A number of gas-particle reactions occur among the strongly acidic particles and atmospheric gasesthrough homogeneous gas or aqueous phase reactions as well as through heterogeneous reactions on particle surfaces. The gas−aerosol particle interface is believed to contribute to the growth of secondary organic aerosols in the atmosphere. Despite its importance, the chemical composition of the interface has not been probed directly because of a lack of suitable interface-specific analytical techniques. Here we developed the interface-specific SHS for in situ chemical analysis of molecules at the gas–aerosol particle interface. As an example, we demonstrated coherent SHS signal of a new SHS probe, crystal violet (CV), from interface of aerosol particle. We found that the combination of a high repetition rate as high as 1 MHz reaches a large signal-to-noise SHS signals from the gas-aerosol particle interfaces. It has greatly improved the detection sensitivity of interfacial molecules by more than 2 orders of magnitude, leading to interfacial detectivity of singlet aerosol particle. To further understand how interface plays a role in the growth of aerosol particle, we have measured interfacial behaviors of molecules of aerosol particles under different relative humidity (RH) by the interface-specific SHS. Since RH can vary the concentration of solutes inside single aerosol particle and interfacial hydration in local regions, the particle size and the phase of the single aerosol particle can be impacted by the RH. Organic molecules were found to exhibit distinct behaviors at the interfaces and bulk on the single aerosol particle under different RH levels. Our quantitative analyses showed that the interfacial adsorption free energies remain unchanged while interfacial areas increase as the relative humidity increases. Furthermore, the surface tension of single aerosol particle decreases as the RH increases. These experimental results not only provided a thorough analysis of the SHS technique but also built a solid foundation for further development of a new vibrational sum frequency scattering (SFS) technique for chemical structures at the gas−aerosol particle interface. <br/> <br/>

Interfacial analysis of single aerosol particle

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.