Ice nucleation and droplet formation by bare and coated soot particles

Abstract

[1] We have studied ice formation at temperatures relevant to homogeneous and heterogeneous ice nucleation, as well as droplet activation and hygroscopicity, of soot particles of variable size and composition. Coatings of adipic, malic, and oleic acid were applied in order to span an atmospherically relevant range of solubility, and both uncoated and oleic acid coated soot particles were exposed to ozone in order to simulate atmospheric oxidation. The results are interpreted in terms of onset ice nucleation, with a comparison to a mineral dust particle that acts as an efficient ice nucleus, and particle hygroscopicity. At 253 K and 243 K, we found no evidence of heterogeneous ice nucleation occurring above the level of detection for our experimental conditions. Above water saturation, only droplet formation was observed. At 233 K, we observe the occurrence of homogeneous ice nucleation for all particles studied. Coatings also did not significantly alter the ice nucleation behavior of soot particles but aided in the uptake of water. Hygroscopicity studies confirmed that pure soot particles were hydrophobic, and coated soot particles activated as droplets at high water supersaturations. A small amount of heterogeneous ice nucleation either below the detection limit of our instrument or concurrent with droplet formation and/or homogeneous freezing cannot be precluded, but we are able to set limits for its frequency. We conclude that both uncoated and coated soot particles comparable to those generated in our studies are unlikely to significantly contribute to the global budget of heterogeneous ice nuclei at temperatures between 233 K and 253 K.

Mapping the Operation of the Miniature Combustion Aerosol Standard (Mini-CAST) Soot Generator

“…These results are consistent with past studies that failed to find sub-saturated hygroscopic growth or supersaturated CCN activation (s ≤ 1%) for uncoated Mini-CAST soot (Friedman et al 2011;Henning et al 2012). Popovicheva et al (2008) used a gravimetric method to measure sub-saturated water uptake on CAST burner soot at two conditions: flame C/O ratio of 0.29 (4% OC) and 0.4 (27% OC), which are the same conditions examined by Möhler et al (2005).…”

A comprehensive laboratory study on the immersion freezing behavior of illite NX particles: a comparison of 17 ice nucleation measurement techniques

“…Typically, these large ice crystals can be detected and counted by an optical particle counter (OPC) downstream of the instrument while the chamber temperature and humidity conditions are continuously recorded. Since its first appearance in the 1980s with horizontal parallel plates (Hussain and Saunders, 1984;Tomlinson and Fukuta, 1985), several new designs and operational principles have been introduced (e.g., vertically oriented cylinders; Rogers et al, 1988, horizontally oriented parallel plates; Kanji and Abbatt, 2009, vertically oriented parallel plates; Stetzer et al, 2008;Chou et al, 2011;Friedman et al, 2011). An alternative configuration is the continuous flow mixing chamber (e.g., Fast Ice Nucleus Chamber or FINCH; Bundke et al, 2008).…”

Effects of crystallographic properties on the ice nucleation properties of volcanic ash particles

“…The design details of the CIC have been previously described in Stetzer et al [2008] and Friedman et al [2011]. In short, the CIC consists of two vertical parallel plates coated with an ice layer~0.5 mm thick to produce the ice-supersaturated conditions inside of the chamber.…”

“…More details are shown in section S2 including experimental schematic ( Figure S1) . These dispersed (aerosolized) particles were size selected based on their mobility diameter (d m ), in using a differential mobility analyzer (DMA; TSI Inc., Model 3080) and transmitted as aerosol to a compact ice chamber (CIC) [Friedman et al, 2011;Kulkarni et al, 2012] and a condensation particle counter (CPC; TSI Inc, Model 3010). The vacuum aerodynamic diameters of size-selected particles were measured with single particle mass spectrometer, SPLAT II, and used to calculate particle effective density ( ρ eff ), from which particle dynamic shape factors were obtained [Zelenyuk et al, 2006].…”

“…Size-selected ATD particles were also coated with H 2 SO 4 (Sigma Aldrich) in the coating apparatus [Friedman et al, 2011] that was maintained at a temperature of 130°C. Briefly, the coating apparatus unit consists of a H 2 SO 4 bath, which is heated using heating tape and its temperature is controlled using a thermostat.…”