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Atmospheric ice-nucleating particles (INPs) play a critical role in cloud freezing processes, with important implications for precipitation formation and cloud radiative properties, and thus for weather and climate. Additionally, INP emissions respond to changes in the Earth System and climate, for example, desertification, agricultural practices, and fires, and therefore may introduce climate feedbacks that are still poorly understood. As knowledge of the nature and origins of INPs has advanced, regional and global weather, climate, and Earth system models have increasingly begun to link cloud ice processes to model-simulated aerosol abundance and types. While these recent advances are exciting, coupling cloud processes to simulated aerosol also makes cloud physics simulations increasingly susceptible to uncertainties in simulation of INPs, which are still poorly constrained by observations. Advancing the predictability of INP abundance with reasonable spatiotemporal resolution will require an increased focus on research that bridges the measurement and modeling communities. This review summarizes the current state of knowledge and identifies critical knowledge gaps from both observational and modeling perspectives. In particular, we emphasize needs in two key areas: (a) observational closure between aerosol and INP quantities and (b) skillful simulation of INPs within existing weather and climate models. We discuss the state of knowledge on various INP particle types and briefly discuss the challenges faced in understanding the cloud impacts of INPs with present-day models. Finally, we identify priority research directions for both observations and models to improve understanding of INPs and their interactions with the Earth System. [ABSTRACT FROM AUTHOR]

The article provides information about ice-nucleating particles (INPs) in the atmosphere, which play a crucial role in initiating ice formation in clouds, affecting weather and climate. It focuses on bio-INPs, a subset of these particles, and highlights their significance in initiating freezing processes in mixed-phase clouds at warmer temperatures.

The oceans contribute to aerosol particles in the atmosphere through two different physical mechanisms: first by the production of sea spray aerosol (SSA), and second by emitting gases that condense to produce secondary marine aerosol (SMA). These aerosol emissions include three types of chemical compounds: salt particles account for >90% of the mass, most of which is >1 μm dry diameter; sulfate particles are mostly <0.5 μm, typically constituting most of the number and the largest impacts on clouds; organic components include the greatest variety of compounds and the most uncertain effects on clouds. Most SSA particles are expected to form from bubbles as film drops that are <1 μm dry diameter and form from flapping bursting bubbles, although >1 μm film drops can form by ligament fragmentation. SMA particles include contributions from marine biogenic gas emissions, including dimethylsulfide (DMS), isoprene, amines, and monoterpenes. The role of particles from the ocean in the atmosphere varies by region and by season, but since atmospheric concentrations of ocean-derived <1 μm particles are typically much smaller than the concentrations of their continental counterparts, they have the largest impacts on climate in regions where continental sources are limited. Most efforts to quantify global SSA and SMA emissions rely on global models, where representations of marine aerosol sources are constrained by a small number of field measurements. Satellite-based retrievals of coarse and marine aerosol optical depth provide near global coverage that has been linked to coincident wind speed, whitecaps, and biological productivity for >1 μm particles. The current best estimate of SSA flux of 5000 Tg/yr can be used to calculate SSA-related carbon flux as 35 TgC/yr, by approximating <1 μm SSA particles as 10% of SSA flux with 7% organic carbon and > 1 μm particles as 90% of SSA flux with no organic carbon. SMA is estimated to contribute 0.6 TgC/yr as DMS, 0.6 TgC/yr as amines, and an additional trace amount from isoprene and monoterpenes for a total of <2 TgC/yr. Because of the limited availability of observations to constrain SSA and SMA global estimates, oceanic fluxes to aerosol and aerosol precursors could vary by over two orders of magnitude. Key open questions that require additional observational constraints include the variability in >1 μm SSA mass size distributions, the relative contributions of SSA and SMA to number concentrations of particles <0.5 μm, and the regional and seasonal factors that may control these <0.5 μm particle concentrations. [ABSTRACT FROM AUTHOR]

Ice nucleating particles (INPs) are a rare subset of particles that can have an outsized impact relative to their prevalence. To simulate INP variability, models require parameterizations for the most important sources of INPs. Most parameterizations in the literature were developed from laboratory experiments that used proxies for ambient particles. Whether these laboratory models effectively represent ambient aerosol is still not well understood and parameterizations developed from field measurements may be more atmospherically relevant. Expanding on previous work in which we used an ice chamber and a single‐particle mass spectrometer (SPMS) to characterize INP composition, we calculate heterogeneous ice nucleation rate coefficients for ambient particles. We find good agreement between our dust and previous measurements of airborne dust. We also use a Monte Carlo approach to assess the relative contribution of each measurement to the uncertainty and find that the biggest source is the sampling efficiency of the SPMS. Plain Language Summary: Ice nucleation activity is typically parameterized using results from laboratory experiments. However, whether these parameterizations accurately represent the ice nucleation activity of ambient aerosol is not well understood. In this work, we develop a novel framework for deriving ice nucleation rate coefficients from ambient measurements, and apply these methods to an ambient data set using a Monte Carlo approach. Key Points: An integrated CFDC and ATOFMS were used to derive particle‐type specific heterogeneous ice nucleation rate coefficients for ambient aerosolDust ice nucleation rate coefficients were within 2–5‐fold of previous estimatesThese are the first published measurements of nucleation rate coefficients for sea spray aerosol [ABSTRACT FROM AUTHOR]

To resolve the various types of biological ice nuclei (IN) with atmospheric models, an extension of the empirical parameterization (EP) is proposed to predict the active IN from multiple groups of primary biological aerosol particles (PBAPs). Our approach is to utilize coincident observations of PBAP sizes, concentrations, biological composition, and ice nucleating ability. The parameterization organizes PBAPs into five basic groups: 1) fungal spores, 2) bacteria, 3) pollen, 4) viral particles, plant/animal detritus, 5) algae, and their respective fragments. This new biological component of the EP was constructed by fitting predicted concentrations of PBAP IN to those observed at the Amazon Tall Tower Observatory (ATTO) site located in the central Amazon. The fitting parameters for pollen and viral particles and plant/animal detritus, which are much less active as IN than fungal and bacterial groups, are constrained based on their ice nucleation activity from the literature. The parameterization has empirically derived dependencies on the surface area of each group (except algae), and the effects of variability in their mean sizes and number concentrations are represented via their influences on surface area. The concentration of active algal IN is estimated from literature-based measurements. Predictions of this new biological component of the EP are consistent with previous laboratory and field observations not used in its construction. The EP scheme was implemented in a 0D parcel model. It confirms that biological IN account for most of the total IN activation at temperatures warmer than −20°C and at colder temperatures dust and soot become increasingly more important to ice nucleation. [ABSTRACT FROM AUTHOR]