Abstract. Wave-breaking action in bodies of freshwater produces atmospheric aerosols via a similar mechanism to sea spray aerosol (SSA) from seawater. The term lake spray aerosol (LSA) is proposed to describe particles formed by this mechanism, which have been observed over the Laurentian Great Lakes. Though LSA has been identified from size distribution measurements during a single measurement campaign, no measurements of LSA composition or relationship to bubble-bursting dynamics have been conducted. An LSA generator utilizing a plunging jet, similar to many SSA generators, was constructed for the generation of aerosol from freshwater samples and model salt solutions. To evaluate this new generator, bubble and aerosol number size distributions were measured for salt solutions representative of freshwater (CaCO3) and seawater (NaCl) at concentrations ranging from that of freshwater to seawater (0.05–35 g kg−1), synthetic seawater (inorganic), synthetic freshwater (inorganic), and a freshwater sample from Lake Michigan. Following validation of the bubble and aerosol size distributions using synthetic seawater, a range of salt concentrations were investigated. The systematic studies of the model salts, synthetic freshwater, and Lake Michigan sample indicate that LSA is characterized by a larger number size distribution mode diameter of 300 nm (lognormal), compared to seawater at 110 nm. Decreasing salt concentrations from seawater to freshwater led to greater bubble coalescence and formation of larger bubbles, which generated larger particles and lower aerosol number concentrations. This resulted in a bimodal number size distribution with a primary mode (180 ± 20 nm) larger than that of SSA, as well as a secondary mode (46 ± 6 nm) smaller than that of SSA. This new method for studying LSA under isolated conditions is needed as models, at present, utilize SSA parameterizations for freshwater systems, which do not accurately predict the different size distributions observed for LSA or resulting climate properties. Given the abundance of freshwater globally, this potentially important source of aerosol needs to be thoroughly characterized, as the sizes produced are relevant to light scattering, cloud condensation nuclei (CCN), and ice nuclei (IN) concentrations over bodies of freshwater.

Abstract. Wave breaking action in bodies of freshwater produces atmospheric aerosols via a similar mechanism to sea spray aerosol (SSA) from seawater. The term lake spray aerosol (LSA) is proposed to describe particles formed by this mechanism, which have been observed over the Laurentian Great Lakes. Though LSA has been identified from size distribution measurements during a single measurement campaign, no measurements of LSA composition or relationship to bubble bursting dynamics have been conducted. A LSA generator utilizing a plunging jet, similar to many SSA generators, was constructed for the generation of aerosol from freshwater samples and model salt solutions. To evaluate this new generator, bubble and aerosol number size distributions were measured for salt solutions representative of freshwater (CaCO3) and seawater (NaCl) at concentrations ranging from that of freshwater to seawater (0.05–35 g L−1), synthetic seawater (inorganic), synthetic freshwater (inorganic), and a freshwater sample from Lake Michigan. Following validation of the bubble and aerosol size distributions using synthetic seawater, a range of salt concentrations was investigated. Decreasing salt concentrations from seawater to freshwater led to greater bubble coalescence and formation of larger bubbles, which generated larger particles and lower aerosol number concentrations. The systematic studies of the model salts, synthetic freshwater, and Lake Michigan sample indicate that LSA is characterized by a larger bubble size distribution, compared to seawater, with a peak near 300 μm. This resulted in a bimodal aerosol size distribution with a primary mode (180 ± 20 nm) larger than that of SSA, and a secondary mode (46 ± 6 nm) smaller than that of SSA. This new method for studying LSA under isolated conditions is needed as models, at present, utilize SSA parametrizations for freshwater systems, which are not accurate for predicting climate properties of the different size distributions observed for LSA. Given the abundance of freshwater globally, this potentially important source of aerosol needs to be thoroughly characterized, as the sizes produced are relevant to light scattering, cloud condensation nuclei (CCN), and ice nuclei (IN) concentrations over the bodies of freshwater.

Aerosol particles are generated by wind-driven processes in regions with large bodies of freshwater, but the impact of these particles on cloud properties and processes is poorly understood. Lake spray aerosol (LSA) production from freshwater wave breaking has the potential to contribute to cloud formation and modify cloud properties by acting as cloud condensation nuclei (CCN) and ice nucleating particles (INPs). To examine whether LSA reaches cloud height and is incorporated into clouds over the Laurentian Great Lakes, sampling of atmospheric particles and cloud water was conducted over Lake Michigan during a summertime wave-breaking event with wave heights of >1.4 m and wind speeds of >9 m s −1 . Single-particle microscopy and spectroscopy identified ambient LSA that had composition (CaCO 3 and organic material) and morphology (spherical) consistent with LSA generated in the laboratory from surface freshwater collected at the time of ambient sampling. Cloud water was aerosolized in the laboratory, and the resulting composition and morphology of the insoluble residues were similar to ambient and laboratory-generated LSA particles. Elemental mole ratios of LSA and cloud water demonstrated that clouds over the Great Lakes contain similar inorganic salt composition to that of LSA and freshwater lakes. Therefore, LSA is likely a source of CCN and possibly INPs over the Great Lakes, which could potentially influence lake-effect cloud formation and properties. This has important implications for cloud microphysical and radiative properties in the Great Lakes region, as well as other areas with large bodies of freshwater.

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