Complex Aerosol Characterization by Scanning Electron Microscopy Coupled with Energy Dispersive X-ray Spectroscopy

Abstract

Particulate matter (PM) air pollution is a central concern for public health. Current legislation relies on a mass concentration basis, despite broad acceptance that mass alone is insufficient to capture the complexity and toxicity of airborne PM, calling for additional and more comprehensive measurement techniques. We study to what extent scanning electron microscopy coupled with energy dispersive X-ray spectroscopy (SEM/EDS) can be applied for physicochemical characterization of complex aerosols, and investigate its potential for separating particle properties on a single particle basis, even for nanosized particles. SEM/EDS analysis is performed on impactor samples of laboratory generated aerosols, consisting of either NaCl, Halloysite fibers, soot-like Printex90 agglomerates, or their combination. The analysis is automated and performed as EDS maps, covering a statistically relevant number of particles, with analysis times of approximately one hour/sample. Derived size distributions are compared to scanning mobility particle sizer (SMPS) and electric low-pressure impactor (ELPI) results. A method is presented to estimate airborne number concentrations and size distributions directly from SEM results, within a factor 10 of SMPS and ELPI outcomes. A classification scheme is developed based on elemental composition, providing class-specific information with individual particle statistics on shape, size, and mixing state. This can identify primary particles for source apportionment and enables easy distinction between fibrous and dense particle classes, e.g. for targeted risk assessments. Overall, the SEM/EDS analysis provides a more detailed physicochemical characterization of PM than online measurements, e.g. SMPS and ELPI. The method has the potential to improve assessments of PM exposure and risk, and facilitates source identification, even without prior knowledge at sampling.

Analysis of Electron Transparent Beam-Sensitive Samples Using Scanning Electron Microscopy Coupled With Energy-Dispersive X-ray Spectroscopy

“…This fits well with the sampling recommendation of Brostrøm et al (2019). Particles were only observed on the lowest impactor stage, consistent with the expected 100–200 nm sizes, as the lowest stage collects particles with diameters from 73 to 590 nm (Brostrøm et al, 2019, 2020).…”

Characterization of aerosol particles during a high pollution episode over Mexico City

“…After 13:30 LST the growth rate abruptly slows down. Garcia-Franco et al (2018) 23 and Whiteman et al (2000) 24 concluded that the maximum height reached by the ML is > 3 km a.g.l during the dry-warm season (March-May).…”

“…Based on their composition and morphology, urban aerosol particles can be classi ed as soot, tarballs (TB), mineral dust, S-rich and K-rich, sea salt, metallic, among others [20][21][22] . This classi cation can be performed by using Transmission-(TEM) and Scanning electron microscopy (SEM) techniques coupled with the energy dispersed X-ray detector (EDX or EDS) 19,20,23 .…”

Spatial Image Resolution Assessment by Fourier Analysis (SIRAF)

“…For brevity, we will in this work mainly be considering scanning electron microscopy (SEM), but the algorithm can be applied to many other imaging techniques. SEM is a powerful tool used in a broad range of scientific fields including material science, biology, nanotechnology, and medical research (Mumpton & Ormsby, 1976;Dalgleish et al, 2004;Nie et al, 2015;Conti et al, 2018;Brostrøm et al, 2019Brostrøm et al, , 2020Shah et al, 2019). A common use of the instrument is to measure dimensions of objects or structures at the nano and micrometer scales (Crouzier et al, 2019).…”