Physicochemical Properties Of Particles Research Articles

Relative Humidity-Dependent Phase Transitions in Submicron Respiratory Aerosols.

Respiratory viruses, such as influenza and severe acute respiratory syndrome coronavirus 2, represent a substantial public health burden and are largely transmitted through respiratory droplets and aerosols. Environmental factors such as relative humidity (RH) and temperature impact virus transmission rates, and a precise mechanistic understanding of the connection between these environmental factors and virus transmission would improve efforts to mitigate respiratory disease transmission. Previous studies on supermicrometer particles observed RH-dependent phase transitions and linked particle phase state to virus viability. Phase transitions in atmospheric aerosols are dependent on size in the submicrometer range, and actual respiratory particles are expelled over a large size range, including submicrometer aerosols that can transmit diseases over long distances. Here, we directly investigated the phase transitions of submicrometer model respiratory aerosols. A probe molecule, Nile red, was added to particle systems including multiple mucin/salt mixtures, a growth medium, and simulated lung fluid. For each system, the polarity-dependent fluorescence emission was measured following RH conditioning. Notably, the fluorescence measurements of mucin/NaCl and Dulbecco's modified Eagle's medium particles indicated that liquid-liquid phase separation (LLPS) also occurs in submicron particles, suggesting that LLPS can also impact the viability of viruses in submicron particles and thus affect aerosol virus transmission. Furthermore, the utility of fluorescence-based measurements to study submicrometer respiratory particle physicochemical properties in situ is demonstrated.

Analysis of the correlation between mechanical and physicochemical properties of particles based on a diesel oxidation catalytic system

The mechanical and physicochemical properties of diesel engine exhaust particles before and after diesel oxidation catalyst (DOC) treatment are analyzed. It is considered important to explore the interrelationships between these attributes in order to understand their relevance. Understanding of these properties provides insights into the deposition characteristics of particles within the system and the evolution of the particles after the DOC treatment, which may help the selection of appropriate aftertreatment strategies. In this paper, particle samples were collected before and after the DOC to explore the variations in the mechanical and physicochemical properties of the particles under different operating conditions. Atomic force microscopy, thermogravimetric analysis, transmission electron microscopy, and Raman spectroscopy were employed to investigate the attraction force, adhesion force, adhesion energy, oxidative reactivity, primary particle size, nanostructure, and graphitization degree of the particles. The results indicated that under post-injection conditions, the attraction force, adhesion force, and adhesion energy of the particles increased significantly. However, when the particles passed through the DOC, these properties decreased to varying degrees. By analyzing the combination of physicochemical properties, it was determined that the attraction force of the particles was primarily influenced by the primary particle size and the particle's graphite structure. The adhesion force was found to be closely related to the content of soluble organic matter. Additionally, the soluble organic matter affected the degree of particle agglomeration by altering the adhesion energy of the particles.

Quinaldine Red as a Fluorescent Probe for Particle Physicochemical Properties

Quinaldine Red as a Fluorescent Probe for Particle Physicochemical Properties

A hyperspectral view of the nearshore Mississippi River Delta: Characterizing suspended particles in coastal wetlands using imaging spectroscopy

Suspended particle concentration (Total Suspended Solids or TSS) determines sediment availability for deposition, whereas particle physico-chemical properties (e.g. composition and size) can influence sediment transport and accretion. These variables are critical to modeling and understanding nearshore sediment dynamics and coastal soil accretion and erosion. Upcoming satellite imaging spectrometers (e.g., GLIMR, SBG) have the potential to improve the detailed mapping and characterization of suspended particles in nearshore areas. Here, we conducted a detailed feasibility study assessing the capacity of imaging spectroscopy to accurately map suspended particle concentrations and physico-chemical properties in the Mississippi River Deltaic Plain (Louisiana, USA), a nearshore system with extreme coastline vulnerability. To that end, a large dataset of in situ TSS, Particulate Organic Carbon (POC) concentration, particle size, inherent optical properties (IOPs), and hyperspectral remote sensing reflectance (Rrs) was collected during the 2021 NASA Delta-X field campaigns in coastal Louisiana. Analyses of the data revealed that the enhanced spectral information provided by imaging spectroscopy (hyperspectral Rrs) improved the retrieval of TSS and POC/TSS (% organic carbon content), but highlighted the challenge of retrieving particle size in this system. Partial-least-squares-regression (PLSR) algorithms for TSS performed better than existing state-of-the-art algorithms and confirmed the importance of using local measurements and near-infrared Rrs. Implementation on Airborne Visible Infrared Imaging Spectrometer-Next Generation (AVIRIS-NG) imagery generated high-resolution (< 5 m), high-quality maps of TSS and POC/TSS in contrasted areas with a wide range of TSS concentrations from (0.1 to 100 mg L−1), and demonstrated the enhanced potential of upcoming missions such as SBG and GLIMR to inform studies of nearshore sediment dynamics and coastal vulnerability/resilience.

Morphological and chemical characterisation of indoor quasi-ultrafine particles

Particles in the nanoscale range have intrinsic physicochemical characteristics that define their interaction with the human body and ultimately their toxicity. Whilst research has focused on engineered nanomaterials or ambient ultrafine particles, little is known about the morphology, size and elemental composition of particles in the nanoscale range collected in indoor environments, where humans spend the longest time. This study aims to characterise the physicochemical properties of quasi-ultrafine particles (qUFP), with an aerodynamic diameter <250 nm, collected with a Sioutas impactor from 5 indoor environments (3 homes and 2 offices). Morphology, size and elemental composition of individual particles were imaged using a Transmission Electron Microscope coupled with X-ray energy dispersive spectroscopy. Most of the single particles and their aggregates were of irregular shapes, and some fibrous rods, elongated rods, spheres and hexagons were also observed. ImageJ software was used to analyse the surface area, roundness and circularity of the particles, as well as individual particle diameter for the spherical particles. For the non-spherical shaped particle, the particles were manually measured to characterise the maximum Feret diameter. Particle main dimensions (i.e. diameter for spheroids and maximum Feret diameter for irregular particles) ranged from 35 ± 59 nm to 103 ± 160 nm. Shapes for non-spherical particles were assigned by visual description. Si, Fe and S were found in nanoparticles from all indoor locations. Other abundant constituents were K, Cr, Na, Ca, Cl found in 60–80% of locations. Minor constituents of indoor nanoparticles were Cu, Sn, Ti, Mo, Al, P, Be, F, Zn, Rb, Pb, Mn and Co. Sources were related to indoor emissions, e.g. printers, stainless-steel tools, electronics, cooking, house chores, particle re-suspension, aerosol and cleaning products as well as to penetration of outdoor nanoparticles from vehicular emissions, soil and secondary aerosols. Detailed investigation of the physicochemical properties of these particles can help understand their associated hazard and their fate in the human body.

Micro- and nanoplastics (MNPs) and their potential toxicological outcomes: State of science, knowledge gaps and research needs

Plastic waste has been produced at a rapidly growing rate over the past several decades. The environmental impacts of plastic waste on marine and terrestrial ecosystems have been recognized for years. Recently, researchers found that micro- and nanoplastics (MNPs), micron (100 nm – 5 mm) and nanometer (1 – 100 nm) scale particles and fibers produced by degradation and fragmentation of plastic waste in the environment, have become an important emerging environmental and food chain contaminant with uncertain consequences for human health. This review provides a comprehensive summary of recent findings from studies of potential toxicity and adverse health impacts of MNPs in terrestrial mammals, including studies in both in vitro cellular and in vivo mammalian models. Also reviewed here are recently released biomonitoring studies that have characterized the bioaccumulation, biodistribution, and excretion of MNPs in humans. The majority MNPs in the environment to which humans are most likely to be exposed, are of irregular shapes, varied sizes, and mixed compositions, and are defined as secondary MNPs. However, the MNPs used in most toxicity studies to date were commercially available primary MNPs of polystyrene (PS), polyethylene (PE), polyvinyl chloride (PVC), polyethylene terephthalate (PET), and other polymers. The emerging in vitro and in vivo evidence reviewed here suggests that MNP toxicity and bioactivity are largely determined by MNP particle physico-chemical characteristics, including size, shape, polymer type, and surface properties. For human exposure, MNPs have been identified in human blood, urine, feces, and placenta, which pose potential health risks. The evidence to date suggests that the mechanisms underlying MNP toxicity at the cellular level are primarily driven by oxidative stress. Nonetheless, large knowledge gaps in our understanding of MNP toxicity and the potential health impacts of MNP exposures still exist and much further study is needed to bridge those gaps. This includes human population exposure studies to determine the environmentally relevant MNP polymers and exposure concentrations and durations for toxicity studies, as well as toxicity studies employing environmentally relevant MNPs, with surface chemistries and other physico-chemical properties consistent with MNP particles in the environment. It is especially important to obtain comprehensive toxicological data for these MNPs to understand the range and extent of potential adverse impacts of microplastic pollutants on humans and other organisms.

In-situ and real-time nano/microplastic coatings and dynamics in water using nano-DIHM: A novel capability for the plastic life cycle research

A novel nano-digital inline holographic microscope (nano-DIHM) was used to advance in-situ and real-time nano/microplastic physicochemical research, such as particle coatings and dynamic processes in water. Nano-DIHM data provided evidence of distinct coating patterns on nano/microplastic particles by oleic acid, magnetite, and phytoplankton, representing organic, inorganic, and biological coatings widely present in the natural surroundings. A high-resolution scanning transmission electron microscopy confirmed nano-DIHM data, demonstrating its nano/microplastic research capabilities. The sedimentation of two plastic size categories was examined: (a) ∼10 to 700 µm, and (b) ∼ 1 to 5 mm. Particle size was the primary factor affecting the sedimentation for studied (a) microplastics and (b) pellets. Two types of silicone rubbers exhibited different sedimentation processes. We also demonstrated that inorganic ions in seawater and oleic acid organic coatings altered the sedimentation velocity of studied plastics by 9 – 13% and 5 – 9%, respectively. Semi-empirical probability functions were developed and incorporated into a numerical model (CaMPSim-3D) to simulate the transport of studied microplastics and pellets in the Saint John River estuary. Water dynamics was the driving force of plastic transport, yet the accumulation of plastics was selectively dependant on particle physicochemical properties such as size and density by ∼ 7%. The usage of nano-DIHM for targeted identification of nano/microplastic hotspots and aquatic plastic wastes remediation were discussed.

Polystyrene Microplastics of Varying Sizes and Shapes Induce Distinct Redox and Mitochondrial Stress Responses in a Caco-2 Monolayer.

Currently, we lack crucial knowledge on how the physicochemical properties of particles affect cellular health, resulting in an important gap in our understanding of the human toxicity of microplastics (MPs). Our aim was to evaluate the impact of the size and the shape of MPs on uptake and the intracellular effects in a human epithelial colorectal adenocarcinoma (Caco-2) cell line. Spherical (200 nm and 2 µm) and fibre-/fragment-shaped (8.9 ± 10.1 µm by 1.14 ± 0.97 µm) polystyrene microplastics (PS-MPs) were used to study their uptake and the potential to induce redox and mitochondrial stress responses after 24 h of exposure. We demonstrated the cellular uptake of both spherical and fibre-/fragment-shaped MPs in a size-dependent manner. In response to 2 µm spheres, we observed differential expressions of redox-related genes, including HMOX1, CAT, and GPX1. All PS-MPs decreased the intracellular H2O2 levels, which can be attributed to mitochondrial stress responses, such as increased mitochondrial DNA content, footprint, and morphology. Altogether, we demonstrated uptakes and changes in redox and mitochondrial parameters for all PS-MPs, with the 200 nm spheres showing the most profound effects. This suggests that the induction of defensive responses in Caco-2 cells mainly correlates with the number of particles taken up.

Assessing oxidative stress induction ability and oxidative potential of PM2.5 in cities in eastern and western Japan

Oxidative stress is an important cause of respiratory diseases associated with exposure to PM2.5. Accordingly, acellular methods for assessing the oxidative potential (OP) of PM2.5 have been evaluated extensively for use as indicators of oxidative stress in living organisms. However, OP-based assessments only reflect the physicochemical properties of particles and do not consider particle-cell interactions. Therefore, to determine the potency of OP under various PM2.5 scenarios, oxidative stress induction ability (OSIA) assessments were performed using a cell-based method, the heme oxygenase-1 (HO-1) assay, and the findings were compared with OP measurements obtained using an acellular method, the dithiothreitol assay. For these assays, PM2.5 filter samples were collected in two cities in Japan. To quantitatively determine the relative contribution of the quantity of metals and subtypes of organic aerosols (OA) in PM2.5 to the OSIA and the OP, online measurements and offline chemical analysis were also performed. The findings showed a positive relationship between the OSIA and OP for water-extracted samples, confirming that the OP is generally well suited for use as an indicator of the OSIA. However, the correspondence between the two assays differed for samples with a high water-soluble (WS)–Pb content, which had a higher OSIA than would be expected from the OP of other samples. The results of reagent-solution experiments showed that the WS-Pb induced the OSIA, but not the OP, in 15-min reactions, suggesting a reason for the inconsistent relationship between the two assays across samples. Multiple linear regression analyses and reagent-solution experiments showed that WS transition metals and biomass burning OA accounted for approximately 30–40% and 50% of the total OSIA or the total OP of water-extracted PM2.5 samples, respectively. This is the first study to evaluate the association between cellular oxidative stress assessed by the HO-1 assay and the different subtypes of OA.

In vivo pharmacokinetic and pharmacodynamic study of co-spray-dried inhalable pirfenidone microparticles in rats

Pirfenidone (PRF) is the first FDA-approved API in the treatment of idiopathic pulmonary fibrosis (IPF). However, PRF induces serious side effects, such as photophobia and gastrointestinal disorder. PRF inhalation can be expected with a lower effective dose and reduced side effects. In this study, PRF was prepared as inhalable co-spray-dried particles for dry powder inhalation. Mannitol, L-leucine (Leu), and NaCl were used as a stabilizer. The kinds and ratios of stabilizers affecting the physicochemical properties of particles were analyzed, including particle size and surface composition, because of the surface enrichment properties of Leu, the most effective stabilizer. The co-spray-dried PRF and Leu microparticle (SD-PL1:1) have the smallest size and highest aerosol performance. The bioavailability was confirmed by in vivo pharmacokinetics (PK) studies. In addition, in vivo pharmacodynamics (PD) experiments were conducted using a bleomycin-induced IPF rat model. In vivo PK experiments demonstrated that pulmonary administration of SD-PL1:1 was 4 times more effective than the oral route. Similar to the PK results, the therapeutic effect was improved when SD-PL1:1 was administered via the pulmonary route compared to the oral route.

Synthesis and characterization of a calcium phosphate bone cement with quercetin-containing PEEK/PLGA microparticles

This study aimed to describe the synthesis and characterization of a calcium phosphate cement (CPC) with polyetheretherketone/poly (lactic-co-glycolic) acid (PEEK/PLGA) micro-particles containing quercetin. CPC powder was synthesized by mixing dicalcium phosphate anhydrate and tetracalcium phosphate. To synthesize PEEK/PLGA microparticles, PLGA85:15 was mixed with 90 wt% PEEK. The weight ratio of quercetin/PLGA/PEEK was 1:9:90 wt%. PEEK/PLGA/quercetin microparticles with 3, 5, and 6 wt% was added to CPC. The setting time, compressive strength, drug release profile, solubility, pH, and porosity of synthesized cement were evaluated. The morphology and physicochemical properties of particles was analyzed by scanning electron microscopy, Fourier-transform infrared spectroscopy (FTIR), x-ray diffraction (XRD), and inductively coupled plasma. Cytotoxicity was assessed by the methyl thiazolyl tetrazolium assay using dental pulp stem cells. Expression of osteoblastic differentiation genes was evaluated by real-time polymerase chain reaction. Data were analyzed by one-way ANOVA and Tukey’s test (alpha = 0.05). The setting time of 3 wt% CPC was significantly longer than 5 and 6 wt% CPC (P < 0.001). The 6 wt% CPC had significantly higher compressive strength than other groups (P = 0.001). The release of quercetin from CPCs increased for 5 d, and then reached a plateau. XRD and FTIR confirmed the presence of hydroxyapatite in cement composition. Significantly higher expression of osteocalcin (OCN) and osteopontin (OPN) was noted in 3 wt% and 6 wt% CPCs. Addition of quercetin-containing PEEK/PLGA microparticles to CPC enhanced its compressive strength, decreased its setting time, enabled controlled drug release, and up-regulated OPN and OCN.

Mechanisms of Anisotropic Particle Deposition: Prolate Spheroid Layers on Mica

Anisotropic particle deposition was investigated using the streaming potential method complemented with the atomic force microscopy (AFM) determination of the absolute particle coverage. The polymer particles were synthesized using the stretching procedure with consecutive oxidation of surface hydroxyl groups and coupling of polyethyleneimine. The bulk particle physicochemical properties were characterized by scanning electron microscopy (SEM), dynamic light scattering, and laser Doppler velocimetry. The particles were positively charged in the pH range of 3–10, exhibiting a prolate spheroid shape with an axis ratio of five. Thorough AFM and in situ optical microscopy measurements yielded the adsorption kinetics of particles under the diffusion-controlled regime. The experimental data were adequately interpreted in terms of the random sequential adsorption model with the surface blocking function derived from the scaled particle theory. The root-mean-square (rms) parameter of the layers for a broad range of particle coverage was also determined and interpreted using the topographical model developed in this work. The experiments were complemented by the measurements of the streaming potential of particle layers under various ionic strengths and pHs. The ζ (zeta)-potential data acquired in this way enabled to determine the universal hydrodynamic function describing the dependence of the streaming potential on the particle coverage. The function was used to express the ζ-potential of surfaces covered by particles in terms of substrate rms. It was argued that the acquired results, in addition to being significanct to basic science, can be exploited as useful reference systems for quantitative interpretation of bioparticle deposition on abiotic surfaces.

Impact of fuel aromatic content on soot particle physicochemical properties of marine auxiliary diesel engine.

Fuel aromatic content (AC) is one of the main reasons for PM (particulate matter) emissions from ocean-going ships. The present study investigates the influence of AC on physicochemical characteristics of soot particles from marine auxiliary diesel engine. The TEM (transmission electron microscopy), Raman spectroscopy, FTIR (Fourier transform infrared spectroscopy), and TGA (thermalgravimetric analyzer) are employed to jointly characterize samples. The results reveal that soot particles from high-AC fuel have bigger dp (primary particle size), longer fringe length (La), and higher graphitization degree, all of which have significant impacts on chemical properties such as more VOF (volatile organic fraction), higher concentrations of aromatic C-H and C=C groups. These are mainlydue to several aromatic rings decomposed from aromatic components could promote the growth of carbon layer, and incomplete pyrolysis productions arealso present in soot particles. The relative amounts of aromatic C-H and C=C are well correlated with dp and La, respectively.

Advances in Nanotechnology as a Potential Alternative for Plant Viral Disease Management.

Plant viruses cause enormous losses in agricultural production accounting for about 47% of the total overall crop losses caused by plant pathogens. More than 50% of the emerging plant diseases are reported to be caused by viruses, which are inevitable or unmanageable. Therefore, it is essential to devise novel and effective management strategies to combat the losses caused by the plant virus in economically important crops. Nanotechnology presents a new tendency against the increasing challenges in the diagnosis and management of plant viruses as well as plant health. The application of nanotechnology in plant virology, known as nanophytovirology, includes disease diagnostics, drug delivery, genetic transformation, therapeutants, plant defense induction, and bio-stimulation; however, it is still in the nascent stage. The unique physicochemical properties of particles in the nanoscale allow greater interaction and it may knock out the virus particles. Thus, it opens up a novel arena for the management of plant viral diseases. The main objective of this review is to focus on the mounting collection of tools and techniques involved in the viral disease diagnosis and management and to elucidate their mode of action along with toxicological concerns.

Insights into Surface Charge of Single Particles at the Orifice of a Nanopipette.

The dynamic behaviors of particles in various physical fields are related to the physicochemical properties of particles. Herein, we focus on the relationship between surface charge and dynamic behaviors of particles at the orifice of a nanopipette. We interestingly find that angle θ, a parameter related to the asymmetric degree of current spike, exhibits a strong relationship with surface charge of the particles. Both theoretical derivation and finite element simulation validate this relationship and thus could be used for quantifying the surface charge of single particles. Moreover, the gold and silica nanoparticles with the same size but different surface charges could be well distinguished and identified based on this relationship. This study not only gives a comprehensive understanding on the dynamic behaviors of particles outside the nanopipette but also opens a new way for investigating the surface charge of single particles.

Comparison of biological responses between submerged, pseudo-air-liquid interface, and air-liquid interface exposure of A549 and differentiated THP-1 co-cultures to combustion-derived particles

Air liquid interface (ALI) exposure systems are gaining interest, and studies suggest enhanced response of lung cells exposed to particles at ALI as compared to submerged exposure, although the results have been somewhat inconsistent. Previous studies have used monocultures and measured particle deposition using assumptions including consistent particle deposition, particle density, and shape. This study exposed co-cultures of A549 and differentiated THP-1 cells to flame-generated particles using three exposure methods: ALI, pseudo-ALI, and submerged. The dose at ALI was measured directly, reducing the need for assumptions about particle properties and deposition. For all exposure methods an enhanced pro-inflammatory response (TNFα) and Cytochrome P450 (CYP1A1) gene expression, compared to their corresponding negative controls, was observed. ALI exposure induced a significantly greater TNFα response compared to submerged exposure. The submerged exposures exhibited greater induction of CYP1A1 than other exposure methods, although not statistically significant. Some of the factors behind the observed difference in responses for the three exposure methods include differences in physicochemical properties of particles in suspending media, delivered dose, and potential contribution of gas-phase species to cellular response in ALI exposure. However, given the difficulty and expense of ALI exposures, submerged exposure may still provide relevant information for particulate exposures.

Effect of Particulate Properties of Inhaled Dry Powder Formulation on Bioavailability, Dissolution Rate of Drug Particles and Rate of Drug Removal from the Body

Introduction: The use of pulmonary drug delivery as a non-invasive drug delivery system for the systemic treatment of diseases as well as the topical treatment of respiratory diseases is increasing. Among the various inhaled formulations, inhaled dry powders show advantages over the other forms of inhaled medicines due to high stability, bioavailability and ease of use. The effect of particle properties on the rate of drug delivery to the lungs in inhaled dry powders has been investigated in previous papers.&#x0D; Conclusion: Since the physicochemical properties of particles of dry powder inhalation formulations such as particle size, surface and particle shape, as well as the electrical charge of the particles play a decisive role in drug pharmacokinetics, in the present review article we intended to discuss the effect of these parameters of inhaled dry powder formulations on bioavailability, dissolution rate of drug particles and the rate of drug clearance from the body.

Particle Safety Assessment in Additive Manufacturing: From Exposure Risks to Advanced Toxicology Testing.

Additive manufacturing (AM) or industrial three-dimensional (3D) printing drives a new spectrum of design and production possibilities; pushing the boundaries both in the application by production of sophisticated products as well as the development of next-generation materials. AM technologies apply a diversity of feedstocks, including plastic, metallic, and ceramic particle powders with distinct size, shape, and surface chemistry. In addition, powders are often reused, which may change the particles’ physicochemical properties and by that alter their toxic potential. The AM production technology commonly relies on a laser or electron beam to selectively melt or sinter particle powders. Large energy input on feedstock powders generates several byproducts, including varying amounts of virgin microparticles, nanoparticles, spatter, and volatile chemicals that are emitted in the working environment; throughout the production and processing phases. The micro and nanoscale size may enable particles to interact with and to cross biological barriers, which could, in turn, give rise to unexpected adverse outcomes, including inflammation, oxidative stress, activation of signaling pathways, genotoxicity, and carcinogenicity. Another important aspect of AM-associated risks is emission/leakage of mono- and oligomers due to polymer breakdown and high temperature transformation of chemicals from polymeric particles, both during production, use, and in vivo, including in target cells. These chemicals are potential inducers of direct toxicity, genotoxicity, and endocrine disruption. Nevertheless, understanding whether AM particle powders and their byproducts may exert adverse effects in humans is largely lacking and urges comprehensive safety assessment across the entire AM lifecycle—spanning from virgin and reused to airborne particles. Therefore, this review will detail: 1) brief overview of the AM feedstock powders, impact of reuse on particle physicochemical properties, main exposure pathways and protective measures in AM industry, 2) role of particle biological identity and key toxicological endpoints in the particle safety assessment, and 3) next-generation toxicology approaches in nanosafety for safety assessment in AM. Altogether, the proposed testing approach will enable a deeper understanding of existing and emerging particle and chemical safety challenges and provide a strategy for the development of cutting-edge methodologies for hazard identification and risk assessment in the AM industry.

On the evolution of sub- and super-saturated water uptake of secondary organic aerosol in chamber experiments from mixed precursors

Abstract. To better understand the chemical controls of sub- and super-saturated aerosol water uptake, we designed and conducted a series of chamber experiments to investigate the evolution of secondary organic aerosol (SOA) particle physicochemical properties during photo-oxidation of single and mixed biogenic (α-pinene, isoprene) and anthropogenic (o-cresol) volatile organic compounds (VOCs) in the presence of ammonium sulfate seeds. During the 6 h experiments, the cloud condensation nuclei (CCN) activity at super-saturation of water (0.1 %–0.5 %), hygroscopic growth factor at 90 % relative humidity (RH), and non-refractory PM1 chemical composition were recorded concurrently. Attempts to use the hygroscopicity parameter κ to reconcile water uptake ability below and above water saturation from various VOC precursor systems were made, aiming to predict the CCN activity from the sub-saturated hygroscopicity. The thermodynamic model AIOMFAC (aerosol inorganic-organic mixtures functional groups activity coefficients) was used to simulate κ values of model compound mixtures to compare with the observation and to isolate the controlling factors of water uptake at different RHs. The sub- and super-saturated water uptake (in terms of both κHTDMA and κCCN) were mainly controlled by the SOA mass fraction, which depended on the SOA production rate of the precursors, and the SOA composition played a second-order role. For the reconciliation of κHTDMA and κCCN, the κHTDMA/κCCN ratio increased with the SOA mass fraction and this was observed in all investigated single and mixed VOC systems, independent of initial VOC concentrations and sources. For all VOC systems, the mean κHTDMA of aerosol particles was ∼25 % lower than the κCCN at the beginning of the experiments with inorganic seeds. With the increase of condensed SOA on inorganic seed particles throughout the experiments, the discrepancy of κHTDMA and κCCN became weaker (down to ∼0 %) and finally the mean κHTDMA was ∼60 % higher than κCCN on average when the SOA mass fraction approached ∼0.8. As indicated by AIOMFAC model simulations, non-ideality alone cannot fully explain the κ discrepancy at high SOA mass fraction (0.8). A good agreement in κCCN between model and observation was achieved by doubling the molecular weight of the model compounds or by reducing the dry particle size in the CCN counter. This indicates that the evaporation of semi-volatile organics in the CCN counter together with non-ideality could have led to the observed κ discrepancy. As a result, the predicted CCN number concentrations from the κHTDMA and particle number size distribution were ∼10 % lower than CCN counter measurement on average at the beginning, and further even turned to an overestimation of ∼20 % on average when the SOA mass fraction was ∼0.8. This chemical composition-dependent performances of the κ-Köhler approach on CCN prediction can introduce a variable uncertainty in predicting cloud droplet numbers from the sub-saturated water uptake, the influence of which on models still needs to be investigated.

Theoretical Foundation of the Relationship between Three Definitions of Effective Density and Particle Size

Effective density (ρe) is universally used in atmospheric science as an alternative measure of the density (ρ) of aerosol particles, and its definitions can be expressed in terms of the particle mass (mp), ρ, mobility diameter (Dm), vacuum aerodynamic diameter (Dva), and dynamic shape factor (χ), as ρeI = 6mp/(π∙Dm3), ρeII = ρ/χ, and ρeIII = Dva/Dm. However, the theoretical foundation of these three definitions of ρe is still poorly understood before their application. Here, we explore the relationship between ρe and aerosol size through theoretical calculation. This study finds, for the first time, that ρeI and ρeIII inherently decrease with increasing size for aspherical particles with a fixed ρ and χ. We further elucidate that these inherent decreasing tendencies are governed by χ, and the ratio of the Cunningham Slip Correction Factor of the volume-equivalent diameter to that of the mobility diameter (Cc(Dve)/Cc(Dm)), but not by ρ. Taking the variable χ into consideration, the relationships of ρeI and ρeIII to particle size become more complicated, which suggests that the values of ρeI and ρeIII have little indication of the size-resolved physicochemical properties of particles. On the contrary, ρeII is independent on size for fixed χ and ρ, which indicates that the change in ρeII with size can better indicate the change in morphology and the transformation of the chemical compositions of particles. Our new insights into the essence of three ρes provide an accurate and crucial theoretical foundation for their application.