Aerosols impact climate, human health, and the chemistry of the atmosphere, and aerosol pH plays a major role in the physicochemical properties of the aerosol. However, there remains uncertainty as to whether aerosols are acidic, neutral, or basic. In this research, we show that the pH of freshly emitted (nascent) sea spray aerosols is significantly lower than that of sea water (approximately four pH units, with pH being a log scale value) and that smaller aerosol particles below 1 μm in diameter have pH values that are even lower. These measurements of nascent sea spray aerosol pH, performed in a unique ocean−atmosphere facility, provide convincing data to show that acidification occurs “across the interface” within minutes, when aerosols formed from ocean surface waters become airborne. We also show there is a correlation between aerosol acidity and dissolved carbon dioxide but no correlation with marine biology within the seawater. We discuss the mechanisms and contributing factors to this acidity and its implications on atmospheric chemistry.

The SeaSCAPE campaign replicated the marine atmosphere in the laboratory to investigate the links between biological activity in the ocean and the properties of primary sea spray aerosols, volatile organic compounds, and secondary marine aerosols.

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 climate-relevant 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.

Biological aerosols, typically identified through their fluorescence properties, strongly influence clouds and climate. Sea spray aerosol (SSA) particles are a major source of biological aerosols, but detection in the atmosphere is challenging due to potential interference from other sources. Here, the fluorescence signature of isolated SSA, produced using laboratory-based aerosol generation methods, was analyzed and compared with two commonly used fluorescence techniques: excitation–emission matrix spectroscopy (EEMS) and the wideband integrated bioaerosol sensor (WIBS). A range of dynamic biological ocean scenarios were tested to compare EEMS and WIBS analyses of SSA. Both techniques revealed similar trends in SSA fluorescence intensity in response to changes in ocean microbiology, demonstrating the potential to use the WIBS to measure fluorescent aerosols alongside EEMS bulk solution measurements. Together, these instruments revealed a unique fluorescence signature of isolated, nascent SSA and, for the first time, a size-segregated emission of fluorescent species in SSA. Additionally, the fluorescence signature of aerosolized marine bacterial isolates was characterized and showed similar fluorescence peaks to those of SSA, suggesting that bacteria are a contributor to SSA fluorescence. Through investigation of isolated SSA, this study provides a reference for future identification of marine biological aerosols in a complex atmosphere.

Algae cultivation in open raceway ponds is considered the most economical method for photosynthetically producing biomass for biofuels, chemical feedstocks, and other high-value products. One of the primary challenges for open ponds is diminished biomass yields due to attack by grazers, competitors, and infectious organisms. Higher-frequency observations are needed for detection of grazer infections, which can rapidly reduce biomass levels. In this study, real-time measurements were performed using chemical ionization mass spectrometry (CIMS) to monitor the impact of grazer infections on cyanobacterial cultures. Numerous volatile gases were produced during healthy growth periods from freshwater Synechococcus elongatus Pasteur Culture Collection (PCC) 7942, with 6-methyl-5-hepten-2-one serving as a unique metabolic indicator of exponential growth. Following the introduction of a Tetrahymena ciliate grazer, the concentrations of multiple volatile species were observed to change after a latent period as short as 18 h. Nitrogenous gases, including ammonia and pyrroline, were found to be reliable indicators of grazing. Detection of grazing by CIMS showed indicators of infections much sooner than traditional methods, microscopy, and continuous fluorescence, which did not detect changes until 37 to 76 h after CIMS detection. CIMS analysis of gases produced by PCC 7942 further shows a complex temporal array of biomass-dependent volatile gas production, which demonstrates the potential for using volatile gas analysis as a diagnostic for grazer infections. Overall, these results show promise for the use of continuous volatile metabolite monitoring for the detection of grazing in algal monocultures, potentially reducing current grazing-induced biomass losses, which could save hundreds of millions of dollars.