The Chaos of Sea Spray Aerosols

Aerosols, which have gained a renewed focus due to the COVID-19 pandemic, are solid or liquid particles suspended in air. They can include viruses, bacteria, salt, dust, fungi, and chemical pollutants. While aerosols are all around us, they are extremely difficult to isolate and study.

Oceans cover about 75 percent of our globe, and by mass, sea spray aerosols, which are the aerosols produced from breaking waves, are the most common naturally produced aerosol. We are just barely scratching the surface in understanding sea spray aerosols and their subsequent effects.

It is difficult, however, to fully isolate factors of interest such as winds, water temperature, and wave heights when sampling over the ocean so it is vital to replicate ocean conditions in the laboratory. That way, researchers can study the effects of one controlled variable at a time, building towards the full complexity experienced in real ocean conditions. Previous studies in an older glass wave channel here at Scripps Institution of Oceanography at UC San Diego were among the largest attempts at replicating the chemical complexity of breaking waves in a lab setting, but they still left more to be desired, especially in terms of what we, as scientists, could control in the system.

This summer, Scripps Oceanography unveiled an air-sea interaction simulator, the Scripps Ocean Atmosphere Research Simulator (SOARS). SOARS consists of a 120-foot-long wave channel with an accompanying recirculation wind tunnel. What makes this channel different from other wind-wave facilities is its ability to replicate conditions from the equator to the poles, and investigate past, present, and future climates with unmatched control. SOARS is able to control air-side and water-side temperatures, generate meter-tall waves, and induce Category-1 hurricane winds, all within a closed system. This facility is the latest in a large repertoire working to replicate the full complexity of the surface oceans in the laboratory. It opens new opportunities for disciplines such as atmospheric chemistry, biological oceanography, physical oceanography, and polar sciences.

While SOARS is a facility open to researchers worldwide, the first group to take it for a spin was the Center for Aerosol Impacts on the Chemistry of the Environment (CAICE), a National Science Foundation-funded center based at UC San Diego, of which my research group is a part. CAICE focuses on the chemical and physical properties of sea spray aerosols.

As the first group to test drive SOARS, CAICE’s summer campaign was focused on characterizing the system for future users and determining SOARS’ capabilities. The two-month research campaign was dubbed CHAOS: Characterizing Atmosphere-Ocean parameters in SOARS. We carried out mass spectrometric analyses of the composition of aerosols and gases, collection of aerosols on filters, and aerosol and bubble size distributions, among other valuable measurements. On a larger spatial scale, we also took measurements to understand the impact these aerosols have on cloud formation and their role in a changing climate. 

Being the first group to put to work such a large simulator came with challenges that required adaptation and ingenuity. As a student early in my career, I valued being able to work with and learn from people with novel perspectives. It was also a great experience working with dozens of undergrads, graduates, and mentors attempting to balance our collective goals. I think as students we are used to only having to balance our own ideas and motivations for a given research project (maybe along with our advisors’ motivations), so this experience showed us all what goes into making a large-scale collaboration successful.

We had collaborators from UC Davis, Colorado State University, University of Iowa, University of Wisconsin-Madison, and UC San Diego to better understand the physical and chemical properties of sea spray aerosols.  Each morning, the team met to discuss the previous day’s data and make plans for the current day. With a simulator like SOARS, the possibilities are almost endless, so it was quite a challenge to focus everyone’s ambitions into an actionable plan that still accomplished as many goals as possible. Being a part of these discussions to develop a solid science plan in this field was eye-opening, particularly for such an interdisciplinary study.

While we are all basking in the data we have collected and excitedly looking forward to filling in gaps in knowledge, we are thankful for this experience. The summer days at SOARS were long and hot, but it was a fun and rewarding experience. Whether we were undergraduates who had never stepped foot in a laboratory or experienced scientists at yet another campaign, we all worked together and accomplished some great feats against some mighty challenges.

By working on the CHAOS experiment, our team learned about the complexities of working together and sharing an instrument. More instruments were sent to Scripps than personnel, so it became a balancing act of worrying about your instrument and helping look after instruments for another group.

For me, this consisted of maintaining aerosol size distribution instruments (looking at the number and size of sea spray aerosols) over the length of the channel and across varying wind conditions to estimate aerosol production as a function of wind speed. On top of this, because aerosols are all around us, we had to measure background levels in the room air as well as  inside SOARS. This may already sound like a lot to balance, but running SOARS was also an involved job and so everyone pitched in to help run and maintain the operation. We were all in it together, so it was a great experience working with other researchers to maintain our own instruments and learn new methods from collaborators, all while fulfilling the common study goal of characterizing sea spray produced in SOARS for the first time.

“Adaptability” and “ingenuity” are the key words I would use to describe our summer, and I think everyone learned a lot from this campaign. We’re all excited to return to our home institutions (or continue to take in the lovely views here at Scripps) and spread the lessons we learned. We were fortunate enough to experience a research campaign here at Scripps Oceanography, but the lessons in communication and adaptability are applicable to every aspect of science.

Raymond J. Leibensperger III is a third-year PhD student in the labs of Kimberly Prather and Grant Deane.