Heterogeneous ice nucleation on dust particles sourced from nine deserts worldwide – Part 2: Deposition nucleation and condensation freezing

Abstract

Abstract. Mineral dust particles from deserts are amongst the most common ice nucleating particles in the atmosphere. The mineralogy of desert dust differs depending on the source region and can further fractionate during the dust emission processes. Mineralogy to a large extent explains the ice nucleation behavior of desert aerosol, but not entirely. Apart from pure mineral dust, desert aerosol particles often exhibit a coating or are mixed with small amounts of biological material. Aging on the ground or during atmospheric transport can deactivate nucleation sites, thus strong ice nucleating minerals may not exhibit their full potential. In the partner paper of this work, it was shown that mineralogy determines most but not all of the ice nucleation behavior in the immersion mode found for desert dust. In this study, the influence of semi-volatile organic compounds and the presence of crystal water on the ice nucleation behavior of desert aerosol is investigated. This work focuses on the deposition and condensation ice nucleation modes at temperatures between 238 and 242 K of 18 dust samples sourced from nine deserts worldwide. Chemical imaging of the particles' surface is used to determine the cause of the observed differences in ice nucleation. It is found that, while the ice nucleation ability of the majority of the dust samples is dominated by their quartz and feldspar content, in one carbonaceous sample it is mostly caused by organic matter, potentially cellulose and/or proteins. In contrast, the ice nucleation ability of an airborne Saharan sample is found to be diminished, likely by semi-volatile species covering ice nucleation active sites of the minerals. This study shows that in addition to mineralogy, other factors such as organics and crystal water content can alter the ice nucleation behavior of desert aerosol during atmospheric transport in various ways.

Revisiting the differential freezing nucleus spectra derived from drop-freezing experiments: methods of calculation, applications, and confidence limits

“…Frequently, for added emphasis, the term is given as active site density and denoted as n s . This quantity has already seen extended use in the literature (e.g., Connolly et al, 2009;Niedermeier et al, 2015;Beydoun et al, 2016;Paramonov et al, 2018;Boose et al, 2019). As stated in Sect.…”

The ice-nucleating ability of quartz immersed in water and its atmospheric importance compared to K-feldspar

“…Hence, historically icenucleation studies have focused on the clay group of minerals (e.g. Broadley et al, 2012;Murray et al, 2011;Wex et al, 2014;Mason and Maybank, 1958;Pinti et al, 2012;Roberts and Hallett, 1968;Hoose and Möhler, 2012). However, more recent work shows that K-rich feldspars (K-feldspars) are very effective INPs when immersed in supercooled water (Whale et al, 2017;Zolles et al, 2015;Tarn et al, 2018;Peckhaus et al, 2016;DeMott et al, 2018;Reicher et al, 2018;Harrison et al, 2016;Niedermeier et al, 2015;Atkinson et al, 2013).…”

Abundance and viability of particle-attached and free-floating bacteria in dusty and nondust air

“…Proteins in bacteria are ice nucleation active sites and are well protected when bacteria adhere to mineral dust surfaces (Conen et al, 2011). The attachment of bacteria to dust particles possibly increases the number of sites for ice nucleation and consequently the ice nucleation ability of dust particles (Boose et al, 2019;Conen et al, 2011). The present results show that up to one-tenth or more dust particles could be bacteria carriers, and the concentration of particle-attached bacteria, i.e., the number of bacteria-dust contact sites in dust episodes, was on average 3 times larger than that during nondust periods ( Table 1).…”

“…The cooccurrence of dust and high concentrations of bacteria has been observed frequently in different locations, indicating the widespread nature and dissemination of bacteria with dust at local, regional and even global scales (Griffin, 2007;Hara and Zhang, 2012;Iwasaka et al, 2009). Limited available observations have revealed the coexistence of mineral and biological contents in ice crystals (Creamean et al, 2013;Pratt et al, 2009), and laboratory experiments have demonstrated that the ice nucleation ability of dust particles is enhanced by biological components, including bacteria in the particles (Boose et al, 2019;Tobo et al, 2019;Conen et al, 2011). Recent toxicological studies with mouse exposure found that the internal mixture of dust and pathogenic bacteria exacerbated pneumonia (He et al, 2012).…”