Liquid–Liquid Phase Separation in Aerosol Particles: Imaging at the Nanometer Scale

O’Brien, Rachel E.; Wang, Bingbing; Kelly, Stephen T.; Lundt, Nils; You, Yuan; Bertram, Allan K.; Leone, Stephen R.; Laskin, Alexander; Gilles, Mary K.

doi:10.1021/acs.est.5b00062

Cited by 94 publications

(122 citation statements)

References 36 publications

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“…HMML or there is a barrier to 2MGA volatilization. For example, if organic-inorganic phase separation occurs at RH between efflorescence and deliquescence, 54,55 the reaction of gas-phase HMML with water and solvated ions and the volatilization of aqueous 2MGA may be hindered by an organic shell. Additionally, when liquid water content is lower (and thus, ionic strength is higher), organic acids such as 2MGA may form involatile salts with NH 4 + and other cations.…”

Section: Atmospheric Fate Of Hmmlmentioning

confidence: 99%

Mechanism of the hydroxyl radical oxidation of methacryloyl peroxynitrate (MPAN) and its pathway toward secondary organic aerosol formation in the atmosphere

Nguyen

Bates

Crounse

et al. 2015

Phys. Chem. Chem. Phys.

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118

150

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Methacryloyl peroxynitrate (MPAN), the acyl peroxynitrate of methacrolein, has been suggested to be an important secondary organic aerosol (SOA) precursor from isoprene oxidation. Yet, the mechanism by which MPAN produces SOA through reaction with the hydroxyl radical (OH) is unclear. We systematically evaluate three proposed mechanisms in controlled chamber experiments and provide the first experimental support for the theoretically-predicted lactone formation pathway from the MPAN + OH reaction, producing hydroxymethyl-methyl-a-lactone (HMML). The decomposition of the MPAN-OH adduct yields HMML + NO 3 (B75%) and hydroxyacetone + CO + NO 3 (B25%), out-competing its reaction with atmospheric oxygen. The production of other proposed SOA precursors, e.g., methacrylic acid epoxide (MAE), from MPAN and methacrolein are negligible (o2%). Furthermore, we show that the beta-alkenyl moiety of MPAN is critical for lactone formation. Alkyl radicals formed cold via H-abstraction by OH do not decompose to HMML, even if they are structurally identical to the MPAN-OH adduct. The SOA formation from HMML, from polyaddition of the lactone to organic compounds at the particle interface or in the condensed phase, is close to unity under dry conditions. However, the SOA yield is sensitive to particle liquid water and solvated ions. In hydrated inorganic particles, HMML reacts primarily with H 2 O to produce the monomeric 2-methylglyceric acid (2MGA) or with aqueous sulfate and nitrate to produce the associated organosulfate and organonitrate, respectively. 2MGA, a tracer for isoprene SOA, is semivolatile and its accommodation in aerosol water decreases with decreasing pH. Conditions that enhance the production of neutral 2MGA suppress SOA mass from the HMML channel. Considering the liquid water content and pH ranges of ambient particles, 2MGA will exist largely as a gaseous compound in some parts of the atmosphere.

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Section: Atmospheric Fate Of Hmmlmentioning

confidence: 99%

Mechanism of the hydroxyl radical oxidation of methacryloyl peroxynitrate (MPAN) and its pathway toward secondary organic aerosol formation in the atmosphere

Nguyen

Bates

Crounse

et al. 2015

Phys. Chem. Chem. Phys.

Self Cite

118

150

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“…[12][13][14][15][16][17][18] Hence, it represents a significant improvement over more commonly used optical microscopy (OM) approaches. [19][20][21][22][23][24][25] Complemented with X-rays microanalysis, ESEM has the potential to conduct microscopy studies of ice nucleation along with chemical characterization of the INPs.…”

Section: Introductionmentioning

confidence: 99%

Direct observation of ice nucleation events on individual atmospheric particles

Wang

Knopf

China

et al. 2016

Phys. Chem. Chem. Phys.

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The work presents microscopic observations of heterogeneous ice nucleation from experiments conducted inside an environmental scanning electron microscope. Observations of ice formation on kaolinite particles demonstrate that ice preferentially nucleates at the edges of the stacked platelets, rather than on the basal planes. This platform is applied for directly detecting and tracking ice nucleating particles in ambient aerosol samples and is complemented by micro-spectroscopic chemical imaging. This technique opens a path to new physical chemistry studies of ice formation in atmospheric science, cryobiology, and material science.www.rsc.org/pccp Heterogeneous ice nucleation is a physical chemistry process of critical relevance to a range of topics in the fundamental and applied sciences and technologies. Heterogeneous ice nucleation remains insufficiently understood, partially due to the lack of experimental methods capable of obtaining in situ microscopic details of ice formation over nucleating substrates or particles. We present microscopic observations of ice nucleation events on kaolinite particles at the nanoscale and demonstrate the capability of direct tracking and micro-spectroscopic characterization of individual ice nucleating particles (INPs) in an authentic atmospheric sample. This approach utilizes a custom-built ice nucleation cell, interfaced with an Environmental Scanning Electron Microscope (IN-ESEM platform) operated at temperatures and relative humidities relevant for heterogeneous ice nucleation. The IN-ESEM platform allows dynamic observations of individual ice formation events over particles in isobaric and isothermal experiments. Isothermal experiments on individual kaolinite particles demonstrate that ice crystals preferably nucleate at the edges of the stacked kaolinite platelets, rather than on their basal planes.These experimental observations of the location of ice nucleation provide direct information for further theoretical chemistry predictions of ice formation on kaolinite.

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“…These can be broadly categorized as a homogeneously mixed single-phase structure, and liquid-liquid phase-separated (LLPS) structures (Kwamena et al 2010;Song et al 2013;You et al 2014;Stewart et al 2015;You and Bertram 2015;Metcalf et al 2016). For the phase-separated particles, the predominant morphological states are a core-shell or partially engulfed structure (Buajarern et al 2007a;Reid et al 2011;Song et al 2013;O'Brien et al 2015).…”

Section: Introductionmentioning

confidence: 99%

Advanced aerosol optical tweezers chamber design to facilitate phase-separation and equilibration timescale experiments on complex droplets

Gorkowski

Beydoun

Aboff

et al. 2016

Aerosol Science and Technology

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The phase-separation of mixed aerosol particles and the resulting morphology plays an important role in determining the interactions of liquid aerosols with their gas-phase environment. We present the application of a new aerosol optical tweezers chamber for delivering a uniformly mixed aerosol flow to the trapped droplet's position for performing experiments that determine the phaseseparation and resulting properties of complex mixed droplets. This facilitates stable trapping when adding additional phases through aerosol coagulation, and reproducible measurements of the droplet's equilibration timescale. We demonstrate the trapping of pure organic carbon droplets, which allows us to study the morphology of droplets containing pure hydrocarbon phases to which a second phase is added by coagulation. A series of experiments using simple compounds are presented to establish our ability to use the cavity enhanced Raman spectra to distinguish between homogeneous single-phase, and phase-separated core-shell or partially engulfed morphologies. The core-shell morphology is distinguished by the pattern of the whispering gallery modes (WGMs) in the Raman spectra where the WGMs are influenced by refraction through both phases. A coreshell optimization algorithm was developed to provide a more accurate and detailed analysis of the WGMs than is possible using the homogeneous Mie scattering solution. The unique analytical capabilities of the aerosol optical tweezers provide a new approach for advancing our understanding of the chemical and physical evolution of complex atmospheric particulate matter, and the important environmental impacts of aerosols on atmospheric chemistry, air quality, human health, and climate change. EDITORThomas Kirchstetter

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Liquid–Liquid Phase Separation in Aerosol Particles: Imaging at the Nanometer Scale

Cited by 94 publications

References 36 publications

Mechanism of the hydroxyl radical oxidation of methacryloyl peroxynitrate (MPAN) and its pathway toward secondary organic aerosol formation in the atmosphere

Mechanism of the hydroxyl radical oxidation of methacryloyl peroxynitrate (MPAN) and its pathway toward secondary organic aerosol formation in the atmosphere

Direct observation of ice nucleation events on individual atmospheric particles

Advanced aerosol optical tweezers chamber design to facilitate phase-separation and equilibration timescale experiments on complex droplets

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