Observation of viscosity transition in &lt;i&gt;α&lt;/i&gt;-pinene secondary organic aerosol

Abstract. Under certain conditions, secondary organic aerosol (SOA) particles can exist in the atmosphere in an amorphous solid or semi-solid state. To determine their relevance to processes such as ice nucleation or chemistry occurring within particles requires knowledge of the temperature and relative humidity (RH) range for SOA to exist in these states. In the Cosmics Leaving Outdoor Droplets (CLOUD) experiment at The European Organisation for Nuclear Research (CERN), we deployed a new in situ optical method to detect the viscous state of α-pinene SOA particles and measured their transition from the amorphous highly viscous state to states of lower viscosity. The method is based on the depolarising properties of laboratory-produced non-spherical SOA particles and their transformation to non-depolarising spherical particles at relative humidities near the deliquescence point. We found that particles formed and grown in the chamber developed an asymmetric shape through coagulation. A transition to a spherical shape was observed as the RH was increased to between 35 % at −10 °C and 80 % at −38 °C, confirming previous calculations of the viscosity-transition conditions. Consequently, α-pinene SOA particles exist in a viscous state over a wide range of ambient conditions, including the cirrus region of the free troposphere. This has implications for the physical, chemical, and ice-nucleation properties of SOA and SOA-coated particles in the atmosphere.

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Observation of viscosity transition in α-pinene secondary organic aerosol

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-15-28575-2015 ◽

2015 ◽

Vol 15 (20) ◽

pp. 28575-28617 ◽

Cited By ~ 4

Author(s):

E. Järvinen ◽

K. Ignatius ◽

L. Nichman ◽

T. B. Kristensen ◽

C. Fuchs ◽

...

Keyword(s):

Secondary Organic Aerosol ◽

Spherical Shape ◽

Amorphous Solid ◽

Organic Aerosol ◽

Ice Nucleation ◽

Ambient Conditions ◽

Wide Range ◽

Asymmetric Shape ◽

Semi Solid

Abstract. Under certain conditions, secondary organic aerosol (SOA) particles can exist in the atmosphere in an amorphous solid or semi-solid state. To determine their relevance to processes such as ice nucleation or chemistry occurring within particles requires knowledge of the temperature and relative humidity (RH) range for SOA to exist in these states. In the CLOUD experiment at CERN, we deployed a new in-situ optical method to detect the viscosity of α-pinene SOA particles and measured their transition from the amorphous viscous to liquid state. The method is based on the depolarising properties of laboratory-produced non-spherical SOA particles and their transformation to non-depolarising spherical liquid particles during deliquescence. We found that particles formed and grown in the chamber developed an asymmetric shape through coagulation. A transition to spherical shape was observed as the RH was increased to between 35 % at −10 °C and 80 % at −38 °C, confirming previous calculations of the viscosity transition conditions. Consequently, α-pinene SOA particles exist in a viscous state over a wide range of ambient conditions, including the cirrus region of the free troposphere. This has implications for the physical, chemical and ice-nucleation properties of SOA and SOA-coated particles in the atmosphere.

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Heterogeneous ice nucleation of viscous secondary organic aerosol produced from ozonolysis of <i>α</i>-pinene

Atmospheric Chemistry and Physics ◽

10.5194/acp-16-6495-2016 ◽

2016 ◽

Vol 16 (10) ◽

pp. 6495-6509 ◽

Cited By ~ 33

Author(s):

Karoliina Ignatius ◽

Thomas B. Kristensen ◽

Emma Järvinen ◽

Leonid Nichman ◽

Claudia Fuchs ◽

...

Keyword(s):

Secondary Organic Aerosol ◽

Solid Phase ◽

Particle Surface ◽

Amorphous Solid ◽

Organic Aerosol ◽

Ice Nucleation ◽

Cloud Formation ◽

Particle Surface Area ◽

Semi Solid ◽

Heterogeneous Ice Nucleation

Abstract. There are strong indications that particles containing secondary organic aerosol (SOA) exhibit amorphous solid or semi-solid phase states in the atmosphere. This may facilitate heterogeneous ice nucleation and thus influence cloud properties. However, experimental ice nucleation studies of biogenic SOA are scarce. Here, we investigated the ice nucleation ability of viscous SOA particles. The SOA particles were produced from the ozone initiated oxidation of α-pinene in an aerosol chamber at temperatures in the range from −38 to −10 °C at 5–15 % relative humidity with respect to water to ensure their formation in a highly viscous phase state, i.e. semi-solid or glassy. The ice nucleation ability of SOA particles with different sizes was investigated with a new continuous flow diffusion chamber. For the first time, we observed heterogeneous ice nucleation of viscous α-pinene SOA for ice saturation ratios between 1.3 and 1.4 significantly below the homogeneous freezing limit. The maximum frozen fractions found at temperatures between −39.0 and −37.2 °C ranged from 6 to 20 % and did not depend on the particle surface area. Global modelling of monoterpene SOA particles suggests that viscous biogenic SOA particles are indeed present in regions where cirrus cloud formation takes place. Hence, they could make up an important contribution to the global ice nucleating particle budget.

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Volatility and lifetime against OH heterogeneous reaction of ambient Isoprene Epoxydiols-Derived Secondary Organic Aerosol (IEPOX-SOA)

10.5194/acp-2016-418 ◽

2016 ◽

Cited By ~ 2

Author(s):

Weiwei Hu ◽

Brett B. Palm ◽

Douglas A. Day ◽

Pedro Campuzano-Jost ◽

Jordan E. Krechmer ◽

...

Keyword(s):

Flow Reactor ◽

Secondary Organic Aerosol ◽

Heterogeneous Reaction ◽

Ambient Air ◽

Organic Aerosol ◽

Amazon Forest ◽

Reaction Products ◽

Ambient Conditions ◽

Forested Areas ◽

Humidity Dependence

Abstract. Isoprene epoxydiols-derived secondary organic aerosol (IEPOX-SOA) can contribute substantially to organic aerosol (OA) concentrations in forested areas under low NO conditions, hence significantly influencing the regional and global OA budgets, accounting for example for 16–36 % of the submicron OA in the SE US summer. Particle evaporation measurements from a thermodenuder show that the volatility of ambient IEPOX-SOA is lower than that of bulk OA and also much lower than that of known monomer IEPOX-SOA tracer species, indicating that IEPOX-SOA likely exists mostly as oligomers in the aerosol phase. The OH aging process of ambient IEPOX-SOA was investigated with an oxidation flow reactor (OFR). New IEPOX-SOA formation in the reactor was negligible, as the OFR cannot accelerate processes such as aerosol uptake and reactions that do not scale with OH. Simulation results indicate that adding ~ 100 µg m−3 of pure H2SO4 to the ambient air allows to efficiently form IEPOX-SOA in the reactor. The heterogeneous reaction rate coefficient of ambient IEPOX-SOA with OH radical (kOH) was estimated as 4.0 ± 2.0 × 10−13 cm3 molec−1 s−1, which is equivalent to more than a 2-week lifetime. A similar kOH was found for measurements of OH oxidation of ambient Amazon forest air in an OFR. At higher OH exposures in the reactor (> 1 × 1012 molec. cm−3 s), the mass loss of IEPOX-SOA due to heterogeneous reaction was mainly due to revolatilization of fragmented reaction products. We report for the first time OH reactive uptake coefficients (γOH = 0.59 ± 0.33 in SE US and γOH = 0.68 ± 0.38 in Amazon) for SOA under ambient conditions. A relative humidity dependence of kOH and γOH was observed, consistent with surface area-limited OH uptake. No decrease of kOH was observed as OH concentrations increased. These observation of physicochemical properties of IEPOX-SOA can help to constrain OA impact on air quality and climate.

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Liquid-liquid phase separation and viscosity within secondary organic aerosol generated from diesel fuel vapors

10.5194/acp-2019-367 ◽

2019 ◽

Author(s):

Mijung Song ◽

Adrian M. Maclean ◽

Yuanzhou Huang ◽

Natalie R. Smith ◽

Sandra L. Blair ◽

...

Keyword(s):

Phase Separation ◽

Liquid Phase ◽

Diesel Fuel ◽

Diffusion Coefficients ◽

Secondary Organic Aerosol ◽

Organic Aerosol ◽

Liquid Phase Separation ◽

Small Diffusion ◽

Wide Range ◽

Liquid Liquid Phase Separation

Abstract. Information on liquid-liquid phase separation (LLPS) and viscosity (or diffusion) within secondary organic aerosol (SOA) is needed to improve predictions of particle size, mass, reactivity, and cloud nucleating properties in the atmosphere. Here we report on LLPS and viscosities within SOA generated by the photooxidation of diesel fuel vapors. Diesel fuel contains a wide range of volatile organic compounds, and SOA generated by the photooxidation of diesel fuel vapors may be a good proxy for SOA from anthropogenic emissions. In our experiments, LLPS occurred over the relative humidity (RH) range of ~ 70 % to ~ 100 %, resulting in an organic-rich outer phase and a water-rich inner phase. These results may have implications for predicting the cloud nucleating properties of anthropogenic SOA since the organic-rich outer phase can lower the kinetic barrier for activation to a cloud droplet. At &leq; 10 % RH, the viscosity was in the range of &geq; 1 × 108 Pa s, which corresponds to roughly the viscosity of tar pitch. At 38–50 % RH the viscosity was in the range of 1 × 108–3 × 105 Pa s. These measured viscosities are consistent with predictions based on oxygen to carbon elemental ratio (O : C) and molar mass as well as predictions based on the number of carbon, hydrogen, and oxygen atoms. Based on the measured viscosities and the Stokes–Einstein relation, at &leq; 10 % RH diffusion coefficients of organics within diesel fuel SOA is &leq; 5.4 × 10−17cm2 s−1 and the mixing time of organics within 200 nm diesel fuel SOA particles (τmixing) is &gtrsim; 50 h. These small diffusion coefficients and large mixing times may be important in laboratory experiments, where SOA is often generated and studied using low RH conditions and on time scales of minutes to hours. At 38–50 % RH, the calculated organic diffusion coefficients are in the range of 5.4 × 10−17 to 1.8 × 10−13 cm2 s−1 and calculated τmixing values are in the range of ~ 0.01 h to ~ 50 h. These values provide important constraints for the physicochemical properties of anthropogenic SOA.

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Liquid–liquid phase separation and viscosity within secondary organic aerosol generated from diesel fuel vapors

Atmospheric Chemistry and Physics ◽

10.5194/acp-19-12515-2019 ◽

2019 ◽

Vol 19 (19) ◽

pp. 12515-12529 ◽

Cited By ~ 5

Author(s):

Mijung Song ◽

Adrian M. Maclean ◽

Yuanzhou Huang ◽

Natalie R. Smith ◽

Sandra L. Blair ◽

...

Keyword(s):

Phase Separation ◽

Liquid Phase ◽

Diesel Fuel ◽

Diffusion Coefficients ◽

Secondary Organic Aerosol ◽

Organic Aerosol ◽

Liquid Phase Separation ◽

Small Diffusion ◽

Wide Range ◽

Liquid Liquid Phase Separation

Abstract. Information on liquid–liquid phase separation (LLPS) and viscosity (or diffusion) within secondary organic aerosol (SOA) is needed to improve predictions of particle size, mass, reactivity, and cloud nucleating properties in the atmosphere. Here we report on LLPS and viscosities within SOA generated by the photooxidation of diesel fuel vapors. Diesel fuel contains a wide range of volatile organic compounds, and SOA generated by the photooxidation of diesel fuel vapors may be a good proxy for SOA from anthropogenic emissions. In our experiments, LLPS occurred over the relative humidity (RH) range of ∼70 % to ∼100 %, resulting in an organic-rich outer phase and a water-rich inner phase. These results may have implications for predicting the cloud nucleating properties of anthropogenic SOA since the presence of an organic-rich outer phase at high-RH values can lower the supersaturation with respect to water required for cloud droplet formation. At ≤10 % RH, the viscosity was ≥1×108 Pa s, which corresponds to roughly the viscosity of tar pitch. At 38 %–50 % RH, the viscosity was in the range of 1×108 to 3×105 Pa s. These measured viscosities are consistent with predictions based on oxygen to carbon elemental ratio (O:C) and molar mass as well as predictions based on the number of carbon, hydrogen, and oxygen atoms. Based on the measured viscosities and the Stokes–Einstein relation, at ≤10 % RH diffusion coefficients of organics within diesel fuel SOA is ≤5.4×10-17 cm2 s−1 and the mixing time of organics within 200 nm diesel fuel SOA particles (τmixing) is 50 h. These small diffusion coefficients and large mixing times may be important in laboratory experiments, where SOA is often generated and studied using low-RH conditions and on timescales of minutes to hours. At 38 %–50 % RH, the calculated organic diffusion coefficients are in the range of 5.4×10-17 to 1.8×10-13 cm2 s−1 and calculated τmixing values are in the range of ∼0.01 h to ∼50 h. These values provide important constraints for the physicochemical properties of anthropogenic SOA.

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Heterogeneous Ice Nucleation on Simulated Secondary Organic Aerosol

Environmental Science & Technology ◽

10.1021/es4046428 ◽

2014 ◽

Vol 48 (3) ◽

pp. 1675-1682 ◽

Cited By ~ 45

Author(s):

Gregory P. Schill ◽

David O. De Haan ◽

Margaret A. Tolbert

Keyword(s):

Secondary Organic Aerosol ◽

Organic Aerosol ◽

Ice Nucleation ◽

Heterogeneous Ice Nucleation

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Heterogeneous ice nucleation of viscous secondary organic aerosol produced from ozonolysis of α-pinene

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-15-35719-2015 ◽

2015 ◽

Vol 15 (24) ◽

pp. 35719-35752 ◽

Cited By ~ 2

Author(s):

K. Ignatius ◽

T. B. Kristensen ◽

E. Järvinen ◽

L. Nichman ◽

C. Fuchs ◽

...

Keyword(s):

Secondary Organic Aerosol ◽

Solid Phase ◽

Particle Surface ◽

Organic Aerosol ◽

Ice Nucleation ◽

Cloud Formation ◽

Cirrus Cloud ◽

Particle Surface Area ◽

Semi Solid ◽

Heterogeneous Ice Nucleation

Abstract. There are strong indications that particles containing secondary organic aerosol (SOA) exhibit amorphous solid or semi-solid phase states in the atmosphere. This may facilitate deposition ice nucleation and thus influence cirrus cloud properties. However, experimental ice nucleation studies of biogenic SOA are scarce. Here, we investigated the ice nucleation ability of viscous SOA particles. The SOA particles were produced from the ozone initiated oxidation of α-pinene in an aerosol chamber at temperatures in the range from −38 to −10 °C at 5–15 % relative humidity with respect to water to ensure their formation in a highly viscous phase state, i.e. semi-solid or glassy. The ice nucleation ability of SOA particles with different sizes was investigated with a new continuous flow diffusion chamber. For the first time, we observed heterogeneous ice nucleation of viscous α-pinene SOA in the deposition mode for ice saturation ratios between 1.3 and 1.4 significantly below the homogeneous freezing limit. The maximum frozen fractions found at temperatures between −36.5 and −38.3 °C ranged from 6 to 20 % and did not depend on the particle surface area. Global modelling of monoterpene SOA particles suggests that viscous biogenic SOA particles are indeed present in regions where cirrus cloud formation takes place. Hence, they could make up an important contribution to the global ice nuclei (IN) budget.

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The efficiency of secondary organic aerosol particles to act as ice nucleating particles at mixed-phase cloud conditions

10.5194/acp-2017-1223 ◽

2018 ◽

Author(s):

Wiebke Frey ◽

Dawei Hu ◽

James Dorsey ◽

M. Rami Alfarra ◽

Aki Pajunoja ◽

...

Keyword(s):

Secondary Organic Aerosol ◽

Aerosol Particles ◽

Organic Aerosol ◽

Ice Nucleation ◽

Mixed Phase ◽

Dust Particles ◽

Ice Cloud ◽

Liquid Saturation ◽

Reference Experiment ◽

Mixed Phase Clouds

Abstract. Secondary Organic Aerosol (SOA) particles have been found to be efficient ice nucleating particles under the cold conditions of (tropical) upper tropospheric cirrus clouds. Whether they also are efficient at initiating freezing at slightly warmer conditions as found in mixed phase clouds remains undetermined. Here, we study the ice nucleating ability of photo-chemically produced SOA particles with the combination of the Manchester Aerosol and Ice Cloud Chambers. Three SOA systems were tested resembling biogenic/anthropogenic particles and particles of different phase state. After the aerosol particles were formed, they were transferred into the cloud chamber where subsequent quasi-adiabatic cloud evacuations were performed. Additionally, the ice forming abilities of ammonium sulfate and kaolinite were investigated as a reference to test the experimental setup. Clouds were formed in the temperature range of −20 °C to −28.6 °C. Only the reference experiment using dust particles showed evidence of ice nucleation. No ice particles were observed in any other experiment. Thus, we conclude that SOA particles produced under the conditions of the reported experiments are not efficient ice nucleating particles starting at liquid saturation under mixed-phase cloud conditions.

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High formation of secondary organic aerosol from the photo-oxidation of toluene

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-9-693-2009 ◽

2009 ◽

Vol 9 (1) ◽

pp. 693-733 ◽

Cited By ~ 3

Author(s):

L. Hildebrandt ◽

N. M. Donahue ◽

S. N. Pandis

Keyword(s):

Air Quality ◽

Secondary Organic Aerosol ◽

Organic Aerosol ◽

Ambient Conditions ◽

Dynamic Nature ◽

Experimental Conditions ◽

Quality Models ◽

Photo Oxidation ◽

Aerosol Mass ◽

Photochemical Aging

Abstract. Toluene and other aromatics have long been viewed as the dominant anthropogenic secondary organic aerosol (SOA) precursors, but the SOA mass yields from toluene reported in previous studies vary widely. Experiments conducted in the Carnegie Mellon University environmental chamber to study SOA formation from the photo-oxidation of toluene show significantly larger SOA production than parameterizations employed in current air-quality models. Aerosol mass yields depend on experimental conditions: yields are higher under higher UV intensity, under low-NOx conditions and at lower temperatures. The extent of oxidation of the aerosol also varies with experimental conditions, consistent with ongoing, progressive photochemical aging of the toluene SOA. Measurements using a thermodenuder system suggest that the aerosol formed under high- and low-NOx conditions is semi-volatile. These results suggest that SOA formation from toluene depends strongly on ambient conditions. An approximate parameterization is proposed for use in air-quality models until a more thorough treatment accounting for the dynamic nature of this system becomes available.

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