Abstract

Abstract. Atmospheric particles experience various physical and chemical processes and change their properties during their lifetime. Most studies on atmospheric particles, both in laboratory and field measurements, rely on analyzing an ensemble of particles. Because of different mixing states of individual particles, only average properties can be obtained from studies using ensembles of particles. To better understand the fate and environmental impacts of atmospheric particles, investigations on their properties and processes at a single-particle level are valuable. Among a wealth of analytic techniques, single-particle Raman spectroscopy provides an unambiguous characterization of individual particles under atmospheric pressure in a non-destructive and in situ manner. This paper comprehensively reviews the application of such a technique in the studies of atmospheric particles, including particle hygroscopicity, phase transition and separation, and solute–water interactions, particle pH, and multiphase reactions. Investigations on enhanced Raman spectroscopy and bioaerosols on a single-particle basis are also reviewed. For each application, we describe the principle and representative examples of studies. Finally, we present our views on future directions on both technique development and further applications of single-particle Raman spectroscopy in studying atmospheric particles.

Highlights

  • Atmospheric particles or aerosols have considerable effects on climate and human health (Seinfeld and Pandis, 2016)

  • This paper will introduce the general setup of the singleparticle Raman spectrometer, how single particles can be characterized unambiguously, and examples of physical and chemical processes reported in the literature

  • We focus on applications of atmospheric relevance and refer readers to other literature on the principles of Raman spectroscopy and related techniques

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Summary

Background

Atmospheric particles or aerosols have considerable effects on climate and human health (Seinfeld and Pandis, 2016). Secondary particles can be generated by gas-to-particle conversions, such as new particle formation via nucleation and condensation (Pöschl, 2005) During their atmospheric lifetime, both primary and secondary particles are subject to physical and chemical processes, such as partitioning and multiphase reactions. The disadvantage of Raman spectroscopy is that it can only detect Raman-active functional groups but cannot provide information on the exact molecular structures Lightabsorbing chemicals such as humic-like substances (HULIS) or some brown carbon species may generate fluorescence, interfering with the peak identification in the spectra (Ivleva et al, 2007a). This paper will introduce the general setup of the singleparticle Raman spectrometer, how single particles can be characterized unambiguously, and examples of physical and chemical processes reported in the literature. We will provide suggestions on future directions of Raman spectroscopy for atmospheric particle studies

Particle isolation
Electrodynamic balance
Optical trapping
Acoustic levitation
Deposited particles
Raman spectroscopy
Hygroscopicity and phase transition
Solid-phase transition
Molecular interactions between particulate water and solutes
Liquid–liquid phase separation
Multiphase reactions
Multiphase formation of secondary inorganic aerosols (SIAs)
Multiphase formation of SOA
Multiphase oxidation of aerosol particles
Amine and ammonia reactions
Photochemistry of aerosol particles
Enhanced Raman spectroscopy
Bioaerosols
Findings
Future directions
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