Dear Colleagues,

Atmosphere dedicates this Special Issue to the characterization of airborne particulate matter by optical and electron microscopy techniques. Single-particle analytical approaches have been widely improved in the last decade, to support research addressing physico-chemical properties of airborne aerosol, and their implications on climate and health. With respect to others, optical and electron microscopy provide an added value, that is particle imaging. Scanning and transmission electron microscopy are extensively employed, to investigate the aspect, morphology and crystal properties of airborne particles, by means of different imaging techniques. These are often coupled with semiquantitative element composition of single particles, and with mapping, by energy-dispersive X-ray spectroscopy, to deeply probe the linkage between microchemical and microphysical properties.

Among optical techniques, epifluorescence microscopy is recently gaining attention, due to peculiar capabilities of discriminating among different bioaerosols.

Despite the wide variety of ambient particulate samples investigated by these techniques, some topics still remain partially unexplored, or challenging. Characterization by single-particle microscopy of samples collected along vertical profiles, or in indoor environments, would improve discriminating the local from medium/long range transport, and detailing the in/out exchange mechanisms, respectively. A more accurate evaluation of aerosol climate-relevant properties (hygroscopicity, light absorbing/scattering, etc.) will be possible by enhanced knowledge and methods targeted at describing the chemical mixing state of particles, as well as by probing the differences of matrix structure for particles within same class (e.g. crystalline or amorphous carbonaceous materials). Further exploration of the reciprocal arrangements among particles, as well as of the potential of X-ray mapping, are also needed, e.g. to support the interpretation of collinearity in source apportionment studies. Concerning analytical aspects, estimating the accuracy of X-ray microanalysis results, and comparing between recently developed advanced techniques and traditional ones, are key topics that still need targeted studies.

In this Special Issue, we seek to publish innovative papers focused on, but not limited to, above cited arguments. Cross-cutting studies providing sounded linkages among different topics are particularly welcomed.

Routine microscopy studies are out of the scope of this Special Issue, unless they concern samples from regions and environments poorly explored or of special interest.

Dr. Adriana Pietrodangelo
Guest Editor

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• Airborne Particulate Matter
• Scanning Electron Microscopy
• Transmission Electron Microscopy
• Epifluorescence Optical Microscopy
• Imaging
• Single-particle
• X-ray Microanalysis