Models of Isotopic Water Diffusion in Spherical Aerosol Particles

2016 ◽  
Vol 120 (49) ◽  
pp. 9759-9766 ◽  
Author(s):  
Ali Moridnejad ◽  
Thomas C. Preston
Keyword(s):  
Aerosol Particles ◽  
Water Diffusion ◽  
Isotopic Water

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

2015 ◽  
Vol 15 (17) ◽  
pp. 24473-24511 ◽  
Author(s):  
D. M. Lienhard ◽  
A. J. Huisman ◽  
U. K. Krieger ◽  
Y. Rudich ◽  
C. Marcolli ◽  
...  
Keyword(s):  
Water Uptake ◽  
Condensed Phase ◽  
Aerosol Particles ◽  
Organic Aerosol ◽  
Ice Nucleation ◽  
Water Diffusion ◽  
Tropical Tropopause ◽  
Phase Water ◽  
Very High ◽  
Heterogeneous Ice Nucleation

Abstract. New measurements of water diffusion in aerosol particles produced from secondary organic aerosol (SOA) material and from a number of organic/inorganic model mixtures (3-methylbutane-1,2,3-tricarboxylic acid (3-MBTCA), levoglucosan, levoglucosan/NH4HSO4, raffinose) 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 droplets 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.

scholarly journals Competition between water uptake and ice nucleation by glassy organic aerosol particles

2014 ◽  
Vol 14 (11) ◽  
pp. 16451-16492 ◽  
Author(s):  
T. Berkemeier ◽  
M. Shiraiwa ◽  
U. Pöschl ◽  
T. Koop
Keyword(s):  
Aerosol Particles ◽  
Liquid Core ◽  
Organic Aerosol ◽  
Ice Nucleation ◽  
Empirical Method ◽  
Water Diffusion ◽  
Cloud Formation ◽  
Atmospheric Conditions ◽  
Cloud Droplets ◽  
Organic Particles

Abstract. Organic aerosol particles play a key role in climate by serving as nuclei for clouds and precipitation. Their sources and composition are highly variable, and their phase state ranges from liquid to solid under atmospheric conditions, affecting the pathway of activation to cloud droplets and ice crystals. Due to slow diffusion of water in the particle phase, organic particles may deviate in phase and morphology from their thermodynamic equilibrium state, hampering the prediction of their influence on cloud formation. We overcome this problem by combining a novel semi-empirical method for estimation of water diffusivity with a kinetic flux model that explicitly treats water diffusion. We estimate timescales for particle deliquescence as well as various ice nucleation pathways for a wide variety of organic substances, including secondary organic aerosol (SOA) from the oxidation of isoprene, α-pinene, naphthalene, and dodecane. The simulations show that in typical atmospheric updrafts, glassy states and solid/liquid core-shell morphologies can persist for long enough that heterogeneous ice nucleation in the deposition and immersion mode can dominate over homogeneous ice nucleation. Such competition depends strongly on ambient temperature and relative humidity as well as humidification rates and particle sizes. Due to relatively high glass transition temperature and low hygroscopicity, naphthalene SOA particles have a higher potential to act as heterogeneous ice nuclei than the other investigated substances. Our findings demonstrate that kinetic limitations of water diffusion into organic aerosol particles strongly affect their ice nucleation pathways and require advanced formalisms for the description of ice cloud formation in atmospheric models.

scholarly journals Competition between water uptake and ice nucleation by glassy organic aerosol particles

2014 ◽  
Vol 14 (22) ◽  
pp. 12513-12531 ◽  
Author(s):  
T. Berkemeier ◽  
M. Shiraiwa ◽  
U. Pöschl ◽  
T. Koop
Keyword(s):  
Particle Size ◽  
Relative Humidity ◽  
Molecular Diffusion ◽  
Aerosol Particles ◽  
Liquid Core ◽  
Organic Aerosol ◽  
Ice Nucleation ◽  
Water Diffusion ◽  
Cloud Formation ◽  
Atmospheric Conditions

Abstract. Organic aerosol particles play a key role in climate by serving as nuclei for clouds and precipitation. Their sources and composition are highly variable, and their phase state ranges from liquid to solid under atmospheric conditions, affecting the pathway of activation to cloud droplets and ice crystals. Due to slow diffusion of water in the particle phase, organic particles may deviate in phase and morphology from their thermodynamic equilibrium state, hampering the prediction of their influence on cloud formation. We overcome this problem by combining a novel semi-empirical method for estimation of water diffusivity with a kinetic flux model that explicitly treats water diffusion. We estimate timescales for particle deliquescence as well as various ice nucleation pathways for a wide variety of organic substances, including secondary organic aerosol (SOA) from the oxidation of isoprene, α-pinene, naphthalene, and dodecane. The simulations show that, in typical atmospheric updrafts, glassy states and solid/liquid core-shell morphologies can persist for long enough that heterogeneous ice nucleation in the deposition and immersion mode can dominate over homogeneous ice nucleation. Such competition depends strongly on ambient temperature and relative humidity as well as humidification rate and particle size. Due to differences in glass transition temperature, hygroscopicity and atomic O / C ratio of the different SOA, naphthalene SOA particles have the highest potential to act as heterogeneous ice nuclei. Our findings demonstrate that kinetic limitations of water diffusion into organic aerosol particles are likely to be encountered under atmospheric conditions and can strongly affect ice nucleation pathways. For the incorporation of ice nucleation by organic aerosol particles into atmospheric models, our results demonstrate a demand for model formalisms that account for the effects of molecular diffusion and not only describe ice nucleation onsets as a function of temperature and relative humidity but also include updraft velocity, particle size and composition.

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