Reconsideration of surface tension and phase state effects on cloud condensation nuclei activity based on the atomic force microscopy measurement

Abstract

Abstract. Dicarboxylic acids are ubiquitous in atmospheric aerosol particles, but their roles as surfactants in cloud condensation nuclei (CCN) activity remain unclear. In this study, we investigated CCN activity of inorganic salt (sodium chloride and ammonium sulfate) and dicarboxylic acid (including malonic acid (MA), phenylmalonic acid (PhMA), succinic acid (SA), phenylsuccinic acid (PhSA), adipic acid (AA), pimelic acid (PA), and octanedioic acid (OA)), mixed particles with varied organic volume fractions (OVFs), and then directly determined their surface tension and phase state at high relative humidity (over 99.5 %) via atomic force microscopy (AFM). Our results show that CCN-derived κCCN of studied dicarboxylic acids ranged from 0.003 to 0.240. A linearly positive correlation between κCCN and solubility was obtained for slightly dissolved species, while negative correlation was found between κCCN and molecular volume for highly soluble species. For most inorganic salts and dicarboxylic acids (MA, PhMA, SA, PhSA and PA), a good closure within 30 % relative bias between κCCN and chemistry-derived κChem was obtained. However, κCCN values of inorganic salt–AA and inorganic salt–OA systems were surprisingly 0.3–3.0 times higher than κChem, which was attributed to surface tension reduction, as AFM results showed that their surface tensions were 20 %–42 % lower than that of water (72 mN m−1). Meanwhile, semisolid phase states were obtained for inorganic salt–AA and inorganic salt–OA and also affected hygroscopicity closure results. Our study highlights that surface tension reduction should be considered when investigating aerosol–cloud interactions.

Direct observation for relative-humidity-dependent mixing states of submicron particles containing organic surfactants and inorganic salts

“…The process of aerosol generation and collection was described in detail by Xiong et al (2022). In brief, particles were nebulized from solutions of organic and inorganic matter (∼ 5 g L −1 ) mixed with deionized water (Millipore; resistivity = 18.2 M ).…”

Evidence of Surface-Tension Lowering of Atmospheric Aerosols by Organics from Field Observations in an Urban Atmosphere: Relation to Particle Size and Chemical Composition

“…However, measuring surface tension is not a routine operation in field campaigns, and the role of surfactants in CCN activity is not well quantified by field observations. Most work and techniques focus on laboratory measurements of surface tension for droplets with specified size and/or known chemical composition. ,− Surface tension can also be estimated by thermodynamical, statistical, and empirical models built upon and verified by laboratory and observational data. ,,,,,− However, models require knowledge of droplet size, composition, and activity coefficient, which are usually very complex and not measured in field campaigns. Also, only 10–30% of the organic mass is identified at a molecular level .…”

Interactions between SOA-like droplets and water vapor using acoustic levitation

“…Surface properties of atmospheric particles such as surface tension can directly affect interactions of a particle with the water vapor and hence its activation into cloud droplet. [2,3] However, the complexity of aerosol aging processes occurring at the gas/particle interface is not well described. Recent developments using single particle approaches allow studying various chemical aging processes, and microphysical properties at the particle scale.…”