Linking variations in sea spray aerosol particle hygroscopicity to composition during two microcosm experiments

Abstract

Abstract. The extent to which water uptake influences the light scattering ability of marine sea spray aerosol (SSA) particles depends critically on SSA chemical composition. The organic fraction of SSA can increase during phytoplankton blooms, decreasing the salt content and therefore the hygroscopicity of the particles. In this study, subsaturated hygroscopic growth factors at 85 % relative humidity (GF(85 %)) of predominately submicron SSA particles were quantified during two induced phytoplankton blooms in marine aerosol reference tanks (MARTs). One MART was illuminated with fluorescent lights and the other was illuminated with sunlight, referred to as the "indoor" and "outdoor" MARTs, respectively. Optically weighted GF(85 %) values for SSA particles were derived from measurements of light scattering and particle size distributions. The mean optically weighted SSA diameters were 530 and 570 nm for the indoor and outdoor MARTs, respectively. The GF(85 %) measurements were made concurrently with online particle composition measurements, including bulk composition (using an Aerodyne high-resolution aerosol mass spectrometer) and single particle (using an aerosol time-of-flight mass spectrometer) measurement, and a variety of water-composition measurements. During both microcosm experiments, the observed optically weighted GF(85 %) values were depressed substantially relative to pure inorganic sea salt by 5 to 15 %. There was also a time lag between GF(85 %) depression and the peak chlorophyll a (Chl a) concentrations by either 1 (indoor MART) or 3-to-6 (outdoor MART) days. The fraction of organic matter in the SSA particles generally increased after the Chl a peaked, also with a time lag, and ranged from about 0.25 to 0.5 by volume. The observed depression in the GF(85 %) values (relative to pure sea salt) is consistent with the large observed volume fractions of non-refractory organic matter (NR-OM) comprising the SSA. The GF(85 %) values exhibited a reasonable negative correlation with the SSA NR-OM volume fractions after the peak of the blooms (i.e., Chl a maxima); i.e., the GF(85 %) values generally decreased when the NR-OM volume fractions increased. The GF(85 %) vs. NR-OM volume fraction relationship was interpreted using the Zdanovskii–Stokes–Robinson (ZSR) mixing rule and used to estimate the GF(85 %) of the organic matter in the nascent SSA. The estimated pure NR-OM GF(85 %) values were 1.16 ± 0.09 and 1.23 ± 0.10 for the indoor and outdoor MARTS, respectively. These measurements demonstrate a clear relationship between SSA particle composition and the sensitivity of light scattering to variations in relative humidity. The implications of these observations to the direct climate effects of SSA particles are discussed.

Linking hygroscopicity and the surface microstructure of model inorganic salts, simple and complex carbohydrates, and authentic sea spray aerosol particles

“…The maximum in the OVF value and the corresponding depression of the GF on July 17 is highly corroborated with the trend of the values obtained with the model system shown in Table 1 which shows that an increase in the OVF results in a lower GF at RH = 80%. As previously seen in field studies, [42][43][44] the reduction in the hygroscopicity of individual SSA particles highlights the role of organics in the interaction of individual atmospheric SSAs with water vapor. The variable responses of authentic SSA particles to water vapor underline the increasing level of chemical complexity 34,45 that can only be addressed in single particle-level studies that are otherwise obscured when probed using ensemble methods.…”

The Impact of Divalent Cations on the Enrichment of Soluble Saccharides in Primary Sea Spray Aerosol

“…It is important to note that the presence of salt ions in solution has been shown to interact with the carboxylic acid head group of fatty acids [65,66] which decreases the effective pK a . For this reason, both compounds used in this study were expected to form anions in solution at pH 8, and we hypothesized that divalent metal cations play a critical role, Atmosphere 2018, 9,476 4 of 17 by acting as an ionic bridge between insoluble and soluble organic molecules that is necessary for the transfer of soluble saccharides to the SSA.…”

“…Each of these processes depends on SSA chemical composition, size, morphology, and phase. Previous laboratory and field investigations have shown that the chemical composition of SSA is a complex function of chemical [9][10][11][12] and biological processes occurring in the surface ocean [10,[13][14][15][16][17]. SSA chemical composition is also dependent on the physics of wave breaking, 2 of 17 which determines the distribution of organic material at the air-sea interface and how it is transported from the ocean surface into aerosol particles [10,[18][19][20].…”

Sea Spray Aerosol: The Chemical Link between the Oceans, Atmosphere, and Climate

“…4 Such changes in SSA composition include a relative increase in the abundance of distinct, insoluble organic particles types 5,8 as well as their organic volume fractions. 27 The ability to accurately reproduce the physical processes and biology that ultimately control the surface composition of SSA was a critical step in linking the ocean to climate that has now led to studies probing climate-relevant interactions of SSA particles with reactive gases and water uptake as well as the ability to nucleate ice.…”