The House Observations of Microbial and Environmental Chemistry (HOMEChem) study was a large-scale collaborative experimental investigation probing indoor air composition and chemistry.

Individual airborne sea spray aerosol (SSA) particles show diversity in their morphologies and water uptake properties that are highly dependent on the biological, chemical, and physical processes within the sea subsurface and the sea surface microlayer. In this study, hygroscopicity data for model systems of organic compounds of marine origin mixed with NaCl are compared to data for authentic SSA samples collected in an ocean-atmosphere facility providing insights into the SSA particle growth, phase transitions and interactions with water vapor in the atmosphere. In particular, we combine single particle morphology analyses using atomic force microscopy (AFM) with hygroscopic growth measurements in order to provide important insights into particle hygroscopicity and the surface microstructure. For model systems, a range of simple and complex carbohydrates were studied including glucose, maltose, sucrose, laminarin, sodium alginate, and lipopolysaccharides. The measured hygroscopic growth was compared with predictions from the Extended-Aerosol Inorganics Model (E-AIM). It is shown here that the E-AIM model describes well the deliquescence transition and hygroscopic growth at low mass ratios but not as well for high ratios, most likely due to a high organic volume fraction. AFM imaging reveals that the equilibrium morphology of these single-component organic particles is amorphous. When NaCl is mixed with the organics, the particles adopt a core-shell morphology with a cubic NaCl core and the organics forming a shell similar to what is observed for the authentic SSA samples. The observation of such core-shell morphologies is found to be highly dependent on the salt to organic ratio and varies depending on the nature and solubility of the organic component. Additionally, single particle organic volume fraction AFM analysis of NaCl : glucose and NaCl : laminarin mixtures shows that the ratio of salt to organics in solution does not correspond exactly for individual particles -showing diversity within the ensemble of particles produced even for a simple two component system. IntroductionCovering a substantial area of the Earth's surface, the ocean serves as one of the main sources of particulate matter in the atmosphere. Sea spray aerosols (SSAs) are generated by breaking waves in marine environments and account for the largest atmospheric aerosol flux. it has a profound influence on the composition of aerosol particles as they escape across the interface. The SSML is a rich mixture of organic compounds such as fatty acids, fatty alcohols, sterols, carbohydrates, proteins and more complex colloids and aggregates exuded by phytoplankton such as lipopolysaccharides (LPSs). 11,12In the authentic samples collected from a pristine region of the Pacific Ocean, Gagosian and coworkers 13 detected alcohols, fatty acid salts and esters as specific tracers of ocean-derived organic compounds in atmospheric aerosols. The organic compounds include saccharides, fatty acids, and a few other organic classes. 13 Progress in analytic...

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.

Photochemical processes drive much of the daytime gas-phase chemistry in the atmosphere. Within condensed phases, such as aerosol particles and thin films enriched in organics, much less is understood about these processes. An investigation aimed at better understanding photosensitized reactions that can occur within marine-relevant condensed-phase systems is described herein. In particular, photosensitized reactions have been investigated between a fatty acid model system and different photosensitizers within thin organic films representative of molecular species found in the sea surface microlayer and sea spray aerosols. Photosensitized reactions of thin films containing nonanoic acid and three different photosensitizers, including 4-benzoylbenzoic acid, humic acid, and marine-derived dissolved organic matter, were probed using a suite of analytical techniques, including vibrational spectroscopy, excitation–emission matrix spectroscopy, and ultra-high-resolution mass spectrometry. Considerable differences were found in the photosensitizing capability for each of these systems. We also present an analysis of the molecular differences between the different photosensitizers to explain their unique characteristics and light-absorbing properties. Overall, this study sheds light on the relevance of such reactions in the marine environment.