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Investigations Into the Physical Properties of Mixed Organic-Inorganic Aerosol Particles.

Record Type:	Language materials, manuscript : Monograph/item
Title/Author:	Investigations Into the Physical Properties of Mixed Organic-Inorganic Aerosol Particles./
Author:	Wallace, Brandon J.
Description:	1 online resource (226 pages)
Notes:	Source: Dissertations Abstracts International, Volume: 85-11, Section: B.
Contained By:	Dissertations Abstracts International85-11B.
Subject:	Volatile organic compounds--VOCs. -
Online resource:	click for full text (PQDT)
ISBN:	9798382617510

Investigations Into the Physical Properties of Mixed Organic-Inorganic Aerosol Particles.
Wallace, Brandon J.

Investigations Into the Physical Properties of Mixed Organic-Inorganic Aerosol Particles. - 1 online resource (226 pages)

Source: Dissertations Abstracts International, Volume: 85-11, Section: B.

Thesis (Ph.D.)--McGill University (Canada), 2023.

Includes bibliographical references

Aerosol particles are ubiquitous in nature and are important regulators of the atmosphere and our climate. When predicting the heating of our atmosphere, aerosol remain one of the largest uncertainties. For atmospheric aerosol, many fundamental microphysical questions still remain which contribute to these uncertainties. To improve our understanding of atmospheric aerosol at a fundamental level, we employ experimental and modelling methods to investigate the microphysical properties of single aerosol particles.In the atmosphere, organic aerosol can exist in highly viscous and glassy states. In these phases, diffusion becomes limited. One consequence of this is that water uptake and loss in response to a relative humidity (RH) change will be slow. This will affect the size, optical properties and role in cloud activation processes of these aerosol. In this work, we derive an analytical expression for the time-dependent radius during a RH step. This is achieved using the convection-diffusion equation and a moving boundary condition. We then derive an expression for the characteristic equilibration timescale. When compared to full numerical simulations, the analytical expression for equilibration times yields excellent agreement. Furthermore, we explore fundamental properties of mass transport in diffusion-limited systems, such as the importance of the final state.We then investigate mass transport in a multicomponent aerosol system consisting of a viscous organic mixed with an inorganic salt. As atmospheric aerosol are multicomponent in nature, it is important to understand how interactions between solutes may influence the properties of the aerosol particle. Using a linear quadrupole electrodynamic balance (LQ-EDB), we suspend a single aerosol particle in a contact-free environment. After quickly changing the RH, we quantify equilibration times by measuring the spectral change in morphology-dependent resonances (MDRs) over time. Equilibration times are found to deviate from simple mixing rules, wherein at certain molar ratios of organic to inorganic, equilibration times exceed either limiting binary case. To understand the fundamental properties leading to this result, we develop a multicomponent diffusion model using the Maxwell-Stefan (MS) framework, whereby mass transport is driven by gradients in chemical potential. We report satisfactory agreement between modelled and measured equilibration times. We conclude the observed trend in equilibration time with respect to molar ratio is a result of thermodynamic nonideality, where the nonideal interactions lead to reduced water content at certain molar ratios and slower mass transport.Lastly, we investigate the pH and gas-particle partitioning of aerosol containing dicarboxylic acids (DCAs), which are model semi-volatile organic compounds (SVOCs), in multicomponent mixtures with an inorganic base. Experimentally, this is achieved using a dual-beam optical trap and cavity-enhanced Raman spectroscopy (CERS). By monitoring the change in MDR positions over time, we quantify the evaporation properties of DCAs. Simultaneously, by measuring the relative Raman signal of a conjugate acid-base pair, we probe the acidity of the aerosol particle. We show that by increasing the pH, the DCAs become increasingly deprotonated and as a result, more stable in the condensed phase of the aerosol particle. This result is confirmed through the development of a Maxwell-type partitioning model and a pH model. Furthermore, through the continual evaporation of a DCA over time, we observe a time-dependent pH and reduced evaporation of the DCA. These results demonstrate a pathway for increased organic content in aerosol and also present a mechanism for a time-dependent pH in these systems.

Electronic reproduction.
Ann Arbor, Mich. :
ProQuest,
2024

Mode of access: World Wide Web

ISBN: 9798382617510Subjects--Topical Terms:

1437711
Volatile organic compounds--VOCs.
Index Terms--Genre/Form:

554714
Electronic books.

Investigations Into the Physical Properties of Mixed Organic-Inorganic Aerosol Particles.
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520 $a Aerosol particles are ubiquitous in nature and are important regulators of the atmosphere and our climate. When predicting the heating of our atmosphere, aerosol remain one of the largest uncertainties. For atmospheric aerosol, many fundamental microphysical questions still remain which contribute to these uncertainties. To improve our understanding of atmospheric aerosol at a fundamental level, we employ experimental and modelling methods to investigate the microphysical properties of single aerosol particles.In the atmosphere, organic aerosol can exist in highly viscous and glassy states. In these phases, diffusion becomes limited. One consequence of this is that water uptake and loss in response to a relative humidity (RH) change will be slow. This will affect the size, optical properties and role in cloud activation processes of these aerosol. In this work, we derive an analytical expression for the time-dependent radius during a RH step. This is achieved using the convection-diffusion equation and a moving boundary condition. We then derive an expression for the characteristic equilibration timescale. When compared to full numerical simulations, the analytical expression for equilibration times yields excellent agreement. Furthermore, we explore fundamental properties of mass transport in diffusion-limited systems, such as the importance of the final state.We then investigate mass transport in a multicomponent aerosol system consisting of a viscous organic mixed with an inorganic salt. As atmospheric aerosol are multicomponent in nature, it is important to understand how interactions between solutes may influence the properties of the aerosol particle. Using a linear quadrupole electrodynamic balance (LQ-EDB), we suspend a single aerosol particle in a contact-free environment. After quickly changing the RH, we quantify equilibration times by measuring the spectral change in morphology-dependent resonances (MDRs) over time. Equilibration times are found to deviate from simple mixing rules, wherein at certain molar ratios of organic to inorganic, equilibration times exceed either limiting binary case. To understand the fundamental properties leading to this result, we develop a multicomponent diffusion model using the Maxwell-Stefan (MS) framework, whereby mass transport is driven by gradients in chemical potential. We report satisfactory agreement between modelled and measured equilibration times. We conclude the observed trend in equilibration time with respect to molar ratio is a result of thermodynamic nonideality, where the nonideal interactions lead to reduced water content at certain molar ratios and slower mass transport.Lastly, we investigate the pH and gas-particle partitioning of aerosol containing dicarboxylic acids (DCAs), which are model semi-volatile organic compounds (SVOCs), in multicomponent mixtures with an inorganic base. Experimentally, this is achieved using a dual-beam optical trap and cavity-enhanced Raman spectroscopy (CERS). By monitoring the change in MDR positions over time, we quantify the evaporation properties of DCAs. Simultaneously, by measuring the relative Raman signal of a conjugate acid-base pair, we probe the acidity of the aerosol particle. We show that by increasing the pH, the DCAs become increasingly deprotonated and as a result, more stable in the condensed phase of the aerosol particle. This result is confirmed through the development of a Maxwell-type partitioning model and a pH model. Furthermore, through the continual evaporation of a DCA over time, we observe a time-dependent pH and reduced evaporation of the DCA. These results demonstrate a pathway for increased organic content in aerosol and also present a mechanism for a time-dependent pH in these systems.
520 $a Les particules d'aerosols sont omnipresentes dans la nature et constituent d'importants regulateurs de l'atmosphere et de notre climat. Lorsqu'il s'agit de prevoir le rechauffement de notre atmosphere, les aerosols restent l'une des plus grandes incertitudes. Pour les aerosols atmospheriques, de nombreuses questions microphysiques fondamentales subsistent et contribuent a ces incertitudes. Pour ameliorer notre comprehension des aerosols atmospheriques a un niveau fondamental, nous utilisons des methodes experimentales et de modelisation pour etudier les proprietes microphysiques des particules d'aerosol individuelles.Dans l'atmosphere, les aerosols organiques peuvent exister dans des etats hautement visqueux ou vitreux. Dans ces phases, la diffusion est limitee. Entre autre, la prise et la perte d'eau en reponse a une variation de l'humidite relative ambiente (HR) sera lente, ce qui affectera de nombreuses proprietes de l'aerosol dont sa taille, ses proprietes optiques et son role dans l'activation des nuages. Dans ce travail, nous derivons une expression analytique pour le rayon dependant du temps lors d'un changement d'humidite relative. Pour ce faire, nous utilisons l'equation de convection-diffusion avec une condition de limite mobile. Par la suite, nous derivons une expression pour le temps caracteristique d'equilibrage. Comparee a des simulations numeriques completes, l'expression analytique donne d'excellents resultats. En outre, nous explorons les forces motrices fondamentales du transport de masse dans les systemes limites par la diffusion, telles que l'importance de l'etat final.Nous etudions ensuite le transport de masse dans un systeme d'aerosol multicomposant consistant d'un organique visqueux melange a un sel inorganique. Puisque les aerosols atmospheriques sont multicomposants par nature, il est important de comprendre comment les interactions entre les solutes peuvent influencer les proprietes de la particule d'aerosol. A l'aide d'une balance electrodynamique a quadripole lineaire, nous suspendons une particule d'aerosol dans un environnement sans contact. Suivant un changement rapide de l'humidite relative, nous quantifions les temps d'equilibrage en mesurant le changement spectral en fonction du temps des resonances dependantes de la morphologie (RDM). Les temps d'equilibrage ne suivent pas les regles simples de melange, dans la mesure ou, pour certains rapports molaires entre organique et inorganique, les temps d'equilibrage depassent l'un ou l'autre des cas binaires limitatifs. Pour comprendre les proprietes fondamentales conduisant a ce resultat, nous developpons un modele de diffusion multicomposant utilisant le cadre de Maxwell-Stefan (MS), dans lequel le transport de masse est dicte par des gradients de potentiel chimique. Nous constatons un accord satisfaisant entre les temps d'equilibrage modelises et mesures. Nous concluons que la tendance observee dans le temps d'equilibrage en fonction du rapport molaire est le resultat d'une non-idealite thermodynamique, ou les interactions non ideales conduisent a une teneur en eau reduite a certains rapports molaires et a un transport de masse plus lent.Enfin, nous etudions le pH et le partage gaz-particules d'un aerosol contenant des acides dicarboxyliques (ADC), qui sont des composes organiques semi-volatils, dans des melanges multicomposants avec une base inorganique. Experimentalement, on utilise un piege optique a double faisceau et la spectroscopie Raman amelioree par la cavite. En surveillant le changement des positions du RDM en fonction du temps, nous quantifions les proprietes d'evaporation des ADC.
533 $a Electronic reproduction. $b Ann Arbor, Mich. : $c ProQuest, $d 2024
538 $a Mode of access: World Wide Web
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