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.

Abstract. Heterogeneous uptake of hydroperoxyl radicals (HO2) onto aerosols has been proposed to be a significant sink of HOx, hence impacting the atmospheric oxidation capacity. Accurate calculation of the HO2 uptake coefficient γHO2 is key to quantifying the potential impact of this atmospheric process. Laboratory studies show that γHO2 can vary by orders of magnitude due to changes in aerosol properties, especially aerosol soluble copper (Cu) concentration and aerosol liquid water content (ALWC). In this study we present a state-of-the-art model called MARK to simulate both gas- and aerosol-phase chemistry for the uptake of HO2 onto Cu-doped aerosols. Moreover, a novel parameterization of HO2 uptake was developed that considers changes in relative humidity (RH) and condensed-phase Cu ion concentrations and which is based on a model optimization using previously published and new laboratory data included in this work. This new parameterization will be applicable to wet aerosols, and it will complement current IUPAC recommendations. The new parameterization is as follows (the explanations for symbols are in the Appendix): 1γHO2=1αHO2+3×υHO24×106×RdHcorrRT×(5.87+3.2×ln⁡(ALWC/[PM]+0.067))×[PM]-0.2×Cu2+eff0.65+υHO2l4RTHorgDorgε. All parameters used in the paper are summarized in Table A1. Using this new equation, field data from a field campaign were used to evaluate the impact of the HO2 uptake onto aerosols on the ROx (= OH + HO2 + RO2) budget. Highly variable values for HO2 uptake were obtained for the North China Plain (median value < 0.1).