Virtual Issue on Atmospheric Aerosol Research

Geiger, Franz M.; McNeill, V. Faye; Orr-Ewing, Andrew J.

doi:10.1021/acs.jpca.2c04827

Cited by 2 publications

(5 citation statements)

References 31 publications

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“…In situ surface-specific observations of droplets in air may fill in the gaps left by ex situ , destructive, or non-interface-specific methods. One of the most relevant applications of such a technique is to atmospheric science and chemistry, as the chemical and physical properties of the aerosol surface are crucial to atmospheric processes and cannot be approximated effectively. ,,,, The very small radius of curvature of aerosol surfaces makes their analogy to the planar air/liquid interface convoluted. Furthermore, replacing the surrounding medium with a liquid in which particles or droplets are suspended results in extensive particle/medium interactions, inefficient transmitted signal collection, and different scattering patterns.…”

Section: Second-order Nonlinear Optical Scattering From Droplets In Airmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

“…Although the droplet surface is generally ascribed to cause such accelerations, analyses into reaction mechanisms often imply mechanisms based on non-surface-selective methods. The surfaces of atmospheric aerosol droplets are continuously relevant to atmospheric chemistry and climate science . However, modern developments in our understanding of aerosol surface reactions and uptake stem from computations and studying planar analogs.…”

Section: Introductionmentioning

confidence: 99%

“…Nano-and microdroplet surfaces are fundamentally intertwined with atmospheric chemistry through aerosols which govern heterogeneous atmospheric chemical reactions and cloud nucleation, directly impacting climate and environmental health. 11 Some of the unique properties of aerosol droplets are illustrated in Figure 1. The surface of aerosol droplets facilitates important processes of evaporation and condensation, which can affect the solute concentration and surface tension of the droplet.…”

Section: ■ Introductionmentioning

confidence: 99%

“…The surfaces of atmospheric aerosol droplets are continuously relevant to atmospheric chemistry and climate science. 11 However, modern developments in our understanding of aerosol surface reactions and uptake stem from computations and studying planar analogs. The models developed from these studies may also benefit from experiments that can directly observe such processes with interfacial sensitivity.…”

Section: ■ Introductionmentioning

confidence: 99%

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In Situ Probing of the Surface Properties of Droplets in the Air

et al. 2023

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Surface properties of nanodroplets and microdroplets are intertwined with their immense applicability in biology, medicine, production, catalysis, the environment, and the atmosphere. However, many means for analyzing droplets and their surfaces are destructive, non-interface-specific, not conducted under ambient conditions, require sample substrates, conducted ex situ, or a combination thereof. For these reasons, a technique for surface-selective in situ analyses under any condition is necessary. This feature article presents recent developments in second-order nonlinear optical scattering techniques for the in situ interfacial analysis of aerosol droplets in the air. First, we describe the abundant utilization of such droplets across industries and how their unique surface properties lead to their ubiquitous usage. Then, we describe the fundamental properties of droplets and their surfaces followed by common methods for their study. We next describe the fundamental principles of sum-frequency generation (SFG) spectroscopy, the Langmuir adsorption model, and how they are used together to describe adsorption processes at planar liquid and droplet surfaces. We also discuss the history of developments of second-order scattering from droplets suspended in dispersive media and introduce second-harmonic scattering (SHS) and sum-frequency scattering (SFS) spectroscopies. We then go on to outline the developments of SHS, electronic sum-frequency scattering (ESFS), and vibrational sum-frequency scattering (VSFS) from droplets in the air and discuss the fundamental insights about droplet surfaces that the techniques have provided. Finally, we describe some of the areas of nonlinear scattering from airborne droplets which need improvement as well as potential future directions and utilizations of SHS, ESFS, and VSFS throughout environmental systems, interfacial chemistry, and fundamental physics. The goal of this feature article is to spread knowledge about droplets and their unique surface properties as well as introduce second-order nonlinear scattering to a broad audience who may be unaware of recent progress and advancements in their applicability.

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Section: Second-order Nonlinear Optical Scattering From Droplets In Airmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: ■ Introductionmentioning

confidence: 99%

Section: ■ Introductionmentioning

confidence: 99%

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In Situ Probing of the Surface Properties of Droplets in the Air

et al. 2023

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Quantitative Signal Analysis of Sum-Frequency Scattering Experiments from Aerosol Surfaces

Brown,

Qian,

Wang

et al. 2024

Anal. Chem.

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Droplet interfaces are instrumental in processes of biology, engineering, production, and environmental systems. The chemical and physical properties of heterogeneous interfaces are known to be different from those of their underlying bulk phases, and different again when considering the curved surface of submicron aerosol droplets. The recently developed technique of vibrational sum-frequency scattering (VSFS) spectroscopy from airborne particles has emerged as an interface-specific method for the in situ analysis of this unique system. While the technique has shown promise in debut works, a quantitative analysis of the VSFS system has not yet been performed. Here we provide a comprehensive analysis of a VSFS spectrometer with reference to the welldocumented planar analog. We decompose the VSFS signal into coherent and incoherent as well as resonant and nonresonant components as a function of incident pulse delay time. We then quantify and compare resonant and nonresonant VSFS and VSFG experimental data using the same laser and detection systems. Using the air/water interface as a guide, we show that the resonant and nonresonant contributions to the SF responses are comparable for the two systems by extracting second-order susceptibilities and hyperpolarizabilities, and using them to estimate single-particle susceptibilities. A quantitative analysis of the signal detection systems for the scattering and planar geometries is made, and conversion efficiencies for VSFG, VSFS, and other nonlinear scattering experiments are compared. Lastly, the possibility of a low-repetition (1 kHz) VSFS spectrometer is considered, determining that it may be possible with modern laser technology but is inevitably less efficient than a high-repetition (100 kHz) system. Though this multistep analysis we obtain a better understanding of the components of the VSFS signal from aerosol particles, further validate the feasibility of the experiments, and provide insight to those wishing to conduct similar experiments and how they may be improved.

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Virtual Issue on Atmospheric Aerosol Research

Cited by 2 publications

References 31 publications

In Situ Probing of the Surface Properties of Droplets in the Air

In Situ Probing of the Surface Properties of Droplets in the Air

Quantitative Signal Analysis of Sum-Frequency Scattering Experiments from Aerosol Surfaces

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