The impact of sea spray aerosols (SSAs) on Earth's climate remains uncertain in part due to size-dependent particle-to-particle variability in SSA physicochemical properties such as morphology, composition, phase state, and water uptake that can be further modulated by the environment relative humidity (RH). The current study investigates these properties as a function of particle size and RH, while focusing on submicrometer nascent SSA (0.1−0.6 μm) collected throughout a phytoplankton bloom. Filter-based thermal optical analysis, atomic force microscopy (AFM), and AFM photothermal infrared spectroscopy (AFM−PTIR) were utilized in this regard. AFM imaging at 20% RH identified five main SSA morphologies: prism-like, core−shell, rounded, rod, and aggregate. The majority of smaller SSAs throughout a bloom were rounded, while larger SSAs were core−shell. Filter-based measurements revealed an increasing organic mass fraction with decreasing SSA size. The organic matter is shown to primarily reside in a rounded and core−shell SSA, while the prism-like and rod SSA are predominantly inorganic salts (i.e., sodium chloride, nitrates, and sulfates) with relatively low organic content, as determined by AFM−PTIR spectroscopy. AFM phase state measurements at 20% RH revealed an increasing abundance of core−shell SSA with semisolid shells and rounded SSA with a solid phase state, as the particle size decreases. At 60% RH, shells of core−shell and rounded SSA uptake water, become less viscous, and their phase states change into either semisolid or liquid. Collectively, findings reveal the dynamic and size-dependent nature of SSA's morphology, composition, phase states, and water uptake, which should be considered to accurately predict their climate-related effects.

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.

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...

Sea spray aerosols (SSA) play an important role in radiative forcing by directly scattering solar radiation and indirectly by acting as cloud condensation or ice nuclei. These climate-relevant aerosol processes strongly depend on the mixing state and morphology of the individual aerosol. In this work, the distribution of different morphologies within nascent SSA as a function of particle size is investigated. SSA generated from wave breaking of natural seawater were collected for offline analysis using complementary scanning electron microscopy (SEM), thermal optical analysis, and atomic force microscopy-based photothermal infrared (AFM-PTIR) spectroscopy methods. SEM data revealed six key morphologies of SSAprism-like, core−shell, rounded, rod-inclusion, aggregate, and rod. Of these, prism-like, core−shell, and rounded morphologies accounted for more than 99% of the entire SSA population and exhibited size-dependent trends. Thermal optical analysis data revealed a significant increase in the organic mass fraction of SSA with decreasing particle size. Concurrently, the SEM data showed a significant decrease in the relative abundance of prism-like morphology and corresponding increase of rounded and core−shell morphologies. AFM-PTIR spectroscopy showed that the SSA prism-like morphology is largely inorganic in nature, whereas the shell of the core−shell and rounded morphologies are predominantly organic. The study demonstrates that, instead of a single "representative" SSA morphology, the physicochemical mixing state of SSA is dynamic with respect to particle size. This should be taken into account to accurately predict the magnitude of the radiative forcing of SSA.

Deposition and surface-mediated reactions of adsorbed species can play a role in the level of exposure of occupants to indoor pollutants, which include gases and particles. Detailed molecular-level descriptions of these processes occurring on indoor surfaces are difficult to obtain because of the ever-increasing types of surfaces and their proximity to a variety of different indoor emission sources. The results of an investigation of interactions of glass surfaces in unique indoor environments are described here. Window glass, a ubiquitous indoor surface, was placed vertically in six different locations to assess differences in particle and coating depositions. Atomic force microscopy− photothermal infrared (AFM−PTIR) spectroscopic analysis of these glass surfaces reveals differences in morphology and chemical composition, which reflects the diversity of surface processes found in local environments indoors. Overall, this detailed microspectroscopic imaging method shows deposition of particles and the formation of organic thin films that increase the surface area and surface roughness of the glass surface. PTIR spectroscopy demonstrates that depositions can be linked to primary emitters intrinsic to each of the different local environments.

Microspectroscopic analyses of glass surfaces following a single day of cooking events reveal organic depositions that can be traced back to emission sources and airborne distributions.

Organic films on indoor surfaces serve as a medium for reactions and for partitioning of semi-volatile organic compounds and thus play an important role in indoor chemistry. However, the chemical...

In this study, we have investigated the effect of hydroxyl radical (OH) oxidation reactions on the formation and chemical composition of marine-derived aerosols. Marine aerosols can be classified into two categories: primary sea spray aerosol (SSA) produced upon the breaking of waves, and secondary marine aerosol (SMA) produced upon the oxidation of gas phase species. Here we simultaneously investigated the impact of heterogeneous OH oxidation reactions on chemically complex supermicron SSA as well as the formation of SMA in the submicron regime through the oxidation of volatile organic compounds (VOCs). A marine aerosol reference tank (MART) filled with water from a labgrown phytoplankton bloom was used to produce SSA particles and VOCs representative of those found over the ocean, which were then sent through a potential aerosol mass (PAM) reactor where they were exposed to OH radicals. Online and offline methods were used to compare unreacted nascent primary SSA to the marine aerosols that resulted from sending the MART headspace, which includes any gases and existing primary SSA, through the PAM. Several single particle methods of analysis, including micro-Raman spectroscopy and atomic force microscopy−photothermal infrared (AFM-PTIR) spectroscopy, were used to investigate composition and size of substrate deposited particles. In situ composition measurements of PM1 particles were made using an aerosol mass spectrometer (AMS) to understand submicron marine aerosol chemistry. Raman spectra of SSA showed that heterogeneous OH oxidation reactions significantly lower the amount of organic matter found in supermicron SSA particles, which are dominated, in part, by nitrogen containing species (e.g., amino sugars/amino acids) during periods of high biological productivity. Furthermore, AFM and AMS analyses showed the formation of secondary marine aerosols in the submicron size regime due to oxidation of biologically produced VOCs. To our knowledge, this is the first study in which lab-produced authentic marine aerosols produced during a phytoplankton bloom have been exposed to OH radicals. The results provide important insights to how the combined effects of ocean biological activity and OH oxidation reactions both ultimately play roles in determining the chemical composition of marine aerosols (SMA and SSA) across multiple size regimes and formation mechanisms.