On the implications of aerosol liquid water and phase separation for modeled organic aerosol mass

Water is an important component of PM2.5 Many traditional SOA species are highly soluble and thus can be considered extractable Water can influence the partitioning of compounds traditionally considered insoluble in models Organic aerosol takes up water according to RH Organic aerosol interacts with inorganic water Deviations in ideality (solubility) must be considered

Using Advanced Mass Spectrometry Techniques to Fully Characterize Atmospheric Organic Carbon: Current Capabilities and Remaining Gaps

Organic compounds in the atmosphere vary widely in their molecular composition and chemical properties, so no single instrument can reasonably measure the entire range of ambient compounds. Over the past decade, a new generation of in-situ, field-deployable mass spectrometers has dramatically improved our ability to detect, identify, and quantify these organic compounds, but no systematic approach has been developed to assess the extent to which currently available tools capture the entire space of chemical identity and properties that is expected in the atmosphere. Reduced-parameter frameworks that have been developed to describe atmospheric mixtures are exploited here to characterize the range of chemical properties accessed by a suite of instruments. Multiple chemical spaces (e.g. oxidation state of carbon vs. volatility, and oxygen number vs. carbon number) were populated with ions measured by several mass spectrometers, with gas- and particle-phase -pinene oxidation products serving as the test mixture of organic compounds. Few gaps are observed in the coverage of the parameter spaces by the instruments employed in this work, though the full extent to which comprehensive measurement was achieved is difficult to assess due to uncertainty in the composition of the mixture. Overlaps between individual ions and regions in parameter space were identified, both between gas- and particle-phase measurements, and within each phase. These overlaps were conservatively found to account for little (<10%) of the measured mass. However, challenges in identifying overlaps and in accurately converting molecular formulas into chemical properties (such as volatility or reactivity) highlight a continued need to incorporate structural information into atmospheric measurements

Field intercomparison of the gas/particle partitioning of oxygenated organics during the Southern Oxidant and Aerosol Study (SOAS) in 2013

We present results of the first intercomparison of real-time instruments for gas/particle partitioning of organic species. Four recently-developed instruments that directly measure gas/particle partitioning in near-real time were deployed in Centreville, Alabama during the Southern Oxidant Aerosol Study (SOAS) in 2013. Two instruments were filter inlet for gases and aerosols high-resolution chemical ionization mass spectrometers (FIGAERO-HRToF-CIMS) with acetate (A-CIMS) and iodide (I-CIMS) ionization sources, respectively; the third was a semi-volatile thermal desorption aerosol GC-MS (SV-TAG); and the fourth was a high-resolution thermal desorption proton-transfer reaction mass spectrometer (HR-TD-PTRMS). Signals from these instruments corresponding to several organic acids were chosen for comparison. The campaign average partitioning fractions show good correlation. A similar level of agreement with partitioning theory is observed. Thus the intercomparison exercise shows promise for these new measurements, as well as some confidence on the measurement of low versus high particle-phase fractions. However, detailed comparison show several systematic differences that lie beyond estimated measurement errors. These differences may be due to at least eight different effects: (1) underestimation of uncertainties under low signal-to-noise; (2) inlet and/or instrument adsorption/desorption of gases; (3) differences in particle size ranges sampled; (4) differences in the methods used to quantify instrument backgrounds; (5) errors in high-resolution fitting of overlapping ion groups; (6) differences in the species included in each measurement due to different instrument sensitivities; and differences in (7) negative or (8) positive thermal decomposition (or ion fragmentation) artifacts. The available data are insufficient to conclusively identify the reasons, but evidence from these instruments and available data from an ion mobility spectrometer shows the particular importance of effects 6–8 in several cases. This comparison highlights the difficulty of this measurement and its interpretation in a complex ambient environment, and the need for further improvements in measurement methodologies, including isomer separation, and detailed study of the possible factors leading to the observed differences. Further intercomparisons under controlled laboratory and field conditions are strongly recommended

Soil gas composition - remediated VA residences

Composition of soil gas at the site of remediated home heating oil discharges in Virginia, United States. Samples are collected at a depth of ~2 meters at or near the exact location of a remediated underground storage tank. Gases are sampled onto an adsorbent tube and analyzed by gas chromatography coupled to mass spectrometry. Composition is characterized by total mass concentration (ug/m3) of each hydrocarbon group defined by the number of carbon atoms (N_C) and number of degrees of unsaturation (N_DBE), with saturated and mono-unsaturated (N_DBE = 1) classes further broken down into branched and unbranched compounds. Each sample is listed by a unique number, and a sequential site number indicating at which site the sample was collected; all identifying information has been removed to ensure compliance with university-approved privacy protocols. Methodological details are described in Isaacman-VanWertz et al., doi: 10.1021/acs.analchem.0c02308 . R2 changes: Added concentrations of benzene and toluene. Added Hazard Quotient of TPH and cancer risk of benzene, ethylbenzene (treating all mass with N_C = 8, ND_BE = 4 as ethylbenzene) and naphthalene

Soil gas composition - remediated VA residences

Composition of soil gas at the site of remediated home heating oil discharges in Virginia, United States. Samples are collected at a depth of ~2 meters at or near the exact location of a remediated underground storage tank. Gases are sampled onto an adsorbent tube and analyzed by gas chromatography coupled to mass spectrometry. Composition is characterized by total mass concentration (ug/m3) of each hydrocarbon group defined by the number of carbon atoms (N_C) and number of degrees of unsaturation (N_DBE), with saturated and mono-unsaturated (N_DBE = 1) classes further broken down into branched and unbranched compounds. Each sample is listed by a unique number, and a sequential site number indicating at which site the sample was collected; all identifying information has been removed to ensure compliance with university-approved privacy protocols. Methodological details are described in Isaacman-VanWertz et al., doi: 10.1021/acs.analchem.0c02308

SMILES and physicochemical parameters - pinene, decane, toluene oxidation products

This dataset includes 182,127 SMILES strings generated by 5 generations of oxidation using the GECKO-A model for alpha-pinene, decane, and toluene under typical continental atmospheric conditions. For each compound, physicochemical parameters (vapor pressure, Henry's law constant, and gas phase reaction rate constant with the hydroxyl radical) are estimated using several structure-activity relationships. Compounds are flagged according to in which oxidation systems they exceed a threshold of 0.1% of total modeled mass of their given molecular formula. Descriptions of this dataset and the parameter estimation are provided in Isaacman-VanWertz and Aumont, "Impact of organic molecular structure on the estimation of atmospherically relevant physicochemical parameters", Atmospheric Chemistry and Physics. The subset of compounds 38,594 compounds used in the core analyses of that work are also flagged

Soil gas composition - remediated VA residences

Composition of soil gas at the site of remediated home heating oil discharges in Virginia, United States. Samples are collected at a depth of ~2 meters at or near the exact location of a remediated underground storage tank. Gases are sampled onto an adsorbent tube and analyzed by gas chromatography coupled to mass spectrometry. Composition is characterized by total mass concentration (ug/m3) of each hydrocarbon group defined by the number of carbon atoms (N_C) and number of degrees of unsaturation (N_DBE), with saturated and mono-unsaturated (N_DBE = 1) classes further broken down into branched and unbranched compounds. Each sample is listed by a unique number, and a sequential site number indicating at which site the sample was collected; all identifying information has been removed to ensure compliance with university-approved privacy protocols. Methodological details are described in Isaacman-VanWertz et al., doi: 10.1021/acs.analchem.0c02308 . R2 changes: Added concentrations of benzene and toluene. Added Hazard Quotient of TPH and cancer risk of benzene, ethylbenzene (treating all mass with N_C = 8, ND_BE = 4 as ethylbenzene) and naphthalene

Soil gas composition - remediated VA residences

Composition of soil gas at the site of remediated home heating oil discharges in Virginia, United States. Samples are collected at a depth of ~2 meters at or near the exact location of a remediated underground storage tank. Gases are sampled onto an adsorbent tube and analyzed by gas chromatography coupled to mass spectrometry. Composition is characterized by total mass concentration (ug/m3) of each hydrocarbon group defined by the number of carbon atoms (N_C) and number of degrees of unsaturation (N_DBE), with saturated and mono-unsaturated (N_DBE = 1) classes further broken down into branched and unbranched compounds. Each sample is listed by a unique number, and a sequential site number indicating at which site the sample was collected; all identifying information has been removed to ensure compliance with university-approved privacy protocols. Methodological details are described in Isaacman-VanWertz et al., doi: 10.1021/acs.analchem.0c02308