Ice-nucleating ability of aerosol particles and possible sources at three coastal marine sites

Abstract

Abstract. Despite the importance of ice-nucleating particles (INPs) for climate and precipitation, our understanding of these particles is far from complete. Here, we investigated INPs at three coastal marine sites in Canada, two at mid-latitude (Amphitrite Point and Labrador Sea) and one in the Arctic (Lancaster Sound). For Amphitrite Point, 23 sets of samples were analyzed, and for Labrador Sea and Lancaster Sound, one set of samples was analyzed for each location. At all three sites, the ice-nucleating ability on a per number basis (expressed as the fraction of aerosol particles acting as an INP) was strongly dependent on the particle size. For example, at diameters of around 0.2 µm, approximately 1 in 106 particles acted as an INP at −25 ∘C, while at diameters of around 8 µm, approximately 1 in 10 particles acted as an INP at −25 ∘C. The ice-nucleating ability on a per surface-area basis (expressed as the surface active site density, ns) was also dependent on the particle size, with larger particles being more efficient at nucleating ice. The ns values of supermicron particles at Amphitrite Point and Labrador Sea were larger than previously measured ns values of sea spray aerosols, suggesting that sea spray aerosols were not a major contributor to the supermicron INP population at these two sites. Consistent with this observation, a global model of INP concentrations under-predicted the INP concentrations when assuming only marine organics as INPs. On the other hand, assuming only K-feldspar as INPs, the same model was able to reproduce the measurements at a freezing temperature of −25 ∘C, but under-predicted INP concentrations at −15 ∘C, suggesting that the model is missing a source of INPs active at a freezing temperature of −15 ∘C.

Ice-nucleating particles in a coastal tropical site

“…Although Al, Si, Ca, and Fe were found at low concentrations ( Fig. 8a), Tables 2 and S2 suggest that mineral dust particles are an important source of INPs in Sisal at temperatures ranging from −20 to −30 • C. This is in close agreement with the results obtained by Si et al (2019) in the Canadian High Arctic. From the correlation of the [INP] and the aerosol chemical composition at −15 • C, Mg was the only element showing a correlation that is statistically significant at the 95 % confidence interval (p < 0.05).…”

Deposition of ionic species and black carbon to the Arctic snowpack: combining snow pit observations with modeling

“…8). Multiple photochemical processes occur in the sea ice-snow-atmosphere system of the Arctic, acting upon the variation between bromide and sodium (Simpson et al, 2007;Jacobi et al, 2012). On solid surfaces (aerosols, snow, sea ice) bromide can be transformed into volatile bromine compounds that are released to the atmosphere and subsequently deposited.…”

“…Therefore, bromide can be already depleted in the sea salt aerosols generated over sea ice, which would cause a wet and dry deposition flux lower than estimated based on the standard seawater ratio, or it can be diminished in the surface snow after deposition (Jacobi et al, 2012), explaining the average bromide-to-sodium ratios below the seawater ratio in both snow pits. Nevertheless, since the released bromide is subsequently deposited, a snowpack with layers enriched in bromide is also possible depending on the dominating influence of the release vs. the additional deposition of bromide (Simpson et al, 2007). This can also explain the contrasting results found on top of the Holtedahlfonna glacier, located approximately 40 km to the northeast of Ny-Ålesund, in April 2012.…”

Characterization of aerosol particles at Cape Verde close to sea and cloud level heights – Part 2: ice nucleating particles in air, cloud and seawater

“…CC BY 4.0 License. with results from Si et al (2018) and Irish et al (2019a), both done in the Arctic, where it was also concluded that SSA only contributed little to the INP population.…”