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Abstract Supercooled liquid clouds are ubiquitous over the Southern Ocean (SO), even to temperatures below −20°C, and comprise a large fraction of the marine boundary layer (MBL) clouds. Earth system models and reanalysis products have struggled to reproduce the observed cloud phase distribution and occurrence of cloud ice in the region. Recent simulations found the microphysical representation of ice nucleation and growth has a large impact on these properties, however, measurements of SO ice nucleating particles (INPs) to validate simulations are sparse. This study presents measurements of INPs from simultaneous aircraft and ship campaigns conducted over the SO in austral summer 2018, which include the first in situ observations in and above cloud in the region. Our results confirm recent observations that INP concentrations are uniformly lower than measurements made in the late 1960s. While INP concentrations below and above cloud are similar, higher ice nucleation efficiency above cloud supports model simulations that the dominant INP composition varies with height. Model parameterizations based solely on aerosol properties capture the mean relationship between INP concentration and temperature but not the observed variability, which is likely related to the only modest correlations observed between INPs and environmental or aerosol metrics. Including wind speed in addition to activation temperature in a marine INP parameterization reduces bias but does not explain the large range of observed INP concentrations. Direct and indirect inference of marine INP size suggests MBL INPs, at least during Austral summer, are dominated by particles with diameters smaller than 500 nm. 

Abstract The oxidation of carbonyl sulfide (OCS) is the primary, continuous source of stratospheric sulfate aerosol particles, which can scatter shortwave radiation and catalyze heterogeneous reactions in the stratosphere. While it has been estimated that the oxidation of dimethyl sulfide (DMS), emitted from the surface ocean accounts for 8%–20% of the global OCS source, there is no existing DMS oxidation mechanism relevant to the marine atmosphere that is consistent with an OCS source of this magnitude. We describe new laboratory measurements and theoretical analyses of DMS oxidation that provide a mechanistic description for OCS production from hydroperoxymethyl thioformate, a ubiquitous, soluble DMS oxidation product. We incorporate this chemical mechanism into a global chemical transport model, showing that OCS production from DMS is a factor of 3 smaller than current estimates, displays a maximum in the tropics consistent with field observations and is sensitive to multiphase cloud chemistry. 

Abstract Aerosols significantly influence atmospheric processes such as cloud nucleation, heterogeneous chemistry, and heavy‐metal transport in the troposphere. The chemical and physical complexity of atmospheric aerosols results in large uncertainties in their climate and health effects. In this article, we review recent advances in scientific understanding of aerosol processes achieved by the application of quantum chemical calculations. In particular, we emphasize recent work in two areas: new particle formation and heterogeneous processes. Details in quantum chemical methods are provided, elaborating on computational models for prenucleation, secondary organic aerosol formation, and aerosol interface phenomena. Modeling of relative humidity effects, aerosol surfaces, and chemical kinetics of reaction pathways is discussed. Because of their relevance, quantum chemical calculations and field and laboratory experiments are compared. In addition to describing the atmospheric relevance of the computational models, this article also presents future challenges in quantum chemical calculations applied to aerosols. 

Abstract Oceans are, generally, relatively weak sources of ice nucleating particles (INPs). Thus, dust transported from terrestrial regions can dominate atmospheric INP concentrations even in remote marine regions. Studies of ocean‐emitted INPs have focused upon sea spray aerosols containing biogenic species. Even though large concentrations of dust are transported over marine regions, resuspended dust has never been explicitly considered as another possible source of ocean‐emitted INPs. Current models assume that deposited dust is not re‐emitted from surface waters. Our laboratory studies of aerosol particles produced from coastal seawater and synthetic seawater doped with dust show that dust can indeed be ejected from water during bubble bursting. INP concentration measurements show these ejected dust particles retain ice nucleating activity. Doping synthetic seawater to simulate a strong dust deposition event produced INPs active at temperatures colder than −13°C and INP concentrations 1 to 2 orders of magnitude greater than either lab sea spray or marine boundary layer measurements. The relevance of these laboratory findings is highlighted by single‐particle composition measurements along the Californian coast where at least 9% of dust particles were mixed with sea salt. Additionally, global modeling studies show that resuspension of dust from the ocean could exert the most impact over the Southern Ocean, where ocean‐emitted INPs are thought to dominate atmospheric INP populations. More work characterizing the factors governing the resuspension of dust particles is required to understand the potential impact upon clouds. 

Abstract The formation of ice in clouds can strongly impact cloud properties and precipitation processes during storms, including atmospheric rivers. Sea spray aerosol (SSA) particles are relatively inefficient as ice nucleating particles (INPs) compared to mineral dust. However, due to the vast coverage of the Earth's surface by the oceans, a number of recent studies have focused on identifying sources of marine INPs, particularly in regions lacking a strong influence from dust. This study describes the integration, validation, and application of a system coupling a continuous flow diffusion chamber with a single particle mass spectrometer using a pumped counterflow virtual impactor to remove nonnucleated particles and selectively measure the composition of INPs with a detection efficiency of 3.10×10⁻⁴. In situ measurements of immersion freezing INP composition were made at a coastal site in California using the integrated system. Mineral dust particles were the most abundant ice crystal residual type during the sampling period and found to be ice active despite having undergone atmospheric processing. SSA were more abundant in ambient measurements but represented only a minor fraction of the ice crystal residual population at −31 °C. Notably, the SSA particles that activated were enriched with organic nitrogen species that were likely transferred from the ocean. Calculations of ice nucleation active site densities were within good agreement with previous studies of mineral dust and SSA. 

Immersion freezing temperatures of substrate-deposited lipid particles depend on solubility and viscosity. 

Background: Glyoxal has been implicated as a significant contributor to the formation of secondary organic aerosols, which play a key role in our ability to estimate the impact of aerosols on climate. Elevated concentrations of glyoxal over remote ocean waters suggests that there is an additional source, distinct from urban and forest environments, which has yet to be identified. Herein, we demonstrate that the ocean can serve as an appreciable source of glyoxal in the atmosphere due to microbiological activity. Methods and Results: Based on mass spectrometric analyses of nascent sea spray aerosols and the sea surface microlayer (SSML) of naturally occurring algal blooms, we provide evidence that during the algae death phase phospholipids become enriched in the SSML and undergo autoxidation thereby generating glyoxal as a degradation product. Conclusions: We propose that the death phase of an algal bloom could serve as an important and currently missing source of glyoxal in the atmosphere.