Enrichment of saccharides and divalent cations in sea spray aerosol during two phytoplankton blooms.
Environmental Science & Technology. 50:11511-11520. 10.1021/acs.est.6b02988 Abstract
Sea spray aerosol (SSA) is a globally important source of particulate matter. A mesocosm study was performed to determine the relative enrichment of saccharides and inorganic ions in nascent fine (PM2.5) and coarse (PM102.5) SSA and the sea surface microlayer (SSML) relative to bulk seawater. Saccharides comprise a significant fraction of organic matter in fine and coarse SSA (11 and 27%, respectively). Relative to sodium, individual saccharides were enriched 141314-fold in fine SSA, 3138-fold in coarse SSA, but only up to 1.016.2-fold in SSML. Enrichments in SSML were attributed to rising bubbles that scavenge surface-active species from seawater, while further enrichment in fine SSA likely derives from bubble films. Mean enrichment factors for major ions demonstrated significant enrichment in fine SSA for potassium (1.3), magnesium (1.4), and calcium (1.7), likely because of their interactions with organic matter. Consequently, fine SSA develops a salt profile significantly different from that of seawater. Maximal enrichments of saccharides and ions coincided with the second of two phytoplankton blooms, signifying the influence of ocean biology on selective mass transfer across the oceanair interface.
Phytoplankton blooms weakly influence the cloud forming ability of sea spray aerosol.
Geophysical Research Letters. 43:9975-9983. 10.1002/2016gl069922 Abstract
After many field studies, the establishment of connections between marine microbiological processes, sea spray aerosol (SSA) composition, and cloud condensation nuclei (CCN) has remained an elusive challenge. In this study, we induced algae blooms to probe how complex changes in seawater composition impact the ability of nascent SSA to act as CCN, quantified by using the apparent hygroscopicity parameter (kappa(app)). Throughout all blooms, kappa(app) ranged between 0.7 and 1.4 (average 0.95 +/- 0.15), consistent with laboratory investigations using algae-produced organic matter, but differing from climate model parameterizations and in situ SSA generation studies. The size distribution of nascent SSA dictates that changes in kappa(app) associated with biological processing induce less than 3% change in expected CCN concentrations for typical marine cloud supersaturations. The insignificant effect of hygroscopicity on CCN concentrations suggests that the SSA production flux and/or secondary aerosol chemistry may be more important factors linking ocean biogeochemistry and marine clouds.
The relationships between insoluble precipitation residues, clouds, and precipitation over California’s southern Sierra Nevada during winter storms.
Atmospheric Environment. 140:298-310. 10.1016/j.atmosenv.2016.06.016 Abstract
Ice formation in orographic mixed-phase clouds can enhance precipitation and depends on the type of aerosols that serve as ice nucleating particles (INPs). The resulting precipitation from these clouds is a viable source of water, especially for regions such as the California Sierra Nevada. Thus, a better understanding of the sources of INPs that impact orographic clouds is important for assessing water availability in California. This study presents a multi-site, multi-year analysis of single-particle insoluble residues in precipitation samples that likely influenced cloud ice and precipitation formation above Yosemite National Park. Dust and biological particles represented the dominant fraction of the residues (64% on average). Cloud glaciation, determined using satellite observations, not only depended on high cloud tops (>5.9 km) and low temperatures (<−23 °C), but also on the presence of what were likely dust and biological INPs. The greatest prevalence of ice-phase clouds occurred in conjunction with biologically-rich residues and mineral dust rich in calcium, followed by iron and aluminosilicates. Dust and biological particles are known to be efficient INPs, thus these residues likely influenced ice formation in clouds above the sites and subsequent precipitation quantities reaching the surface during events with similar meteorology. The goal of this study is to use precipitation chemistry information to gain a better understanding of the potential sources of INPs in the south-central Sierra Nevada, where cloud-aerosol-precipitation interactions are poorly understood and where mixed-phase orographic clouds represent a key element in the generation of precipitation and thus the water supply in California.
Heterogeneous chemistry of lipopolysaccharides with gas-phase nitric acid: Reactive sites and reaction pathways.
Journal of Physical Chemistry A. 120:6444-6450. 10.1021/acs.jpca.6b07023 Abstract
Recent studies have shown that sea spray aerosol (SSA) has a size-dependent, complex composition consisting of biomolecules and biologically derived organic compounds in addition to salts. This additional chemical complexity most likely influences the heterogeneous reactivity of SSA, as these other components will have different reactive sites and reaction pathways. In this study, we focus on the reactivity of a class of particles derived from some of the biological components of sea spray aerosol including lipopolysaccharides (LPS) that undergo heterogeneous chemistry within the reactive sites of the biological molecule. Examples of these reactions and the relevant reactive sites are proposed as follows: R-COONa(s) + HNO3(g) -> NaNO3 + R-COOH and R-HPO4Na(s) + HNO3(g) -> NaNO3 + R-H2PO4. These reactions may be a heterogeneous pathway not only for sea spray aerosol but also for a variety of other types of atmospheric aerosol as well.
Linking variations in sea spray aerosol particle hygroscopicity to composition during two microcosm experiments.
Atmospheric Chemistry and Physics. 16:9003-9018. 10.5194/acp-16-9003-2016 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 nonrefractory 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 NROM 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.
CalWater field studies designed to quantify the roles of atmospheric rivers and aerosols in modulating US West Coast precipitation in a changing climate.
Bulletin of the American Meteorological Society. 97:1209-1228. 10.1175/bams-d-14-00043.1 Abstract
The variability of precipitation and water supply along the U.S. West Coast creates major challenges to the region’s economy and environment, as evidenced by the recent California drought. This variability is strongly influenced by atmospheric rivers (ARs), which deliver much of the precipitation along the U.S. West Coast and can cause flooding, and by aerosols (from local sources and transported from remote continents and oceans) that modulate clouds and precipitation. A better understanding of these processes is needed to reduce uncertainties in weather predictions and climate projections of droughts and floods, both now and under changing climate conditions.To address these gaps, a group of meteorologists, hydrologists, climate scientists, atmospheric chemists, and oceanographers have created an interdisciplinary research effort, with support from multiple agencies. From 2009 to 2011 a series of field campaigns [California Water Service (CalWater) 1] collected atmospheric chemistry, cloud microphysics, and meteorological measurements in California and associated modeling and diagnostic studies were carried out. Based on the remaining gaps, a vision was developed to extend these studies offshore over the eastern North Pacific and to enhance land-based measurements from 2014 to 2018 (CalWater-2). The dataset and selected results from CalWater-1 are summarized here. The goals of CalWater-2, and measurements to date, are then described.CalWater is producing new findings and exploring new technologies to evaluate and improve global climate models and their regional performance and to develop tools supporting water and hydropower management. These advances also have potential to enhance hazard mitigation by improving near-term weather prediction and subseasonal and seasonal outlooks.
Sea spray aerosol as a unique source of ice nucleating particles.
Proceedings of the National Academy of Sciences of the United States of America. 113:5797-5803. 10.1073/pnas.1514034112 Abstract
Ice nucleating particles (INPs) are vital for ice initiation in, and precipitation from, mixed-phase clouds. A source of INPs from oceans within sea spray aerosol (SSA) emissions has been suggested in previous studies but remained unconfirmed. Here, we show that INPs are emitted using real wave breaking in a laboratory flume to produce SSA. The number concentrations of INPs from laboratory-generated SSA, when normalized to typical total aerosol number concentrations in the marine boundary layer, agree well with measurements from diverse regions over the oceans. Data in the present study are also in accord with previously published INP measurements made over remote ocean regions. INP number concentrations active within liquid water droplets increase exponentially in number with a decrease in temperature below 0 degrees C, averaging an order of magnitude increase per 5 degrees C interval. The plausibility of a strong increase in SSA INP emissions in association with phytoplankton blooms is also shown in laboratory simulations. Nevertheless, INP number concentrations, or active site densities approximated using "dry" geometric SSA surface areas, are a few orders of magnitude lower than corresponding concentrations or site densities in the surface boundary layer over continental regions. These findings have important implications for cloud radiative forcing and precipitation within low-level and midlevel marine clouds unaffected by continental INP sources, such as may occur over the Southern Ocean.
Analysis of organic anionic surfactants in fine and coarse fractions of freshly emitted sea spray aerosol.
Environmental Science & Technology. 50:2477-2486. 10.1021/acs.est.5b04053 Abstract
The inclusion of organic compounds in freshly emitted sea spray aerosol (SSA) has been shown to be size-dependent, with an increasing organic fraction in smaller particles. Here we have used electrospray ionization-high resolution mass spectrometry in negative ion mode to identify organic compounds in nascent sea spray collected throughout a 25 day mesocosm experiment. Over 280 organic compounds from ten major homologous series were tentatively identified, including saturated (C-18-C-24) and unsaturated (C-12-C-22) fatty acids, fatty acid derivatives (including saturated oxo-fatty acids (C-5-C-18) and saturated hydroxy-fatty acids (C-5-C-18), organosulfates (C-2-C-7, C-12-C-17) and sulfonates (C-16-C-22). During the mesocosm, the distributions of molecules within some homologous series responded to variations among the levels of phytoplankton and bacteria in the seawater. The average molecular weight and carbon preference index of saturated fatty acids significantly decreased within fine SSA during the progression of the mesocosm, which was not observed in coarse SSA, sea-surface microlayer or in fresh seawater. This study helps to define the molecular composition of nascent SSA and biological processes in the ocean relate to SSA composition.