Browsing by Author "Keutsch, Frank N."
Now showing 1 - 11 of 11
Results Per Page
Sort Options
Item Airborne measurements of organosulfates over the continental U.S(AGU Pubication, 2015-02-28) Liao, Jin; Froyd, Karl D.; Murphy, Daniel M.; Keutsch, Frank N.; Yu, Ge; Wennberg, Paul O.; St. Clair, Jason; 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.Item Emissions of Glyoxal and Other Carbonyl Compounds from Agricultural Biomass Burning Plumes Sampled by Aircraft(ACS Publications) Zarzana, Kyle J.; Min, Kyung-Eun; Washenfelder, Rebecca A.; Kaiser, Jennifer; Krawiec-Thayer, Mitchell; Peischl, Jeff; Neuman, J. Andrew; Nowak, John B.; Wagner, Nicholas L.; Dube, William P.; St. Clair, Jason; Wolfe, Glenn M.; Hanisco, Thomas F.; Keutsch, Frank N.; Ryerson, Thomas B.; Brown, Steven S.We report enhancements of glyoxal and methylglyoxal relative to carbon monoxide and formaldehyde in agricultural biomass burning plumes intercepted by the NOAA WP-3D aircraft during the 2013 Southeast Nexus and 2015 Shale Oil and Natural Gas Nexus campaigns. Glyoxal and methylglyoxal were measured using broadband cavity enhanced spectroscopy, which for glyoxal provides a highly selective and sensitive measurement. While enhancement ratios of other species such as methane and formaldehyde were consistent with previous measurements, glyoxal enhancements relative to carbon monoxide averaged 0.0016 ± 0.0009, a factor of 4 lower than values used in global models. Glyoxal enhancements relative to formaldehyde were 30 times lower than previously reported, averaging 0.038 ± 0.02. Several glyoxal loss processes such as photolysis, reactions with hydroxyl radicals, and aerosol uptake were found to be insufficient to explain the lower measured values of glyoxal relative to other biomass burning trace gases, indicating that glyoxal emissions from agricultural biomass burning may be significantly overestimated. Methylglyoxal enhancements were three to six times higher than reported in other recent studies, but spectral interferences from other substituted dicarbyonyls introduce an estimated correction factor of 2 and at least a 25% uncertainty, such that accurate measurements of the enhancements are difficult.Item Glyoxal yield from isoprene oxidation and relation to formaldehyde: chemical mechanism, constraints from SENEX aircraft observations, and interpretation of OMI satellite data(Copernicus Publications, 2017-07-18) Miller, Christopher Chan; Jacob, Daniel J.; Marais, Eloise A.; Yu, Karen; Travis, Katherine R.; Kim, Patrick S.; Fisher, Jenny A.; Zhu, Lei; Wolfe, Glenn M.; Hanisco, Thomas F.; Keutsch, Frank N.; Kaiser, Jennifer; Min, Kyung-Eun; Brown, Steven S.; Washenfelder, Rebecca A.; Abad, Gonzalo González; 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.Item Impact of evolving isoprene mechanisms on simulated formaldehyde: An inter-comparison supported by in situ observations from SENEX(Elsevier, 2017-05-30) Marvin, Margaret R.; Wolfe, Glenn M.; Salawitch, Ross J.; Canty, Timothy P.; Roberts, Sandra J.; Travis, Katherine R.; Aikin, Kenneth C.; Gouw, Joost A. de; Graus, Martin; Hanisco, Thomas F.; Holloway, John S.; Hübler, Gerhard; Kaiser, Jennifer; Keutsch, Frank N.; Peischl, Jeff; Pollack, Ilana B.; Roberts, James M.; Ryerson, Thomas B.; Veres, Patrick R.; Warneke, CarstenIsoprene oxidation schemes vary greatly among gas-phase chemical mechanisms, with potentially significant ramifications for air quality modeling and interpretation of satellite observations in biogenic-rich regions. In this study, in situ observations from the 2013 SENEX mission are combined with a constrained 0-D photochemical box model to evaluate isoprene chemistry among five commonly used gas-phase chemical mechanisms: CB05, CB6r2, MCMv3.2, MCMv3.3.1, and a recent version of GEOS-Chem. Mechanisms are evaluated and inter-compared with respect to formaldehyde (HCHO), a high-yield product of isoprene oxidation. Though underestimated by all considered mechanisms, observed HCHO mixing ratios are best reproduced by MCMv3.3.1 (normalized mean bias = −15%), followed by GEOS-Chem (−17%), MCMv3.2 (−25%), CB6r2 (−32%) and CB05 (−33%). Inter-comparison of HCHO production rates reveals that major restructuring of the isoprene oxidation scheme in the Carbon Bond mechanism increases HCHO production by only ∼5% in CB6r2 relative to CB05, while further refinement of the complex isoprene scheme in the Master Chemical Mechanism increases HCHO production by ∼16% in MCMv3.3.1 relative to MCMv3.2. The GEOS-Chem mechanism provides a good approximation of the explicit isoprene chemistry in MCMv3.3.1 and generally reproduces the magnitude and source distribution of HCHO production rates. We analytically derive improvements to the isoprene scheme in CB6r2 and incorporate these changes into a new mechanism called CB6r2-UMD, which is designed to preserve computational efficiency. The CB6r2-UMD mechanism mimics production of HCHO in MCMv3.3.1 and demonstrates good agreement with observed mixing ratios from SENEX (−14%). Improved simulation of HCHO also impacts modeled ozone: at ∼0.3 ppb NO, the ozone production rate increases ∼3% between CB6r2 and CB6r2-UMD, and rises another ∼4% when HCHO is constrained to match observations.Item Investigation of a potential HCHO measurement artifact from ISOPOOH(Copernicus Publications, 2016-09-16) St. Clair, Jason; Rivera-Rios, Jean C.; Crounse, John D.; Praske, Eric; Kim, Michelle J.; Wolfe, Glenn M.; Keutsch, Frank N.; Wennberg, Paul O.; Hanisco, Thomas F.Recent laboratory experiments have shown that a first generation isoprene oxidation product, ISOPOOH, can decompose to methyl vinyl ketone (MVK) and methacrolein (MACR) on instrument surfaces, leading to overestimates of MVK and MACR concentrations. Formaldehyde (HCHO) was suggested as a decomposition co-product, raising concern that in situ HCHO measurements may also be affected by an ISOPOOH interference. The HCHO measurement artifact from ISOPOOH for the NASA In Situ Airborne Formaldehyde instrument (ISAF) was investigated for the two major ISOPOOH isomers, (1,2)-ISOPOOH and (4,3)-ISOPOOH, under dry and humid conditions. The dry conversion of ISOPOOH to HCHO was 3 ± 2 % and 6 ± 4 % for (1,2)-ISOPOOH and (4,3)-ISOPOOH, respectively. Under humid (relative humidity of 40–60 %) conditions, conversion to HCHO was 6 ± 4 % for (1,2)-ISOPOOH and 10 ± 5 % for (4,3)-ISOPOOH. The measurement artifact caused by conversion of ISOPOOH to HCHO in the ISAF instrument was estimated for data obtained on the 6 September 2013 flight of the Studies of Emissions and Atmospheric Composition, Clouds and Climate Coupling by Regional Surveys (SEAC⁴RS) campaign. Prompt ISOPOOH conversion to HCHO was the source of < 4 % of the observed HCHO, including in the high-isoprene boundary layer. Time-delayed conversion, where previous exposure to ISOPOOH affects measured HCHO later in the flight, was conservatively estimated to be < 10 % of observed HCHO, and is significant only when high ISOPOOH sampling periods immediately precede periods of low HCHO.Item Kinetics and Product Yields of the OH Initiated Oxidation of Hydroxymethyl Hydroperoxide(ACS Publications) Allen, Hannah M.; Crounse, John D.; Bates, Kelvin H.; Teng, Alexander Paichung; Krawiec-Thayer, Mitchell P.; Rivera-Rios, Jean C.; Keutsch, Frank N.; St. Clair, Jason; Hanisco, Thomas F.; Møller, Kristian H.; Kjaergaard, Henrik G.; Wennberg, Paul O.Hydroxymethyl hydroperoxide (HMHP), formed in the reaction of the C₁ Criegee intermediate with water, is among the most abundant organic peroxides in the atmosphere. Although reaction with OH is thought to represent one of the most important atmospheric removal processes for HMHP, this reaction has been largely unstudied in the laboratory. Here, we present measurements of the kinetics and products formed in the reaction of HMHP with OH. HMHP was oxidized by OH in an environmental chamber; the decay of the hydroperoxide and the formation of formic acid and formaldehyde were monitored over time using CF₃O⁻ chemical ionization mass spectrometry (CIMS) and laser-induced fluorescence (LIF). The loss of HMHP by reaction with OH is measured relative to the loss of 1,2-butanediol [k1,2-butanediol+OH = (27.0 ± 5.6) × 10⁻¹² cm³ molecule⁻¹s⁻¹]. We find that HMHP reacts with OH at 295 K with a rate coefficient of (7.1 ± 1.5) × 10⁻¹² cm³ molecule⁻¹s⁻¹, with the formic acid to formaldehyde yield in a ratio of 0.88 ± 0.21 and independent of NO concentration (3 × 10¹0 – 1.5 × 10¹³ molecules cm⁻³). We suggest that, exclusively, abstraction of the methyl hydrogen of HMHP results in formic acid, while abstraction of the hydroperoxy hydrogen results in formaldehyde. We further evaluate the relative importance of HMHP sinks and use global simulations from GEOS-Chem to estimate that HMHP oxidation by OH contributes 1.7 Tg yr⁻¹ (1–3%) of global annual formic acid production.Item Modeling Ozone in the Eastern U.S. using a Fuel-Based Mobile Source Emissions Inventory(ACS Publications, 2018-06-05) McDonald, Brian C.; McKeen, Stuart A.; Cui, Yu Yan; Ahmadov, Ravan; Kim, Si-Wan; Frost, Gregory J.; Pollack, Ilana B.; Peischl, Jeff; Ryerson, Thomas B.; Holloway, John S.; Graus, Martin; Warneke, Carsten; Gilman, Jessica B.; Gouw, Joost A. de; Kaiser, Jennifer; Keutsch, Frank N.; Hanisco, Thomas F.; Wolfe, Glenn M.; Trainer, MichaelRecent studies suggest overestimates in current U.S. emission inventories of nitrogen oxides (NOx = NO + NO₂). Here, we expand a previously developed fuel-based inventory of motor-vehicle emissions (FIVE) to the continental U.S. for the year 2013, and evaluate our estimates of mobile source emissions with the U.S. Environmental Protection Agency’s National Emissions Inventory (NEI) interpolated to 2013. We find that mobile source emissions of NOx and carbon monoxide (CO) in the NEI are higher than FIVE by 28% and 90%, respectively. Using a chemical transport model, we model mobile source emissions from FIVE, and find consistent levels of urban NOx and CO as measured during the Southeast Nexus (SENEX) Study in 2013. Lastly, we assess the sensitivity of ozone (O₃) over the Eastern U.S. to uncertainties in mobile source NOx emissions and biogenic volatile organic compound (VOC) emissions. The ground-level O₃ is sensitive to reductions in mobile source NOx emissions, most notably in the Southeastern U.S. and during O₃ exceedance events, under the revised standard proposed in 2015 (>70 ppb, 8 h maximum). This suggests that decreasing mobile source NOx emissions could help in meeting more stringent O₃ standards in the future.Item A new laser-based and ultra-portable gas sensor for indoor and outdoor formaldehyde (HCHO) monitoring(Copernicus Publications, 2019-11-22) Shutter, Joshua D.; Allen, Norton T.; Hanisco, Thomas F.; Wolfe, Glenn M.; St. Clair, Jason; Keutsch, Frank N.n this work, a new commercially available, laser-based, and ultra-portable formaldehyde (HCHO) gas sensor is characterized, and its usefulness for monitoring HCHO mixing ratios in both indoor and outdoor environments is assessed. Stepped calibrations and intercomparison with well-established laser-induced fluorescence (LIF) instrumentation allow a performance evaluation of the absorption-based, mid-infrared HCHO sensor from Aeris Technologies, Inc. The Aeris sensor displays linear behavior (R2 > 0.940) when compared with LIF instruments from Harvard and NASA Goddard. A nonlinear least-squares fitting algorithm developed independently of the sensor's manufacturer to fit the sensor's raw absorption data during post-processing further improves instrument performance. The 3σ limit of detection (LOD) for 2, 15, and 60 min integration times are 2190, 690, and 420 pptv HCHO, respectively, for mixing ratios reported in real time, though the LOD improves to 1800, 570, and 300 pptv HCHO, respectively, during post-processing. Moreover, the accuracy of the sensor was found to be ± (10 % + 0.3) ppbv when compared against LIF instrumentation sampling ambient air. The aforementioned precision and level of accuracy are sufficient for most HCHO levels measured in indoor and outdoor environments. While the compact Aeris sensor is currently not a replacement for the most sensitive research-grade instrumentation available, its usefulness for monitoring HCHO is clearly demonstrated.Item Observational constraints on glyoxal production from isoprene oxidation and its contribution to organic aerosol over the Southeast United States(AGU Pubication, 2016-07-31) Li, Jingyi; Mao, Jingqiu; Min, Kyung‐Eun; Washenfelder, Rebecca A.; Brown, Steven S.; Kaiser, Jennifer; Keutsch, Frank N.; Volkamer, Rainer; Wolfe, Glenn M.; Hanisco, Thomas F.; Pollack, Ilana B.; Ryerson, Thomas B.; Graus, Martin; Gilman, Jessica B.; Lerner, Brian M.; Warneke, Carsten; Gouw, Joost A. de; Middlebrook, Ann M.; Liao, Jin; Welti, André; Henderson, Barron H.; McNeill, V. Faye; Hall, Samuel R.; Ullmann, Kirk; Donner, Leo J.; Paulot, Fabien; Horowitz, Larry W.We use a 0‐D photochemical box model and a 3‐D global chemistry‐climate model, combined with observations from the NOAA Southeast Nexus (SENEX) aircraft campaign, to understand the sources and sinks of glyoxal over the Southeast United States. Box model simulations suggest a large difference in glyoxal production among three isoprene oxidation mechanisms (AM3ST, AM3B, and Master Chemical Mechanism (MCM) v3.3.1). These mechanisms are then implemented into a 3‐D global chemistry‐climate model. Comparison with field observations shows that the average vertical profile of glyoxal is best reproduced by AM3ST with an effective reactive uptake coefficient γglyx of 2 × 10⁻³ and AM3B without heterogeneous loss of glyoxal. The two mechanisms lead to 0–0.8 µg m⁻³ secondary organic aerosol (SOA) from glyoxal in the boundary layer of the Southeast U.S. in summer. We consider this to be the lower limit for the contribution of glyoxal to SOA, as other sources of glyoxal other than isoprene are not included in our model. In addition, we find that AM3B shows better agreement on both formaldehyde and the correlation between glyoxal and formaldehyde (RGF = [GLYX]/[HCHO]), resulting from the suppression of δ‐isoprene peroxy radicals. We also find that MCM v3.3.1 may underestimate glyoxal production from isoprene oxidation, in part due to an underestimated yield from the reaction of isoprene epoxydiol (IEPOX) peroxy radicals with HO2. Our work highlights that the gas‐phase production of glyoxal represents a large uncertainty in quantifying its contribution to SOA.Item Observations of VOC emissions and photochemical products over US oil- and gas-producing regions using high-resolution H₃O⁺ CIMS (PTR-ToF-MS)(Copernicus Publications, 2017-08-16) Koss, Abigail; Yuan, Bin; Warneke, Carsten; Gilman, Jessica B.; Lerner, Brian M.; Veres, Patrick R.; Peischl, Jeff; Eilerman, Scott; Wild, Rob; Brown, Steven S.; Thompson, Chelsea R.; Ryerson, Thomas; Hanisco, Thomas; Wolfe, Glenn M.; St. Clair, Jason; Thayer, Mitchell; Keutsch, Frank N.; Murphy, Shane; Gouw, Joost deVOCs 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.Item Validation of satellite formaldehyde (HCHO) retrievals using observations from 12 aircraft campaigns(Copernicus Publications, 2020-10-29) Zhu, Lei; Abad, Gonzalo González; Nowlan, Caroline R.; Miller, Christopher Chan; Chance, Kelly; Apel, Eric C.; DiGangi, Joshua P.; Fried, Alan; Hanisco, Thomas F.; Hornbrook, Rebecca S.; Hu, Lu; Kaiser, Jennifer; Keutsch, Frank N.; Permar, Wade; St. Clair, Jason; Wolfe, GlennFormaldehyde (HCHO) has been measured from space for more than 2 decades. Owing to its short atmospheric lifetime, satellite HCHO data are used widely as a proxy of volatile organic compounds (VOCs; please refer to Appendix A for abbreviations and acronyms), providing constraints on underlying emissions and chemistry. However, satellite HCHO products from different satellite sensors using different algorithms have received little validation so far. The accuracy and consistency of HCHO retrievals remain largely unclear. Here we develop a validation platform for satellite HCHO retrievals using in situ observations from 12 aircraft campaigns with a chemical transport model (GEOS-Chem) as the intercomparison method. Application to the NASA operational OMI HCHO product indicates negative biases (−44.5 % to −21.7 %) under high-HCHO conditions, while it indicates high biases (+66.1 % to +112.1 %) under low-HCHO conditions. Under both conditions, HCHO a priori vertical profiles are likely not the main driver of the biases. By providing quick assessment of systematic biases in satellite products over large domains, the platform facilitates, in an iterative process, optimization of retrieval settings and the minimization of retrieval biases. It is also complementary to localized validation efforts based on ground observations and aircraft spirals.