Shining New Light on the Kinetics of Water Uptake by Organic Aerosol Particles

Abstract

The uptake of water vapor by various organic aerosols is important in a number of applications ranging from medical delivery of pharmaceutical aerosols to cloud formation in the atmosphere. The coefficient that describes the probability that the impinging gas-phase molecule sticks to the surface of interest is called the mass accommodation coefficient, αM. Despite the importance of this coefficient for the description of water uptake kinetics, accurate values are still lacking for many systems. In this Feature Article, we present various experimental techniques that have been evoked in the literature to study the interfacial transport of water and discuss the corresponding strengths and limitations. This includes our recently developed technique called photothermal single-particle spectroscopy (PSPS). The PSPS technique allows for a retrieval of αM values from three independent, yet simultaneous measurements operating close to equilibrium, providing a robust assessment of interfacial mass transport. We review the currently available data for αM for water on various organics and discuss the few studies that address the temperature and relative humidity dependence of αM for water on organics. The knowledge of the latter, for example, is crucial to assess the water uptake kinetics of organic aerosols in the Earth’s atmosphere. Finally, we argue that PSPS might also be a viable method to better restrict the αM value for water on liquid water.

Microphysics of liquid water in sub-10 nm ultrafine aerosol particles

“…Figure 6 shows α * as a function of 1/D based on our results (circles) and previous studies of aerosols containing liquid water and organic matter (stars) (Ma et al, 2011;Chakraborty and Zachariah, 2008;Li et al, 2019;Takahama and Russell, 2011;Diveky et al, 2019;Duffey et al, 2013;Diveky et al, 2021). The α * -values of the droplets containing pure or salty water (f s = 0) show no apparent dependence on salinity but an increase with droplet size.…”

“…The mass accommodation coefficient of water molecules on nano-aerosol particles, defined as the probability that a water vapor molecule that impinges on the particle surface becomes incorporated in the particle, is a fundamental factor that governs the hygroscopic growth kinetics of atmospheric aerosols (Diveky et al, 2021;Seinfeld and Pandis, 2008). Its precise value in atmospheric conditions remains highly uncertain (within a range of 0.01 to 1) despite decades of study because of its complex dependence on particle composition, phase-mixing state, and surface curvature (Diveky et al, 2021;Shiraiwa and Pöschl, 2021;Barclay and Lukes, 2019;Davis, 2006;Winkler et al, 2004).…”

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

“…Recent advances include the application of acoustic levitation with ultraviolet/visible (UV/vis) spectroscopy to measure changes in droplet pH, 71 the use of a dual-balance electrodynamic trap to monitor phase and viscosity, 72 the combination of a linear quadrupole electrodynamic balance with paper spray mass spectrometry to probe chemical composition, 73 and photothermal single-particle spectroscopy to determine mass accommodation coefficients. 74,75 In addition, several techniques have been developed specically to study nascent sea spray aerosol (SSA) particles in the laboratory. These will be discussed later in Section 8.3.2.…”

Evaporation and Molecular Beam Scattering from a Flat Liquid Jet

“…18 Mass spectrometry-based experiments 3 on thin films as well as droplets in microemulsions and the gas phase have shown significantly enhanced surface chemical reaction rates compared to bulk liquids. [19][20][21] Molecular beam scattering, originally developed to probe interactions between pairs of gas-phase molecules 22,23 and gas-phase molecules with solid surfaces, 24,25 has proved to be a direct and powerful means for investigating the dynamics of elementary chemical reactions. Nathanson and others have shown that molecular beam scattering from liquids offers a unique probe of gas-liquid interfacial interactions.…”