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2017
Sultana, CM, Collins DB, Prather KA.  2017.  Effect of structural heterogeneity in chemical composition on online single-particle mass spectrometry analysis of sea spray aerosol particles. Environmental Science & Technology. 51:3660-3668.   10.1021/acs.est.6b06399   AbstractWebsite

Knowledge of the surface composition of sea spray aerosols (SSA) is critical for understanding and predicting climate-relevant impacts. Offline microscopy and spectroscopy studies have shown that dry supermicron SSA tend to be spatially heterogeneous particles with sodium- and chloride-rich cores surrounded by organic enriched surface layers containing minor inorganic seawater components such as magnesium and calcium. At the same time, single-particle mass spectrometry reveals several different mass spectral ion patterns, suggesting that there may be a number of chemically distinct particle types. This study investigates factors controlling single particle mass spectra of nascent supermicron SSA. Depth profiling experiments conducted on SSA generated by a fitted bubbler and total ion intensity analysis of SSA generated by a marine aerosol reference tank were compared with observations of ambient SSA observed at two coastal locations. Analysis of SSA produced by utilizing controlled laboratory methods reveals that single-particle mass spectra with weak sodium ion signals can be produced by the desorption of the surface of typical dry SSA particles composed of salt cores and organic-rich coatings. Thus, this lab-based study for the first time unifies findings from offline and online measurements as well as lab and field studies of the SSA particle-mixing state.

Sultana, CM, Cornwell GC, Rodriguez P, Prather KA.  2017.  FATES: a flexible analysis toolkit for the exploration of single-particle mass spectrometer data. Atmospheric Measurement Techniques. 10:1323-1334.   10.5194/amt-10-1323-2017   AbstractWebsite

Single-particle mass spectrometer (SPMS) analysis of aerosols has become increasingly popular since its invention in the 1990s. Today many iterations of commercial and lab-built SPMSs are in use worldwide. However, supporting analysis toolkits for these powerful instruments are outdated, have limited functionality, or are versions that are not available to the scientific community at large. In an effort to advance this field and allow better communication and collaboration between scientists, we have developed FATES (Flexible Analysis Toolkit for the Exploration of SPMS data), a MATLAB toolkit easily extensible to an array of SPMS designs and data formats. FATES was developed to minimize the computational demands of working with large data sets while still allowing easy maintenance, modification, and utilization by novice programmers. FATES permits scientists to explore, without constraint, complex SPMS data with simple scripts in a language popular for scientific numerical analysis. In addition FATES contains an array of data visualization graphic user interfaces (GUIs) which can aid both novice and expert users in calibration of raw data; exploration of the dependence of mass spectral characteristics on size, time, and peak intensity; and investigations of clustered data sets.

Gaston, CJ, Pratt KA, Suski KJ, May NW, Gill TE, Prather KA.  2017.  Laboratory studies of the cloud droplet activation properties and corresponding chemistry of saline playa dust. Environmental Science & Technology. 51:1348-1356.   10.1021/acs.est.6b04487   AbstractWebsite

Playas emit large quantities of dust that can facilitate the activation of cloud droplets. Despite the potential importance of playa dusts for cloud formation, most climate models assume that all dust is nonhygroscopic; however, measurements are needed to clarify the role of dusts in aerosol-cloud interactions. Here, we report measurements of CCN activation from playa dusts and parameterize these results in terms of both kappa-Kohler theory and adsorption activation theory for inclusion in atmospheric models. kappa ranged from 0.002 +/- 0.001 to 0.818 +/- 0.094, whereas Frankel-Halsey-Hill (FHH) adsorption parameters of A(FHH) = 2.20 +/- 0.60 and B-FHH = 1.24 +/- 0.14 described the water uptake properties of the dusts. Measurements made using aerosol time-of flight mass spectrometry (ATOFMS) revealed the presence of halite, sodium sulfates, and sodium carbonates that were strongly correlated with kappa underscoring the role that mineralogy, including salts, plays in water uptake by dust. Predictions of kappa made using bulk chemical techniques generally showed good agreement with measured values. However, several samples were poorly predicted suggesting that chemical heterogeneities as a function of size or chemically distinct particle surfaces can determine the hygroscopicity of playa dusts. Our results further demonstrate the importance of dust in aerosol-cloud interactions.

Martin, AC, Cornwell GC, Atwood SA, Moore KA, Rothfuss NE, Taylor H, DeMott PJ, Kreidenweis SM, Petters MD, Prather KA.  2017.  Transport of pollution to a remote coastal site during gap flow from California's interior: impacts on aerosol composition, clouds, and radiative balance. Atmospheric Chemistry and Physics. 17:1491-1509.   10.5194/acp-17-1491-2017   AbstractWebsite

During the CalWater 2015 field campaign, ground-level observations of aerosol size, concentration, chemical composition, and cloud activity were made at Bodega Bay, CA, on the remote California coast. A strong anthropogenic influence on air quality, aerosol physicochemical properties, and cloud activity was observed at Bodega Bay during periods with special weather conditions, known as Petaluma Gap flow, in which air from California's interior is transported to the coast. This study applies a diverse set of chemical, cloud microphysical, and meteorological measurements to the Petaluma Gap flow phenomenon for the first time. It is demonstrated that the sudden and often dramatic change in aerosol properties is strongly related to regional meteorology and anthropogenically influenced chemical processes in California's Central Valley. In addition, it is demonstrated that the change in air mass properties from those typical of a remote marine environment to properties of a continental regime has the potential to impact atmospheric radiative balance and cloud formation in ways that must be accounted for in regional climate simulations.

2016
Jayarathne, T, Sultana CM, Lee C, Malfatti F, Cox JL, Pendergraft MA, Moore KA, Azam F, Tivanski AV, Cappa CD, Bertram TH, Grassian VH, Prather KA, Stone EA.  2016.  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   AbstractWebsite

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.

Collins, DB, Bertram TH, Sultana CM, Lee C, Axson JL, Prather KA.  2016.  Phytoplankton blooms weakly influence the cloud forming ability of sea spray aerosol. Geophysical Research Letters. 43:9975-9983.   10.1002/2016gl069922   AbstractWebsite

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.

Creamean, JM, White AB, Minnis P, Palikonda R, Spangenberg DA, Prather KA.  2016.  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.

Trueblood, JV, Estillore AD, Lee C, Dowling JA, Prather KA, Grassian VH.  2016.  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   AbstractWebsite

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.

Forestieri, SD, Cornwell GC, Helgestad TM, Moore KA, Lee C, Novak GA, Sultana CM, Wang XF, Bertram TH, Prather KA, Cappa CD.  2016.  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   AbstractWebsite

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.

Ralph, FM, Prather KA, Cayan D, Spackman JR, DeMott P, Dettinger M, Fairall C, Leung R, Rosenfeld D, Rutledge S, Waliser D, White AB, Cordeira J, Martin A, Helly J, Intrieri J.  2016.  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   AbstractWebsite

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.

DeMott, PJ, Hill TCJ, McCluskey CS, Prather KA, Collins DB, Sullivan RC, Ruppel MJ, Mason RH, Irish VE, Lee T, Hwang CY, Rhee TS, Snider JR, McMeeking GR, Dhaniyala S, Lewis ER, Wentzell JJB, Abbatt J, Lee C, Sultana CM, Ault AP, Axson JL, Martinez MD, Venero I, Santos-Figueroa G, Stokes MD, Deane GB, Mayol-Bracero OL, Grassian VH, Bertram TH, Bertram AK, Moffett BF, Franc GD.  2016.  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   AbstractWebsite

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.

Cochran, RE, Laskina O, Jayarathne T, Laskin A, Laskin J, Lin P, Sultana C, Lee C, Moore KA, Cappa CD, Bertram TH, Prather KA, Grassian VH, Stone EA.  2016.  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   AbstractWebsite

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.

Biteen, JS, Blainey PC, Cardon ZG, Chun MY, Church GM, Dorrestein PC, Fraser SE, Gilbert JA, Jansson JK, Knight R, Miller JF, Ozcan A, Prather KA, Quake SR, Ruby EG, Silver PA, Taha S, van den Engh G, Weiss PS, Wong GCL, Wright AT, Young TD.  2016.  Tools for the Microbiome: Nano and Beyond. Acs Nano. 10:6-37.   10.1021/acsnano.5b07826   AbstractWebsite

The microbiome presents great opportunities for understanding and improving the world around us and elucidating the interactions that compose it. The microbiome also poses tremendous challenges for mapping and manipulating the entangled networks of interactions among myriad diverse organisms. Here, we describe the opportunities, technical needs, and potential approaches to address these challenges, based on recent and upcoming advances in measurement and control at the nanoscale and beyond. These technical needs will provide the basis for advancing the largely descriptive studies of the microbiome to the theoretical and mechanistic understandings that will underpin the discipline of microbiome engineering. We anticipate that the new tools and methods developed will also be more broadly useful in environmental monitoring, medicine, forensics, and other areas.

2015
Ryder, OS, Campbell NR, Morris H, Forestieri S, Ruppel MJ, Cappa C, Tivanski A, Prather K, Bertram TH.  2015.  Role of organic coatings in regulating N2O5 reactive uptake to sea spray aerosol. Journal of Physical Chemistry A. 119:11683-11692.   10.1021/acs.jpca.5b08892   AbstractWebsite

Previous laboratory measurements and field observations have suggested that the reactive uptake of N2O5 to sea spray aerosol particles is a complex function of particle chemical composition and phase, where surface active organics can suppress the reactive uptake by up to a factor of 60. To date, there are no direct studies of the reactive uptake of N2O5 to nascent sea spray aerosol that permit assessment of the role that organic molecules present in sea spray aerosol (SSA) may play in suppressing or enhancing N2O5 uptake kinetics. In this study, SSA was generated from ambient seawater and artificial seawater matrices using a Marine Aerosol Reference Tank (MART), capable of producing nascent SSA representative of ambient conditions. The reactive uptake coefficient of N2O5 (gamma(N2O5)) on nascent SSA was determined using an entrained aerosol flow reactor coupled to a chemical ionization mass spectrometer for measurement of surface area dependent heterogeneous loss rates. Population averaged measurements of gamma(N2O5) for SSA generated from salt water sequentially doped with representative organic molecular mimics, or from ambient seawater, do not deviate statistically from that observed for sodium chloride (gamma(N2O5)(Nacl) = 0.01-0.03) for relative humidity (RH) ranging between 50 and 65%. The results are consistent with measurements made under clean marine conditions at the Scripps Institution of Oceanography Pier and those conducted on nascent SSA generated in the marine aerosol reference tank. The results presented here suggest that organic films present on nascent SSA (at RH greater than 50%) likely do not significantly limit N2O5 reactive uptake.

Lee, C, Sultana CM, Collins DB, Santander MV, Axson JL, Malfatti F, Cornwell GC, Grandquist JR, Deane GB, Stokes MD, Azam F, Grassian VH, Prather KA.  2015.  Advancing model systems for fundamental laboratory studies of sea spray aerosol using the microbial loop. Journal of Physical Chemistry A. 119:8860-8870.   10.1021/acs.jpca.5b03488   AbstractWebsite

Sea spray aerosol (SSA) particles represent one of the most abundant surfaces available for heterogeneous reactions to occur upon and thus profoundly alter the composition of the troposphere. In an effort to better understand tropospheric heterogeneous reaction processes, fundamental laboratory studies must be able to accurately reproduce the chemical complexity of SSA. Here we describe a new approach that uses microbial processes to control the composition of seawater and SSA particle composition. By inducing a phytoplankton bloom, we are able to create dynamic ecosystem interactions between marine microorganisms, which serve to alter the organic mixtures present in seawater. Using this controlled approach, changes in seawater composition become reflected in the chemical composition of SSA particles 4 to 10 d after the peak in chlorophyll-a. This approach for producing and varying the chemical complexity of a dominant tropospheric aerosol provides the foundation for further investigations of the physical and chemical properties of realistic SSA particles under controlled conditions.

Fitzgerald, E, Ault AP, Zauscher MD, Mayol-Bracero OL, Prather KA.  2015.  Comparison of the mixing state of long-range transported Asian and African mineral dust. Atmospheric Environment. 115:19-25.   10.1016/j.atmosenv.2015.04.031   AbstractWebsite

Mineral dust from arid regions represents the second largest global source of aerosols to the atmosphere. Dust strongly impacts the radiative balance of the earth's atmosphere by directly scattering solar radiation and acting as nuclei for the formation of liquid droplets and ice nuclei within clouds. The climate effects of mineral dust aerosols are poorly understood, however, due to their complex chemical and physical properties, which continuously evolve during atmospheric transport. This work focuses on characterizing atmospheric mineral dust from the two largest global dust sources: the Sahara Desert in Africa and the Gobi and Taklamakan Deserts in Asia. Measurements of individual aerosol particle size and chemical mixing state were made at El Yunque National Forest, Puerto Rico, downwind of the Sahara Desert, and Gosan, South Korea, downwind of the Gobi and Taklamakan Deserts. In general, the chemical characterization of the individual dust particles detected at these two sites reflected the dominant mineralogy of the source regions; aluminosilicate-rich dust was more common at El Yunque (similar to 91% of El Yunque dust particles vs. similar to 69% of Gosan dust particles) and calcium-rich dust was more common at Gosan (similar to 22% of Gosan dust particles vs. similar to 2% of El Yunque dust particles). Furthermore, dust particles from Africa and Asia were subjected to different transport conditions and atmospheric processing; African dust showed evidence of cloud processing, while Asian dust was modified via heterogeneous chemistry and direct condensation of secondary species. A larger fraction of dust detected at El Yunque contained the cloud-processing marker oxalate ion compared to dust detected at Gosan (similar to 20% vs similar to 9%). Additionally, nearly 100% of dust detected at Gosan contained nitrate, showing it was aged via heterogeneous reactions with nitric acid, compared to only similar to 60% of African dust. Information on the distinct differences in the chemical composition of mineral dust particles, as well as the mechanisms and extent of atmospheric processing, is critical for assessing its impacts on the earth's radiative budget through scattering, absorption, and nucleating cloud droplets and ice crystals. (C) 2015 Elsevier Ltd. All rights reserved.

Cahill, JF, Darlington TK, Fitzgerald C, Schoepp NG, Beld J, Burkart MD, Prather KA.  2015.  Online analysis of single cyanobacteria and algae cells under nitrogen-limited conditions using aerosol time-of-flight mass spectrometry. Analytical Chemistry. 87:8039-8046.   10.1021/acs.analchem.5b02326   AbstractWebsite

Metabolomics studies typically perform measurements on populations of whole cells which provide the average representation of a collection of many cells. However, key mechanistic information can be lost using this approach. Investigating chemistry at the single cell level yields a more accurate representation of the diversity of populations within a cell sample; however, this approach has many analytical challenges. In this study, an aerosol time-of-flight mass spectrometer (ATOFMS) was used for rapid analysis of single algae and cyanobacteria cells with diameters ranging from 1 to 8 mu m. Cells were aerosolized by nebulization and directly transmitted into the ATOFMS. Whole cells were determined to remain intact inside the instrument through a combination of particle sizing and imaging measurements. Differences in cell populations were observed after perturbing Chlamydomonas reinhardtii cells via nitrogen deprivation. Thousands of single cells were measured over a period of 4 days for nitrogen-replete and nitrogen-limited conditions. A comparison of the single cell mass spectra of the cells sampled under the two conditions revealed an increase in the dipalmitic acid sulfolipid sulfoquinovosyldiacylglycerol (SQDG), a chloroplast membrane lipid, under nitrogen-limited conditions. Single cell peak intensity distributions demonstrate the ability of the ATOFMS to measure metabolic differences of single cells. The ATOFMS provides an unprecedented maximum throughput of 50 Hz, enabling the rapid online measurement of thousands of single cell mass spectra.

Creamean, JM, Ault AP, White AB, Neiman PJ, Ralph FM, Minnis P, Prather KA.  2015.  Impact of interannual variations in sources of insoluble aerosol species on orographic precipitation over California's central Sierra Nevada. Atmospheric Chemistry and Physics. 15:6535-6548.   10.5194/acp-15-6535-2015   AbstractWebsite

Aerosols that serve as cloud condensation nuclei (CCN) and ice nuclei (IN) have the potential to profoundly influence precipitation processes. Furthermore, changes in orographic precipitation have broad implications for reservoir storage and flood risks. As part of the CalWater field campaign (2009-2011), the variability and associated impacts of different aerosol sources on precipitation were investigated in the California Sierra Nevada using an aerosol time-of-flight mass spectrometer for precipitation chemistry, S-band profiling radar for precipitation classification, remote sensing measurements of cloud properties, and surface meteorological measurements. The composition of insoluble residues in precipitation samples collected at a surface site contained mostly local biomass burning and longrange- transported dust and biological particles (2009), local sources of biomass burning and pollution (2010), and longrange transport (2011). Although differences in the sources of insoluble residues were observed from year to year, the most consistent source of dust and biological residues were associated with storms consisting of deep convective cloud systems with significant quantities of precipitation initiated in the ice phase. Further, biological residues were dominant (up to 40 %) during storms with relatively warm cloud temperatures (up to -15 degrees C), supporting the important role bioparticles can play as ice nucleating particles. On the other hand, lower percentages of residues from local biomass burning and pollution were observed over the three winter seasons (on average 31 and 9 %, respectively). When precipitation quantities were relatively low, these insoluble residues most likely served as CCN, forming smaller more numerous cloud droplets at the base of shallow cloud systems, and resulting in less efficient riming processes. Ultimately, the goal is to use such observations to improve the mechanistic linkages between aerosol sources and precipitation processes to produce more accurate predictive weather forecast models and improve water resource management.

White, AB, Neiman PJ, Creamean JM, Coleman T, Ralph FM, Prather KA.  2015.  The impacts of California's San Francisco Bay Area gap on precipitation observed in the Sierra Nevada during HMT and CalWater. Journal of Hydrometeorology. 16:1048-1069.   10.1175/jhm-d-14-0160.1   AbstractWebsite

Atmospheric rivers (ARs) are narrow regions of enhanced water vapor transport, usually found on the warm-sector side of the polar cold front in many midlatitude storms formed primarily over the oceans. Nonbrightband (NBB) rain is a shallow orographic rainfall process driven by collision and coalescence that has been observed in some of these storms. NBB rain accounts for about one-third, on average, of the total winter season rainfall occurring at a coastal mountain site in Northern California. During the California Energy Commission's CalWater project, nearly the same fraction of NBB rain was observed at a northern Sierra Nevada foothills site as compared to the coastal mountains, whereas less than half of the fractional amount of NBB rain was observed at a southern Sierra Nevada foothills site. Both Sierra Nevada sites often experience terrain-induced blocked flow, that is, Sierra barrier jet (SBJ) during landfalling winter storms. However, the northern Sierra Nevada site often is oriented geographically downwind of a gap in the coastal terrain near San Francisco during AR landfall. This gap allows maritime air in the AR to arrive at the northern site and enhance the collision-coalescence process in orographic feeder clouds as compared with the southern site. As a result, a greater amount and intensity of NBB rain and overall precipitation was produced at the northern site. This study uses a variety of observations collected in the coastal and Sierra Nevada ranges from the Hydrometeorology Testbed and CalWater field campaigns to document this behavior. A detailed case study provides additional context on the interaction between AR flow, the SBJ, and precipitation processes.

Gaston, CJ, Furutani H, Guazzotti SA, Coffee KR, Jung J, Uematsu M, Prather KA.  2015.  Direct night-time ejection of particle-phase reduced biogenic sulfur compounds from the ocean to the atmosphere. Environmental Science & Technology. 49:4861-4867.   10.1021/es506177s   AbstractWebsite

The influence of oceanic biological activity on sea spray aerosol composition, clouds, and climate remains poorly understood. The,emission of organic material arid gaseous dimethyl sulfide (DMS) from the ocean represents well-documented biogenic processes that influence particle chemistry in marine environments. However, the direct emission Of particle-phase biogenic sulfur from the ocean remains largely unexplored. Here we present measurements Of ocean,derived particles containing reduced sulfur, detected as elemental sulfur ions (e.g, S-32(+), S-64(2)+) in seven different marine environments using real-time, single particle mass spectrometry; these particles have not been detected outside of the marine environment. These reduced sulfur compounds were associated with primary marine particle types and wind speeds typically between 5 and 10 m/s suggesting that these particles themselves are a primary emission. In studies with measurements of seawater properties, chlorophyll-a and atmospheric DMS concentrations were typically elevated in these same locations suggesting a biogenic source for these sulfur-containing particles. Interestingly, these sulfur-containing particles only appeared at night, likely due to rapid photochemical destruction during the daytime, and comprised up to similar to 67% of the aerosol number fraction, particularly in the supermicrometer size range. These sulfur-containing particles were detected along the California coast, across the Pacific Ocean, and in the southern Indian Ocean suggesting that these particles represent a globally significant biogenic contribution to the marine aerosol burden.

Cahill, JF, Fei H, Cohen SM, Prather KA.  2015.  Characterization of core-shell MOF particles by depth profiling experiments using on-line single particle mass spectrometry. Analyst. 140:1510-1515.   10.1039/c4an01913j   AbstractWebsite

Materials with core-shell structures have distinct properties that lend themselves to a variety of potential applications. Characterization of small particle core-shell materials presents a unique analytical challenge. Herein, single particles of solid-state materials with core-shell structures were measured using on-line aerosol time-of-flight mass spectrometry (ATOFMS). Laser 'depth profiling' experiments verified the core-shell nature of two known core-shell particle configurations (< 2 mu m diameter) that possessed inverted, complimentary core-shell compositions (ZrO2@SiO2 versus SiO2@ZrO2). The average peak area ratios of Si and Zr ions were calculated to definitively show their core-shell composition. These ratio curves acted as a calibrant for an uncharacterized sample - a metal-organic framework (MOF) material surround by silica (UiO-66(Zr)@SiO2; UiO = University of Oslo). ATOFMS depth profiling was used to show that these particles did indeed exhibit a core-shell architecture. The results presented here show that ATOFMS can provide unique insights into core-shell solid-state materials with particle diameters between 0.2-3 mu m.

2014
Creamean, JM, Lee C, Hill TC, Ault AP, DeMott PJ, White AB, Ralph FM, Prather KA.  2014.  Chemical properties of insoluble precipitation residue particles. Journal of Aerosol Science. 76:13-27.   10.1016/j.jaerosci.2014.05.005   AbstractWebsite

Precipitation chemistry can provide unique insights into the composition of aerosol particles involved in precipitation processes. Until recently, precipitation chemistry studies focused predominantly on soluble components. Analyzing the single particle insoluble components in addition to soluble ions in precipitation can provide detailed information on the individual particles originally in the cloud or removed by precipitation as well as the source of the aerosols. Herein, we present an in-depth analysis of resuspended residues from precipitation samples collected at a remote site in the Sierra Nevada Mountains in California during the 2009-2011 winter seasons. In addition, we present results from laboratory control experiments of dust, leaf litter, smoke, and sea salt samples that were conducted to better understand how insoluble and soluble residues are distributed during the atomization process and aid in the classification of the residue compositions in the precipitation samples. Further, immersion freezing ice nuclei (IN) measurements of insoluble residues from precipitation water enabled the determination of residue types that likely seeded clouds. Long-range transported dust mixed with biological material tended to be more IN active, while purely biological residues contained a variety of high and low temperature IN. Overall, results from this study can be used as a benchmark for classification of insoluble precipitation residues in future studies. Knowledge of the precipitation chemistry of insoluble residues coupled with meteorological and cloud microphysical measurements will ultimately improve our understanding of the link between aerosols, clouds, and precipitation. (C) 2014 Published by Elsevier Ltd.

Collins, DB, Zhao DF, Ruppel MJ, Laskina O, Grandquist JR, Modini RL, Stokes MD, Russell LM, Bertram TH, Grassian VH, Deane GB, Prather KA.  2014.  Direct aerosol chemical composition measurements to evaluate the physicochemical differences between controlled sea spray aerosol generation schemes. Atmospheric Measurement Techniques. 7:3667-3683.   10.5194/amt-7-3667-2014   AbstractWebsite

Controlled laboratory studies of the physical and chemical properties of sea spray aerosol (SSA) must be underpinned by a physically and chemically accurate representation of the bubble-mediated production of nascent SSA particles. Bubble bursting is sensitive to the physicochemical properties of seawater. For a sample of seawater, any important differences in the SSA production mechanism are projected into the composition of the aerosol particles produced. Using direct chemical measurements of SSA at the single-particle level, this study presents an intercomparison of three laboratory-based, bubble-mediated SSA production schemes: gas forced through submerged sintered glass filters ("frits"), a pulsed plunging-waterfall apparatus, and breaking waves in a wave channel filled with natural seawater. The size-resolved chemical composition of SSA particles produced by breaking waves is more similar to particles produced by the plunging waterfall than those produced by sintered glass filters. Aerosol generated by disintegrating foam produced by sintered glass filters contained a larger fraction of organic-enriched particles and a different size-resolved elemental composition, especially in the 0.8-2 mu m dry diameter range. Interestingly, chemical differences between the methods only emerged when the particles were chemically analyzed at the single-particle level as a function of size; averaging the elemental composition of all particles across all sizes masked the differences between the SSA samples. When dried, SSA generated by the sintered glass filters had the highest fraction of particles with spherical morphology compared to the more cubic structure expected for pure NaCl particles produced when the particle contains relatively little organic carbon. In addition to an intercomparison of three SSA production methods, the role of the episodic or "pulsed" nature of the waterfall method on SSA composition was undertaken. In organic-enriched seawater, the continuous operation of the plunging waterfall resulted in the accumulation of surface foam and an over-expression of organic matter in SSA particles compared to those produced by a pulsed plunging waterfall. Throughout this set of experiments, comparative differences in the SSA number size distribution were coincident with differences in aerosol particle composition, indicating that the production mechanism of SSA exerts important controls on both the physical and chemical properties of the resulting aerosol with respect to both the internal and external mixing state of particles. This study provides insight into the inextricable physicochemical differences between each of the bubble-mediated SSA generation mechanisms tested and the aerosol particles that they produce, and also serves as a guideline for future laboratory studies of SSA particles.

Spiegel, JK, Buchmann N, Mayol-Bracero OL, Cuadra-Rodriguez LA, Diaz CJV, Prather KA, Mertes S, Eugster W.  2014.  Do cloud properties in a Puerto Rican tropical montane cloud forest depend on occurrence of long-range transported African dust? Pure and Applied Geophysics. 171:2443-2459.   10.1007/s00024-014-0830-y   AbstractWebsite

We investigated cloud properties of warm clouds in a tropical montane cloud forest at Pico del Este (1,051 m a.s.l.) in the northeastern part of Puerto Rico to address the question of whether cloud properties in the Caribbean could potentially be affected by African dust transported across the Atlantic Ocean. We analyzed data collected during 12 days in July 2011. Cloud droplet size spectra were measured using the FM-100 fog droplet spectrometer that measured droplet size distributions in the range from 2 to 49 A mu m, primarily during fog events. The droplet size spectra revealed a bimodal structure, with the first peak (D < 6 A mu m) being more pronounced in terms of droplet number concentrations, whereas the second peak (10 A mu m < D < 20 A mu m) was found to be the one relevant for total liquid water content (LWC) of the cloud. We identified three major clusters of characteristic droplet size spectra by means of hierarchical clustering. All clusters differed significantly from each other in droplet number concentration (), effective diameter (ED), and median volume diameter (MVD). For the cluster comprising the largest droplets and the lowest droplet number concentrations, we found evidence of inhomogeneous mixing in the cloud. Contrastingly, the other two clusters revealed microphysical behavior, which could be expected under homogeneous mixing conditions. For those conditions, an increase in cloud condensation nuclei-e.g., from processed African dust transported to the site-is supposed to lead to an increased droplet concentration. In fact, one of these two clusters showed a clear shift of cloud droplet size spectra towards smaller droplet diameters. Since this cluster occurred during periods with strong evidence for the presence of long-range transported African dust, we hypothesize a link between the observed dust episodes and cloud characteristics in the Caribbean at our site, which is similar to the anthropogenic aerosol indirect effect.

Hatch, LE, Pratt KA, Huffman JA, Jimenez JL, Prather KA.  2014.  Impacts of aerosol aging on laser desorption/ionization in single-particle mass spectrometers. Aerosol Science and Technology. 48:1050-1058.   10.1080/02786826.2014.955907   AbstractWebsite

Single-particle mass spectrometry (SPMS) has been widely used for characterizing the chemical mixing state of ambient aerosol particles. However, processes occurring during particle ablation and ionization can influence the mass spectra produced by these instruments. These effects remain poorly characterized for complex atmospheric particles. During the 2005 Study of Organic Aerosols in Riverside (SOAR), a thermodenuder was used to evaporate the more volatile aerosol species in sequential temperature steps up to 230 degrees C; the residual aerosol particles were sampled by an aerosol mass spectrometer (AMS) and a single-particle aerosol time-of-flight mass spectrometer (ATOFMS). Removal of the secondary species (e.g., ammonium nitrate/sulfate) through heating permitted assessment of the change in ionization patterns as the composition changed for a given particle type. It was observed that a coating of secondary species can reduce the ionization efficiency by changing the degree of laser absorption or particle ablation, which significantly impacted the measured ion peak areas. Nonvolatile aerosol components were used as pseudo-internal standards (or "reference components") to correct for this LDI effect. Such corrected ATOFMS ion peak areas correlated well with the AMS measurements of the same species up to 142 degrees C. This work demonstrates the potential to accurately relate SPMS peak areas to the mass of specific aerosol components.