Ice-nucleating particles in a coastal tropical site

Abstract

Abstract. Atmospheric aerosol particles that can nucleate ice are referred to as ice-nucleating particles (INPs). Recent studies have confirmed that aerosol particles emitted by the oceans can act as INPs. This very relevant information can be included in climate and weather models to predict the formation of ice in clouds, given that most of them do not consider oceans as a source of INPs. Very few studies that sample INPs have been carried out in tropical latitudes, and there is a need to evaluate their availability to understand the potential role that marine aerosol may play in the hydrological cycle of tropical regions. This study presents results from the first measurements obtained during a field campaign conducted in the tropical village of Sisal, located on the coast of the Gulf of Mexico of the Yucatan Peninsula in Mexico in January–February 2017, and one of the few data sets currently available at such latitudes (i.e., 21∘ N). Aerosol particles sampled in Sisal are shown to be very efficient INPs in the immersion freezing mode, with onset freezing temperatures in some cases as high as −3 ∘C, similarly to the onset temperature from Pseudomonas syringae. The results show that the INP concentration in Sisal was higher than at other locations sampled with the same type of INP counter. Air masses arriving in Sisal after the passage of cold fronts have surprisingly higher INP concentrations than the campaign average, despite their lower total aerosol concentration. The high concentrations of INPs at warmer ice nucleation temperatures (T>-15 ∘C) and the supermicron size of the INPs suggest that biological particles may have been a significant contributor to the INP population in Sisal during this study. However, our observations also suggest that at temperatures ranging between −20 and −30 ∘C mineral dust particles are the likely source of the measured INPs.

Size-dependent ice nucleation by airborne particles during dust events in the eastern Mediterranean

“…between events, possibly due to different composition of the particles or higher sensitivity to atmospheric processing during long-range transport. In general, supermicron particles contributed the most to the INP concentration, in agreement with other previous studies (Mason et al, 2016;Huffman et al, 2013;Ladino et al, 2019). However, our current study is probably the only case in which mineral dust dominated the samples.…”

“…Mason et al (2016) studied the immersion freezing abilities of airborne particles in North America and Europe and found that supermicron particles dominated the freezing, especially at relatively high temperature (258 K). Recent measurements in a coastal tropical site conducted by Ladino et al (2019) also found high concentrations of INPs at relatively high temperatures (> 258 K) due to supermicron particles. In these studies, however, mineral dust is not expected to dominate the samples, and bioaerosol particles are thought to dominate the freezing at high temperatures (> 258 K).…”

“…In these studies, however, mineral dust is not expected to dominate the samples, and bioaerosol particles are thought to dominate the freezing at high temperatures (> 258 K). At lower temperatures (below 253 K), Ladino et al (2019) suggested that mineral dust dominated the freezing. Moreover, DeMott et al (2010) found that INP concentrations are correlated with particles > 0.5 µm.…”

“…It was shown that atmospheric aging processes can change the size, morphology and surface chemistry of the particles. This includes, for example, the adsorption of organic components on AMD (Murphy et al, 2006;DeMott et al, 2003a;Falkovich et al, 2004) or coatings of nitrates, chlorides and sulfates that enhance the hygroscopicity of the particles (Krueger et al, 2004;Laskin et al, 2005;Li and Shao, 2009). Levin et al (1996) found that AMD particles transported over the Mediterranean Sea were often coated with sulfate and other soluble materials, which affect cloud microphysical properties and can eventually result in enhanced ice nucleation.…”

The UNAM-droplet freezing assay: An evaluation of the ice nucleating capacity of the sea-surface microlayer and surface mixed layer in tropical and subpolar waters (edited by Dr. Michel Grutter)

“…Marine aerosol particles can influence mixed-phase and cirrus cloud formation because a fraction of them are able to act as ice nucleating particles (INPs), facilitating ice crystal formation via different heterogeneous ice nucleation pathways (e.g., Bigg, 1973;Schnell and Vali, 1975;Schnell, 1975Schnell, , 1977Schnell, , 1982Rosinski et al, 1987Rosinski et al, , 1988Mason et al, 2015;DeMott et al, 2016;McCluskey et al, 2017McCluskey et al, , 2018Welti et al, 2018;Si et al, 2018;Creamean et al, 2018;Ladino et al, 2019;Gong et al, 2020). As summarized by Burrows et al (2013), marine microorganisms, EPS aggregates, glassy organics, and crystalline hydrated NaCl are types of aerosol particles that have the potential to nucleate ice in marine environments.…”