Iceland is an episodic source of atmospheric ice-nucleating particles relevant for mixed-phase clouds

Abstract

Ice-nucleating particles (INPs) have the potential to remove much of the liquid water in climatically important mid- to high-latitude shallow supercooled clouds, markedly reducing their albedo. The INP sources at these latitudes are very poorly defined, but it is known that there are substantial dust sources across the high latitudes, such as Iceland. Here, we show that Icelandic dust emissions are sporadically an important source of INPs at mid to high latitudes by combining ice-nucleating active site density measurements of aircraft-collected Icelandic dust samples with a global aerosol model. Because Iceland is only one of many high-latitude dust sources, we anticipate that the combined effect of all these sources may strongly contribute to the INP population in the mid- and high-latitude northern hemisphere. This is important because these emissions are directly relevant for the cloud-phase climate feedback and because high-latitude dust emissions are expected to increase in a warmer climate.

Opinion: Cloud-phase climate feedback and the importance of ice-nucleating particles

“…The x axis of these plots is approximately 4500 km, while the y axis is approximately 3900 km. latitude sources (Sanchez-Marroquin et al, 2020). Taking all this together, the INP population in the Northern Hemisphere high latitudes appears to be a complex mixture of different INP types from the marine and terrestrial environment.…”

“…4c). For example, it has been suggested that less snow and ice cover may lead to more widespread emission sources and higher dust emissions rates at high latitudes (Tobo et al, 2019;Prospero et al, 2012;Sanchez-Marroquin et al, 2020;Amino et al, 2020) (we discuss this further in Sect. 6).…”

“…Over recent years it has become increasingly apparent that there are significant dust emissions from a plethora of high-latitude sources, such as pro-glacial deposits (Bullard et al, 2016;Prospero et al, 2012). Samples from a handful of these sources have been shown to nucleate ice (Tobo et al, 2019;Paramonov et al, 2018;Sanchez-Marroquin et al, 2020), and dust from Iceland's deserts has been shown to be an important INP type across the North Atlantic and low Arctic (Sanchez-Marroquin et al, 2020). Further evidence for a strong terrestrial source of INPs in the Arctic was found by Irish et al (2019a), with a correlation between INP concentrations and the time that air spent over bare land during late summer.…”

“…Modelling (Vergara-Temprado et al, 2017) and measurements (McCluskey et al, 2018b;McCluskey et al, 2018a) suggests that this source produces sea spray aerosol that are relatively ineffective INPs, with activities orders of magnitude smaller (on a per-surface-area basis) than mineral dust. Marine biogenic INPs may define a baseline INP concentration in environments that lack other more active INP types (Mc-Cluskey et al, 2018a;Vergara-Temprado et al, 2017;Schill et al, 2020), and it is conceivably an important source in windy CAOs. In the Northern Hemisphere, even the small quantities of dust transported from the low-latitude source regions may dominate over marine sources of INPs much of the time (Vergara-Temprado et al, 2017), and local terrestrial sources may episodically swamp both marine and low- Vergara-Temprado et al, 2018).…”

Mineral and biological ice-nucleating particles above the South East of the British Isles

“…INPs have been measured using a lter droplet-on-lter assay that has been previously used during other FAAM BAe-146 eld campaigns. 55,56 This technique is a combination of the techniques used in previous studies. 53,65 Teon lters where aerosol samples have been collected using the lter inlet system on board of the FAAM BAe-146 are placed on top of glass slides (Ted Pella cover glass, 48 Â 60 Â 0.15 mm), whose surface was made hydrophobic by applying Turtle Wax ClearVue Rain repellent solution.…”