:10.3390/atmos8090162 www.mdpi.com/journal/atmosphere
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