The ice-nucleating activity of African mineral dust in the Caribbean boundary layer

Abstract

Abstract. African mineral dust is transported many thousands of kilometres from its source regions and, because of its ability to nucleate ice, it plays a major role in cloud glaciation around the globe. The ice-nucleating activity of desert dust is influenced by its mineralogy, which varies substantially between source regions and across particle sizes. However, in models it is often assumed that the activity (expressed as active sites per unit surface area as a function of temperature) of atmospheric mineral dust is the same everywhere on the globe. Here, we find that the ice-nucleating activity of African desert dust sampled in the summertime marine boundary layer of Barbados (July and August, 2017) is substantially lower than parameterizations based on soil from specific locations in the Saharan desert or dust sedimented from dust storms. We conclude that the activity of dust in Barbados’ boundary layer is primarily defined by the low K-feldspar content of the dust, which is around 1 %. We propose that the dust we sampled in the Caribbean was from a region in West Africa (in and around the Sahel in Mauritania and Mali), which has a much lower feldspar content than other African sources across the Sahara and Sahel.

Aircraft ice-nucleating particle and aerosol composition measurements in the Western North American Arctic

“…Hence, we suggest that the enhanced ice-nucleation ability of our samples is due to the presence of biological material. This is consistent with other studies, for example Wex et al (2019) and Porter et al (2022) who also provides evidence that Arctic INP samples have a substantial biological component.…”

“…Although the literature INP concentrations have been measured in close locations at a similar time of the year than the ones reported in this study, the measurements were performed in different years when the INP population may have been different. Our measurements are still well within the range of literature INP measurements from across the Arctic presented in Porter et al (2022). Hence it seems that during March 2018 the INP concentrations where sometimes higher in the Western North American Arctic by about 1-2 orders of magnitude than defined by Creamean et al and Borys et al, but are consistent with the highest concentrations measured by Wex et al (2019).…”

“…It is known that fertile soil dusts contain biological ice nucleating material (O'Sullivan et al, 2014), hence this suggests that the samples from Alaska contained some biological ice nucleating material. Although our INP concentrations would also be comparable with those predicted using the desert dust parameterization by Ullrich et al (2017), the latter is usually higher than the activity of samples of airborne desert dust at temperatures greater than about -20°C from other studies (Boose et al, 2016;Price et al, 2018;Harrison et al, 2022;Reicher et al, 2018;Gong et al, 2020). It has been suggested that dust that has been transported far from its source regions is less active than arid soil dusts that have been recently aerosolised and also there appears to be substantial differences in activity of dust from different source regions (Boose et al, 2016;Harrison et al, 2022).…”

“…Although substantial amounts of anthropogenic pollutants exist in the Arctic during the spring, they do not seem to significantly contribute to the INP concentration (Creamean et al, 2018;Borys, 1989). Measurements at the summertime North Pole indicate highly variable INP concentrations, with air masses that have spent the preceding week or so over ice-covered surfaces having very low INP particle concentrations, and air masses originating from lower latitude ice-free regions along the Russian coast having very high biological INP concentrations (Porter et al, 2022).…”

“…Some of these sources of high-latitude dust have been found to contribute to the Arctic INP population (Tobo et al, 2019;Sanchez-Marroquin et al, 2020;Si et al, 2019). A fraction the INP in the Arctic are also of biogenic origin (Wex et al, 2019;Porter et al, 2022), some of which may be associated with biogenic material in sea spray and some of which may be from terrestrial sources (Wilson et al, 2015;DeMott et al, 2016;Vergara-Temprado et al, 2017;Irish et al, 2017;McCluskey et al, 2018;Bigg and Leck, 2001;Creamean et al, 2019;Hartmann et al, 2020). Other types of aerosol particles such as volcanic ash or biomass burning particles could also contribute to the INP population in the Arctic (Prenni et al, 2009).…”