Emerging investigator series: surfactants, films, and coatings on atmospheric aerosol particles: a review

Abstract

Surfactants are surface-active molecules or ions that can often be found at the surface of atmospheric aerosol particles. Some surfactants, such as biomolecules in marine aerosol and cooking oils in urban aerosol, are directly emitted into the atmosphere, whereas others form from secondary reactions in the atmosphere. Environmentally relevant surfactants have long been studied in laboratory experiments and computational models, but recent developments in mass spectrometry, spectroscopy, imaging, and colorimetry have greatly expanded measurements of surfactants in ambient aerosol. This review focuses on advances surrounding the following themes: techniques for measuring and modeling surfactants on aerosol particles, the morphology of surfactant-coated aerosol particles, the impact of surfactants on cloud droplet activation and ice nucleation, multiphase reactions and photochemical reactions on surfactant-coated particles, and finally, field observations of surfactants on ambient particulate matter. An exciting area for future work is the continued advancement of single-particle techniques to simultaneously monitor morphology and composition of individual aerosol particles. Along with an expansion of field sampling campaigns, more laboratory studies of increasingly complicated aerosol systems are needed to bridge the gap between complex observations from the field and fundamental investigations in the laboratory. Characterizing surfactants, films, and coatings on atmospheric aerosol particles can provide insights relevant to how particulate matter impacts climate, air quality, and human health.