Size-dependent ice nucleation by airborne particles during dust events in the eastern Mediterranean

Abstract

Abstract. The prediction of cloud ice formation in climate models remains a challenge, partly due to the complexity of ice-related processes. Mineral dust is a prominent aerosol in the troposphere and is an important contributor to ice nucleation in mixed-phase clouds, as dust can initiate ice heterogeneously at relatively low supercooling conditions. We characterized the ice nucleation properties of size-segregated mineral dust sampled during dust events in the eastern Mediterranean. The sampling site allowed us to compare the properties of airborne dust from several sources with diverse mineralogy that passed over different atmospheric paths. We focused on particles with six size classes determined by the Micro-Orifice Uniform Deposit Impactor (MOUDI) cutoff sizes: 5.6, 3.2, 1.8, 1.0, 0.6 and 0.3 µm. Ice nucleation experiments were conducted in the Weizmann Supercooled Droplets Observation on a Microarray (WISDOM) setup, whereby the particles are immersed in nanoliter droplets using a microfluidics technique. We observed that the activity of airborne particles depended on their size class; supermicron and submicron particles had different activities, possibly due to different composition. The concentrations of ice-nucleating particles and the density of active sites (ns) increased with the particle size and particle concentration. The supermicron particles in different dust events showed similar activity, which may indicate that freezing was dominated by common mineralogical components. Combining recent data of airborne mineral dust, we show that current predictions, which are based on surface-sampled natural dust or standard mineral dust, overestimate the activity of airborne dust, especially for the submicron class. Therefore, we suggest including information on particle size in order to increase the accuracy of ice formation modeling and thus weather and climate predictions.

Size-Resolved Atmospheric Ice Nucleating Particles during East Asian Dust Events

“…The elution process lasted 30 minutes, and was kept in an ice-water bath to avoid the effects of ultrasound-induced heating. The ultrasonic shaker is effective for particle removal into the water solution, and is widely used (Reicher et al, 2019;Chen et al, 2018b;Ardon-Dryer and Levin, 2014).…”

“…The Stokes diameter measured by SMPS was transformed to aerodynamic diameter assuming a particle density of 1.5 g cm -3 , which is commonly used for small size particles in urban atmospheres (Hu et al, 2012;Qiao et al, 2018). In order to estimate the total surface area sampled on each MOUDI stage, similar to the approach in Reicher et al (2019), a transformation matrix https://doi.org/10.5194/acp-2020-678 Preprint. Discussion started: 15 September 2020 c Author(s) 2020.…”

“…Due to the limitation of substrates and solid particles, the bounce is unavoidable. However, as many previous studies showed, the losses rapidly decreased as the particles size decreased, and the collection efficiency curves of each stage are sharp, indicating that MOUDI is a high accuracy cascade impactor for collecting size-resolved particle samples, and was widely used in many laboratory experiments and field measurements (Marple et al, 1991;Mason et al, 2015;Mason et al, 2016;Si et al, 2018;Reicher et al, 2019).…”

On-chip density-based sorting of supercooled droplets and frozen droplets in continuous flow

“…Appropriate analyses on the collected droplet populations for INP identification could include scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDS), 59,[80][81][82][83][84] DNA analysis, 77,[85][86][87] Raman spectroscopy, 88 and a variety of other microscopic and spectroscopic techniques used in aerosol particle analysis. 82,[89][90][91] The identification and characterisation of the INPs present in the frozen droplet populations would then help to inform on their sources and global transport.…”

“…This concept is particularly timely given the recent surge in microfluidic platforms being developed for the droplet-based study of ice nucleation, [43][44][45][46][47][48] including for applications such as cryobiology [49][50][51][52][53] and atmospheric science. 34,[54][55][56][57][58][59][60][61][62]…”