Ice Nucleating Particle Connections to Regional Argentinian Land Surface Emissions and Weather During the Cloud, Aerosol, and Complex Terrain Interactions Experiment

Abstract

Here, we present a multi‐season study of ice‐nucleating particles (INPs) active via the immersion freezing mechanism, which took place in north‐central Argentina, a worldwide hotspot for mesoscale convective storms. INPs were measured untreated, after heating to 95°C, and after hydrogen peroxide digestion. No seasonal cycle of INP concentrations was observed. Heat labile INPs, which we define as “biological” herein, dominated the population active at −5 to −20°C, while non‐heat‐labile organic INPs (decomposed by peroxide) dominated at lower temperatures, from −20 to −28°C. Inorganic INPs (remaining after peroxide digestion), were minor contributors to the overall INP activity. Biological INP concentration active around −12°C peaked during rain events and under high relative humidity, reflecting emission mechanisms independent of the background aerosol concentration. The ratio of non‐heat‐labile organic and inorganic INPs was generally constant, suggesting they originated from the same source, presumably from regional arable topsoil based on air mass histories. Single particle mass spectrometry showed that soil particles aerosolized from a regionally common agricultural topsoil contained known mineral INP sources (K‐feldspar and illite) as well as a significant organic component. The INP activity observed in this study correlates well with agricultural soil INP activities from this and other regions of the world, suggesting that the observed INP spectra might be typical of many arable landscapes. These results demonstrate the strong influence of regional continental landscapes, emitting INPs of types that are not yet well represented in global models.

Bioaerosols are the dominant source of warm-temperature immersion-mode INPs and drive uncertainties in INP predictability

“…contributing 10 to 40% of the INPs active at −19°C. These results are consistent with previous literature showing that bio-INPs make up a greater fraction of continental boundary layer INPs at warmer temperatures than at colder temperatures (19,25,36).…”

“…1). Although the observations we use for this study are taken from a single field campaign, they provide a direct and quantitative corroboration for a growing body of studies suggesting that bio-INPs play a critical role at warmer freezing temperatures in many locations globally (9,12,25).…”

How Can Ice Emerge at 0 °C?

“…One can see that the buffer per se freezes between −8 and −10 °C, and that the addition of either CuO or P. syringae to the buffer results in an increase in the freezing temperature (to between −1 and −2 °C in the case of P. syringae , and to between −5 and −7 °C in the case of CuO). It should be noted that, in spite of the fact that CuO nucleates ice at lower temperatures than the conventional AgI (for this comparison, the corresponding literature data for AgI are also included in Table 3 ), the ice-nucleating activity of CuO observed in our experiments was higher than that of many other inorganic ice nucleators described in the literature [ 33 , 56 , 57 ].…”

Export of ice-nucleating particles from watersheds: results from the Amazon and Tocantins river plumes

“…We expected differences in land cover between both watersheds to result in different INP populations in the plumes of the Amazon and Tocantins rivers. These differences should emerge primarily in INPs active at −15°C or above (INP −15 ), because most INP −15 are of biological origin and are ultimately derived from plants and associated microorganisms [18][19][20].…”