scholarly journals Liquid-liquid phase separation in secondary organic aerosol particles produced from α-pinene ozonolysis and α-pinene photo-oxidation with/without ammonia

2019 ◽  
Author(s):  
Suhan Ham ◽  
Zaeem Bin Babar ◽  
Jaebong Lee ◽  
Hojin Lim ◽  
Mijung Song
Keyword(s):  
Phase Separation ◽  
Liquid Phase ◽  
Secondary Organic Aerosol ◽  
Cloud Condensation Nuclei ◽  
Aerosol Particles ◽  
Organic Aerosol ◽  
Liquid Phase Separation ◽  
Photo Oxidation ◽  
Different Types ◽  
Liquid Liquid Phase Separation

Abstract. Recently, liquid–liquid phase separation (LLPS) of secondary organic aerosol (SOA) particles free of inorganic salts has been intensively studied because of their importance on cloud condensation nuclei (CCN) properties. Herein, we investigated LLPS in four different types of SOA particles generated from α-pinene ozonolysis and α-pinene photo-oxidation in the absence and presence of NH3. LLPS was observed in SOA particles produced from α-pinene ozonolysis at ~ 95.8 % relative humidity (RH) and α-pinene ozonolysis with NH3 at ~ 95.4 % RH. However, LLPS was not observed in SOA particles produced from α-pinene photo-oxidation and α-pinene photo-oxidation with NH3. With datasets of average oxygen to carbon elemental ratio (O : C) for different types of SOA particles of this study and previous studies, LLPS occurred when the O : C ratio was less than ~ 0.44 and LLPS did not occur when the O : C ratio was greater than ~ 0.40. When LLPS was observed, the two liquid phases were present up to ~ 100 % RH. This result can help to predict more accurate results of CCN properties of organic aerosol particles.

scholarly journals Liquid–liquid phase separation in secondary organic aerosol particles produced from <i>α</i>-pinene ozonolysis and <i>α</i>-pinene photooxidation with/without ammonia

2019 ◽  
Vol 19 (14) ◽  
pp. 9321-9331 ◽  
Author(s):  
Suhan Ham ◽  
Zaeem Bin Babar ◽  
Jae Bong Lee ◽  
Ho-Jin Lim ◽  
Mijung Song
Keyword(s):  
Phase Separation ◽  
Liquid Phase ◽  
Secondary Organic Aerosol ◽  
Cloud Condensation Nuclei ◽  
Aerosol Particles ◽  
Organic Aerosol ◽  
Liquid Phase Separation ◽  
Liquid Phases ◽  
Different Types ◽  
Liquid Liquid Phase Separation

Abstract. Recently, liquid–liquid phase separation (LLPS) of secondary organic aerosol (SOA) particles free of inorganic salts has been intensively studied due to the importance of cloud condensation nuclei (CCN) properties. In this study, we investigated LLPS in four different types of SOA particles generated from α-pinene ozonolysis and α-pinene photooxidation in the absence and presence of ammonia (NH3). LLPS was observed in SOA particles produced from α-pinene ozonolysis at ∼95.8 % relative humidity (RH) and α-pinene ozonolysis with NH3 at ∼95.4 % RH. However, LLPS was not observed in SOA particles produced from α-pinene photooxidation and α-pinene photooxidation with NH3. Based on datasets of the average oxygen to carbon elemental ratio (O:C) for different types of SOA particles from this study and from previous studies, there appears to be a relationship between the occurrence of LLPS and the O:C of the SOA particles. When LLPS was observed, the two liquid phases were present up to ∼100 % RH. This result can help more accurately predict the CCN properties of organic aerosol particles.

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

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 &amp;leq; 10 % RH, the viscosity was in the range of &amp;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 &amp;leq; 10 % RH diffusion coefficients of organics within diesel fuel SOA is &amp;leq; 5.4 × 10−17cm2 s−1 and the mixing time of organics within 200 nm diesel fuel SOA particles (τmixing) is &amp;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.

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

2019 ◽  
Vol 19 (19) ◽  
pp. 12515-12529 ◽  
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.

scholarly journals Self-limited uptake of α-pinene-oxide to acidic aerosol: the effects of liquid-liquid phase separation and implications for the formation of secondary organic aerosol and organosulfates from epoxides

2013 ◽  
Vol 13 (3) ◽  
pp. 7151-7174
Author(s):  
G. T. Drozd ◽  
J. L. Woo ◽  
V. F. McNeill
Keyword(s):  
Phase Separation ◽  
Liquid Phase ◽  
Partition Coefficients ◽  
Secondary Organic Aerosol ◽  
Organic Aerosol ◽  
Organic Content ◽  
Liquid Phase Separation ◽  
Wide Range ◽  
Acidic Sulfate ◽  
Liquid Liquid Phase Separation

Abstract. The reactive uptake of α-pinene oxide (αPO) to acidic sulfate aerosol was studied under humid conditions in order to gain insight into the effects of liquid-liquid phase separation on aerosol heterogeneous chemistry and further elucidate the formation of secondary organic aerosol and organosulfates from epoxides. A continuous flow environmental chamber was used to monitor changes in diameter of monodisperse, deliquesced, acidic sulfate particles exposed to αPO at 30 and 50% RH. In order to induce phase separation and probe potential limits to particle growth from acidic uptake, αPO was introduced over a wide range of concentrations, from 200 ppb to 5 ppm. Uptake was observed to be highly dependent on initial aerosol pH. Significant uptake of αPO to aerosol was observed with initial pH < 0. When exposed to 200 ppb αPO, aerosol with pH = −1 doubled in volume, and 6% volume growth was observed at pH = 0. Aerosol with pH = 1 showed no growth. The extreme acidity required for efficient αPO uptake suggests that this chemistry is typically not a major route to formation of aerosol mass or organosulfates in the atmosphere. Partition coefficients (Kp) ranged from 0.2–1.6 × 10−4 m3 μg−1 and were correlated to initial particle acidity and particle organic content; particles with higher organic content had lower partition coefficients. Effective uptake coefficients (γ) ranged from 0.4 to 4.7 × 10−5 and are much lower than recently reported for uptake to bulk solutions. In experiments in which αPO was added to bulk H2SO4 solutions, phase separation was observed for mass loadings similar to those observed with particles, and product distributions were dependent on acid concentration. Liquid-liquid phase separation in bulk experiments, along with our observations of decreased uptake to particles with the largest growth factors, suggest an organic coating forms upon uptake to particles, limiting reactive uptake.

scholarly journals Self-limited uptake of α-pinene oxide to acidic aerosol: the effects of liquid–liquid phase separation and implications for the formation of secondary organic aerosol and organosulfates from epoxides

2013 ◽  
Vol 13 (16) ◽  
pp. 8255-8263 ◽  
Author(s):  
G. T. Drozd ◽  
J. L. Woo ◽  
V. F. McNeill
Keyword(s):  
Phase Separation ◽  
Liquid Phase ◽  
Partition Coefficients ◽  
Secondary Organic Aerosol ◽  
Organic Aerosol ◽  
Organic Content ◽  
Liquid Phase Separation ◽  
Wide Range ◽  
Acidic Sulfate ◽  
Liquid Liquid Phase Separation

Abstract. The reactive uptake of α-pinene oxide (αPO) to acidic sulfate aerosol was studied under humid conditions in order to gain insight into the effects of liquid–liquid phase separation on aerosol heterogeneous chemistry and to elucidate further the formation of secondary organic aerosol and organosulfates from epoxides. A continuous flow environmental chamber was used to monitor changes in diameter of monodisperse, deliquesced, acidic sulfate particles exposed to αPO at 25% and 50% RH (relative humidity). In order to induce phase separation and probe potential limits to particle growth from acidic uptake, αPO was introduced over a wide range of concentrations, from 200 ppb to 5 ppm. Uptake was observed to be highly dependent on initial aerosol pH. Significant uptake of αPO to aerosol was observed with initial pH < 0. When exposed to 200 ppb αPO, aerosol with pH = -0.5 showed 23% growth, and 6% volume growth was observed at pH = 0. Aerosol with pH = 1 showed no growth. The extreme acidity required for efficient αPO uptake suggests that this chemistry is typically not a major route to formation of aerosol mass or organosulfates in the atmosphere. Effective partition coefficients (Kp, eff) were in the range of (0.1–2) x 10-4 m3μg-1 and were correlated to initial particle acidity and particle organic content; particles with higher organic content had lower partition coefficients. Effective uptake coefficients (γeff) ranged from 0.1 to 1.1 x 10-4 and are much lower than recently reported for uptake to bulk solutions. In experiments in which αPO was added to bulk H2SO4 solutions, phase separation was observed for mass loadings similar to those observed with particles, and product distributions were dependent on acid concentration. Liquid–liquid phase separation in bulk experiments, along with our observations of decreased uptake to particles with the largest growth factors, suggests an organic coating forms upon uptake to particles, limiting reactive uptake.

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