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Many challenges remain before we can fully understand the multifaceted role that natural organic matter (NOM) plays in soil and aquatic systems. These challenges remain despite the considerable progress that has been made in understanding NOM’s properties and reactivity using the latest analytical techniques. For nearly 4 decades, the International Humic Substances Society (IHSS, which is a non-profit scientific society) has distributed standard substances that adhere to strict isolation protocols and reference materials that are collected in bulk and originate from clearly defined sites. These NOM standard and reference samples offer relatively uniform materials for designing experiments and developing new analytical methods. The protocols for isolating NOM, and humic and fulvic acid fractions of NOM utilize well-established preparative scale column chromatography and reverse osmosis methods. These standard and reference NOM samples are used by the international scientific community to study NOM across a range of disciplines from engineered to natural systems, thereby seeding the transfer of knowledge across research fields. Recently, powerful new analytical techniques used to characterize NOM have revealed complexities in its composition that transcend the “microbial” vs. “terrestrial” precursor paradigm. To continue to advance NOM research in the Anthropocene epoch, a workshop was convened to identify potential new sites for NOM samples that would encompass a range of sources and precursor materials and would be relevant for studying NOM’s role in mediating environmental and biogeochemical processes. We anticipate that expanding the portfolio of IHSS reference and standard NOM samples available to the research community will enable this diverse group of scientists and engineers to better understand the role that NOM plays globally under the influence of anthropogenic mediated changes.

With the increased occurrence of wildfires around the world, interest in the chemistry of pyrogenic organic matter (pyOM) and its fate in the environment has increased. Upon leaching from soils by rain events, significant amounts of dissolved pyOM (pyDOM) enter the aquatic environment and interact with microbial communities that are essential for cycling organic matter within the different biogeochemical cycles. To evaluate the biodegradability of pyDOM, aqueous extracts of laboratory-produced biochars were incubated with soil microbes, and the molecular changes to the composition of pyDOM were probed using ultrahigh-resolution mass spectrometry (Fourier transform–ion cyclotron resonance–mass spectrometry). Given that solar irradiation significantly affects the composition of pyDOM during terrestrial-to-marine export, the effects of photochemistry were also evaluated in the context of pyDOM biodegradability. Ultrahigh-resolution mass spectrometry revealed that many different (both aromatic and aliphatic) compounds were biodegraded. New labile compounds were produced, 22 %–40 % of which were peptide-like. These results indicated that a portion of pyDOM has been labilized into microbial biomass during the incubations. Fluorescence excitation–emission matrix spectra revealed that some fraction of these new bio-produced molecules is associated with proteinaceous fluorophores. Two-dimensional 1H–1H total correlation nuclear magnetic resonance (NMR) spectroscopy identified a peptidoglycan-like backbone within the microbially produced compounds. These results are consistent with previous observations of peptidoglycans within the soil and ocean nitrogen cycles where remnants of biodegraded pyDOM are expected to be observed. Interestingly, the exact nature of the bio-produced organic matter was found to vary drastically among samples indicating that the microbial consortium used may produce different exudates based on the composition of the initial pyDOM. Another potential explanation for the vast diversity of molecules is that microbes only consume low molecular-weight compounds, but they also produce reactive oxygen species (ROS), which initiate oxidative and recombination reactions that degrade high molecular-weight compounds and produce new molecules. Some of the bio-produced molecules (212–308 molecular formulas) were identified in estuarine and marine (surface and abyssal oceanic), and 81–192 of these formulas were of molecular composition attributed to carboxyl-rich alicyclic molecules (CRAM). These results indicate that some of the pyDOM biodegradation products have an oceanic fate and can be sequestered into the deep ocean. The observed microbially mediated diversification of pyDOM suggests that pyDOM contributes to the observed large complexity of natural organic matter observed in riverine and oceanic systems. More broadly, our research shows that pyDOM can be substrate for microbial growth and be incorporated into environmental food webs within the global carbon and nitrogen cycles.

Pyrogenic organic matter (pyOM) is the solid residue left after pyrolysis of organic matter, a process occurring in nature during forest fires. Upon rain events, pyrogenic dissolved organic matter (pyDOM) leaches into the rain water and is transferred to the aquatic environment where it has been identified as an important component of the global carbon cycle. Overall, pyDOM consists of highly condensed aromatic compounds (ConAC) and poorly characterized aliphatic molecules. While the ConAC are thought to be persistent in the environment, a large ConAC accumulation that would match the calculated fluxes of pyDOM formation and export has not been observed. Photo-degradation has been identified as a major pyDOM sink, and it can potentially account for the discrepancy in the global mass balance of pyDOM. Photochemistry of pyDOM has been studied to a certain extent, but neither the structural transformation pathways of pyDOM nor how they relate to pyrolysis temperature and parent feedstocks are well understood. In response to this need, we have examined the products after photo-irradiation of pyDOM derived from a temperature series (250, 400, 525, 650 °C) of oak biochars made under controlled laboratory conditions, which can be considered model pyrogenic substances. Ultrahigh resolution mass spectrometry (FT-ICR-MS), one-dimensional 1H NMR, and two-dimensional 1H-1H total correlation spectroscopy (TOCSY) NMR were used to evaluate the compositional changes that occurred with photo-irradiation. In agreement with previous studies, pyDOM aryl groups were the most photo-labile, and alkyl and O-alkyl groups were photo-produced. A new finding is that polysubstituted olefinic moieties of pyDOM were also photo-degraded. Using TOCSY we identified several small molecular weight compounds whose abundances changed non-linearly across the combustion continuum which suggests that different radical processes occur in the different char leachates. Using mass spectrometric data we observed that pyDOM from oak chars made at lower temperatures (250 and 400 °C), as well as pyDOM from a grass char prepared at 650 °C, photo-transformed to a more hydrogenated and oxygenated composition. In contrast, pyDOM from higher temperature char leachates (525 and 650 °C) transformed predominantly into smaller aliphatic compounds. To explain these differences, we propose a photo-transformation mechanism for ConAC which includes oxygenation of ConAC, ring-opening reactions, and sequential decarboxylation yielding small aliphatic N-rich molecules (marine-like composition). These structures could be further polymerized by reactive oxygen species to form straight-chain alkanes if not consumed by microorganisms. Results from these controlled experiments reveal that the extent of photo-transformation appears to be a function of production temperature and parent feedstock. This study enhances our understanding of ConAC and pyDOM, their terrestrial-to-marine transfers, geochemical stability, and eventual fate in sunlit environments. Here we also show the value of structural characterization of pyDOM, and reveal the many unknowns left to be answered for this complex and analytically challenging type of organic matter.

Deciphering the origin, age, and composition of deep marine organic carbon remains a challenge in understanding the dynamics of the marine carbon cycle. In particular, the composition of aged organic carbon and what allows its persistence in the deep ocean and in sediment is unresolved. Here, we observe that both high and low temperature hydrothermal vents at the 9° 50′ N; 104° 17.5 W East Pacific Rise (EPR) vent field are a source for (sub)micron-sized graphite particles. We demonstrate that commonly applied analytical techniques for quantification of organic carbon detect graphite. These analyses thereby classify graphite as either dissolved or particulate organic carbon, depending on the particle size and filtration method, and overlook its relevance as a carbon source to the deep ocean. Settling velocity calculations indicate the potential for these (sub)micron particles to become entrained in the buoyant plume and distributed far from the vent fields. Thus, our observations provide direct evidence for hydrothermal vents acting as a source of old carbon to the deep ocean., Deciphering the origin, age, and composition of deep marine organic carbon remains a challenge for understanding the dynamics of the marine carbon cycle. Here, the authors identify (sub)micron-sized graphite emanating from both high and low temperature hydrothermal vents along the East Pacific Rise, and suggest graphite is a source of old carbon in the deep ocean.

Microbes (bacteria, phytoplankton) in the ocean are responsible for the copious production of exopolymeric substances (EPS) that include transparent exopolymeric particles. These materials act as a matrix to form marine snow. After the Deepwater Horizon oil spill, marine oil snow (MOS) formed in massive quantities and influenced the fate and transport of oil in the ocean. The processes and pathways of MOS formation require further elucidation to be better understood, in particular we need to better understand how dispersants affect aggregation and degradation of oil. Toward that end, recent work has characterized EPS as a function of microbial community and environmental conditions. We present a conceptual model that incorporates recent findings in our understanding of the driving forces of MOS sedimentation and flocculent accumulation (MOSSFA) including factors that influence the scavenging of oil into MOS and the routes that promote decomposition of the oil post MOS formation. In particular, the model incorporates advances in our understanding of processes that control interactions between oil, dispersant, and EPS in producing either MOS that can sink or dispersed gels promoting microbial degradation of oil compounds. A critical element is the role of protein to carbohydrate ratios (P/C ratios) of EPS in the aggregation process of colloid and particle formation. The P/C ratio of EPS provides a chemical basis for the “stickiness” factor that is used in analytical or numerical simulations of the aggregation process. This factor also provides a relative measure for the strength of attachment of EPS to particle surfaces. Results from recent laboratory experiments demonstrate (i) the rapid formation of microbial assemblages, including their EPS, on oil droplets that is enhanced in the presence of Corexit-dispersed oil, and (ii) the subsequent rapid oil oxidation and microbial degradation in water. These findings, combined with the conceptual model, further improve our understanding of the fate of the sinking MOS (e.g., subsequent sedimentation and preservation/degradation) and expand our ability to predict the behavior and transport of spilled oil in the ocean, and the potential effects of Corexit application, specifically with respect to MOS processes (i.e., formation, fate, and half-lives) and Marine Oil Snow Sedimentation and Flocculent Accumulation.

With the increased occurrence of forest fires around the world, interest in the chemistry of pyrogenic organic matter (pyOM) and its fate in the environment has increased. Upon leaching from soils by rain events, significant amounts of dissolved pyOM (pyDOM) enter the aquatic environment and interact with microbial communities that are essential for cycling organic matter within the different biogeochemical cycles. To evaluate the bio-reactivity of pyDOM, aqueous extracts of laboratory-produced chars were incubated with soil microbes and the molecular changes to the composition of pyDOM were probed using ultrahigh resolution mass spectrometry (Fourier transform – ion cyclotron resonance – mass spectrometry). Given that photo-degradation also affects the composition and reactivity of pyDOM during terrigenous-to-marine export, the effects of photochemistry were also evaluated in the context of the bio-reactivity of pyDOM. Ultrahigh resolution mass spectrometry revealed that, after incubation, many different (both aromatic and aliphatic) compounds were degraded, and new labile compounds, 22–40 % of which were peptide-like, were produced. This indicated that a portion of pyDOM has been labilized into microbial biomass during the incubations. Fluorescence excitation-emission matrix spectra revealed that some fraction of these new molecules is associated with fluorophores from proteinaceous and/or autochthonous/microbial biomass origin. Two-dimensional 1H-1H total correlation NMR spectroscopy identified a peptidoglycan-like backbone within the microbially produced compounds. These results are consistent with previous observations of nitrogen from peptidoglycans within the soil and ocean nitrogen cycles. Interestingly, the exact nature of the bio-produced organic matter was found to vary drastically among samples indicating that the used microbial consortium may produce different exudates based on the composition of the initial pyDOM. Another potential explanation for the vast diversity of molecules is that microbes only consume low molecular weight compounds, but they also produce reactive oxygen species (ROS), which initiate oxidative and recombination reactions that produce new molecules. The observed microbially-mediated diversification of pyDOM suggests that pyDOM contributes to the observed large complexity of natural organic matter. More broadly, pyDOM can be substrate for microbial growth and be incorporated in environmental food webs.

Pyrogenic dissolved organic matter (pyDOM) is known to be an important biogeochemical constituent of aquatic ecosystems and the carbon cycle. While our knowledge of pyDOM’s production, compos...

Following the Deepwater Horizon oil spill in the Gulf of Mexico, natural marine snow interacted with oil and dispersants forming marine oil snow (MOS) that sank from the water column to sediments. Mesocosm simulations demonstrate that Macondo surrogate oil incorporates into MOS and can be isolated, extracted, and analyzed via Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS). Up to 47% of the FTICR-MS signal from MOS extracts can be attributed to formulas also found in Macondo surrogate oil demonstrating extensive oil incorporation. Additionally, oxygenation patterns for MOS extracts provide evidence for degraded oil compounds. Formulas having similar double bond equivalents but higher oxygen content (MOS CHO: CHO2-9, DBE2-16, MOS CHON: CHO0-7N1, DBE9-18; Macondo CHO: CHO1-4, DBE2-15, CHON: CHO0-3N1, DBE9-21) were found in MOS extracts generating isoabundance distributions similar to those of environmentally aged oil. Such shifts in molecular composition are consistent with the transformation of high DBE oil components, unobservable by FTICR-MS until oxygenation in the mesocosms. Low light conditions and the rapid proliferation of hydrocarbon-degraders observed in parallel studies suggest biological activity as the primary cause of oil degradation. MOS may thus represent an important microenvironment for oil degradation especially during its long transit below the euphotic zone to sediments.

Large amounts of mucous-rich oil-containing marine snow formed in surface waters adjacent to the Deepwater Horizon spill. This marine oil snow (MOS) was implicated in oil delivery to the seafloor. Whether the use of chemical dispersants increased or decreased MOS sedimentation remains controversial. We conducted mesocosm experiments testing the effects of oil and oil plus a dispersant on MOS formation and sedimentation, in coastal seawater . The four treatments used were a surrogate Macondo oil water accommodated fraction (“WAF”), two concentrations of chemically-enhanced WAF (“CEWAF” and diluted CEWAF, “DCEWAF”) containing a dispersant and oil, and Controls (no additions). Based on radiocarbon and 13 C NMR results, the presence of dispersants enhanced the amounts of petro-carbon being incorporated into the sinking oil-carrying aggregates (aka MOS). However, most of the chemically-dispersed oil preferentially partitioned into the colloidal and suspended particulate fractions rather than into the rapidly forming MOS. Thus the oil and non-petro-carbon sedimentation efficiency in treatments with a dispersant was much lower, compared to those in the Control and WAF treatments, during the four-day mesocosm experiment. Formation of MOS and its subsequent sinking sequestered the oil in two stages: first via terrestrial-derived detritus containing humic compounds, and subsequently via freshly produced material, such as exopolymeric substances produced by phytoplankton and bacteria.

Large-scale exopolymeric substances (EPS) formation was observed in contaminated surface waters of the Gulf of Mexico , after the Deepwater Horizon oil spill. The conditions under which EPS are produced can cause variations in their physico-chemical properties , affecting the fate of the oil through either emulsification or coagulation with particles, followed by aggregation and marine oil snow (MOS) sedimentation . Here, we report results from a four-day mesocosm experiment that examined EPS production, the change in the bulk chemical composition (mainly polysaccharides and proteins), as well as the partitioning into different size fractions (suspended particulate matter (SPM), colloidal fraction, and sinking MOS). The treatments included 1) natural coastal seawater (Control), 2) a water accommodated fraction of oil (WAF), 3) a chemically-enhanced WAF with addition of oil dispersant Corexit (CEWAF), and 4) a diluted CEWAF (DCEWAF). Generally, the presence of WAF stimulated more extracellular polysaccharide production, whereas the addition of Corexit promoted more protein production. Moreover, marine aggregates changed from a terrestrial signature (higher aromaticity, lower EPS content and more uniform monosaccharide distribution) in the early stages of the experiment, to a fresher autochthonous signature (less aromatic, higher EPS content and glucose-dominated monosaccharide distribution) in the later stage of the mesocosm experiment. Corexit promoted the association between oil and proteins, assisting to emulsify the oil in colloids and SPM and delay the settling of EPS and oil (MOS) for the duration of the mesocosm. Furthermore, when oil, especially Corexit-dispersed oil, was present, extracellular polysaccharides were preferentially incorporated into sinking MOS relative to proteins, as evidenced from a lower protein-C/carbohydrate-C ratio of the sinking MOS than those of SPM and colloidal fraction in WAF, CEWAF and DCEWAF, respectively. This is in contrast to a higher protein-C/carbohydrate-C ratio in the sinking marine snow than those of SPM and colloidal fraction in the control. Likely, microbially-mediated extracellular polysaccharides are the key component that anchors the mineral ballast until the aggregates become dense enough and overcome the buoyancy added to the aggregates as a result of their association with oil/Corexit. We conclude that interactions between Corexit and EPS components regulate petroleum hydrocarbon distribution between the water column and sinking MOS.

Pyrogenic carbon (pyC) or fire-derived organic C (e.g., charcoal and soot), while generally considered stable in soils and sediments, can leach into pore waters forming dissolved pyrogenic organic carbon (pyDOC). This pyDOC may be exported to the ocean (about 10% riverine DOC may be pyrogenic). Yet, the processes which control this export and how pyrogenic dissolved organic matter (pyDOM) lability is related to its chemical composition are poorly understood. Thus, pyDOM was leached from a thermal series of oak and grass chars (250-650 °C) and photoirradiated in a solar simulator. About 10-20% of oak char leachate pyDOC was mineralized over five days, with greater proportions lost from leachates of higher temperature parent chars. Proton NMR revealed decreased relative amounts of aryl-C and increased low molecular weight C1 and alkyl-C components during the photo-incubation. Quantification of benzenepolycarboxylic acid (BPCA), molecular markers for condensed aromatic carbon (ConAC), indicated that 75-94% of ConAC was lost during the first five days of photoincubation, the majority of which occurred within the first 2 days, with a preference toward loss of ConAC of larger cluster sizes. Over 96-day microbial incubations, 37 to 48% of pyDOC was lost with modelled half-lives of about 13 days. Much of this was low molecular weight C1 compounds, while only 1 to 2% of ConAC was lost, with a preference for losses of smaller cluster size ConAC. Slightly greater proportions of both total pyC and ConAC was lost from pre-photodegraded pyDOM leachates. These results highlight the large portion of pyDOM that is potentially remineralized or transformed in aquatic systems at short timescales, and the need to examine both condensed and non-condensed portions of pyDOM to understand the effects of fires on aquatic biogeochemistry.

The Deepwater Horizon oil spill stimulated the release of marine snow made up of dead/living plankton/bacteria and their exopolymeric polysaccharide substances (EPS), termed marine oil snow (MOS), promoting rapid removal of oil from the water column into sediments near the well site. Mesocosm simulations showed that Macondo surrogate oil readily associates with the marine snow. Quantitative solid-state 13C NMR readily distinguishes this oil from naturally formed marine snow and reveals that adding the dispersant Corexit enhances the amount of oil associated with the MOS, thus contributing to rapid removal from the water column. Solvent extraction of MOS removes the oil-derived compounds for analysis by one and two-dimensional GC/MS and evaluation of potential transformations they undergo when associated with the EPS. The results reveal that the oil associated with EPS is subjected to rapid transformation, in a matter of days, presumably by bacteria and fungi associated with EPS.

We report here for the first time rainwater organic carbon (OC) concentration and composition collected from open waters over the Gulf of Mexico. Rainwater OC concentrations ranged from 3.7 to 17.3 mg L−1. The δ13C of these rainwater samples ranged from −26.7 to −24.2‰ pointing toward terrestrial and/or fossil fuel OC sources (64–100%) combined with marine OC sources. Colored dissolved OM absorbance and EEM fluorescence spectra were indicative of secondary organic aerosol from terrestrial sources as well as aromatic fossil fuel compounds. Air mass back trajectory analyses along with these results indicate that rainwater OC in the Gulf of Mexico may be influenced by oil and gas infrastructure and emissions from known lanes of shipping traffic within the Gulf. These results also suggest that anthropogenic and biogenic emissions from the southeastern continental USA impact rainwater OC in the Gulf of Mexico.

Evidence suggests that reactive oxygen species (ROS) are important in transforming the chemical composition of the large pool of terrestrially-derived dissolved organic matter (DOM) exported from land to water annually. However, due to the challenges inherent in isolating the effects of individual ROS on DOM composition, the role of ROS in the photochemical alteration of DOM remains poorly characterized. In this work, terrestrial DOM was independently exposed to singlet oxygen (1O2), and superoxide ( O 2 - under controlled laboratory conditions). Using ultra-high resolution mass spectrometry to track molecular level alterations of DOM by ROS, these findings suggest exposure to 1O2 (generated using Rose Bengal and visible light) removed formulas with an O/C > 0.3, and primarily resulted in DOM comprised of formulas with higher oxygen content, while O 2 - exposure (from KO2 in DMSO) removed formulas with O/C 1.5). Comparison of DOM altered by ROS in this study to riverine and coastal DOM showed that (20–80%) overlap in formulas, providing evidence for the role of ROS in shaping the composition of DOM exported from rivers to oceans.

In this study, the abundance of transparent exopolymer particles (TEP) is examined across a surface water gradient of organic carbon from a phytoplankton bloom region in the western North Atlantic to oligotrophic waters in the Sargasso Sea, including a coastal region sampled near Cape Cod. TEP are macrogels that reach up to millimeters in size and abiotically assemble from dissolved acidic polysaccharides secreted by phytoplankton. Due to their great stickiness, TEP self aggregate and also form aggregates with non-TEP particulate organic carbon (POC). Aggregation enhances ballasting, thereby mutually facilitating export and subsequent sedimentation of both TEP and POC, increasing the efficiency of the biological pump. Here, four distinct regions with varying chlorophyll a concentrations, temperature, and salinity were sampled in the upper column, at the surface, and from the sea surface microlayer (SML). While TEP in seawater shows no correlation to chlorophyll a, nutrients, or total organic carbon (TOC) concentration, a strong correlation exists between TEP and TOC in the SML; and concentrations of both variables are inversely proportional to surface productivity as indicated by chlorophyll a concentrations. As open ocean regions show greater enrichments of TEP and TOC in the SML compared to the coastal region, we suggest that the role of the SML in organic carbon cycling is dependent on regional biogeochemistry and productivity. We hypothesize that a lower abundance of particles in oligotrophic regions compared to bloom regions limits TEP export by sinking, thus increasing the residence time of TEP in the upper water column and the SML.

Pyrogenic organic matter (Py-OM), generated via the incomplete combustion of biomass, is well studied due to the presence of slow-cycling, condensed aromatic compounds (ConAC) known to sequester in soils and sediments. Recently, dissolved Py-OM (Py-DOM) has received interest, due to its higher mobility and potential to be transferred through watersheds to aquatic systems. Py-DOM quantities, molecular identities and importance to global carbon budgets and cycles are only beginning to be understood. Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS) analyses were performed on Py-DOM isolated from oak and grass biochars produced over a range of temperatures (250–650 °C), and the data are compared to complementary 1H NMR spectroscopic and benzenepolycarboxylic acid biomarker (BPCAs) analyses. Py-DOM is revealed to be a heterogeneous mixture of compounds ranging in relative aromaticity and oxygenation. FTICR-MS analyses demonstrate a decrease in Py-DOM relative oxygen content and a concurrent increase in aliphatic character and heteroatomic (N, Cl) content. 1H NMR and BPCAs analyses detail low O/C dissolved ConAC not observed by FTICR-MS, demonstrating the necessity for a multiple proxy approach to Py-DOM characterization. Heterogeneous Py-DOM is explained as resulting from pyrolysis-initiated and radical-mediated functional group cleavage, aromatic condensation and aromatic ring-opening reactions. Oak biomass progresses faster along a char maturity continuum for a given pyrolysis temperature, perhaps due to its greater lignin content or radical quenching by grass cuticular material. Biomass species and pyrolysis temperature likely result in different Py-DOM compositions and fates and must be considered when evaluating the impacts of wildfires and biochar applications.

While pyrogenic dissolved organic matter (pyDOM) is known to be photolabile, the rates and components of pyDOM that are lost via photochemical degradation, and how these vary with pyrogenic source, are poorly understood. Thus, pyDOM was leached from an oak thermal series and a grass chars (250–650 °C) and photoirradiated in a solar simulator. About 10–20% of oak char leachate organic C was mineralized over five days, with greater proportions lost from leachates of higher temperature parent chars. Ultraviolet and fluorescence spectroscopy suggested that mainly aromatic components (e.g., fulvic-, humic-, aromatic-like) were lost. Quantification of benzenepolycarboxylic acids (BPCAs), molecular markers indicated that 75–94% of condensed aromatic C was lost during the first five days of photoincubation, with preferential loss of larger aromatic clusters. Using a 2-component exponential decay model, this most photolabile fraction was calculated to have experimental half-lives of about 1 day. It represented 16 to 23% of the dissolved C, was primarily condensed aromatics, and was likely lost through primary photoreactions. A non-condensed component was lost at half-lives of about 1–2 d, likely through radical-driven propagation reactions. Using the same model, about 43% of pyrogenic C was predicted to be photomineralized over the course of 1 year. These results highlight the contrasting reactivity of condensed and non-condensed portions of pyDOM, and both should be considered when evaluating the potential of pyDOM to alter aquatic ecology and the environmental mobility of priority pollutants.

Though pyrogenic carbon (pyC) has been assumed to be predominantly stable, degradation and transfers of pyC between various pools have been found to influence its cycling and longevity in the environment. Dissolution via leaching may be the main control on loss processes such as microbial or abiotic oxidation, mineral sorption, or export to aquatic systems. Yet, little is known of the controls on pyrogenic dissolved organic matter (pyDOM) generation or composition. Here, the yield and composition of pyDOM generated through batch leaching of a thermal series of oak and grass biochars, as well as several non-pyrogenic reference materials, was compared to that of their parent solids. Over 17 daily leaching cycles, biochars made from oak at 250 to 650° C released decreasing amounts of C on both a weight (16.9 to 0.3%, respectively) and C yield basis (7.4 to 0.2% C, respectively). Aryl-C represented an estimated 32 to 82% of C in the parent solids (identified by 13C-NMR), but only 7 to 38% in the leachates (identified by 1H-NMR), though both increased with pyrolysis temperature. PyC, often operationally defined as condensed aromatic carbon (ConAC), was quantified using the benzenepolycarboxylic acid (BPCA) method. Tri- and tetra-carboxylated BPCAs were formed from non-pyrogenic reference materials, thus, only penta- and hexa-carboxylated BPCAs were used to derive a BPCA-C to ConAC conversion factor of 7.04. ConAC made up 24 to 57% of the pyrogenic solid C (excluding the 250 °C biochar), but only about 9 to 23% of their respective leachates’ DOC, though both proportions generally increased with pyrolysis temperature. Weighted BPCA compound distributions, or the BPCA Aromatic Condensation (BACon) Index, indicate that ConAC cluster size increased in pyrogenic solids but not in leachates. Additional evidence presented suggests that both aromatic cluster size and O-containing functional group contents in the pyrogenic solid control pyC solubility. Overall, pyDOM was found to be compositionally dissimilar from its parent chars and contained a complex mixture of organic compound groups. Thus, it is expected that estimates of dissolved pyC production and export, made only by detection of ConAC, are too low by factors of 4 to 11.

Aerosol water soluble organic carbon (WSOC) and iron (Fe) loadings were examined in aerosols collected during the 2011 US GEOTRACES cruise in the North Atlantic Ocean to explore the feasibility of a role for water soluble organic matter (WSOM) organic complexation in determining the higher fractional solubility of Fe (%Fe S ) observed in North American-influenced relative to North African-influenced aerosols. Proton nuclear magnetic resonance spectroscopy ( 1 H NMR) was employed to characterize the WSOM, and principal component analysis was then applied to differentiate North American-influenced from North African-influenced aerosol WSOM and provide clues to the molecular identities of organic ligands. As has been found in previous studies, North African-influenced samples had orders of magnitude higher total Fe (Fe T ) loadings (8.9–101 nmol Fe m − 3 air) and orders of magnitude lower %Fe S (0.12–0.29%) than those found in North American-influenced (Fe T : 0.03–1.4 nmol Fe m − 3 air; %Fe S : 0.67–3.62%) and Marine (minimal recent continental influence; Fe T : 0.02–0.25 nmol Fe m − 3 air; %Fe S : 1.1–10.7%) samples. Aerosol %Fe S values were positively correlated with WSOC/Fe T ratios with North American combustion-influenced (39–540) and Marine (30–850) aerosol samples having orders of magnitude more moles of WSOC per mole of Fe T than North African (0.42–3.8) aerosol samples. The high WSOC/Fe T ratios in the North American combustion-influenced samples suggest a realistic role for organic ligands binding with Fe and accounting for some portion of the higher aerosol %Fe S also observed for these samples. Principal component analyses of 1 H NMR spectra show North American-influenced aerosol WSOM to have higher contributions from hydrogens in aliphatic carbon chains attached to heteroatomic functional groups such as those in nitrate, amine, ether, ester, and carboxylate compounds compared to North African mineral dust-influenced aerosol WSOM. These multifunctional aliphatic WSOM compounds are suggested as candidate Fe binding ligands to be explored with future work.

Ratios of certain organochlorine pollutants in fish tissues are significantly different between the eastern and western North Atlantic and have been used to identify recent (

Size-fractionated aerosol impactor samples (n = 3) representing North American, North African, and marine air mass influences were collected over the North Atlantic Ocean as part of the 2011 US GEOTRACES cruise (GEOTRACES GA03), and a molecular-level chemical characterization of the water soluble organic matter (WSOM) was obtained using electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry. Remarkable differences were found between the molecular characteristics of WSOM from the fine ( 7.2 μm fraction of marine-influenced aerosols. Principal component analysis (PCA) showed the 1.5) ratios including many heteroatom (N, S, P) containing formulas. Condensed aromatic compounds, which originate from anthropogenic sources and can affect the global climate by absorbing solar radiation, as well as compounds that can be attributed to secondary organic aerosols (SOA), were found in all 17 WSOM fractions analyzed. This indicates the ubiquitous nature of these types of compounds across aerosol size fractions and air mass influences, even in aerosols collected over the middle of the ocean. These results provide an indication of size-fractionated aerosol composition, and future molecular characterization work should be paired with physical characteristics to inform size-fractionated and source-resolved models of aerosol OM impacts in the atmosphere.

The Deepwater Horizon oil spill stimulated the release of marine snow made up of dead/living plankton/bacteria and their exopolymeric polysaccharide substances (EPS), termed marine oil snow (MOS), promoting rapid removal of oil from the water column into sediments near the well site. Mesocosm simulations showed that Macondo surrogate oil readily associates with the marine snow. Quantitative solid-state

The chemical composition of organic aerosols in the atmosphere is strongly influenced by human emissions. The effect these have on the environment, human health, and climate change is determined by the molecular nature of these chemical species. The complexity of organic aerosol samples limits the ability to study the chemical composition, and therefore the associated properties and the impacts they have. Many studies have addressed the water-soluble fraction of organic aerosols and have had much success in identifying specific molecular formulas for thousands of compounds present. However, little attention is given to the water-insoluble portion, which can contain most of the fossil material that is emitted through human activity. Here we compare the organic aerosols present in water extracts and organic solvent extracts (pyridine and acetonitrile) of an ambient aerosol sample collected in a rural location that is impacted by natural and anthropogenic emission sources. A semiquantitative method was developed using proton nuclear magnetic resonance spectroscopy to determine that the amount of organic matter extracted by pyridine is comparable to that of water. Electrospray ionization Fourier transform ion cyclotron resonance mass spectra show that pyridine extracts a molecularly unique fraction of organic matter compared to water or acetonitrile, which extract chemically similar organic matter components. The molecular formulas unique to pyridine were less polar, more aliphatic, and reveal formulas containing sulfur to be an important component of insoluble aerosol organic matter.

Rainwater dissolved organic matter (DOM) was characterized in two sequential coastal rainstorms of different geographic origins: an Atlantic hurricane (Hurricane Irene [2011]) and a terrestrial squall. Using a multiproxy approach incorporating electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (FTICR), stable carbon isotope analysis, and excitation–emission fluorescence spectroscopy, we demonstrate the unique composition of marine-derived organic matter in Atlantic hurricane rainwater. Hurricane Irene rainwater DOM (DOMIrene) was molecularly distinct from that of the terrestrial squall (DOMsquall). For example, δ13CDOC of Irene rainwater was − 19.2 ± 0.13‰ while that of the squall was − 26.3 ± 0.01‰. Peaks assigned using FTICR which were unique to DOMIrene contained a greater relative number of molecular formulas containing nitrogen (representing any of several isomeric CHON, CHONS, CHONP compounds) relative to those unique to the DOMsquall. Although there was insufficient rainwater available to test DOMsquall for its bioavailability, a simple room-temperature incubation of Irene rainwater over 30 days in the dark resulted in its dissolved organic carbon decreasing from 2.3 to 1.5 mg L− 1. When coupled with the abundant precipitation generally-associated with hurricanes, these results suggest that marine DOM in rainwater may exert unique but substantial impacts to organic matter in coastal aquatic ecosystems.

The atmospheric delivery of soluble and bioavailable iron (Fe) is essential for the biogeochemical functioning of many oceanic ecosystems where Fe is a limiting micronutrient for biological production. Aerosol samples associated with air masses characterized as European-influenced, primarily marine (no continental influence within 5 day back trajectories), or North African-influenced were collected along a cruise track in the eastern North Atlantic Ocean during a 2010 US GEOTRACES cruise. Aerosols were analyzed for total and soluble Fe and aluminum (Al) and organic matter (OM) loadings and OM chemical characteristics, to explore potential relationships between aerosol OM and Fe and Al that contribute to higher Fe and Al solubilities in combustion-influenced aerosols. Similar to the results from previous studies, North African-influenced air masses contained higher aerosol Fe (4.7–86 nmol m − 3 ) and Al (13–240 nmol m − 3 ) total loadings than European-influenced air masses (Fe: 0.63–2.7 nmol m − 3 ; Al: 2.5–5.9 nmol m − 3 ), but Fe and Al relative solubilities were much higher for European (Fe: 2.1–4.6%; Al: 1.9–3.2%) versus North African-influenced aerosols (Fe: 0.22–0.70%; Al: 0.39–1.1%). Water soluble organic carbon (WSOC) to trace metal ratios correlated positively with this trend in Fe and Al relative solubilities, as European-influenced WSOC/trace metal ratios ranged from ~ 2 to 32 while North African-influenced aerosol WSOC/trace metal ratios ranged from 0.04 to 0.51. Aerosols from primarily marine air masses showed the lowest Fe, Al, and OM loadings of all samples and Fe (0.71–2.5%) and Al (0.36–9.2%) solubilities that were variable and did not fit the patterns described for the continentally-influenced samples. Principal component analysis was employed on aerosol water soluble OM (WSOM) solution state 1 H nuclear magnetic resonance spectra and revealed the European-influenced aerosol WSOM to be characterized by higher contributions from acetic acid (a common photoproduct of atmospheric OM) and aliphatic hydrogens, while North African-influenced aerosol WSOM was characterized by carbohydrate-like compounds and compounds with unsaturations. The abundance of the acetic acid photoproduct in European-influenced aerosol WSOM suggests this WSOM to be rich in carboxyl groups that are thought to be strong Fe-binding ligands and provides evidence for the potential role of WSOM in maintaining aerosol Fe and Al solubilities.

Over forty scientists from six countries convened in Raleigh, NC on June 4-6 2012 to review the status and prospects of sea spray aerosol research. Participants were researchers from the oceanography and atmospheric science communities, including academia, private industry, and government agencies. The recommendations from the working groups are summarized in a science prioritization matrix that is meant to prioritize the research agenda and identify areas of investigation by the magnitude of their impact on proposed science questions. Str

A method for quantifying the diffusive air-sea exchange of gaseous organic carbon (OC) was developed. OC compounds were separated into two operational pools—those that were kinetically air limited in diffusion across the air-sea interface and those that were water limited—during simultaneous air/water sampling. The method separates OC compounds into low Henrys H > ~0.1 L atm mol−1) compounds were collected on solid sorbent tubes downstream from the water traps and were analyzed by gas chromatography-flame ionization detection (GC-FID). Separating OC based on H, rather than measuring OC as one bulk pool, allows improved estimates of OC concentration gradients and fluxes. A 10-month field study in the York River Estuary in Gloucester Point, VA revealed an average VOC flux of 138 µg C m−2 d−1 and an average SOC flux of 832 mg C m−2 d−1 (positive fluxes denote sea to air transfer).

Organic aerosols (OA) are universally regarded as an important component of the atmosphere that have far-ranging impacts on climate forcing and human health. Many of these impacts are related to OA molecular characteristics. Despite the acknowledged importance, current uncertainties related to the source apportionment of molecular properties and environmental impacts make it difficult to confidently predict the net impacts of OA. Here we evaluate the specific molecular compounds as well as bulk structural properties of total suspended particulates in ambient OA collected from key emission sources (marine, biomass burning, and urban) using ultrahigh resolution mass spectrometry (UHR-MS) and proton nuclear magnetic resonance spectroscopy (1H NMR). UHR-MS and 1H NMR show that OA within each source is structurally diverse, and the molecular characteristics are described in detail. Principal component analysis (PCA) revealed that (1) aromatic nitrogen species are distinguishing components for these biomass burning aerosols; (2) these urban aerosols are distinguished by having formulas with high O/C ratios and lesser aromatic and condensed aromatic formulas; and (3) these marine aerosols are distinguished by lipid-like compounds of likely marine biological origin. This study provides a unique qualitative approach for enhancing the chemical characterization of OA necessary for molecular source apportionment.

Desorption kinetics and sources (fossil vs. contemporary) of the water soluble organic carbon (WSOC) component of aerosol particles were examined at two sites on the east coast of the United States. Experiments revealed that WSOC is released either rapidly as one homogeneous pool or via biphasic kinetics with one rapidly and one slowly desorbing pool. The majority (>85%) of WSOC was desorbed within the first 15 min of immersion in water, suggesting that this material can be rapidly incorporated into rainwater pre-depositionally or surface waters post-depositionally and transported through watersheds. Radiocarbon (14C) measurements showed that on average 12 ± 4% and 14 ± 2% of WSOC from sites in New York and Virginia, respectively, was derived from fossil sources. By contrast, mass balance calculations revealed water-insoluble organic carbon to have significantly greater fossil contributions. These findings suggest that contemporary biogenic aerosol OC is preferentially incorporated into the aqueous phase and may be transported relatively rapidly through watersheds and aquatic systems. In contrast, the more highly aged and fossil aerosol component remains in particulate form and is more likely to be retained on particles or in soils or aquatic sediments.

Despite the acknowledged relevance of aerosol-derived water-soluble organic carbon (WSOC) to climate and biogeochemical cycling, characterization of aerosol WSOC has been limited. Electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI FT-ICR MS) was utilized in this study to provide detailed molecular level characterization of the high molecular weight (HMW; m/z>223) component of aerosol-derived WSOC collected from rural sites in Virginia and New York, USA. More than 3000 peaks were detected by ESI FT-ICR MS within a m/z range of 223–600 for each sample. Approximately 86% (Virginia) and 78% (New York) of these peaks were assigned molecular formulas using only carbon (C), hydrogen (H), oxygen (O), nitrogen (N), and sulfur (S) as elemental constituents. H/C and O/C molar ratios were plotted on van Krevelen diagrams and indicated a strong contribution of lignin-like and lipid-like compounds to the aerosol-derived WSOC samples. Approximately 1–4% of the peaks in the aerosol-derived WSOC mass spectra were classified as black carbon (BC) on the basis of double bond equivalents calculated from the assigned molecular formulas. In addition, several high-magnitude peaks in the mass spectra of samples from both sites corresponded to molecular formulas proposed in previous secondary organic aerosol (SOA) laboratory investigations indicating that SOAs are important constituents of the WSOC. Overall, ESI FT-ICR MS provides a level of resolution adequate for detailed compositional and source information of the HMW constituents of aerosol-derived WSOC.

Primary producer (angiosperms, macroalgae, submerged aquatic vegetation), suspended particulate matter, andFundulus heteroclitus isotope values (δ13C, δ15N, δ34S) were examined to assess their use as indicators for changes in food web support functions in tidally-restored salt marshes. Study sites, located throughout the southern New England region (USA), ranged fromSpartina alterniflora-dominated reference marshes, marshes under various regimes and histories of tide restoration, and a severely tide-restrictedPhragmites australis marsh.Fundulus δ13C values were greater for fish from referenceSpartina marshes than for fish from adjacent tide-restricted or tide-restored marshes where higher percent cover of C3 plants, lower water column salinities, and more negative dissolved inorganic δ13C values were observed. The difference inFundulus δ13C values between a tide-restrictedPhragmites marsh and an adjacent referenceSpartina marsh was great compared to the difference between marshes at various stages of tide restoration and their respective reference marshes, suggesting that food web support functions are restored as the degree of tidal restriction is lessened. While a multiple isotopic approach can provide valuable information for determining specific food sources to consumers, this study demonstrates that monitoringFundulus δ13C values alone may be useful to evaluate the trajectory of ecological change for marshes undergoing tidal restoration.

The molecular characteristics of aerosol organic matter (OM) determines to a large extent its impacts on the atmospheric radiative budget and ecosystem function in terrestrial and aquatic environments, yet the OM molecular details of aerosols from different sources are not well established. Aerosol particulate samples with North American-influenced, North African-influenced, and marine (minimal recent continental influence) air mass back trajectories were collected as part of the 2011 trans-North Atlantic US GEOTRACES cruise and analyzed for their water soluble OM (WSOM) molecular characteristics using electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry. Principal component analysis (PCA) separated the samples into five groups defined by distinct molecular formula characteristics. An abundance of nitrogen containing compounds with molecular formulas consistent with amino acid derivatives defined the two samples comprising the primary marine group (henceforth referred to as Primary Marine), which suggest a primary marine biological source to their WSOM in spite of their North American-influenced air mass trajectories. A second group of samples (aged marine, henceforth referred to as Aged Marine) with marine air mass trajectories was characterized by an abundance of low O / C (0.15–0.45) sulfur containing compounds consistent with organosulfate compounds formed via secondary aging reactions in the atmosphere. Several samples having North American-influenced air mass trajectories formed another group again characterized by organosulfate and nitrooxyorganosulfate type compounds with higher O / C ratios (0.5–1.0) than the Aged Marine samples reflecting the combustion influence from the North American continent. All the samples with North African-influenced air mass trajectories were grouped together in the PCA and were characterized by a lack of heteroatom (N, S, P) containing molecular formulas covering a wide O / C range (0.15–0.90) reflecting the desert source of this WSOM. The two marine groups showed molecular formulas that, on average, had higher H / C ratios and lower O / C ratios and modified aromaticity indices than the two continentally influenced groups, which suggests that these properties are characteristic of marine vs. continental aerosol WSOM. The final sample group, the mixed source samples (henceforth referred to as Mixed Source), showed intermediate molecular characteristics, which suggests no dominant continental or marine source. The source-specific OM details described here will aid efforts to link aerosol OM source with molecular characteristics and impacts in the environment.

This study describes a method for evaluating the reproducibility of replicate mass spectra acquired for complex natural organic matter (NOM) samples analyzed by electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry, with regard to both peak detection and peak magnitude. Because studies of NOM characterization utilize not only the emergence and disappearance of peaks but also changes in relative peak magnitude, it is important to establish that the differences between samples are significantly larger than those between sample replicates. Here, a method is developed for correcting strict signal-to-noise thresholds, along with a new scheme for assessing the reproducibility of peak magnitudes. Furthermore, a systematic approach for discerning when the comparison of samples by the presence or absence of peaks is appropriate and when it is necessary to compare based on the relative magnitude of the peaks is presented. A variety of 10 different types of NOM samples are analyzed in duplicate or triplicate instrumental injections or experimental extractions. A framework for these procedures is provided, and acceptable reproducibility levels are recommended.

nd 0.22 0.47 0.34 0.29 0.16 0.26 0.24 0.28 WIOC d d 13 C( ‰ )n d � 26.0 � 25.1 � 25.6 � 26.7 � 26.8 � 24.2 � 25.9 � 25.8 D 14 C( ‰ )n d � 45 42 � 1 � 367 � 461 � 231 � 353 � 212 fWIOC nd 0.78 0.53 0.66 0.71 0.84 0.74 0.76 0.72 TSE e d 13 C( ‰) � 27.0 nd � 26.2 � 26.6 nd � 27.3 � 28.2 � 27.6 � 27.2 D 14 C( ‰) � 476 nd � 90 � 283 nd � 430 � 119 � 190 � 227 fTSE 0.67 nd 0.90 0.79 nd 0.43 0.74 0.59 0.69 Aliphatic d 13 C( ‰) � 28.6 � 27.7 nd f � 28.2 nd � 27.3 � 28.9 � 28.1 � 28.1 D 14 C( ‰) � 794 � 820 � 961 � 858 nd � 834 � 858 � 846 � 853 faliphatic 0.007 0.001 0.003 0.0039 nd 0.007 0.002 0.004 0.004 Aromatic d 13 C( ‰) � 27.8 � 29.6 � 28.3 � 28.6 � 28.3 � 28.4 � 27.8 � 28.2 � 28.4 D 14 C( ‰) � 692 � 77 � 446 � 405 � 466 � 540 � 446 � 484 � 444 faromatic 0.015 0.009 0.004 0.009 0.009 0.007 0.003 0.007 0.006 Polar d 13 C( ‰) � 27.8 � 26.1 � 28.0 � 27.3 � 28.6 nd � 26.2 � 27.4 � 27.3 D 14 C( ‰) � 750 24 � 93 � 273 � 168 nd � 240 � 204 � 245 fpolar 0.24 0.039 0.25 0.18 0.063 nd 0.066 0.065 0.13 a All reported d 13 C and D 14 C values were corrected for blank contributions following procedures outlined in the text. b ‘nd’ denotes samples for which values were not determined. c Values represent the fraction of TOC accounted for by the parameter of interest (f

[1] Carbon isotopic signatures (δ13C, Δ14C) of aerosol particulate matter total organic carbon (TOC) and operationally defined organic carbon (OC) components were measured in samples from two background sites in the eastern U.S. TOC and water-soluble OC (WSOC)δ13C values (−27 to −24‰) indicated predominantly terrestrial C3 plant and fossil derived sources. Total solvent extracts (TSE) and their aliphatic, aromatic, and polar OC components were depleted in δ13C (−30 to −26‰) relative to TOC and WSOC. Δ14C signatures of aerosol TOC and TSE (−476 to +25‰) suggest variable fossil contributions (∼5–50%) to these components. Aliphatic OC while comprising a small portion of the TOC (

[1] Atmospheric particulate matter samples were collected from mid-Atlantic and northeastern U.S. (Virginia and New York, respectively) sites to assess the fossil versus contemporary sources contributing to aerosol organic carbon (OC) and the implications for its deposition to watersheds. Mean particulate matter total OC (TOC) deposition rates (wet + dry deposition) were calculated to be 1.6 and 2.4 mg C m−2 d−1 for the Virginia and New York sites, respectively. Wet deposition of particulate TOC was determined to be the dominant depositional mode, accounting for >65% (Virginia) and >80% (New York) of total aerosol TOC deposition. Isotopic mass balances suggest that, on average, the deposited aerosol TOC consisted of 66% (Virginia) and 68% (New York) contemporary biomass-derived material. The balance was fossil-derived material (34% and 32% for Virginia and New York, respectively), indicating significant anthropogenic fossil fuel contributions to aerosol TOC. When considered within representative northeastern U.S. watershed OC budgets, aerosol TOC depositional flux was up to 10% of net soil OC accumulation rates, and 5–70% of the OC throughfall flux for forested regions. When scaled to the entire Hudson and York River watersheds, estimated aerosol TOC depositional fluxes ranged from 6.1 to 9.7 × 1010 g C yr−1 and from 8.9 to 14 × 109 g C yr−1, respectively, and were similar in magnitude to the mean annual river OC export for these two systems (Hudson, 7.2 × 1010 g C yr−1; York, 8.4 × 109 g C yr−1). These findings underscore the potential importance of both natural and fossil fuel-derived aerosol OC inputs to watersheds.

A detailed understanding of the sources, transformations and fates of organic species in the environment is crucial because of the central roles that they play in human health, biogeochemical cycles and the Earth's climate. However, such an understanding is hindered by the immense chemical complexity of environmental mixtures of organics; for example, atmospheric organic aerosol consists of at least thousands of individual compounds, all of which likely evolve chemically over their atmospheric lifetimes. Here, we demonstrate the utility of describing organic aerosol (and other complex organic mixtures) in terms of average carbon oxidation state, a quantity that always increases with oxidation, and is readily measured using state-of-the-art analytical techniques. Field and laboratory measurements of the average carbon oxidation state, using several such techniques, constrain the chemical properties of the organics and demonstrate that the formation and evolution of organic aerosol involves simultaneous changes to both carbon oxidation state and carbon number.