The Sea Spray Chemistry and Particle Evolution Study (SeaSCAPE): Overview and Experimental Methods

Abstract

Marine aerosols strongly influence climate through their interactions with solar radiation and clouds. However, significant questions remain regarding the influences of biological activity and seawater chemistry on the flux, chemical composition, and climaterelevant properties of marine aerosols and gases. Wave channels, a traditional tool of physical oceanography, have been adapted for large-scale ocean-atmosphere mesocosm experiments in the laboratory. These experiments enable the study of aerosols under controlled conditions which isolate the marine system from atmospheric anthropogenic and terrestrial influences.Here, we present an overview of the 2019 Sea Spray Chemistry and Particle Evolution (SeaSCAPE) study, which was conducted in an 11,800 L wave channel which was modified to facilitate atmospheric measurements. The SeaSCAPE campaign sought to determine the influence of biological activity in seawater on the production of primary sea spray aerosols, volatile organic compounds (VOCs), and secondary marine aerosols. Notably, the SeaSCAPE experiment also focused on understanding how photooxidative aging processes transform the composition of marine aerosols. In addition to a broad range of aerosol, gas, and seawater measurements, we present key results which highlight the experimental capabilities during the campaign, including the phytoplankton bloom dynamics, VOC production, and the effects of photochemical aging on aerosol production, morphology, and chemical composition. Additionally, we discuss the modifications made to the wave channel to improve aerosol production and reduce background contamination, as well as subsequent characterization experiments. The SeaSCAPE experiment provides unique insight into the connections between marine biology, atmospheric chemistry, and climate-relevant aerosol properties, and demonstrates how an ocean-atmosphere-interaction facility can be used to isolate and study reactions in the marine atmosphere in the laboratory under more controlled conditions. Environmental Significance StatementThe ocean-atmosphere system influences Earth's radiative balance, cloud formation and precipitation, and air quality, all of which directly impact human health and well-being.Laboratory control experiments play a key role in improving our understanding of the marine 65 atmosphere and allow for measurements of aerosols and gases under clean, isolated, and environmentally relevant conditions. Here, we describe the design and operation of an 11,800 L wave channel for replicating the ocean-atmosphere environment, with specific details provided on the production of representative sea spray aerosols, marine microbiology, biogenic gases, and secondary marine aerosols. The findings presented herein demonstrate best 70 experimentation practices and illustrate challenges that exist when working to replicate and ultimately understand chemical reactions and biology feedbacks in the ocean-atmosphere system.

Nitrous Acid (HONO) Formation from the Irradiation of Aqueous Nitrate Solutions in the Presence of Marine Chromophoric Dissolved Organic Matter: Comparison to Other Organic Photosensitizers

“…All experiments were carried out in aqueous solutions of sodium nitrate with added organics and acidified to the desired pH as described in more detail below. The m-DOM used was collected from the NSF-SeaSCAPE 2019 campaign . The desired concentration of m-DOM was created by weighing the dried sample and then placing in Milli-Q water and dissolving the mixture by sonication for 3 h. Humic acid used was Suwannee River humic acid from the International Humic Substance Society, 4-BBA was from Sigma-Aldrich, and the ethylene glycol used was from Fisher Chemicals.…”

“…Laboratory studies can provide insights into the mechanisms and kinetics of HONO formation; therefore, we have investigated the photochemistry of nitrate solutions to represent aged sea spray aerosols, in the presence of different photosensitizers and organic compounds to elucidate information into the relevant environmental conditions leading to HONO formation. Specifically, we have focused on measurements of gas-phase NO 2 and HONO produced from the simulated solar irradiation of nitrate in the presence of marine dissolved organic matter (m-DOM) collected from a large-scale mesocosm campaign, SeaSCAPE . We compared these results to nitrate solutions in the presence and absence of humic acid (HA), 4-benzoylbenzoic acid (4-BBA), and ethylene glycol (EG).…”

Ice Nucleating Activity and Residual Particle Morphology of Bulk Seawater and Sea Surface Microlayer

“…Samples were collected at various stages of an algae bloom from the Scripps Institute of Oceanography waveflume at La Jolla, CA in the summer of 2019 during the SeaSCAPE experiment . The waveflume was filled with coastal seawater from the Pacific Ocean near the Scripps Pier at the start of three SeaSCAPE blooms.…”

“…For the current work, IN spectra and the chemical properties of seawater and SSML are studied with three complementary sets of instrumentation to connect IN spectra with dry-particle morphology as well as biological and organic contributions. Samples were collected during a large multi-institute experiment called SeaSCAPE (Sea Spray Chemistry and Particle Evolution) at the Scripps Institute of Oceanography, La Jolla, CA . A sealed 30 m long channel (“waveflume”) was filled with coastal Pacific Ocean seawater collected to a depth of 2 m. A piston was used to create waves that broke on a simulated beach within the waveflume to generate nascent SSAs.…”

“…A sealed 30 m long channel (“waveflume”) was filled with coastal Pacific Ocean seawater collected to a depth of 2 m. A piston was used to create waves that broke on a simulated beach within the waveflume to generate nascent SSAs. Both online and offline measurements of SSA and the bulk water were performed using an array of physical, chemical, and biological characterization equipment during SeaSCAPE (described in Sauer et al).…”