Ice Nucleating Particle Connections to Regional Argentinian Land Surface Emissions and Weather During the Cloud, Aerosol, and Complex Terrain Interactions Experiment. Issue 23 (30th November 2021)

• Record Type: Journal Article
• Authors: Testa, Baptiste; Hill, Thomas C. J.; Marsden, Nicholas A.; Barry, Kevin R.; Hume, Carson C.; Bian, Qijing; Uetake, Jun; Hare, Hannah; Perkins, Russell J.; Möhler, Ottmar; Kreidenweis, Sonia M.; DeMott, Paul J.
• Is Part Of: Journal of geophysical research. Volume 126:Issue 23(2021)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2021-11-30
• Subjects: ice nucleating particles -- aerosols -- soil dust -- minerals -- bioaerosols; Atmospheric physics -- Periodicals; Geophysics -- Periodicals; 551.5
• DOI: 10.1029/2021JD035186
• Languages: English
• ISSNs: 2169-897X

Abstract

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. Plain Language Summary: The Cloud, Aerosol, and Complex Terrain Interactions campaign studied how extreme thunderstorms above the Sierras de Córdoba range of Argentina form in dependence on meteorology, local terrain, and particles that feed cloud formation. We studied rare ice nucleating particles, which act as seeds for snow crystals (without them, water droplets supercool to above approximately −38°C—the threshold for homogeneous freezing of micron‐sized cloud droplets—before spontaneously freezing). This freezing begins the process of rain (starting as snow) and hail precipitation. To measure the numbers of atmospheric ice nucleating particles, we filtered air, suspended all collected particles in water and cooled aliquots of suspensions until they froze. To characterize their origin, we heated suspensions to deactivate biological particles (proteins, fungi, bacteria) and retested freezing. Then we digested with hydrogen peroxide to remove all organic molecules (e.g., from windblown soil organic matter) and retested freezing. What remained were inorganic ice nucleating particles (e.g., mineral dust). Biological types froze first at −5°C, and accounted for most ice nucleating particles down to −20°C. Their concentrations were enhanced by rainfall and high humidity. Other organic particles predominated below −20°C, always exceeding the contribution from inorganics. These composition and freezing properties suggested most came from regional agricultural soils, thus connecting human land activities to regional weather. Key Points: Biological components dominated ice nucleating particles active >−20°C, and those active >−15°C were enhanced by rain or high RH events Non‐heat‐labile organic components dominated the activity of ice nucleating particles below −20°C, exceeding mineral contributions Ice nucleating particle composition and characteristics suggested the majority originated from regional agricultural soils