Search for: All records

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. Understanding the impact of sea spray aerosol (SSA) on theclimate and atmosphere requires quantitative knowledge of their chemicalcomposition and mixing states. Furthermore, single-particle measurements areneeded to accurately represent large particle-to-particle variability. Toquantify the mixing state, the organic volume fraction (OVF), defined as therelative organic volume with respect to the total particle volume, ismeasured after generating and collecting aerosol particles, often usingdeposition impactors. In this process, the aerosol streams are either driedor kept wet prior to impacting on solid substrates. However, the atmosphericcommunity has yet to establish how dry versus wet aerosol depositioninfluences the impacted particle morphologies and mixing states. Here, weapply complementary offline single-particle atomic force microscopy (AFM)and bulk ensemble high-performance liquid chromatography (HPLC) techniquesto assess the effects of dry and wet deposition modes on thesubstrate-deposited aerosol particles' mixing states. Glucose and NaClbinary mixtures that form core–shell particle morphologies were studied asmodel systems, and the mixing states were quantified by measuring the OVF ofindividual particles using AFM and compared to the ensemble measured byHPLC. Dry-deposited single-particle OVF data positively deviated from thebulk HPLC data by up to 60 %, which was attributed to significantspreading of the NaCl core upon impaction with the solid substrate. This ledto underestimation of the core volume. This problem was circumvented by (a) performing wet deposition and thus bypassing the effects of the solid corespreading upon impaction and (b) performing a hydration–dehydration cycle ondry-deposited particles to restructure the deformed NaCl core. Bothapproaches produced single-particle OVF values that converge well with thebulk and expected OVF values, validating the methodology. These findingsillustrate the importance of awareness in how conventional particledeposition methods may significantly alter the impacted particlemorphologies and their mixing states.