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

Abstract

Abstract. Mineral dust particles are thought to be an important type of ice-nucleating particle (INP) in the mixed-phase cloud regime around the globe. While K-rich feldspar (K-feldspar) has been identified as being a particularly important component of mineral dust for ice nucleation, it has been shown that quartz is also relatively ice-nucleation active. Given quartz typically makes up a substantial proportion of atmospheric desert dust, it could potentially be important for cloud glaciation. Here, we survey the ice-nucleating ability of 10 α-quartz samples (the most common quartz polymorph) when immersed in microlitre supercooled water droplets. Despite all samples being α-quartz, the temperature at which they induce freezing varies by around 12 ∘C for a constant active site density. We find that some quartz samples are very sensitive to ageing in both aqueous suspension and air, resulting in a loss of ice-nucleating activity, while other samples are insensitive to exposure to air and water over many months. For example, the ice-nucleation temperatures for one quartz sample shift down by ∼2 ∘C in 1 h and 12 ∘C after 16 months in water. The sensitivity to water and air is perhaps surprising, as quartz is thought of as a chemically resistant mineral, but this observation suggests that the active sites responsible for nucleation are less stable than the bulk of the mineral. We find that the quartz group of minerals is generally less active than K-feldspars by roughly 7 ∘C, although the most active quartz samples are of a similar activity to some K-feldspars with an active site density, ns(T), of 1 cm−2 at −9 ∘C. We also find that the freshly milled quartz samples are generally more active by roughly 5 ∘C than the plagioclase feldspar group of minerals and the albite end member has an intermediate activity. Using both the new and literature data, active site density parameterizations have been proposed for freshly milled quartz, K-feldspar, plagioclase and albite. Combining these parameterizations with the typical atmospheric abundance of each mineral supports previous work that suggests that K-feldspar is the most important ice-nucleating mineral in airborne mineral dust.

Profiles of cloud condensation nuclei, dust mass concentration, and ice-nucleating-particle-relevant aerosol properties in the Saharan Air Layer over Barbados from polarization lidar and airborne in situ measurements

“…However, although the Saharan dust was transported over several thousands of kilometers across the Atlantic Ocean, observations suggest that the dust in the SAL remained nearly unprocessed (Lieke et al, 2011;Denjean et al, 2015;Weinzierl et al, 2017;Kandler et al, 2018). Therefore, κ should not change significantly during transport and be closer to the value for fresh Saharan dust which is taken from laboratory studies (Koehler et al, 2009;Herich et al, 2009;Kumar et al, 2011a, b). Twohy et al (2009) found good agreement for their CCN measurements with a κ of 0.05 in the eastern Atlantic.…”

“…Cloud-processed Saharan dust particles (mimicked by wetgenerated dust samples) may have changed their hygroscopic properties (higher κ value) so that their CCN efficacy increased. Laboratory studies with wet-generated dust particles (in contrast to dry-generated fresh dust particles) reported higher κ values (Koehler et al, 2009;Herich et al, 2009;Kumar et al, 2011b). However, although the Saharan dust was transported over several thousands of kilometers across the Atlantic Ocean, observations suggest that the dust in the SAL remained nearly unprocessed (Lieke et al, 2011;Denjean et al, 2015;Weinzierl et al, 2017;Kandler et al, 2018).…”

“…Twohy et al (2009) found good agreement for their CCN measurements with a κ of 0.05 in the eastern Atlantic. Herich et al (2009) concluded that the activation diameter for Saharan dust (dry generated) is most probably 200 nm at a supersaturation of 0.2 %. This is confirmed by studies of Shinozuka et al (2015) and Lv et al (2018).…”

Ice-nucleating particle versus ice crystal number concentrationin altocumulus and cirrus layers embedded in Saharan dust:a closure study

“…Recent field activities with a focus on ice-nucleating particle concentration (INPC) were reported by Schrod et al (2017), Welti et al (2018), McCluskey et al (2017McCluskey et al ( , 2018a, Price et al (2018), and Wex et al (2019). More than 30 years of airborne observations in mixed-phase and cirrus clouds have improved our understanding of ice formation processes and have provided a wealth of information on the microphysical properties of ice clouds (see the review articles of Heymsfield et al, 2017. Prenni et al (2009) were, to our knowledge, the first who successfully performed closure studies on the relationship between the INPC and ice crystal number concentration (ICNC), based on airborne in situ observations.…”

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

“…Overall, heat-sensitive components dominated the freezing at higher temperatures (above -15 ℃), and their contribution decreased pronouncedly at lower temperatures. Recently, Harrison et al (2019) found that some quartz samples are sensitive to aging in aqueous suspension. We can't rule out the presence of quartz, or determine the fraction of specific quartz in heatsensitive INPs at -20 ℃.…”