Liquid-Liquid Phase Separation Can Drive Aerosol Droplet Growth in Supersaturated Regimes.

It is well known that atmospheric aerosol size and composition impact air quality, climate, and health. The aerosol composition is typically a mixture and consists of a wide range of organic and inorganic particles that interact with each other. Furthermore, water vapor is ubiquitous in the atmosphere, in indoor air, and within the human body's respiratory system, and the presence of water can alter the aerosol morphology and propensity to form droplets.

Heterogeneous Ice Nucleation in Model Crystalline Porous Organic Polymers: Influence of Pore Size on Immersion Freezing.

Heterogeneous ice nucleation activity is affected by aerosol particle composition, crystallinity, pore size, and surface area. However, these surface properties are not well understood, regarding how they act to promote ice nucleation and growth to form ice clouds. Therefore, synthesized materials for which surface properties can be tuned were examined in immersion freezing mode in this study.

Significance of the surface silica/alumina ratio and surface termination on the immersion freezing of ZSM-5 zeolites.

Heterogeneous ice nucleation in the atmosphere impacts climate, but the magnitude of the effect of ice clouds on radiative forcing is uncertain. Surfaces that promote ice nucleation are varied. Because O, Si, and Al are the most abundant elements in the Earth's crust, understanding how the Si : Al ratio impacts the ice nucleation activity of aluminosilicates through exploration of synthetic ZSM-5 samples provides a good model system.

Accurate Prediction of Organic Aerosol Evaporation Using Kinetic Multilayer Modeling and the Stokes-Einstein Equation.

Organic aerosol can adopt a wide range of viscosities, from liquid to glass, depending on the local humidity. In highly viscous droplets, the evaporation rates of organic components are suppressed to varying degrees, yet water evaporation remains fast. Here, we examine the coevaporation of semivolatile organic compounds (SVOCs), along with their solvating water, from aerosol particles levitated in a humidity-controlled environment.

Direct Determination of Aerosol pH: Size-Resolved Measurements of Submicrometer and Supermicrometer Aqueous Particles.

Measuring the acidity of atmospheric aerosols is critical, as many key multiphase chemical reactions involving aerosols are highly pH-dependent. These reactions impact processes, such as secondary organic aerosol (SOA) formation, that impact climate and health. However, determining the pH of atmospheric particles, which have minute volumes (10-10 L), is an analytical challenge due to the nonconservative nature of the hydronium ion, particularly as most chemical aerosol measurements are made offline or under vacuum, where water can be lost and acid-base equilibria shifted.

Influence of particle viscosity on mass transfer and heterogeneous ozonolysis kinetics in aqueous-sucrose-maleic acid aerosol.

Mass transfer between the gas and condensed phases in aerosols can be limited by slow bulk diffusion within viscous particles. During the heterogeneous and multiphase reactions of viscous organic aerosol particles, it is necessary to consider the interplay of numerous mass transfer processes and how they are impacted by viscosity, including the partitioning kinetics of semi-volatile organic reactants, water and oxidants. To constrain kinetic models of the heterogeneous chemistry, measurements must provide information on as many observables as possible.

Phase Behavior of Ammonium Sulfate with Organic Acid Solutions in Aqueous Aerosol Mimics Using Microfluidic Traps.

Water-soluble organic acids such as dicarboxylic acids are known to form a significant fraction of organic aerosol mass, yet the chemical composition and interactions between components in an organic acid-inorganic salt mixed particle remain unclear. In this study, phase behavior of different mixing ratios of the salt and organic acids, here 3-methyl glutaric acid and 3-methyl adipic acid, are investigated with respect to their water activity. A microfluidic pervaporation approach is used to study different phase transitions of internally mixed aqueous droplets.

Isotherm-Based Thermodynamic Model for Solute Activities of Asymmetric Electrolyte Aqueous Solutions.

Adsorption isotherm-based statistical thermodynamic models can be used to determine solute concentration and solute and solvent activities in aqueous solutions. Recently, the number of adjustable parameters in the isotherm model of Dutcher et al. J.

Spectroscopic Determination of Aerosol pH from Acid-Base Equilibria in Inorganic, Organic, and Mixed Systems.

Atmospheric aerosol acidity impacts key multiphase processes, such as acid-catalyzed reactions leading to secondary organic aerosol formation, which impact climate and human health. However, traditional indirect methods of estimating aerosol pH often disagree with thermodynamic model predictions, resulting in aerosol acidity still being poorly understood in the atmosphere. Herein, a recently developed method coupling Raman microspectroscopy with extended Debye-Hückel activity calculations to directly determine the acidity of individual particles (1-15 μm projected area diameter, average 6 μm) was applied to a range of atmospherically relevant inorganic and organic acid-base equilibria systems (HNO/NO, HCO/CO, CHCOOH/CHCOO, and HCO/CO) covering a broad pH range (-1 to 10), as well as an inorganic-organic mixture (sulfate-oxalate).

Isotherm-Based Thermodynamic Models for Solute Activities of Organic Acids with Consideration of Partial Dissociation.

Organic acids make up a significant fraction of the organic mass in atmospheric aerosol particles. The calculation of gas-liquid-solid equilibrium partitioning of the organic acid is therefore critical for accurate determination of atmospheric aerosol physicochemical properties and processes such as new particle formation and activation to cloud condensation nuclei. Previously, an adsorption isotherm-based statistical thermodynamic model was developed for capturing solute concentration-activity relationships for multicomponent aqueous solutions over the entire concentration range (Dutcher et al.

Direct Measurement of pH in Individual Particles via Raman Microspectroscopy and Variation in Acidity with Relative Humidity.

Atmospheric aerosol acidity is an important characteristic of aqueous particles, which has been linked to the formation of secondary organic aerosol by catalyzing reactions of oxidized organic compounds that have partitioned to the particle phase. However, aerosol acidity is difficult to measure and traditionally estimated using indirect methods or assumptions based on composition. Ongoing disagreements between experiments and thermodynamic models of particle acidity necessitate improved fundamental understanding of pH and ion behavior in high ionic strength atmospheric particles.