Complexity of Measuring and Representing the Hygroscopicity of Mixed Component Aerosol

The validation of approaches to predict the hygroscopicity of complex mixtures of organic components in aerosol is important for understanding the hygroscopic response of organic aerosol in the atmosphere. We report new measurements of the hygroscopicity of mixtures of dicarboxylic acids and amino acids using a comparative kinetic electrodynamic balance (CK-EDB) approach, inferring the equilibrium water content of the aerosol from close to a saturation relative humidity (100%) down to 80%. We show that the solution densities and refractive indices of the mixtures can be estimated with an accuracy of better than ±2% using the molar refractive index mixing rule and densities and refractive indices for the individual binary organic–aqueous solutions. Further, we show that the often-used mass-, volume-, and mole-weighted mixing rules to estimate the hygroscopicity parameter κ can overestimate the hygroscopic parameter by a factor of as much as 3, highlighting the need to understand the specific nonideal interactions that may arise synergistically in mixtures and cannot be represented by simple models. Indeed, in some extreme cases the hygroscopicity of a multicomponent mixture can be very close to that for the least hygroscopic component. For mixtures of similar components for which no additional synergistic interactions need be considered, the hygroscopicity of the mixed component aerosol can be estimated with high accuracy from the hygroscopic response of the binary aqueous–organic aerosol. In conclusion, we suggest that the hygroscopicity of multicomponent organic aerosol can be highly nonadditive and that simple correlations of hygroscopicity with composition may often misrepresent the level of complexity essential to interpreting aerosol hygroscopicity

Hygroscopic properties of aminium sulfate aerosols

Alkylaminium sulfates originate from the neutralisation reaction between short-chained amines and sulfuric acid and have been detected in atmospheric aerosol particles. Their physicochemical behaviour is less well characterised than their inorganic equivalent, ammonium sulfate, even though they play a role in atmospheric processes such as the nucleation and growth of new particles and cloud droplet formation. In this work, a comparative evaporation kinetics experimental technique using a cylindrical electrodynamic balance is applied to determine the hygroscopic properties of six short-chained alkylaminium sulfates, specifically mono-, di-, and tri-methylaminium sulfate and mono-, di-, and tri-ethyl aminium sulfate. This approach allows for the retrieval of a water-activity-dependent growth curve in less than 10 s, avoiding the uncertainties that can arise from the volatilisation of semi-volatile components. Measurements are made on particles > 5 µm in radius, avoiding the need to correct equilibrium measurements for droplet-surface curvature with assumed values of the droplet-surface tension. Variations in equilibrium solution droplet composition with varying water activity are reported over the range 0.5 to > 0.98, along with accurate parameterisations of solution density and refractive index. The uncertainties in water activities associated with the hygroscopicity measurements are typically  0.9 and  ∼  ±1 % below 0.9, with maximum uncertainties in diameter growth factors of ±0.7 %. Comparison with previously reported measurements show deviation across the entire water activity range

Hygroscopic properties of aminium sulfate aerosols

Alkylaminium sulfates originate from the neutralisation reaction between short-chained amines and sulfuric acid and have been detected in atmospheric aerosol particles. Their physicochemical behaviour is less well characterised than their inorganic equivalent, ammonium sulfate, even though they play a role in atmospheric processes such as the nucleation and growth of new particles and cloud droplet formation. In this work, a comparative evaporation kinetics experimental technique using a cylindrical electrodynamic balance is applied to determine the hygroscopic properties of six short-chained alkylaminium sulfates, specifically mono-, di-, and tri-methylaminium sulfate and mono-, di-, and tri-ethyl aminium sulfate. This approach allows for the retrieval of a water-activity-dependent growth curve in less than 10 s, avoiding the uncertainties that can arise from the volatilisation of semi-volatile components. Measurements are made on particles > 5 µm in radius, avoiding the need to correct equilibrium measurements for droplet-surface curvature with assumed values of the droplet-surface tension. Variations in equilibrium solution droplet composition with varying water activity are reported over the range 0.5 to > 0.98, along with accurate parameterisations of solution density and refractive index. The uncertainties in water activities associated with the hygroscopicity measurements are typically  0.9 and  ∼  ±1 % below 0.9, with maximum uncertainties in diameter growth factors of ±0.7 %. Comparison with previously reported measurements show deviation across the entire water activity range

Probing the Evaporation Dynamics of Ethanol/Gasoline Biofuel Blends Using Single Droplet Manipulation Techniques

Peer reviewedPublisher PD

The medicinal plant Tabebuia impetiginosa potently reduces pro-inflammatory cytokine responses in primary human lymphocytes

Bark from the Handroanthus impetiginosus (Mart. ex DC.) Mattos (Bignoniaceae) tree has long been used in traditional South American healing practises to treat inflammation. However, its anti-inflammatory activity has not been closely examined. Here we use chemical extraction, qualitative phytochemical examination, toxicity testing and quantitative examination of anti-inflammatory activity on human cells ex vivo. All extracts were found to be nontoxic. We found different extracts exhibited unique cytokine profiles with some extracts outperforming a positive control used in the clinic. These results verify the immunomodulatory activity of Handroanthus impetiginosus (Mart. ex DC.) Mattos (Bignoniaceae) tree bark-derived compounds. Collectively, combining a lack of toxicity and potency in human immune cells supports further fractionation and research

A purely kinetic description of the evaporation of water droplets

The process of water evaporation, although deeply studied, does not enjoy a kinetic description that captures known physics and can be integrated with other detailed processes such as drying of catalytic membranes embedded in vapor-fed devices and chemical reactions in aerosol whose volumes are changing dynamically. In this work, we present a simple, three-step kinetic model for water evaporation that is based on theory and validated by using well-established thermodynamic models of droplet size as a function of time, temperature, and relative humidity as well as data from time-resolved measurements of evaporating droplet size. The kinetic mechanism for evaporation is a combination of two limiting processes occurring in the highly dynamic liquid-vapor interfacial region: direct first order desorption of a single water molecule and desorption resulting from a local fluctuation, described using third order kinetics. The model reproduces data over a range of relative humidities and temperatures only if the interface that separates bulk water from gas phase water has a finite width, consistent with previous experimental and theoretical studies. The influence of droplet cooling during rapid evaporation on the kinetics is discussed; discrepancies between the various models point to the need for additional experimental data to identify their origin

Effect of crystallization kinetics on the properties of spray dried microparticles

<p>A droplet chain technique was used to study the influence of the crystallization process on the morphology of spray dried microparticles. A piezoceramic dispenser produced a chain of monodisperse solution droplets with an initial diameter in the range of 60–80 µm. Aqueous solutions of sodium nitrate were prepared in concentrations ranging from 5 mg/ml to 5⋅10⁻⁵ mg/ml. The solution droplets were injected into a laminar flow with gas temperatures varying from 25 to 150°C, affecting the droplet temperature and the evaporation rate, accordingly. Dried particles with diameters between 0.3 and 18 µm were collected. The properties of the collected microparticles were studied and correlated with a particle formation model which predicted the onset of saturation and crystallization. The model accounted for the dependence of the diffusion coefficient of sodium nitrate in water on droplet viscosity. The viscosity trend for sodium nitrate solutions was determined by studying the relaxation time observed during coalescence of two aqueous sodium nitrate droplets levitated in optical tweezers. The combination of theoretical derivations and experimental results showed that longer time available for crystallization correlates with larger crystal size and higher degrees of crystallinity in the final microparticles.</p> <p>© 2016 American Association for Aerosol Research</p

Mass Accommodation of Water: Bridging the Gap Between Molecular Dynamics Simulations and Kinetic Condensation Models

The condensational growth of submicrometer aerosol particles to climate relevant sizes is sensitive to their ability to accommodate vapor molecules, which is described by the mass accommodation coefficient. However, the underlying processes are not yet fully understood. We have simulated the mass accommodation and evaporation processes of water using molecular dynamics, and the results are compared to the condensation equations derived from the kinetic gas theory to shed light on the compatibility of the two. Molecular dynamics simulations were performed for a planar TIP4P-Ew water surface at four temperatures in the range 268–300 K as well as two droplets, with radii of 1.92 and 4.14 nm at T = 273.15 K. The evaporation flux from molecular dynamics was found to be in good qualitative agreement with that predicted by the simple kinetic condensation equations. Water droplet growth was also modeled with the kinetic multilayer model KM-GAP of Shiraiwa et al. [ Atmos. Chem. Phys. 2012, 12, 2777]. It was found that, due to the fast transport across the interface, the growth of a pure water droplet is controlled by gas phase diffusion. These facts indicate that the simple kinetic treatment is sufficient in describing pure water condensation and evaporation. The droplet size was found to have minimal effect on the value of the mass accommodation coefficient. The mass accommodation coefficient was found to be unity (within 0.004) for all studied surfaces, which is in agreement with previous simulation work. Additionally, the simulated evaporation fluxes imply that the evaporation coefficient is also unity. Comparing the evaporation rates of the mass accommodation and evaporation simulations indicated that the high collision flux, corresponding to high supersaturation, present in typical molecular dynamics mass accommodation simulations can under certain conditions lead to an increase in the evaporation rate. Consequently, in such situations the mass accommodation coefficient can be overestimated, but in the present cases the corrected values were still close to unity with the lowest value at ≈0.99

Immunological responses to envenomation

Venoms are complex mixtures of toxic compounds delivered by bite or sting. In humans, the consequences of envenomation range from self-limiting to lethal. Critical host defence against envenomation comprises innate and adaptive immune strategies targeted towards venom detection, neutralisation, detoxification, and symptom resolution. In some instances, venoms mediate immune dysregulation that contributes to symptom severity. This review details the involvement of immune cell subtypes and mediators, particularly of the dermis, in host resistance and venom-induced immunopathology. We further discuss established venom-associated immunopathology, including allergy and systemic inflammation, and investigate Irukandji syndrome as a potential systemic inflammatory response. Finally, this review characterises venom-derived compounds as a source of immune modulating drugs for treatment of disease