Person: Keutsch, Frank
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Keutsch
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Keutsch, Frank
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Publication Formaldehyde (HCHO) As a Hazardous Air Pollutant: Mapping Surface Air Concentrations from Satellite and Inferring Cancer Risks in the United States(American Chemical Society (ACS), 2017-05-05) Zhu, Lei; Jacob, Daniel; Keutsch, Frank; Mickley, Loretta; Scheffe, Richard; Strum, Madeleine; González Abad, Gonzalo; Chance, Kelly; Yang, Kai; Rappenglück, Bernhard; Millet, Dylan; Baasandorj, Munkhbayar; Jaeglé, Lyatt; Shah, ViralFormaldehyde (HCHO) is the most important carcinogen in outdoor air among the 187 hazardous air pollutants (HAPs) identified by the U.S. Environmental Protection Agency (EPA), not including ozone and particulate matter. However, surface observations of HCHO are sparse and the EPA monitoring network could be prone to positive interferences. Here we use 2005–2016 summertime HCHO column data from the OMI satellite instrument, validated with high-quality aircraft data and oversampled on a 5 × 5 km2 grid, to map surface air HCHO concentrations across the contiguous U.S. OMI-derived summertime HCHO values are converted to annual averages using the GEOS-Chem chemical transport model. Results are in good agreement with high-quality summertime observations from urban sites (−2% bias, r = 0.95) but a factor of 1.9 lower than annual means from the EPA network. We thus estimate that up to 6600–12 500 people in the U.S. will develop cancer over their lifetimes by exposure to outdoor HCHO. The main HCHO source in the U.S. is atmospheric oxidation of biogenic isoprene, but the corresponding HCHO yield decreases as the concentration of nitrogen oxides (NOx ≡ NO + NO2) decreases. A GEOS-Chem sensitivity simulation indicates that HCHO levels would decrease by 20–30% in the absence of U.S. anthropogenic NOx emissions. Thus, NOx emission controls to improve ozone air quality have a significant cobenefit in reducing HCHO-related cancer risks.Publication Atmospheric Chemistry and the Biosphere: General Discussion(Royal Society of Chemistry (RSC), 2017) Archibald, Alexander; Freedman, Arnold; Bejan, Lustian; Brown, Steven; Brüggemann, Martin; Carpenter, Lucy; Collins, John; Evans, Mathew; Finlayson-Pitts, Barbara; George, Christian; Hastings, Meredith; Heard, Dwayne; Hewitt, Christopher; Isaacman-VanWertz, Gabriel; Kalberer, Markus; Keutsch, Frank; Kiendler-Scharr, Astrid; Knopf, Daniel; Lelieveld, Jos; Marais, Eloise; Petzold, Andreas; Ravishankara, A.; Reid, Jonathan; Rovelli, Grazia; Scott, Catherine; Sherwen, Tomás; Shindell, Drew; Tinel, Liselotte; Unger, Nadine; Wallington, Timothy J.; Wahner, Andreas; Williams, Jonathan; Young, Timothy; Zelenyuk, Alla; Wallington, TimothyLucy Carpenter opened discussion of the paper by Christian George: Your previous work has emphasised the abiotic production of VOCs from surface ocean processes, mainly from photosensitized chemistry of surfactants. Does this work indicate that decay of microbial cells is the really dominant source of these VOC-producing surfactants and photosensitizers, and if so - does this really mean this is an abiotic process? Christian George responded: As shown in our paper, VOC emissions increased drastically when the microbial cells were dying. Moreover, the highest VOC production was observed for the cellular fraction of the biofilms, i.e. intracellular material and cellular debris.Publication Polloneite, a New Complex Pb(-Ag)-as-Sb Sulfosalt From the Pollone Mine, Apuan Alps, Tuscany, Italy(Mineralogical Society, 2017-12) Topa, Dan; Keutsch, Frank; Makovicky, Emil; Kolitsch, Uwe; Paar, WernerPolloneite, ideally AgPb46As26Sb23S120, is a new N = 4 member of the sartorite homologous series. It occurs in a matrix of baryte from the Pizzone level of the Pollone baryte-pyrite-(Pb-Zn-Ag) deposit at Valdicastello Carducci, near Pietrasanta, in the Apuan Alps, Tuscany, Italy, as anhedral grains up to 0.5 mm across. The mineral is opaque, greyish black with a metallic lustre. In reflected light polloneite is white, bireflectance is moderate. Internal reflections are absent. Under crossed polars, anisotropism is moderate with rotation tints in brown-violet and deep grey. The reflectance data (%, air) are: 30.2, 42.4 at 470 nm, 28.8, 41.0 at 546 nm, 27.9, 39.8 at 589 nm and 26.0, 37.4 at 650 nm. Mohs hardness is 3–3½, microhardness VHN50 exhibits a mean value of 200 kg mm-2. The average results of 15 electronmicroprobe analyses of three grains are Ag 0.71(5), Pb 52.05(21), As 10.61(22), Sb 15.40(12), S 21.16(8), total 99.92(15) wt.%, corresponding to Ag1.20Pb45.76As25.79Sb23.04S120.21 (on the basis of Me + S = 216 apfu). The simplified formula AgPb46As26Sb23S120 is in accordance with the results of a crystal structure determination. The calculated density is 5.77 g cm–3. Polloneite is monoclinic, space group P21, a = 8.413(2), b = 25.901(5), c = 23.818(5) Å, β = 90.01(3)°, V = 5189.8(18)Å3, Z = 1. The strongest eight lines in the calculated powder-diffraction pattern [d in Å(I)hkl] are 3.795(100)(026), 3.414(60)(233), 3.238(69)(080), 3.020(97)(253), 2.922(82)(066), 2.738(73)(236), 2.375(79)(290) and 2.103(64)(400). Polloneite is a new N = 4 member of the sartorite homologous series with substantial Sb and small, but important, Ag content. It is a three-fold superstructure with a tripled unit-cell parameter, 7.9 Å, of sartorite homologues. In the As-Sb rich slabs, several types of crankshaft chains and isolated (As,Sb)–S polyhedra occur. A sequence of three different, tightly bonded double-layer fragments (broad ribbons) contains two asymmetric fragments with long crankshaft chains whereas the third fragment type, with Ag, contains small mirror-symmetrical metalloid groups and no crankshaft chains. This configuration can potentially cause order-disorder phenomena in the structure. The threefold superstructure and the mixed As-Sb character distinguish polloneite from veenite and from dufrénoysite, respectively.Publication Observations of VOC Emissions and Photochemical Products Over US Oil- and Gas-Producing Regions Using High-Resolution H3O+ CIMS (PTR-ToF-MS)(Copernicus GmbH, 2017-08-16) Koss, Abigail; Yuan, Bin; Warneke, Carsten; Gilman, Jessica; Lerner, Brian; Veres, Patrick; Peischl, Jeff; Eilerman, Scott; Wild, Robert; Brown, Steven; Thompson, Chelsea; Ryerson, Thomas; Hanisco, Thomas; Wolfe, Glenn; St. Clair, Jason; Thayer, Mitchell; Keutsch, Frank; Murphy, Shane; de Gouw, JoostAbstract. VOCs related to oil and gas extraction operations in the United States were measured by H3O+ chemical ionization time-of-flight mass spectrometry (H3O+ ToF-CIMS/PTR-ToF-MS) from aircraft during the Shale Oil and Natural Gas Nexus (SONGNEX) campaign in March–April 2015. This work presents an overview of major VOC species measured in nine oil- and gas-producing regions, and a more detailed analysis of H3O+ ToF-CIMS measurements in the Permian Basin within Texas and New Mexico. Mass spectra are dominated by small photochemically produced oxygenates and compounds typically found in crude oil: aromatics, cyclic alkanes, and alkanes. Mixing ratios of aromatics were frequently as high as those measured downwind of large urban areas. In the Permian, the H3O+ ToF-CIMS measured a number of underexplored or previously unreported species, including aromatic and cycloalkane oxidation products, nitrogen heterocycles including pyrrole (C4H5N) and pyrroline (C4H7N), H2S, and a diamondoid (adamantane) or unusual monoterpene. We additionally assess the specificity of a number of ion masses resulting from H3O+ ion chemistry previously reported in the literature, including several new or alternate interpretations.Publication Isoprene photo-oxidation products quantify the effect of pollution on hydroxyl radicals over Amazonia(American Association for the Advancement of Science, 2018) Liu, Yingjun; Seco, Roger; Kim, Saewung; Guenther, Alex B.; Goldstein, Allen H.; Keutsch, Frank; Springston, Stephen R.; Watson, Thomas B.; Artaxo, Paulo; Souza, Rodrigo A. F.; McKinney, Karena; Martin, ScotNitrogen oxides (NOx) emitted from human activities are believed to regulate the atmospheric oxidation capacity of the troposphere. However, observational evidence is limited for the low-to-median NOx concentrations prevalent outside of polluted regions. Directly measuring oxidation capacity, represented primarily by hydroxyl radicals (OH), is challenging, and the span in NOx concentrations at a single observation site is often not wide. Concentrations of isoprene and its photo-oxidation products were used to infer the equivalent noontime OH concentrations. The fetch at an observation site in central Amazonia experienced varied contributions from background regional air, urban pollution, and biomass burning. The afternoon concentrations of reactive nitrogen oxides (NOy), indicative of NOx exposure during the preceding few hours, spanned from 0.3 to 3.5 parts per billion. Accompanying the increase of NOy concentration, the inferred equivalent noontime OH concentrations increased by at least 250% from 0.6 × 106 to 1.6 × 106 cm−3. The conclusion is that, compared to background conditions of low NOx concentrations over the Amazon forest, pollution increased NOx concentrations and amplified OH concentrations, indicating the susceptibility of the atmospheric oxidation capacity over the forest to anthropogenic influence and reinforcing the important role of NOx in sustaining OH concentrations.Publication Airborne measurements of organosulfates over the continental U.S.(John Wiley & Sons, Ltd, 2015) Liao, Jin; Froyd, Karl D; Murphy, Daniel M; Keutsch, Frank; Yu, Ge; Wennberg, Paul O; St Clair, Jason M; Crounse, John D; Wisthaler, Armin; Mikoviny, Tomas; Jimenez, Jose L; Campuzano-Jost, Pedro; Day, Douglas A; Hu, Weiwei; Ryerson, Thomas B; Pollack, Ilana B; Peischl, Jeff; Anderson, Bruce E; Ziemba, Luke D; Blake, Donald R; Meinardi, Simone; Diskin, GlennOrganosulfates are important secondary organic aerosol (SOA) components and good tracers for aerosol heterogeneous reactions. However, the knowledge of their spatial distribution, formation conditions, and environmental impact is limited. In this study, we report two organosulfates, an isoprene-derived isoprene epoxydiols (IEPOX) (2,3-epoxy-2-methyl-1,4-butanediol) sulfate and a glycolic acid (GA) sulfate, measured using the NOAA Particle Analysis Laser Mass Spectrometer (PALMS) on board the NASA DC8 aircraft over the continental U.S. during the Deep Convective Clouds and Chemistry Experiment (DC3) and the Studies of Emissions and Atmospheric Composition, Clouds, and Climate Coupling by Regional Surveys (SEAC4RS). During these campaigns, IEPOX sulfate was estimated to account for 1.4% of submicron aerosol mass (or 2.2% of organic aerosol mass) on average near the ground in the southeast U.S., with lower concentrations in the western U.S. (0.2–0.4%) and at high altitudes (<0.2%). Compared to IEPOX sulfate, GA sulfate was more uniformly distributed, accounting for about 0.5% aerosol mass on average, and may be more abundant globally. A number of other organosulfates were detected; none were as abundant as these two. Ambient measurements confirmed that IEPOX sulfate is formed from isoprene oxidation and is a tracer for isoprene SOA formation. The organic precursors of GA sulfate may include glycolic acid and likely have both biogenic and anthropogenic sources. Higher aerosol acidity as measured by PALMS and relative humidity tend to promote IEPOX sulfate formation, and aerosol acidity largely drives in situ GA sulfate formation at high altitudes. This study suggests that the formation of aerosol organosulfates depends not only on the appropriate organic precursors but also on emissions of anthropogenic sulfur dioxide (SO2), which contributes to aerosol acidity. Key Points IEPOX sulfate is an isoprene SOA tracer at acidic and low NO conditions Glycolic acid sulfate may be more abundant than IEPOX sulfate globally SO2 impacts IEPOX sulfate by increasing aerosol acidity and water uptakePublication Glyoxal Yield From Isoprene Oxidation and Relation to Formaldehyde: Chemical Mechanism, Constraints From SENEX Aircraft Observations, and Interpretation of OMI Satellite Data(Copernicus GmbH, 2017-07-18) Miller, Christopher; Jacob, Daniel; Marais, Elose; Yu, Karen; Travis, Katherine; Kim, Patrick S.; Fisher, Jenny A.; Zhu, Lei; Wolfe, Glenn M.; Hanisco, Thomas F.; Keutsch, Frank; Kaiser, Jennifer; Min, Kyung-Eun; Brown, Steven S.; Washenfelder, Rebecca A.; Gonzalez Abad, Gonzalo; Chance, KellyGlyoxal (CHOCHO) is produced in the atmosphere by the oxidation of volatile organic compounds (VOCs). Like formaldehyde (HCHO), another VOC oxidation product, it is measurable from space by solar backscatter. Isoprene emitted by vegetation is the dominant source of CHOCHO and HCHO in most of the world. We use aircraft observations of CHOCHO and HCHO from the SENEX campaign over the southeast US in summer 2013 to better understand the CHOCHO time-dependent yield from isoprene oxidation, its dependence on nitrogen oxides (NOx ≡ NO + NO2), the behavior of the CHOCHO–HCHO relationship, the quality of OMI CHOCHO satellite observations, and the implications for using CHOCHO observations from space as constraints on isoprene emissions. We simulate the SENEX and OMI observations with the Goddard Earth Observing System chemical transport model (GEOS-Chem) featuring a new chemical mechanism for CHOCHO formation from isoprene. The mechanism includes prompt CHOCHO formation under low-NOx conditions following the isomerization of the isoprene peroxy radical (ISOPO2). The SENEX observations provide support for this prompt CHOCHO formation pathway, and are generally consistent with the GEOS-Chem mechanism. Boundary layer CHOCHO and HCHO are strongly correlated in the observations and the model, with some departure under low-NOx conditions due to prompt CHOCHO formation. SENEX vertical profiles indicate a free-tropospheric CHOCHO background that is absent from the model. The OMI CHOCHO data provide some support for this free-tropospheric background and show southeast US enhancements consistent with the isoprene source but a factor of 2 too low. Part of this OMI bias is due to excessive surface reflectivities assumed in the retrieval. The OMI CHOCHO and HCHO seasonal data over the southeast US are tightly correlated and provide redundant proxies of isoprene emissions. Higher temporal resolution in future geostationary satellite observations may enable detection of the prompt CHOCHO production under low-NOx conditions apparent in the SENEX data.Publication Technical note: Conversion of isoprene hydroxy hydroperoxides (ISOPOOHs) on metal environmental simulation chamber walls(Copernicus GmbH, 2017-03-24) Bernhammer, Anne-Kathrin; Breitenlechner, Martin; Keutsch, Frank; Hansel, ArminSources and sinks of isoprene oxidation products from low-NOx isoprene chemistry have been studied at the CERN CLOUD (Cosmics Leaving Outdoor Droplets) chamber with a custom-built selective reagent ion time-of-flight mass spectrometer (SRI-ToF-MS), which allows quantitative measurement of isoprene hydroxy hydroperoxides (ISOPOOHs). The measured concentrations of the main oxidation products were compared to chemical box model simulations based on the Leeds Master Chemical Mechanism (MCM) v3.3. The modeled ISOPOOH concentrations are a factor of 20 higher than the observed concentrations, and methyl vinyl ketone (MVK) and methacrolein (MACR) concentrations are up to a factor of 2 lower compared to observations, despite the artifact-free detection method. Addition of catalytic conversion of 1,2-ISOPOOH and 4,3-ISOPOOH to methyl vinyl ketone (MVK) and methacrolein (MACR) on the stainless-steel surface of the chamber to the chemical mechanism resolves the discrepancy between model predictions and observation. This suggests that isoprene chemistry in a metal chamber under low-NOx conditions cannot be described by a pure gas phase model alone. Biases in the measurement of ISOPOOH, MVK, and MACR can be caused not only intra-instrumentally but also by the general experimental setup. The work described here extends the role of heterogeneous reactions affecting gas phase composition and properties from instrumental surfaces, described previously, to general experimental setups. The role of such conversion reactions on real environmental surfaces is yet to be explored.Publication Molecular Composition and Volatility of Isoprene Photochemical Oxidation Secondary Organic Aerosol Under Low- and High-NOx Conditions(Copernicus GmbH, 2017-01-04) D'Ambro, Emma; Leeming, Benjamin; Liu, Jiumeng; Shilling, John; Gaston, Cassandra; Lopez-Hilfiker, Felipe; Schobesberger, Siegfried; Zaveri, Rahul; Mohr, Claudia; Lutz, Anna; Zhang, Zhenfa; Gold, Avram; Surratt, Jason; Rivera-Rios, Jean; Keutsch, Frank; Thornton, JoelWe present measurements of secondary organic aerosol (SOA) formation from isoprene photochemical oxidation in an environmental simulation chamber at a variety of oxidant conditions and using dry neutral seed particles to suppress acid-catalyzed multiphase chemistry. A high-resolution time-of-flight chemical ionization mass spectrometer (HR-ToF-CIMS) utilizing iodide-adduct ionization coupled to the Filter Inlet for Gases and Aerosols (FIGAERO) allowed for simultaneous online sampling of the gas and particle composition. Under high-HO2 and low-NO conditions, highly oxygenated (O:C ≥ 1) C5 compounds were major components (∼ 50%) of SOA. The SOA composition and effective volatility evolved both as a function of time and as a function of input NO concentrations. Organic nitrates increased in both the gas and particle phases as input NO increased, but the dominant non-nitrate particle-phase components monotonically decreased. We use comparisons of measured and predicted gas-particle partitioning of individual components to assess the validity of literature-based group-contribution methods for estimating saturation vapor concentrations. While there is evidence for equilibrium partitioning being achieved on the chamber residence timescale (5.2h) for some individual components, significant errors in group-contribution methods are revealed. In addition, >30% of the SOA mass, detected as low-molecular-weight semivolatile compounds, cannot be reconciled with equilibrium partitioning. These compounds desorb from the FIGAERO at unexpectedly high temperatures given their molecular composition, which is indicative of thermal decomposition of effectively lower-volatility components such as larger molecular weight oligomers.