Crystallization of Aqueous Ammonium Sulfate Particles Internally Mixed with Soot and Kaolinite:  Crystallization Relative Humidities and Nucleation Rates

Pant, Atul; Parsons, Matthew T.; Bertram, Allan K.

doi:10.1021/jp060985s

Cited by 93 publications

(123 citation statements)

References 67 publications

Supporting

Mentioning

114

Contrasting

Order By: Relevance

“…Water droplets containing clay particles were produced from a dust-in-water suspension of a known concentration using a custom made nebuliser (Murray et al, 2011b;Pant et al, 2006). The droplets were deposited on a glass cover slip inside a chamber maintained at saturation, so that the droplets did not grow or shrink through evaporation or condensation once they exited the nebuliser.…”

Section: Methodsmentioning

confidence: 99%

Immersion mode heterogeneous ice nucleation by an illite rich powder representative of atmospheric mineral dust

et al. 2012

View full text Add to dashboard Cite

Abstract. Atmospheric dust rich in illite is transported globally from arid regions and impacts cloud properties through the nucleation of ice. We present measurements of ice nucleation in water droplets containing known quantities of an illite rich powder under atmospherically relevant conditions. The illite rich powder used here, NX illite, has a similar mineralogical composition to atmospheric mineral dust sampled in remote locations, i.e. dust which has been subject to long range transport, cloud processing and sedimentation. Arizona Test Dust, which is used in other ice nucleation studies as a model atmospheric dust, has a significantly different mineralogical composition and we suggest that NX illite is a better surrogate of natural atmospheric dust.Using optical microscopy, heterogeneous nucleation in the immersion mode by NX illite was observed to occur dominantly between 246 K and the homogeneous freezing limit. In general, higher freezing temperatures were observed when larger surface areas of NX illite were present within the drops. Homogenous nucleation was observed to occur in droplets containing low surface areas of NX illite. We show that NX illite exhibits strong particle to particle variability in terms of ice nucleating ability, with ∼1 in 10 5 particles dominating ice nucleation when high surface areas were present. In fact, this work suggests that the bulk of atmospheric mineral dust particles may be less efficient at nucleating ice than assumed in current model parameterisations.For droplets containing ≤2×10 −6 cm 2 of NX illite, freezing temperatures did not noticeably change when the cooling rate was varied by an order of magnitude. The data obtained during cooling experiments (surface area ≤2×10 −6 cm 2 ) is shown to be inconsistent with the single component stochastic model, but is well described by the singular model (n s (236.2 K≤T ≤247.5 K) = exp(6.53043×10 4 − 8.2153088. However, droplets continued to freeze when the temperature was held constant, which is inconsistent with the time independent singular model. We show that this apparent discrepancy can be resolved using a multiple component stochastic model in which it is assumed that there are many types of nucleation sites, each with a unique temperature dependent nucleation coefficient. Cooling rate independence can be achieved with this time dependent model if the nucleation rate coefficients increase very rapidly with decreasing temperature, thus reconciling our measurement of nucleation at constant temperature with the cooling rate independence.

show abstract

Section: Methodsmentioning

confidence: 99%

Immersion mode heterogeneous ice nucleation by an illite rich powder representative of atmospheric mineral dust

et al. 2012

View full text Add to dashboard Cite

show abstract

“…Droplets containing a known quantity of mineral dust were produced using a home-made nebuliser similar in design to one used by Pant et al (2006). The nebuliser did not become blocked by clay particles for the range of concentrations of the dust-in-water suspensions used in these experiments.…”

Section: Methodsmentioning

confidence: 99%

“…Combining Eqs. (11), (12), and (13) we see that the heterogeneous nucleation rate can be expressed as (Mullin, 2001;Pant et al, 2006;Parsons et al, 2006):…”

Section: Fitting Kaolinite Ice Nucleation Rate Coefficients To Heteromentioning

confidence: 99%

Heterogeneous freezing of water droplets containing kaolinite particles

et al. 2011

View full text Add to dashboard Cite

Abstract. Clouds composed of both ice particles and supercooled liquid water droplets exist at temperatures above ∼236 K. These mixed phase clouds, which strongly impact climate, are very sensitive to the presence of solid particles that can catalyse freezing. In this paper we describe experiments to determine the conditions at which the clay mineral kaolinite nucleates ice when immersed within water droplets. These are the first immersion mode experiments in which the ice nucleating ability of kaolinite has been determined as a function of clay surface area, cooling rate and also at constant temperatures. Water droplets containing a known amount of clay mineral were supported on a hydrophobic surface and cooled at rates of between 0.8 and 10 K min −1 or held at constant sub-zero temperatures. The time and temperature at which individual 10-50 µm diameter droplets froze were determined by optical microscopy. For a cooling rate of 10 K min −1 , the median nucleation temperature of 10-40 µm diameter droplets increased from close to the homogeneous nucleation limit (236 K) to 240.8 ± 0.6 K as the concentration of kaolinite in the droplets was increased from 0.005 wt% to 1 wt%. This data shows that the probability of freezing scales with surface area of the kaolinite inclusions. We also show that at a constant temperature the number of liquid droplets decreases exponentially as they freeze over time. The constant cooling rate experiments are consistent with the stochastic, singular and modified singular descriptions of heterogeneous nucleation; however, freezing during cooling and at constant temperature can be reconciled best with the stochastic approach. We report temperature dependent nucleation rate coefficients (nucleation events per unit Correspondence to: B. J. Murray (b.j.murray@leeds.ac.uk) time per unit area) for kaolinite and present a general parameterisation for immersion nucleation which may be suitable for cloud modelling once nucleation by other important ice nucleating species is quantified in the future.

show abstract

“…For the bead-mobility and poke-flow techniques, however, particle sizes 20-60 µm in diameter are needed. To generate these large sizes, the hydrophobic slides containing the SOM particles were placed inside an RH-and temperature-controlled flow cell (Pant et al, 2006;Bertram et al, 2011;Song et al, 2012) and the RH was increased to > 100 %. This procedure caused particle growth by water uptake and eventual coagulation among particles.…”

Section: Production and Collection Of Secondary Organicmentioning

confidence: 99%

“…As in previous studies, SOM from the photooxidation of toluene serves as a proxy for organic particulate matter from anthropogenic sources in megacities (e.g., Pandis et al, 1992;Robinson et al, 2013). After determining viscosities as a function of RH, the Stokes-Einstein equation is used to convert the viscosities into equivalent diffusion rates of large organic molecules within toluene-derived SOM.…”

Section: Introductionmentioning

confidence: 99%

Relative humidity-dependent viscosity of secondary organic material from toluene photo-oxidation and possible implications for organic particulate matter over megacities

et al. 2016

Self Cite

View full text Add to dashboard Cite

Abstract. To improve predictions of air quality, visibility, and climate change, knowledge of the viscosities and diffusion rates within organic particulate matter consisting of secondary organic material (SOM) is required. Most qualitative and quantitative measurements of viscosity and diffusion rates within organic particulate matter have focused on SOM particles generated from biogenic volatile organic compounds (VOCs) such as α-pinene and isoprene. In this study, we quantify the relative humidity (RH)-dependent viscosities at 295 ± 1 K of SOM produced by photo-oxidation of toluene, an anthropogenic VOC. The viscosities of toluene-derived SOM were 2 × 10 −1 to ∼ 6 × 10 6 Pa s from 30 to 90 % RH, and greater than ∼ 2 × 10 8 Pa s (similar to or greater than the viscosity of tar pitch) for RH ≤ 17 %. These viscosities correspond to Stokes-Einstein-equivalent diffusion coefficients for large organic molecules of ∼ 2 × 10 −15 cm 2 s −1 for 30 % RH, and lower than ∼ 3 × 10 −17 cm 2 s −1 for RH ≤ 17 %. Based on these estimated diffusion coefficients, the mixing time of large organic molecules within 200 nm toluene-derived SOM particles is 0.1-5 h for 30 % RH, and higher than ∼ 100 h for RH ≤ 17 %. As a starting point for understanding the mixing times of large organic molecules in organic particulate matter over cities, we applied the mixing times determined for toluene-derived SOM particles to the world's top 15 most populous megacities. If the organic particulate matter in these megacities is similar to the toluene-derived SOM in this study, in Istanbul, Tokyo, Shanghai, and São Paulo, mixing times in organic particulate matter during certain periods of the year may be very short, and the particles may be wellmixed. On the other hand, the mixing times of large organic molecules in organic particulate matter in Beijing, Mexico City, Cairo, and Karachi may be long and the particles may not be well-mixed in the afternoon (15:00-17:00 LT) during certain times of the year.

show abstract

Crystallization of Aqueous Ammonium Sulfate Particles Internally Mixed with Soot and Kaolinite: Crystallization Relative Humidities and Nucleation Rates

Cited by 93 publications

References 67 publications

Immersion mode heterogeneous ice nucleation by an illite rich powder representative of atmospheric mineral dust

Immersion mode heterogeneous ice nucleation by an illite rich powder representative of atmospheric mineral dust

Heterogeneous freezing of water droplets containing kaolinite particles

Relative humidity-dependent viscosity of secondary organic material from toluene photo-oxidation and possible implications for organic particulate matter over megacities

Contact Info

Product

Resources

About