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.
Atmospheric dust rich in illite is transported globally from arid regions and may impact 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 has a significantly different mineralogical composition and we suggest that NX illite is a better surrogate of natural atmospheric dust. Heterogeneous nucleation by NX illite was observed, using optical microscopy, to occur dominantly between 246 K and the homogeneous freezing limit and higher freezing temperatures were observed with larger surface areas of NX illite present within the droplets. It is shown that there is strong particle to particle variability in terms of ice nucleating ability with a few particles dominating ice nucleation at high surface areas. In fact, this work suggests that the bulk of atmospheric mineral dust particles are less efficient at nucleating ice than assumed in parameterisation currently used in models. For droplets containing ≤2 × 10<sup>−6</sup> cm<sup>2</sup> 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 (with surface areas ≤2 × 10<sup>−6</sup> cm<sup>2</sup>) is shown to be inconsistent with the single component stochastic model, but is well described by the singular model (<i>n</i><sub>s</sub>(236.2 K ≤ <i>T</i> ≤ 247.5 K) = exp(6.53043 × 10<sup>4</sup> − 8.2153088 × 10<sup>2</sup> <i>T</i> + 3.446885376 <i>T</i> <sup>2</sup> − 4.822268 × 10<sup>−3</sup> <i>T</i><sup>3</sup>). 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 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
An experimental study of the system CaC0,-MgC0,-FeCO, was undertaken in order to calibrate the iron correction to the calcite-dolumite geothermometer, which is based on the solubility of magnesium in calcite in the assemblage calcite + dolomite. The experiments, at 450°C and lower temperatures, resulted in products with a very small grain size and incomplete equilibration. However, application of a carefully-devised automatic data processing algorithm to analyses of the phases in experimental charges, combined with a thermodynamic analysis, results in geothermometer diagrams which should be preferred to previous theoretical predictions.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
customersupport@researchsolutions.com
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.