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Scientists from Scripps Institution of Oceanography at the University of California San Diego report they have used an “ocean-in-a-lab” to show that air pollution can change the makeup of gases and aerosols that sea spray releases into the atmosphere and, in turn, potentially alter weather patterns.

Kimberly Prather, a distinguished professor of atmospheric chemistry who holds a joint appointment between the Scripps Institution of Oceanography and the Department of Chemistry and Biochemistry, presented her results today at the American Chemical Society (ACS) Fall 2020 Virtual Meeting & Expo. The findings follow a novel experiment conducted at Scripps Oceanography in summer 2019 called the Sea Spray Chemistry And Particle Evolution project, or SeaSCAPE, a novel experiment in which scientists were able to unravel complex ocean-atmosphere interactions.  

“It’s surprising that we don’t know more about the central role of ocean microbes in controlling climate,” said Prather, the project’s principal investigator. “They have the potential to influence atmospheric composition, cloud formation and weather. Humans can alter these natural processes in two ways: by changing the microbial community structure in the ocean, and by producing air pollutants that react with compounds that the microorganisms produce.”  

Through natural biological processes, ocean microbes –– including bacteria, phytoplankton and viruses –– produce compounds that enter the atmosphere as gases or aerosols when waves break. In addition, the microorganisms themselves can be ejected from the ocean in the form of aerosolized droplets. Some of these particles can seed clouds, absorb or reflect sunlight, or otherwise influence atmospheric conditions and weather.   

“There’s a standard belief that one way the ocean can regulate the temperature of the planet is through emission of gases and particles,” says Prather, who also directs the National Science Foundation-supported Center for Aerosol Impacts on Chemistry of the Environment, the largest federally funded center at UC San Diego.  “Some scientists refer to the ocean as the ‘planetary thermostat.’”  

Prather and colleagues wondered how humans might influence this thermostat but first, they needed to learn how ocean microbes affect climate without humans. To find out, the researchers utilized a 33-meter (108-foot)-long wave channel in the Hydraulics Lab at Scripps and filled it with 3,400 gallons of seawater that was pumped from the Ellen Browning Scripps Memorial Pier seawater system. Continuous waves were then generated using a custom-engineered paddle. Researchers used a wide range of sophisticated equipment to measure the composition of the gases and particles that are emitted as waves break in the channel. 

The science team grew a phytoplankton bloom –– an overgrowth of microscopic algae that occurs naturally in oceans under certain conditions. They continuously monitored the gases and aerosols produced in the air above the water, measuring things such as aerosol size, composition, shape, enzymatic activity and pH. They also studied how natural changes in the microbial community, for example, introducing certain species of bacteria and phytoplankton, affected the cloud-forming potential of the aerosols. 

“The short answer is that the biology had very little effect on sea spray aerosol composition,” Prather says. “Altering natural biological processes in seawater resulted in a very small change in the ability of the primary particles to form cloud droplets.”

In contrast, adding a small amount of an atmospheric oxidant (hydroxyl radical, which can be generated naturally and can be enhanced in polluted atmospheres) caused an immediate shift in the composition and cloud-forming potential of marine aerosols. According to Prather, the oxidant reacted with microbe-produced gases in the air, transforming them into compounds that changed the composition of the primary sea spray aerosol and formed new types of particles. Although the researchers don’t know yet how other individual pollutants affect sea spray aerosols, Prather says that it’s important to study the complete gas phase mixture of pollutants to mimic and understand real-world chemical reactions.

The team is now also exploring how water pollution –– in particular, sewage discharge and pollution run-off that empty into coastal estuaries and oceans ––can restructure microbial communities and affect human health, climate, and air quality. Previous studies have examined how human pollution impacts water quality; however, Prather’s are among the first studies focusing on how waterborne pollution that enters the surf zone impacts air quality and human health. Her research group is making measurements in the ocean and atmosphere in a region known to be impacted by pollution flowing in from a heavily polluted estuary. This project aims to understand which viruses, bacteria and other pollutants become airborne in the surf zone.   

The researchers acknowledge support and funding from the National Science Foundation (NSF) through the NSF Center for Aerosol Impacts on Chemistry of the Environment.

Future research on the ocean and atmosphere will be facilitated by a state-of-the-art instrument that is set to be constructed on the Scripps Oceanography campus. The Scripps Ocean Atmosphere Research Simulator (SOARS), also funded by NSF, will mimic the ocean with unprecedented accuracy, capturing the interactions of wind, waves, microbial marine life, and chemistry at the sea surface in a laboratory setting. It’s expected to be completed in 2021.

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