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

Abstract

Ice-nucleating particles (INPs) are rare atmospheric aerosols that initiate primary ice formation, but accurately simulating their concentrations and variability in large-scale climate models remains a challenge. Doing so requires both simulating major particle sources and parameterizing their ice nucleation (IN) efficiency. Validating and improving model predictions of INP concentrations requires measuring their concentrations delineated by particle type. We present a method to speciate INP concentrations into contributions from dust, sea spray aerosol (SSA), and bioaerosol. Field campaign data from Bodega Bay, California, showed that bioaerosols were the primary source of INPs between −12° and −20°C, while dust was a minor source and SSA had little impact. We found that recent parameterizations for dust and SSA accurately predicted ambient INP concentrations. However, the model did not skillfully simulate bioaerosol INPs, suggesting a need for further research to identify major factors controlling their emissions and INP efficiency for improved representation in models.

Assessing the global contribution of marine, terrestrial bioaerosols, and desert dust to ice-nucleating particle concentrations

“…Our model results show that PBAP are the primary source of INP between −12°C and −20°C. This agrees with a recent observational and modelling study by Cornwell et al (2023). Overall, mineral dust (Fig.…”

“…Reviewing experimental and modeling studies, Burrows et al (2022) summarized the level of understanding and parameterisations of INP activity of 10 particle types that could represent INP in climate models. In immersion freezing, which is the dominant mode of primary ice formation in MPC (Hande and Hoose, 2017), desert dust, marine primary organic aerosols (MPOA) and terrestrial 95 primary biological aerosol particles (PBAP) have emerged as the most relevant INP sources (McCluskey et al, 2018;Chatziparaschos et al, 2023;Spracklen and Heald, 2014;Cornwell et al, 2023). These findings align with the physical understanding that INP are often efficiently activated as cloud condensation nuclei due to internal mixing with soluble components and their large size.…”

“…Cloud-resolved high-resolution modeling studies indicate that clouds can present sensitivity to INP 485 perturbations that exceed one order of magnitude (Fan et al, 2017). For the simulation of INP in models to be deemed satisfactory, prediction errors must be constrained to less than an order of magnitude for the majority of observations (Cornwell et al, 2023). Figure 6 Considering dust minerals as the sole INP precursors leads to underestimation against observations (Fig.…”

Characteristics of Atmospheric Ice Nucleation during Spring: A Case Study on Huangshan

“…This adds complexity to the estimation of the influence of aerosols on clouds [23][24][25]. Increasing knowledge about the characteristics of INPs will improve the accuracy of evaluating the impact of aerosols on clouds and reduce the level of uncertainty involved [18,26].…”

Effect of Acidity on Ice Nucleation by Inorganic–Organic Mixed Droplets

“…For example, mineral dust particles with large emission rates of up to 5000 Tg yr –1 are recognized as the most important INP type because of their generally effective ice nucleation ability. − Previous studies have found that dust particles activate as ice crystals at temperatures above −15 °C in the immersion mode . Additionally, biological aerosols including bacteria, pollen, viruses, fungi, and phytoplankton can also act as effective INPs with freezing temperatures ranging from −3 °C for bacteria to below −38 °C for marine aerosols. − Furthermore, many studies have shown the pervasive presence of ammonium sulfate and sulfuric acid particles in the upper troposphere. These particles exhibit homogeneous freezing temperatures below −38 °C, playing a significant role in the formation of cirrus clouds. − …”