Water-insoluble Organic Matter Research Articles

Molecular characteristics, sources and transformation of water-insoluble organic matter in cloud water

Studies have shown that water-insoluble organic matter (WIOM) accounts for a large part of the organic components in cloud water and significantly contributes to brown carbon. However, the molecular characteristics of WIOM in cloud droplets remain unclear, hampering the understanding of their climate effects. In this study, cloud water was collected at a remote mountain site in South China during the winter of 2020, and WIOM was separated by membrane filtration, extracted by methanol, and characterized using Fourier transform ion cyclotron resonance mass spectrometry coupled with an electrospray ionization source. A total of 697–1637 molecules were identified in WIOM. WIOM is characterized by lower oxidation states of carbon atoms (−1.10 ∼ −0.84 in WIOM vs. −0.58 ∼ −0.51 in water-soluble organic matter (WSOM) on average), higher carbon number (14.12–20.59 vs. 9.87–10.56) and lower unsaturation (double-bond equivalent 4.55–4.95 vs. 4.84–5.23) relative to WSOM. More abundant lipid-like compounds (12.2–41.9% in WIOM vs. <2% in WSOM) but less highly oxygenated compounds (<7% vs. 28.6–35.3%) exist in WIOM. More than 30% of WIOM molecules in cloud water are common with interstitial particles, implying that WIOM in cloud water may originate from aerosol activation and/or collision. Some unique molecules in WIOM in cloud water are identified as aqueous-phase oligomerization products, indicating the aqueous-phase formation of WIOM. Further analysis of the intermolecular relationship shows that WIOM has the potential to transform into WSOM by partitioning into the dissolved phase, oxidation and functionalization by heteroatom-containing groups, representing a previously unidentified pathway for WSOM formation in cloud water. The results provide new insights into the in-cloud chemistry, which would assist in the understanding of the aqueous formation and evolution of WIOM.

Fluorescence of solvent-extractable organics in sub-micrometer forest aerosols in Hokkaido, Japan

Excitation–emission matrix (EEM) fluorescence spectroscopy is an analytical method for obtaining the properties, components, and sources of chromophores of atmospheric organic aerosols (OA). Most studies have been limited to water-soluble OA; the chemical structures of OA associated with chromophores and the sources of chromophores are still not well understood. In this study, the fluorescence properties of solvent-extractable organic components, fractionated based on their polarity in sub-micrometer forest aerosols in Hokkaido, Japan, were characterized on the basis of their EEMs in combination with chemical structural characterization from offline aerosol mass spectrometry. The fluorescence volume normalized by the mass concentration (NFV) and the fluorescence volume (FV) corresponding to the atmospheric abundance for water-insoluble organic matter (WISOM) were higher than those of other OA fractions and highest in the winter. Correlation analyses between the NFVs and the relative intensities of ion groups from the mass spectra from a high-resolution aerosol mass spectrometer suggest that organic compounds containing O and N contributed to the fluorescence of the OA fractions. Although the fluorescence indices used to characterize aquatic dissolved organic matter exhibited comparable values for water-soluble organic matter (WSOM) in this study and in previous studies, they are not applicable in explaining the types or sources of other OA fractions. A parallel factor (PARAFAC) analysis for EEM profiles identified five components. Four components had fluorescence characteristics similar to those associated with humic-like substances (HULIS), and one had fluorescence characteristics associated with protein-like compounds (PLOM). The chromophores commonly associated with HULIS with oxygenated structures contributed significantly to respective OA fractions; this implies that for fluorescence measurements, such as the detection of primary biological aerosol particles (PBAP), contributions from oxygenated organics should be considered in the forest region.

Exploring controls on perfluorocarboxylic acid (PFCA) gas-particle partitioning using a model with observational constraints.

The atmospheric fate of perfluorocarboxylic acids (PFCAs) has attracted much attention in recent decades due to the role of the atmosphere in global transport of these persistent chemicals. There is a gap in our understanding of gas-particle partitioning, limited by availability of reliable atmospheric measurements, partitioning properties, and models of gas-particle interactions. The gas-particle equilibrium phase partitioning of C2-C16 PFCAs in the atmosphere were modeled here by taking account of both deprotonation and phase partitioning equilibria among air, aerosol liquid water, and particulate water-insoluble organic matter using a range of available PFCA partitioning properties. We systematically varied water and organic matter content to simulate the full range of atmospheric conditions. Except in severe organic matter pollution episodes, shorter-chain PFCAs are predicted to mainly partition between air and aqueous phase, while for PFCAs with carbon chains longer than 12, organic matter is more likely to be the dominant particle phase reservoir. The model framework underestimated the particle fraction of C2-C8 PFCAs compared with several ambient observations, with larger discrepancies observed for longer-chain PFCAs. The discrepancy could result from externally mixed dust components, non-ideality of aerosol liquid water, surfactant descriptions at phase boundaries, and missed interactions between organic matter and charged PFCA molecules. Reliable measurements of ambient PFCAs with high time resolution and the measurement of uptake parameters by particle-relevant components will be beneficial to more reliable environmental fate modeling of ambient PFCAs.

Algorithm for vertical distribution of boundary layer aerosol components in remote-sensing data

Abstract. The vertical distribution of atmospheric aerosol components is vital to the estimation of radiative forcing and the catalysis of atmospheric photochemical processes. Based on the synergy of ground-based lidar and sun-photometer in Generalized Aerosol Retrieval from Radiometer and Lidar Combined data (GARRLiC), this paper developed a new algorithm to get the vertical mass concentration profiles of fine-mode aerosol components for the first time. Retrieval of aerosol properties was achieved based on the sky radiance at multiple scatter angles, total optical depth (TOD) at 440, 675, 870, and 1020 nm, and lidar signals at 532 and 1064 nm. In addition, the internal mixing model and normalized volume size distribution (VSD) model were established according to the absorption and water solubility of the aerosol components, to separate the profiles of black carbon (BC), water-insoluble organic matter (WIOM), water-soluble organic matter (WSOM), ammonium nitrate-like (AN), and fine aerosol water (AW) content. Results showed a reasonable vertical distribution of aerosol components compared with in situ observations and reanalysis data. The estimated and observed BC concentrations matched well with a correlation coefficient up to 0.91, while there was an evident overestimation of organic matter (OM = WIOM + WSOM, NMB = 0.98). Moreover, the retrieved AN concentrations were closer to the simulated results (R = 0.85), especially in polluted conditions. The BC and OM correlations were relatively weaker, with a correlation coefficient of ∼ 0.5. Besides, the uncertainties caused by the input parameters (i.e., relative humidity (RH), volume concentration, and extinction coefficients) were assessed using the Monte Carlo method. The AN and AW had smaller uncertainties at higher RH. Herein, the proposed algorithm was also applied to remote-sensing measurements in Beijing with two typical cases. In the clean condition with low RH, there were comparable AN and WIOM, but peaking at different altitudes. On the other hand, in the polluted case, AN was dominant and the maximum mass concentration occurred near the surface. We expected that the algorithm could provide a new idea for lidar inversion and promote the development of aerosol component profiles.

Abundance, chemical structure, and light absorption properties of humic-like substances (HULIS) and other organic fractions of forest aerosols in Hokkaido

Atmospheric organic aerosol (OA) are considered as a significant contributor to the light absorption of OA, but its relationship with abundance, composition and sources are not understood well. In this study, the abundance, chemical structural characteristics, and light absorption property of HULIS and other low-to-high polar organics in PM0.95 collected in Tomakomai Experimental Forest (TOEF) were investigated with consideration of their possible sources. HULIS were the most abundant (51%), and correlation analysis revealed that biogenic secondary organic aerosols significantly contribute to HULIS. The mass spectra obtained using a high-resolution aerosol mass spectrometer (HR-AMS) showed that HULIS and highly polar water-soluble organic matter (HP-WSOM) were substantially oxygenated organic aerosol fractions, whereas water-insoluble organic matter (WISOM) had a low O/C ratio and more hydrocarbon-like structures. The WISOM fraction was the predominant light-absorbing organics. HULIS and WISOM showed a noticeable seasonal change in mass absorption efficiency (MAE365), which was highest in winter. Further, HULIS were shown to be less absorbing than those reported for urban sites. The findings in this study provide insights into the contribution of biogenic secondary OA on aerosol property and radiative forcing under varying contributions from other types of OA.

The Relationship between Molecular Size and Polarity of Atmospheric Organic Aerosol in Singapore and Its Implications for Volatility and Light Absorption Properties

Organic aerosol, which is a complex mixture, has been categorized by both chemical (e.g., degree of oxygenation and molecular weight (MW)) and physical (e.g., water solubility and optical) characteristics. However, the inter-relationships among these characteristics have not been well-established yet. This study developed a novel framework on the inter-relationship among volatility, water solubility, and MW. The framework suggests that water-soluble organic matter (WSOM) can have relatively small MW (<200) because highly polar species tend to have lower volatility. On the other hand, water-insoluble organic matter (WISOM) needs to have larger MW than the threshold, as less polar species tend to be highly volatile. The idea was tested by analyzing aerosol samples collected at Singapore. Both WSOM and WISOM were extracted from the samples. The WSOM fraction was further classified by polarity using the 1-octanol–water method. The samples were analyzed by atmospheric pressure chemical ionization mass spectrometry (APCI-MS). APCI-MS is a soft-ionization technique that dominantly provides [M–H]− ions. The APCI-MS data validated the newly developed idea on the MW distributions for WSOM and WISOM. The positive matrix factorization (PMF) analysis was applied to the APCI-MS data. The analysis for WSOM also supported the inverse relationship between polarity and MW. The PMF outputs were combined with the ultraviolet–visible absorption data for obtaining absorption Ångstrom exponents (AAE) for each factor. The result suggests that highly polar WSOM factors have relatively small values of average MW (≤205) and higher values of AAE (>8.5), connecting polarity and optical properties of OM.

Predicting gas–particle partitioning coefficients of atmospheric molecules with machine learning

Abstract. The formation, properties, and lifetime of secondary organic aerosols in the atmosphere are largely determined by gas–particle partitioning coefficients of the participating organic vapours. Since these coefficients are often difficult to measure and to compute, we developed a machine learning model to predict them given molecular structure as input. Our data-driven approach is based on the dataset by Wang et al. (2017), who computed the partitioning coefficients and saturation vapour pressures of 3414 atmospheric oxidation products from the Master Chemical Mechanism using the COSMOtherm programme. We trained a kernel ridge regression (KRR) machine learning model on the saturation vapour pressure (Psat) and on two equilibrium partitioning coefficients: between a water-insoluble organic matter phase and the gas phase (KWIOM/G) and between an infinitely dilute solution with pure water and the gas phase (KW/G). For the input representation of the atomic structure of each organic molecule to the machine, we tested different descriptors. We find that the many-body tensor representation (MBTR) works best for our application, but the topological fingerprint (TopFP) approach is almost as good and computationally cheaper to evaluate. Our best machine learning model (KRR with a Gaussian kernel + MBTR) predicts Psat and KWIOM/G to within 0.3 logarithmic units and KW/G to within 0.4 logarithmic units of the original COSMOtherm calculations. This is equal to or better than the typical accuracy of COSMOtherm predictions compared to experimental data (where available). We then applied our machine learning model to a dataset of 35 383 molecules that we generated based on a carbon-10 backbone functionalized with zero to six carboxyl, carbonyl, or hydroxyl groups to evaluate its performance for polyfunctional compounds with potentially low Psat. The resulting saturation vapour pressure and partitioning coefficient distributions were physico-chemically reasonable, for example, in terms of the average effects of the addition of single functional groups. The volatility predictions for the most highly oxidized compounds were in qualitative agreement with experimentally inferred volatilities of, for example, α-pinene oxidation products with as yet unknown structures but similar elemental compositions.

Distinctive Sources Govern Organic Aerosol Fractions with Different Degrees of Oxygenation in the Urban Atmosphere.

Understanding how the sources of an atmospheric organic aerosol (OA) govern its burden is crucial for assessing its impact on the environment and adopting proper control strategies. In this study, the sources of OA over Beijing were assessed year-around based on the combination of two separation approaches for OA, one from chemical fractionation into the high-polarity fraction of water-soluble organic matter (HP-WSOM), humic-like substances (HULIS), and water-insoluble organic matter (WISOM), and the other from statistical grouping using positive matrix factorization (PMF) of high-resolution aerosol mass spectra. Among the three OA fractions, HP-WSOM has the highest O/C ratio (1.36), followed by HULIS (0.56) and WISOM (0.17). The major sources of different OA fractions were distinct: HP-WSOM was dominated by more oxidized oxygenated OA (96%); HULIS by cooking-like OA (40%), less oxidized oxygenated OA (27%), and biomass burning OA (21%); and WISOM by fossil fuel OA (77%). In addition, our results provide evidence that mass spectral-based PMF factors are associated with specific substructures in molecules. These structures are further discussed in the context of the FT-IR results. This study presents an overall relationship of OA groups monitored by chemical and statistical approaches for the first time, providing insights for future source apportionment studies.

A two-component parameterization of marine ice-nucleating particles based on seawater biology and sea spray aerosol measurements in the Mediterranean Sea

Abstract. Ice-nucleating particles (INPs) have a large impact on the climate-relevant properties of clouds over the oceans. Studies have shown that sea spray aerosols (SSAs), produced upon bursting of bubbles at the ocean surface, can be an important source of marine INPs, particularly during periods of enhanced biological productivity. Recent mesocosm experiments using natural seawater spiked with nutrients have revealed that marine INPs are derived from two separate classes of organic matter in SSAs. Despite this finding, existing parameterizations for marine INP abundance are based solely on single variables such as SSA organic carbon (OC) or SSA surface area, which may mask specific trends in the separate classes of INP. The goal of this paper is to improve the understanding of the connection between ocean biology and marine INP abundance by reporting results from a field study and proposing a new parameterization of marine INPs that accounts for the two associated classes of organic matter. The PEACETIME cruise took place from 10 May to 10 June 2017 in the Mediterranean Sea. Throughout the cruise, INP concentrations in the surface microlayer (INPSML) and in SSAs (INPSSA) produced using a plunging aquarium apparatus were continuously monitored while surface seawater (SSW) and SML biological properties were measured in parallel. The organic content of artificially generated SSAs was also evaluated. INPSML concentrations were found to be lower than those reported in the literature, presumably due to the oligotrophic nature of the Mediterranean Sea. A dust wet deposition event that occurred during the cruise increased the INP concentrations measured in the SML by an order of magnitude, in line with increases in iron in the SML and bacterial abundances. Increases in INPSSA were not observed until after a delay of 3 days compared to increases in the SML and are likely a result of a strong influence of bulk SSW INPs for the temperatures investigated (T=-18 ∘C for SSAs, T=-15 ∘C for SSW). Results confirmed that INPSSA are divided into two classes depending on their associated organic matter. Here we find that warm (T≥-22 ∘C) INPSSA concentrations are correlated with water-soluble organic matter (WSOC) in the SSAs, but also with SSW parameters (particulate organic carbon, POCSSW and INPSSW,-16C) while cold INPSSA (T&lt;-22 ∘C) are correlated with SSA water-insoluble organic carbon (WIOC) and SML dissolved organic carbon (DOC) concentrations. A relationship was also found between cold INPSSA and SSW nano- and microphytoplankton cell abundances, indicating that these species might be a source of water-insoluble organic matter with surfactant properties and specific IN activities. Guided by these results, we formulated and tested multiple parameterizations for the abundance of INPs in marine SSAs, including a single-component model based on POCSSW and a two-component model based on SSA WIOC and OC. We also altered a previous model based on OCSSA content to account for oligotrophy of the Mediterranean Sea. We then compared this formulation with the previous models. This new parameterization should improve attempts to incorporate marine INP emissions into numerical models.

Distinguishing functional pools of soil organic matter based on solubility in hot water

Evidence is emerging that the solubility of soil organic matter (SOM) in water is a key factor regulating the turnover of carbon (C) and nitrogen (N). We used data from a field trial with a wide range of treatments in a case study to: (1) examine the link between SOM solubility and bioavailability and (2) evaluate whether low water-solubility is a factor contributing to the persistence of refractory SOM. The trial was established in 2000 on a silt loam (Udic Dystocrept) at Lincoln, New Zealand to identify management practices that maintain SOM following the conversion of long-term pasture to arable cropping. The following land use treatments were sampled (0–7.5, 7.5–15 and 15–25 cm) in 2013: (1) long-term ryegrass-white clover pasture; (2) arable cropping rotation, managed using either intensive, minimum, or no tillage; and (3) continuous bare fallow (plots maintained plant-free using herbicide; not cultivated). The bioavailability of SOM was determined by measuring C and N mineralisation in a 98-day incubation at 25°C (soil maintained near field capacity) and water solubility was assessed by measuring hot-water-extractable C and N (16-h extraction at 80°C). After 13 years of arable cropping, C stocks (to 25 cm) were 11 t ha–1 less than in pasture soil (decrease of 14%). Tillage ‘intensity’ had no effect on C stocks in the top 25 cm. Large losses of C were observed in the bare fallow treatment (19 t C ha–1 less than pasture soil). The bioavailability of SOM (CO2-C mineralised as a proportion of soil C) also declined under arable cropping and bare fallow. The relationship between total C and mineralised C had a significant (P &amp;lt; 0.001) intercept, indicating that part of the organic matter (13 g C kg–1) did not contribute to C mineralisation (it was biologically inert). Across treatments and sampling depths, SOM mineralised in 98 days generally corresponded well with that extracted in hot water. A significant fraction of SOM (~9 g C kg–1) did not release C to hot water. Water-insoluble organic matter, including compounds that are strongly bonded to mineral surfaces, may comprise a significant part of the refractory SOM.

Effects of Oxygen-Containing Salts on the Detection of Organic Biomarkers on Mars and in Terrestrial Analog Soils.

The detection of chlorinated hydrocarbons by Curiosity on Mars has been attributed to the presence of unidentified indigenous organic matter. Similarly, oxychlorines on Earth have been proposed to be responsible for the apparent lack of organics in the Atacama Desert. The presence of perchlorate (ClO4-) poses a unique challenge to the measurement of organic matter due to the oxidizing power of oxychlorines during commonly used pyrolysis-gas chromatography-mass spectrometry (py-GC-MS) methods. Here, we show that perchlorates and other oxyanion salts inhibit the detection of organic compounds but that removing these problematic species prior to pyrolysis by using an optimal sample extraction duration and suitable ratios of water to sample mass enables analysis. We have characterized leached and unleached samples containing perchlorates from the Atacama Desert and have found that after leaching, the py-GC-MS chromatograms of the dried mineral residues show identifiable biomarkers associated with indigenous cyanobacteria. Samples which were pyrolyzed without leaching showed no detectable organic matter other than background siloxane and very weak or no trace of detectable polychlorinated benzenes. Dried sample residues remaining after leaching, the mineral matrix and water-insoluble organic matter, showed a strong organic response in all cases when analyzed by py-GC-MS. These residues are most likely the product of the pyrolysis of water-insoluble organics originally present in the samples. In addition, our results imply that previous soil analyses which contained high levels of oxyanions and concluded that organics were either not present or were present at extremely low levels should be reexamined.

Structural and Light-Absorption Characteristics of Complex Water-Insoluble Organic Mixtures in Urban Submicrometer Aerosols.

Submicrometer aerosols in the urban atmosphere of Nagoya, Japan, were collected in late winter and early spring, and the water-insoluble organic matter (WISOM) in the samples were fractionated into six subfractions based on their polarities by using solvent and normal-phase solid-phase extractions: nonpolar (F1), low-polar (F2 and F3), and medium-polar (F4, F5, and F6) fractions. The overall structural characteristics of these subfractions were then analyzed using Fourier transform infrared spectroscopy, nuclear magnetic resonance spectroscopy, and high-resolution aerosol mass spectrometry. Quantitative information related to the overall chemical characteristics of the WISOM in the different polarity fractions, including their elemental compositions, the relative abundances of different functional groups and their fragments from electron impact ionization, was obtained. These water-insoluble fractions accounted for half of the total light absorption by the extracted aerosol matter at 400 nm. The contributions of the medium-polar fractions to both the total organic carbon and light absorption by the extracts were dominant among the contributions from the six subfractions. Large molecules with aromatic and heteroatomic (O and N) groups, including charge transfer complexes, might have greatly contributed to the light absorption by the fraction F4, which is the largest fraction of the extracted water-insoluble organic matter.

Aerosol characteristics and sources in Yangzhou, China resolved by offline aerosol mass spectrometry and other techniques

Detailed chemical characterization of fine aerosols (PM2.5) is important for reducing air pollution in densely populated areas, such as the Yangtze River Delta region in China. This study systematically analyzed PM2.5 samples collected during November 2015 to April 2016 in urban Yangzhou using a suite of techniques, in particular, an Aerodyne soot particle aerosol mass spectrometry (SP-AMS). The techniques used here reconstructed the majority of total PM2.5 measured where extracted species comprised on average 91.2%. Source analyses of inorganic components showed that secondary nitrate, sulfate and chloride were the major species, while primary sources including biomass burning, coal combustion, traffic, industry and re-suspended dust due to nearby demolition activities, could contribute to other species. EC-tracer method estimated that the organic matter (OM) was composed of 65.4% secondary OM (SOM) and 34.6% primary OM (POM), while the SP-AMS analyses showed that the OM was comprised of 60.3% water-soluble OM (WSOM) and 39.7% water-insoluble OM (WIOM). Correlation analyses suggested that WSOM might be rich in secondary organic species, while WIOM was likely mainly comprised of primary organic species. We further conducted positive matrix factorization (PMF) analyses on the WSOM, and identified three primary factors including traffic, cooking and biomass burning, and two secondary factors. We found the secondary factors dominated WSOM mass (68.1%), and their mass contributions increased with the increase of WSOM concentrations. Relatively small contribution of primary sources to WSOM was probably due to their low water solubility, which should be investigated further in future. Overall, our findings improve understanding of the complex aerosol sources and chemistry in this region.

Influence of fireworks displays on the chemical characteristics of PM2.5 in rural and suburban areas in Central and East China

To explore the spatial and chemical characteristics of PM2.5 pollution and the influence of fireworks displays on PM2.5 and its chemical components in rural areas in Central and East China, PM2.5 samples were collected at three rural sites and one suburban site in Henan and Shandong provinces during the 2016 Chinese New Year, and the chemical composition of PM2.5, including water-soluble inorganic ions (WSIIs), organic carbon (OC), elemental carbon (EC), water-soluble organic carbon (WSOC) and trace elements (TEs) was analysed. The concentrations of PM2.5 at the four sites were significantly higher than the Grade I national standard of 35μg/m3, indicating serious PM2.5 pollution in rural and suburban areas. The contributions of secondary WSIIs to total WSIIs at the four sites were lower than in urban areas. The TEs in XP and LC were significantly enriched in PM2.5. A significant difference was found in the main chemical compositions of different sites. Fireworks displays directly increased the concentrations of PM2.5 and many chemicals, especially K+, Cl−, K, Cl, S, Cu and Sr, and concentrations of NO3− and NH4+ ions peaked after the fireworks period in the three rural sites, indicating the influence of firecrackers on the secondary formation of the precursors of NO2. The ratio of WSOC/OC decreased during fireworks displays, indicating the direct influence of firecrackers on water insoluble organic matter. Fireworks-related ions were a key component of the aerosol at the four sites during fireworks displays, accounting for 28–38% of the total measured species.

Marine submicron aerosol gradients, sources and sinks

Abstract. Aerosol principal sources and sinks over eastern North Atlantic waters were studied through the deployment of an aerosol chemistry gradient sampling system. The chemical gradients of primary and secondary aerosol components – specifically, sea salt (SS), water-insoluble organic matter (WIOM), water-soluble organic matter (WSOM), nitrate, ammonium, oxalate, amines, methanesulfonic acid (MSA) and water-soluble organic nitrogen (WSON) – were examined in great detail. Sea salt fluxes were estimated by the boundary layer box model and ranged from 0.3 to 3.5 ng m−2 s−1 over the wind speed range of 5–12 m s−1 and compared well with the derived fluxes from existing sea salt source parameterisations. The observed seasonal pattern of sea salt gradients was mainly driven by wind stress in addition to the yet unquantified effect of marine OM modifying fractional contributions of SS and OM in sea spray. WIOM gradients were a complex combination of rising and waning biological activity, especially in the flux footprint area, and wind-driven primary sea spray production supporting the coupling of recently developed sea spray and marine OM parameterisations.

Impact of diagenetic alteration on brachiopod shell magnesium isotope (δ26Mg) signatures: Experimental versus field data

Due to their thermodynamically stable low-Mg calcite mineralogy, the shells of brachiopods are often counted among the most reliable archives of the physicochemical conditions that occurred during the Phanerozoic in marine waters. Consequently, traditional and non-traditional isotope and elemental proxy data from brachiopod valves have been analyzed in numerous studies and results obtained have been placed in context with ancient seawater properties. This paper tests the sensitivity of brachiopod shell magnesium isotope (δ26Mg) data to diagenetic alteration. We apply a dual approach by: (i) performing hydrothermal alteration experiments using meteoric, marine, and burial reactive fluids; and (ii) comparing these data to naturally altered, ancient brachiopod shells. The degree of alteration of individual shells is assessed by a combination of fluorescence and cathodoluminescence microscopy. The absence of luminescence might indicate both well-preserved shell material, but also the secondary enrichment of quenching elements such as iron along diagenetic pathways. Complementary oxygen isotope data provide insight into the question of open versus closed system behavior of brachiopod shells. Brachiopod shell magnesium isotope values respond to differential fluid temperature, chemistry, and experiment durations. The patterns observed are complicated by the interplay of kinetic and thermodynamic patterns and the presence of variable amounts of water soluble and water insoluble organic matter within these biominerals. Generally, the range in bulk δ26Mg from experimentally altered (1.52‰) and that of bulk samples from ancient, diagenetically altered brachiopod valves (1.53‰) exceed the geochemical variability of δ26Mgbrachiopod bulk values of most recent specimens (1.26‰) in the lower and upper range. More 26Mg enriched (0.8‰) and more 26Mg depleted (0.7‰) values, respectively, are found in altered shells in comparison to unaltered ones. The data shown here are considered significant for those aiming to reconstruct palaeoenvironmental parameters based on brachiopod archives. Consequently, we propose tentative guidelines for magnesium isotope research applied to ancient carbonates.

Chemical Structural Characteristics of HULIS and Other Fractionated Organic Matter in Urban Aerosols: Results from Mass Spectral and FT-IR Analysis

The chemical characteristics of complex organic matter in atmospheric aerosols remain poorly understood. Water-insoluble organic matter (WISOM) and water-soluble organic matter (WSOM) in the total suspended particulates collected in the city of Nagoya in summer/early autumn and winter were extracted using multiple solvents. Two fractions of humic-like substances, showing neutral and acidic behavior (HULIS-n and HULIS-a, respectively), and the remaining highly polar part (HP-WSOM) were fractionated from WSOM using solid phase extraction. The chemical structural characteristics and concentrations of the organic matter were investigated using mass spectrometry and Fourier transform infrared (FT-IR) spectroscopy. WISOM and HULIS-n had low O/C ratios (0.1 and 0.4, respectively) and accounted for a large fraction of the organics in aerosols (70%). HULIS-a and HP-WSOM had higher O/C ratios (0.7 and 1.0, respectively), and their concentrations in summer and early autumn were on average ∼2 times higher than those in winter. The mass spectrum and FT-IR analyses suggest the following: (1) WISOM were high-molecular-weight aliphatics (primarily C27-C32) with small proportions of -CH3, -OH, and C═O groups; (2) HULIS-n was abundant in aliphatic structures and hydroxyl groups (primarily C9-C18) and by branched structures; (3) HULIS-a and HP-WSOM contained relatively large amounts of low-molecular-weight carboxylic acids and alcohols (primarily C4-C10); and (4) WISOM and HULIS-n were relatively abundant in amines and organic nitrates.

Using the chemical equilibrium partitioning space to explore factors influencing the phase distribution of compounds involved in secondary organic aerosol formation

Abstract. Many atmospheric and chemical variables influence the partitioning equilibrium between gas phase and condensed phases of compounds implicated in the formation of secondary organic aerosol (SOA). The large number of factors and their interaction makes it often difficult to assess their relative importance and concerted impact. Here we introduce a two-dimensional space which maps regions of dominant atmospheric phase distribution within a coordinate system defined by equilibrium partition coefficients between the gas phase, an aqueous phase and a water-insoluble organic matter (WIOM) phase. Placing compounds formed from the oxidation of n-alkanes, terpenes and mono-aromatic hydrocarbons on the maps based on their predicted partitioning properties allows for a simple graphical assessment of their equilibrium phase distribution behaviour. Specifically, it allows for the simultaneous visualisation and quantitative comparison of the impact on phase distribution of changes in atmospheric parameters (such as temperature, salinity, WIOM-phase polarity, organic aerosol load, and liquid water content) and chemical properties (such as oxidation state, molecular size, functionalisation, and dimerisation). The graphical analysis reveals that the addition of hydroxyl, carbonyl and carboxyl groups increases the affinity of aliphatic, alicyclic and aromatic hydrocarbons for the aqueous phase more rapidly than their affinity for WIOM, suggesting that the aqueous phase may often be relevant even for substances that are considerably larger than the C2 and C3 compounds that are typically believed to be associated with aqueous SOA. In particular, the maps identify some compounds that contribute to SOA formation if partitioning to both WIOM and aqueous phase is considered but would remain in the gas phase if either condensed phase were neglected. For example, many semi-volatile α-pinene oxidation products will contribute to aqueous SOA under the conditions of high liquid water content encountered in clouds but would remain vapours in wet aerosol. It is conceivable to develop parameterisations of "partitioning basis sets" that group compounds with comparable partitioning properties, which – when combined with data on the abundance of those groups of compounds – could serve in the simulation of SOA formation.

Novel methods for predicting gas–particle partitioning during the formation of secondary organic aerosol

Abstract. Several methods have been presented in the literature to predict an organic chemical's equilibrium partitioning between the water insoluble organic matter (WIOM) component of aerosol and the gas phase, Ki,WIOM, as a function of temperature. They include (i) polyparameter linear free energy relationships calibrated with empirical aerosol sorption data, as well as (ii) the solvation models implemented in SPARC and (iii) the quantum-chemical software COSMOtherm, which predict solvation equilibria from molecular structure alone. We demonstrate that these methods can be used to predict Ki,WIOM for large numbers of individual molecules implicated in secondary organic aerosol (SOA) formation, including those with multiple functional groups. Although very different in their theoretical foundations, these methods give remarkably consistent results for the products of the reaction of normal alkanes with OH, i.e. their partition coefficients Ki,WIOM generally agree within one order of magnitude over a range of more than ten orders of magnitude. This level of agreement is much better than that achieved by different vapour pressure estimation methods that are more commonly used in the SOA community. Also, in contrast to the agreement between vapour pressure estimates, the agreement between the Ki,WIOM estimates does not deteriorate with increasing number of functional groups. Furthermore, these partitioning coefficients Ki,WIOM predicted SOA mass yields in agreement with those measured in chamber experiments of the oxidation of normal alkanes. If a Ki,WIOM prediction method was based on one or more surrogate molecules representing the solvation properties of the mixed OM phase of SOA, the choice of those molecule(s) was found to have a relatively minor effect on the predicted Ki,WIOM, as long as the molecule(s) are not very polar. This suggests that a single surrogate molecule, such as 1-octanol or a hypothetical SOA structure proposed by Kalberer et al. (2004), may often be sufficient to represent the WIOM component of the SOA phase, greatly simplifying the prediction. The presented methods could substitute for vapour-pressure-based methods in studies such as the explicit modelling of SOA formation from single precursor molecules in chamber experiments.

Chemical characterization and source apportionment of indoor and outdoor fine particulate matter (PM2.5) in retirement communities of the Los Angeles Basin

Concurrent indoor and outdoor measurements of fine particulate matter (PM2.5) were conducted at three retirement homes in the Los Angeles Basin during two separate phases (cold and warm) between 2005 and 2006. Indoor-to-outdoor relationships of PM2.5 chemical constituents were determined and sources of indoor and outdoor PM2.5 were evaluated using a molecular marker-based chemical mass balance (MM-CMB) model. Indoor levels of elemental carbon (EC) along with metals and trace elements were found to be significantly affected by outdoor sources. EC, in particular, displayed very high indoor-to-outdoor (I/O) mass ratios accompanied by strong I/O correlations, illustrating the significant impact of outdoor sources on indoor levels of EC. Similarly, indoor levels of polycyclic aromatic hydrocarbons (PAHs), hopanes, and steranes were strongly correlated with their outdoor components and displayed I/O ratios close to unity. On the other hand, concentrations of n-alkanes and organic acids inside the retirement communities were dominated by indoor sources (e.g. food cooking and consumer products), as indicated by their I/O ratios, which exceeded unity. Source apportionment results revealed that vehicular emissions were the major contributor to both indoor and outdoor PM2.5, accounting for 39 and 46% of total mass, respectively. Moreover, the contribution of vehicular sources to indoor levels was generally comparable to its corresponding outdoor estimate. Other water-insoluble organic matter (other WIOM), which accounts for emissions from uncharacterized primary biogenic sources, displayed a wider range of contributions, varying from 2 to 73% of PM2.5, across all sites and phases of the study. Lastly, higher indoor than outdoor contribution of other water-soluble organic matter (other WSOM) was evident at some of the sites, suggesting the production of secondary aerosols as well as direct emissions from primary sources (including cleaning or other consumer products) at the indoor environments.