89 research outputs found
Influence of organic films on the evaporation and condensation of water in aerosol
Uncertainties in quantifying the kinetics of evaporation and condensation of water from atmospheric aerosol are a significant contributor to the uncertainty in predicting cloud droplet number and the indirect effect of aerosols on climate. The influence of aerosol particle surface composition, particularly the impact of surface active organic films, on the condensation and evaporation coefficients remains ambiguous. Here, we report measurements of the influence of organic films on the evaporation and condensation of water from aerosol particles. Significant reductions in the evaporation coefficient are shown to result when condensed films are formed by monolayers of long-chain alcohols [C(n)H((2n+1))OH], with the value decreasing from 2.4 × 10(−3) to 1.7 × 10(−5) as n increases from 12 to 17. Temperature-dependent measurements confirm that a condensed film of long-range order must be formed to suppress the evaporation coefficient below 0.05. The condensation of water on a droplet coated in a condensed film is shown to be fast, with strong coherence of the long-chain alcohol molecules leading to islanding as the water droplet grows, opening up broad areas of uncoated surface on which water can condense rapidly. We conclude that multicomponent composition of organic films on the surface of atmospheric aerosol particles is likely to preclude the formation of condensed films and that the kinetics of water condensation during the activation of aerosol to form cloud droplets is likely to remain rapid
Aerobiology: Experimental considerations, observations and future tools
ABSTRACT
Understanding airborne survival and decay of microorganisms is important for a range of public health and biodefense applications, including epidemiological and risk analysis modeling. Techniques for experimental aerosol generation, retention in the aerosol phase, and sampling require careful consideration and understanding so that they are representative of the conditions the bioaerosol would experience in the environment. This review explores the current understanding of atmospheric transport in relation to advances and limitations of aerosol generation, maintenance in the aerosol phase, and sampling techniques. Potential tools for the future are examined at the interface between atmospheric chemistry, aerosol physics, and molecular microbiology where the heterogeneity and variability of aerosols can be explored at the single-droplet and single-microorganism levels within a bioaerosol. The review highlights the importance of method comparison and validation in bioaerosol research and the benefits that the application of novel techniques could bring to increasing the understanding of aerobiological phenomena in diverse research fields, particularly during the progression of atmospheric transport, where complex interdependent physicochemical and biological processes occur within bioaerosol particles.</jats:p
Dynamics of particle size on inhalation of environmental aerosol and impact on deposition fraction
Inhalation of elevated
levels of particulate air pollution has
been shown to elicit the onset of adverse health effects in humans,
where the magnitude of the response is a product of where in the lung
the particulate dose is delivered. At any point in time during inhalation
the depositional flux of the aerosol is a function of the radius of
the droplet, thus a detailed understanding of the rate and magnitude
of the mass flux of water to the droplet during inhalation is crucial.
In this study, we assess the impact of aerosol hygroscopicity on deposited
dose through the inclusion of a detailed treatment of the mass flux
of water to account for the dynamics of particle size in a modified
version of the standard International Commission on Radiological Protection
(ICRP) whole lung deposition model. The ability to account for the
role of the relative humidity (RH) of the aerosol prior to, and during,
inhalation on the deposition pattern is explored, and found to have
a significant effect on the deposition pattern. The model is verified
by comparison to previously published measurements, and used to demonstrate
that ambient RH affects where in the lung indoor particulate air pollution
is delivered
Identifying time-dependent changes in the morphology of an individual aerosol particle from their light scattering patterns
Water Uptake by Evaporating pMDI Aerosol Prior to Inhalation Affects Both Regional and Total Deposition in the Respiratory System
© 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https://creativecommons.org/licenses/by/4.0/)As pulmonary drug deposition is a function of aerosol particle size distribution, it is critical that the dynamics of particle formation and maturation in pMDI sprays in the interim between generation and inhalation are fully understood. This paper presents an approach to measure the evaporative and condensational fluxes of volatile components and water from and to solution pMDI droplets following generation using a novel technique referred to as the Single Particle Electrodynamic Lung (SPEL). In doing so, evaporating aerosol droplets are shown capable of acting as condensation nuclei for water. Indeed, we show that the rapid vaporisation of volatile components from a volatile droplet is directly correlated to the volume of water taken up by condensation. Furthermore, a significant volume of water is shown to condense on droplets of a model pMDI formulation (hydrofluoroalkane (HFA), ethanol and glycerol) during evaporative droplet ageing, displaying a dramatic shift from a core composition of a volatile species to that of predominantly water (non-volatile glycerol remained in this case). This yields a droplet with a water activity of 0.98 at the instance of inhalation. The implications of these results on regional and total pulmonary drug deposition are explored using the International Commission of Radiological Protection (ICRP) deposition model, with an integrated semi-analytical treatment of hygroscopic growth. Through this, droplets with water activity of 0.98 upon inhalation are shown to produce markedly different dose deposition profiles to those with lower water activities at the point of inspiration.Peer reviewe
Dynamics of aerosol size during inhalation : Hygroscopic growth of commercial nebulizer formulations
We thank the Elizabeth Blackwell Institute (EBI) for financial support through the EBI Early Career Research Fellowship awarded to AEH, and the EPSRC for financial support through a Leadership Fellowship awarded to JPR (grant reference EP/G007713/1). This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution and reproduction in any medium, provided the original author and source are creditedThe size of aerosol particles prior to, and during, inhalation influences the site of deposition within the lung. As such, a detailed understanding of the hygroscopic growth of an aerosol during inhalation is necessary to accurately model the deposited dose. In the first part of this study, it is demonstrated that the aerosol produced by a nebulizer, depending on the airflows rates, may experience a (predictable) wide range of relative humidity prior to inhalation and undergo dramatic changes in both size and solute concentration. A series of sensitive single aerosol analysis techniques are then used to make measurements of the relative humidity dependent thermodynamic equilibrium properties of aerosol generated from four common nebulizer formulations. Measurements are also reported of the kinetics of mass transport during the evaporation or condensation of water from the aerosol. Combined, these measurements allow accurate prediction of the temporal response of the aerosol size prior to and during inhalation. Specifically, we compare aerosol composed of pure saline (150 mM sodium chloride solution in ultrapure water) with two commercially available nebulizer products containing relatively low compound doses: Breath, consisting of a simple salbutamol sulfate solution (5 mg/2.5 mL; 1.7 mM) in saline, and Flixotide Nebules, consisting of a more complex stabilized fluticasone propionate suspension (0.25 mg/mL; 0.5 mM in saline. A mimic of the commercial product Tobi (60 mg/mL tobramycin and 2.25 mg/mL NaC1, pH 5.5-6.5) is also studied, which was prepared in house. In all cases, the presence of the pharmaceutical was shown to have a profound effect on the magnitude, and in some cases the rate, of the mass flux of water to and from the aerosol as compared to saline. These findings provide physical chemical evidence supporting observations from human inhalation studies, and suggest that using the growth dynamics of a pure saline aerosol in a lung inhalation model to represent nebulizer formulations may not be representative of the actual behavior of the aerosolized drug solutions. (C) 2014 Published by Elsevier B.V.Peer reviewe
Transformative Approach To Investigate the Microphysical Factors Influencing Airborne Transmission of Pathogens
Studies of Competing Evaporation Rates of Multiple Volatile Components from a Single Binary-Component Aerosol Droplet
Evaporation kinetics of polyol droplets:determination of evaporation coefficients and diffusion constants
Coalescence Sampling and Analysis of Aerosols using Aerosol Optical Tweezers
We present a first
exploratory study to assess the use of aerosol
optical tweezers as an instrument for sampling and detecting accumulation-
and coarse-mode aerosol. A subpicoliter aqueous aerosol droplet is
captured in the optical trap and used as a sampling volume, accreting
mass from a free-flowing aerosol generated by a medical nebulizer
or atomizer. Real-time measurements of the initial stability in size,
refractive index, and composition of the sampling droplet inferred
from Raman spectroscopy confirm that these quantities can be measured
with high accuracy and low noise. Typical standard deviations in size
and refractive index of the sampling droplet over a period of 200
s are <±2 nm and <±0.0005, respectively, equivalent
to <±0.04% in both measured quantities. A standard deviation
of <±1% over a 200 s period is achieved in the spontaneous
Raman intensity measurement. When sampling coarse-mode aerosol, mass
changes of <10 pg can be detected by the sampling droplet as discrete
coalescence events. With accumulation-mode aerosol, we show that fluxes
as low as 0.068 pg s<sup>–1</sup> can be detected over a 50
s period, equivalent to ∼3 pg of sampled material
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