Changing shapes and implied viscosities of suspended submicron particles

Zhang, Yue; Sanchez, Mcd; Douet, C.; Wang, Yichao; Bateman, Adam P.; Gong, Zhaoheng; Kuwata, Mikinori; Renbaum-Wolff, Lindsay; Sato, B. B.; Liu, Peng Fei; Bertram, Allan K.; Geiger, Franz M.; Martin, Scot T.

doi:10.5194/acp-15-7819-2015

Cited by 115 publications

(178 citation statements)

References 51 publications

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“…COMSOL uses a finite element method and has a number of built-in modules that can be utilized to simulate a specific experimental condition. Recently, several research groups have employed COMSOL in atmospheric and aerosol chemistry studies Sellier et al, 2015;Y. Zhang et al, 2015).…”

Section: Cfd Simulationsmentioning

confidence: 99%

The Caltech Photooxidation Flow Tube reactor: design, fluid dynamics and characterization

et al. 2017

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Abstract. Flow tube reactors are widely employed to study gas-phase atmospheric chemistry and secondary organic aerosol (SOA) formation. The development of a new laminar-flow tube reactor, the Caltech Photooxidation Flow Tube (CPOT), intended for the study of gas-phase atmospheric chemistry and SOA formation, is reported here. The present work addresses the reactor design based on fluid dynamical characterization and the fundamental behavior of vapor molecules and particles in the reactor. The design of the inlet to the reactor, based on computational fluid dynamics (CFD) simulations, comprises a static mixer and a conical diffuser to facilitate development of a characteristic laminar flow profile. To assess the extent to which the actual performance adheres to the theoretical CFD model, residence time distribution (RTD) experiments are reported with vapor molecules (O 3 ) and submicrometer ammonium sulfate particles. As confirmed by the CFD prediction, the presence of a slight deviation from strictly isothermal conditions leads to secondary flows in the reactor that produce deviations from the ideal parabolic laminar flow. The characterization experiments, in conjunction with theory, provide a basis for interpretation of atmospheric chemistry and SOA studies to follow. A 1-D photochemical model within an axially dispersed plug flow reactor (AD-PFR) framework is formulated to evaluate the oxidation level in the reactor. The simulation indicates that the OH concentration is uniform along the reactor, and an OH exposure (OH exp ) ranging from ∼ 10 9 to ∼ 10 12 molecules cm −3 s can be achieved from photolysis of H 2 O 2 . A method to calculate OH exp with a consideration for the axial dispersion in the present photochemical system is developed.

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Section: Cfd Simulationsmentioning

confidence: 99%

The Caltech Photooxidation Flow Tube reactor: design, fluid dynamics and characterization

et al. 2017

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“…In addition, mass concentrations of biogenic SOA are typically ≤ 10 µg m −3 in the atmosphere (Spracklen et al, 2011). As a starting point to quantify how often mixing times of organic molecules are < 1 h within α-pinene SOA generated using low, atmospherically relevant mass concentrations, we developed a temperature-independent parameterization using the room-temperature viscosity data for α-pinene SOA from Zhang et al (2015) (Table S5) and roomtemperature viscosity data for water from (Crittenden et al, 2012) (Table S3). Zhang et al (2015) measured the viscosity of α-pinene SOA over a range of relative humidities (0-60 %), and the SOA used in these experiments was generated in the laboratory using a mass concentration of ∼ 70 µg m −3 .…”

Section: Effect Of Mass Concentration Used To Generate the Soamentioning

confidence: 99%

“…As a starting point to quantify how often mixing times of organic molecules are < 1 h within α-pinene SOA generated using low, atmospherically relevant mass concentrations, we developed a temperature-independent parameterization using the room-temperature viscosity data for α-pinene SOA from Zhang et al (2015) (Table S5) and roomtemperature viscosity data for water from (Crittenden et al, 2012) (Table S3). Zhang et al (2015) measured the viscosity of α-pinene SOA over a range of relative humidities (0-60 %), and the SOA used in these experiments was generated in the laboratory using a mass concentration of ∼ 70 µg m −3 . The median room-temperature viscosities reported by Zhang et al are higher than the median room-temperature viscosities reported by Grayson et al (2016) using a mass concentration of 520 µg m −3 (Fig.…”

Section: Effect Of Mass Concentration Used To Generate the Soamentioning

confidence: 99%

“…If SVOCs are not well mixed within SOA particles on this timescale, then chemical transport models could incorrectly predict SOA mass concentrations by up to an order of magnitude (Shiraiwa and Seinfeld, 2012) and incorrectly predict the size of SOA particles (Zaveri et al, 2014), with implications for air quality and climate predictions (Seinfeld and Pandis, 2006). Recent research has shown that mixing times of organic molecules within SOA particles can be > 1 h at roomtemperature and at low RHs (Abramson et al, 2013;Grayson et al, 2016;Liu et al, 2016;Perraud et al, 2012;RenbaumWolff et al, 2013;Song et al, 2016;Ye et al, 2016;Zhang et al, 2015). In addition, studies have shown that proxies of SOA particles can form glass at low RHs and low temperatures Zobrist et al, 2008).…”

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confidence: 99%

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Mixing times of organic molecules within secondary organic aerosol particles: a global planetary boundary layer perspective

et al. 2017

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Abstract. When simulating the formation and life cycle of secondary organic aerosol (SOA) with chemical transport models, it is often assumed that organic molecules are well mixed within SOA particles on the timescale of 1 h. While this assumption has been debated vigorously in the literature, the issue remains unresolved in part due to a lack of information on the mixing times within SOA particles as a function of both temperature and relative humidity. Using laboratory data, meteorological fields, and a chemical transport model, we estimated how often mixing times are < 1 h within SOA in the planetary boundary layer (PBL), the region of the atmosphere where SOA concentrations are on average the highest. First, a parameterization for viscosity as a function of temperature and RH was developed for α-pinene SOA using room-temperature and low-temperature viscosity data for α-pinene SOA generated in the laboratory using mass concentrations of ∼ 1000 µg m −3 . Based on this parameterization, the mixing times within α-pinene SOA are < 1 h for 98.5 % and 99.9 % of the occurrences in the PBL during January and July, respectively, when concentrations are significant (total organic aerosol concentrations are > 0.5 µg m −3 at the surface). Next, as a starting point to quantify how often mixing times of organic molecules are < 1 h within α-pinene SOA generated using low, atmospherically relevant mass concentrations, we developed a temperatureindependent parameterization for viscosity using the roomtemperature viscosity data for α-pinene SOA generated in the laboratory using a mass concentration of ∼ 70 µg m −3 . Based on this temperature-independent parameterization, mixing times within α-pinene SOA are < 1 h for 27 and 19.5 % of the occurrences in the PBL during January and July, respectively, when concentrations are significant. However, associated with these conclusions are several caveats, and due to these caveats we are unable to make strong conclusions about how often mixing times of organic molecules are < 1 h within α-pinene SOA generated using low, atmospherically relevant mass concentrations. Finally, a parameterization for viscosity of anthropogenic SOA as a function of temperature and RH was developed using sucrose-water data. Based on this parameterization, and assuming sucrose is a good proxy for anthropogenic SOA, 70 and 83 % of the mixing times within anthropogenic SOA in the PBL are < 1 h for January and July, respectively, when concentrations are significant. These percentages are likely lower limits due to the assumptions used to calculate mixing times.

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“…This is mainly because viscosity, bounce factors and glass transition temperatures only provide indirect evidence for kinetic limitations of water diffusivity, whereas diffusion coefficients in the amorphous state span many orders of magnitude. Previous studies investigated the viscosity of atmospherically relevant model systems at around room temperature and used the StokesEinstein relation to derive diffusion coefficients (RenbaumWolff et al, 2013;Hosny et al, 2013;Power et al, 2013;Abramson et al, 2013;Booth et al, 2014;Zhang et al, 2015). However, diffusivity and viscosity decouple below approximately 1.2 T g or higher, where T g refers to the thermal glass transition temperature as measured by differential scanning calorimetry (Mapes et al, 2006;Corti et al, 2008).…”

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confidence: 99%

Viscous organic aerosol particles in the upper troposphere: diffusivity-controlled water uptake and ice nucleation?

Lienhard

Huisman

Krieger³

et al. 2015

Atmos. Chem. Phys.

119

190

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Abstract. New measurements of water diffusion in secondary organic aerosol (SOA) material produced by oxidation of α-pinene and in a number of organic/inorganic model mixtures (3-methylbutane-1,2,3-tricarboxylic acid (3-MBTCA), levoglucosan, levoglucosan/NH 4 HSO 4 , raffinose) are presented. These indicate that water diffusion coefficients are determined by several properties of the aerosol substance and cannot be inferred from the glass transition temperature or bouncing properties. Our results suggest that water diffusion in SOA particles is faster than often assumed and imposes no significant kinetic limitation on water uptake and release at temperatures above 220 K. The fast diffusion of water suggests that heterogeneous ice nucleation on a glassy core is very unlikely in these systems. At temperatures below 220 K, model simulations of SOA particles suggest that heterogeneous ice nucleation may occur in the immersion mode on glassy cores which remain embedded in a liquid shell when experiencing fast updraft velocities. The particles absorb significant quantities of water during these updrafts which plasticize their outer layers such that these layers equilibrate readily with the gas phase humidity before the homogeneous ice nucleation threshold is reached. Glass formation is thus unlikely to restrict homogeneous ice nucleation. Only under most extreme conditions near the very high tropical tropopause may the homogeneous ice nucleation rate coefficient be reduced as a consequence of slow condensed-phase water diffusion. Since the differences between the behavior limited or non limited by diffusion are small even at the very high tropical tropopause, condensed-phase water diffusivity is unlikely to have significant consequences on the direct climatic effects of SOA particles under tropospheric conditions.

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Changing shapes and implied viscosities of suspended submicron particles

Cited by 115 publications

References 51 publications

The Caltech Photooxidation Flow Tube reactor: design, fluid dynamics and characterization

The Caltech Photooxidation Flow Tube reactor: design, fluid dynamics and characterization

Mixing times of organic molecules within secondary organic aerosol particles: a global planetary boundary layer perspective

Viscous organic aerosol particles in the upper troposphere: diffusivity-controlled water uptake and ice nucleation?

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