Lake spray aerosol generation: A method for producing representative particles from freshwater wave breaking

Abstract

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.

Probability density of irradiance for optical waves propagating underwater in the presence of air bubbles

“…Thus, the bubble size distribution should follow a normal curve. Experimental observations support this conclusion for bubble diameters in the micron range 18‐20 . For larger bubble diameters, the bubble distribution follows a power law as a function of the diameter 20,21 …”

Export of ice nucleating particles from a watershed

“…Neither is the case. Although some of the INP −8 are probably produced in the freshwater system [ 23 , 24 ], our data strongly suggest that the majority of INP −8 in Rhine water at Basel are transported by surface or subsurface flow to the freshwater system. Most likely sources of the INP −8 are plant surfaces [ 25 ], plant litter [ 9 , 26 ] and soil [ 4 , 17 , 18 ], with only smaller contributions of wet fallout deposition due to the rain events (wash-out from the atmosphere).…”

A Systematic Analysis of the Salinity Effect on Air Bubbles Evolution: Laboratory Experiments in a Breaking Wave Analog

“…Many previous experimental studies have used continuous water jets as an analog of air entrainment from breaking waves (Hultin et al, ; King et al, ; May et al, ; Salter et al, ). While Stokes et al () incorporated an intermittent plunging sheet, no previous studies have systematically investigated the effect of the air entrainment intermittency on bubble clouds characteristics.…”

“…Recent studies have suggested that breaking waves and the subsequent spray aerosols in freshwater lakes can be a vessel for the transfer of harmful algal bloom toxins from the lakes into the surrounding residential areas (May et al, , ). Yet, few studies have investigated aerosolization from breaking waves in freshwater bodies as compared to the large body of literature on aerosolization from seawater (May et al, ). Accordingly, understanding the effect of water salinity on air entrainment and whitecap coverage helps to better characterize air‐water interactions and their implications on the climate and air quality.…”

“…Due to the difficulty of reproducing air entrainment from breaking waves in small‐scale laboratory systems, researchers have used different experimental setups to generate subsurface bubbles including porous glass tubes (Mårtensson et al, ; Scott, ), overturning buckets (Carey et al, ; Haines & Johnson, ), continuous jets (May et al, ; Salter et al, ), intermittent water sheets (Stokes et al, , ), and wave channels (Deane & Stokes, ; Li et al, ; Loewen et al, ). The validity of such setups to faithfully reproduce air‐water interactions from breaking waves depends on their ability to replicate the in situ bubbles and aerosols size distributions (Fuentes et al, ; Stokes et al, ).…”