Search

Nano-plastics have been found in snow and evidence shows that they can act as nuclei. The aerosol water-uptake ability is an important property that will determine wet deposition, a potential main route for nano-plastics to fall to the ground. In this work, we measure the hygroscopicity of three nano-plastics: low-density polyethylene (LDPE), polyethylene terephthalate (PET) and polyvinyl chloride (PVC), and a fourth compound, cellulose, with in-situ aerosol techniques via a cloud condensation nuclei counter. Cellulose is a high-molecular weight compound and a main component of commonly used paper products. Ultrafine nano-plastic particles in the range of 20 to 200 nm are explored. Nano-plastic materials LDPE, PET, and PVC form droplets more readily than cellulose nanoparticles. The high hygroscopicity of nano-plastics indicates that the nano-plastics are either oligomers or a polymer with properties for water adsorption. Furthermore, a single parameter hygroscopicity, κ, derived from different droplet activation models (Flory Huggins Köhler and Frenkel-Halsey-Hill adsorption theory) are reported. Moreover, the molecular weights of the leached oligomers are predicted by Flory Huggins Köhler theory assuming ideal polymer mixing. The observed intrinsic hygroscopicity is size-dependent, hence the adsorption-based hygroscopicity model could be applied. Nano-plastics can be incorporated into clouds, transported globally, and may also be removed from the atmosphere via wet deposition processes. The analysis of hygroscopicity help estimating the lifetime and transport of nano-plastic particles in the atmosphere. [ABSTRACT FROM AUTHOR]

The impact of molecular level surface chemistry for aerosol water-uptake and droplet growth is not well understood. In this work, spherical, non-porous, monodisperse Polystyrene Latex particles treated with different surface functional groups are exploited to isolate the effects of aerosol surface chemistry for droplet activation. PSL is effectively water-insoluble and changes in the particle surface may be considered a critical factor in the initial water-uptake of water insoluble material. The droplet growth of two surface modified types of PSL (PSL-NH2 and PSL-COOH) along with plain PSL was measured in a supersaturated environment with a Cloud Condensation Nuclei Counter (CCNC). Three droplet growth models - traditional Köhler (TK), Flory-Huggins Köhler (FHK) and the Frenkel-Halsey-Hill adsorption theory (FHH-AT) were compared to experimental data. The experimentally determined single hygroscopicity parameter, was found in the range from 0.002 to 0.04. The traditional Köhler prediction assumes Raoult's law solute dissolution and underestimates the water-uptake ability of the PSL particles. FHK can be applied to polymeric aerosol; however, FHK assumes the polymer is soluble and hydrophilic. Thus, the FHK model generates a negative result for hydrophobic PSL and predicts non-activation behavior that disagrees with the experimental observation. The FHH-AT model assumes that a particle is water-insoluble and can be fit with 2 empirical parameters (AFHH and BFHH). The FHH-AT prediction agrees with the experimental data and can differentiate the water uptake behavior of the particles due to surface modification of PSL surface. PSL-NH2 exhibits slightly higher hygroscopicity than the PSL-COOH, while plain PSL is the least hygroscopic among the three. This result is consistent with the polarity of surface functional groups and their affinity to water molecules. Thus, changes in AFHH and BFHH can be quantified when surface modification is isolated for the study of water-uptake. The fitted AFHH for PSL-NH2, PSL-COOH and plain PSL is 0.23, 0.21 and 0.18 when BFHH is unity. To simplify the use of FHH-AT for use in cloud activation models, we also present and test a new single parameter framework for insoluble compounds, FHH. FHH is within 5% agreement of the experimental data and can be applied to describe a single-parameter hygroscopicity for water-insoluble aerosol with surface modified properties. [ABSTRACT FROM AUTHOR]

In this work, we studied the Cloud Condensation nuclei (CCN) activity and subsaturated droplet growth of Phthalic acid (PTA), isophthalic acid, (IPTA) and terephthalic acid (TPTA), significant benzene polycarboxylic acids and structural isomers found in the atmosphere. Köhler Theory can be effectively applied for hygroscopicity analysis of PTA due to its higher aqueous solubility compared to IPTA and TPTA. As with other hygroscopicity studies of partially water-soluble and effectively water insoluble species, the supersaturated and subsaturated hygroscopicity derived from (KT) principles do not agree. To address the disparities in the sub- and supersaturated droplet growth, we developed a new analytical framework called the Hybrid Activity Model (HAM). HAM incorporates the aqueous solubility of a solute within an adsorption-based activation framework. Frenkel-Halsey-Hill (FHH)-Adsorption Theory (FHH-AT) was combined with the aqueous solubility of the compound to develop HAM. Analysis from HAM was validated using laboratory measurements of pure PTA, IPTA, TPTA and PTA-IPTA internal mixtures. Furthermore, the results generated using HAM were tested against traditional KT and FHH-AT to compare their water uptake predictive capabilities. A single-hygroscopicity parameter was also developed based on the HAM framework. Results show that the HAM based hygroscopicity parameter based can successfully simulate the water uptake behavior of the pure and internally mixed samples. Results indicate that the HAM framework may be applied to atmospheric aerosols of varying chemical structures and aqueous solubility. [ABSTRACT FROM AUTHOR]

The Aerodynamic Aerosol Classifier (AAC) is a novel instrument that size-selects aerosol particles based on their mechanical mobility. So far, the application of an AAC for Cloud Condensation Nuclei (CCN) activity analysis of aerosols has yet to be explored. Traditionally, a Differential Mobility Analyzer (DMA) is used for aerosol classification in a CCN experimental setup. A DMA classifies particles based on their electrical mobility. Substituting the DMA with an AAC can eliminate multiple charging artefacts as classification using an AAC does not require particle charging. In this work, we describe an AAC-based CCN experimental setup and CCN analysis method. We also discuss and develop equations to quantify the uncertainties associated with aerosol particle sizing. To do so, we extend the AAC transfer function analysis and calculate the measurement uncertainties of the aerodynamic diameter from the resolution of the AAC. The analyses framework has been packaged into a Python-based CCN Analysis Tool (PyCAT 1.0) open source code, which is available on GitHub for public use. Results show that the AAC size-selects robustly (AAC resolution is 10.1, diffusion losses are minimal and particle transmission is high) at larger aerodynamic diameters (= ~85nm). The size-resolved activation ratio is ideally sigmoidal since no charge corrections are required. Moreover, the uncertainties in the critical particle aerodynamic diameter at a given supersaturation can propagate through droplet activation and the subsequent uncertainties with respect to the single-hygroscopicity parameter (?) are reported. For a known aerosol such as sucrose, the ? derived from the critical dry aerodynamic diameter can be up to ~50% different from the theoretical ?. In this work, we do additional measurements to obtain dynamic shape factor information and convert the sucrose aerodynamic to volume equivalent diameter. The volume equivalent diameter applied to ?- Köhler theory improves the agreement between measured and theoretical ?. Given the limitations of the coupled AAC-CCN experimental setup, this setup is best used for low hygroscopicity aerosol (?=0.2) CCN measurements. [ABSTRACT FROM AUTHOR]

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. Specifically, aerosol mixtures can undergo liquid-liquid phase separation (LLPS) in the presence of water vapor. However, the experimental conditions for which LLPS impacts water uptake and the subsequent prediction of aerosol mixtures are poorly understood. To improve our understanding of aerosol mixtures and droplets, this study explores two ternary systems that undergo LLPS, namely, the 2MGA system (sucrose + ammonium sulfate + 2-methylglutaric acid) and the PEG1000 system (sucrose + ammonium sulfate + polyethylene glycol 1000). In this study, the ratio of species and the O:C ratios are systematically changed, and the hygroscopic properties of the resultant aerosol were investigated. Here, we show that the droplet activation above 100% RH of the 2MGA system was influenced by LLPS, while the droplet activation of the PEG1000 system was observed to be linearly additive regardless of chemical composition, O:C ratio, and LLPS. A theoretical model that accounts for LLPS with O:C ratios was developed and predicts the water uptake of internally mixed systems of different compositions and phase states. Hence, this study provides a computationally efficient algorithm to account for the LLPS and solubility parameterized by the O:C ratio for droplet activation at supersaturated relative humidity conditions and may thus be extended to mixed inorganic-organic aerosol populations with unspeciated organic composition found in the ambient environment., Competing Interests: The authors declare no competing financial interest., (© 2023 The Authors. Published by American Chemical Society.)