12 results on '"Meghan Stell"'
Search Results
2. Chemical feedbacks weaken the wintertime response of particulate sulfate and nitrate to emissions reductions over the eastern United States
- Author
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Viral Shah, Lyatt Jaeglé, Joel A. Thornton, Felipe D. Lopez-Hilfiker, Ben H. Lee, Jason C. Schroder, Pedro Campuzano-Jost, Jose L. Jimenez, Hongyu Guo, Amy P. Sullivan, Rodney J. Weber, Jaime R. Green, Marc N. Fiddler, Solomon Bililign, Teresa L. Campos, Meghan Stell, Andrew J. Weinheimer, Denise D. Montzka, and Steven S. Brown
- Published
- 2018
- Full Text
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3. Cloud System Evolution in the Trades-CSET: Following the Evolution of Boundary Layer Cloud Systems with the NSF/NCAR GV
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Patrick Minnis, Jeremy McGibbon, John Allison, Johannes Mohrmann, Edwin W. Eloranta, Julie Haggerty, Pei-Sang Tsai, Louis L. Lussier, Alison D. Nugent, Teresa Campos, Raymond A. Shaw, Sebastian Schmidt, Robindra Paliknoda, Greg Stossmeister, Mampi Sarkar, Michael J. Reeves, Susanne Glienke, Stuart Beaton, Paquita Zuidema, Robert Wood, Meghan Stell, Virendra P. Ghate, Scott Ellis, Christopher S. Bretherton, Christian Schwartz, Jacob P. Fugal, Shaunna L. Donaher, Jothiram Vivekanandan, Robert A. Rilling, Samuel R. Hall, Bruce A. Albrecht, and Jørgen Jensen
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Atmospheric Science ,010504 meteorology & atmospheric sciences ,Meteorology ,business.industry ,Cloud systems ,0207 environmental engineering ,Cloud computing ,02 engineering and technology ,01 natural sciences ,Article ,Aerosol ,Boundary layer ,Environmental science ,020701 environmental engineering ,business ,0105 earth and related environmental sciences - Abstract
The Cloud System Evolution in the Trades (CSET) study was designed to describe and explain the evolution of the boundary layer aerosol, cloud, and thermodynamic structures along trajectories within the North Pacific trade winds. The study centered on seven round trips of the National Science Foundation–National Center for Atmospheric Research (NSF–NCAR) Gulfstream V (GV) between Sacramento, California, and Kona, Hawaii, between 7 July and 9 August 2015. The CSET observing strategy was to sample aerosol, cloud, and boundary layer properties upwind from the transition zone over the North Pacific and to resample these areas two days later. Global Forecast System forecast trajectories were used to plan the outbound flight to Hawaii with updated forecast trajectories setting the return flight plan two days later. Two key elements of the CSET observing system were the newly developed High-Performance Instrumented Airborne Platform for Environmental Research (HIAPER) Cloud Radar (HCR) and the high-spectral-resolution lidar (HSRL). Together they provided unprecedented characterizations of aerosol, cloud, and precipitation structures that were combined with in situ measurements of aerosol, cloud, precipitation, and turbulence properties. The cloud systems sampled included solid stratocumulus infused with smoke from Canadian wildfires, mesoscale cloud–precipitation complexes, and patches of shallow cumuli in very clean environments. Ultraclean layers observed frequently near the top of the boundary layer were often associated with shallow, optically thin, layered veil clouds. The extensive aerosol, cloud, drizzle, and boundary layer sampling made over open areas of the northeast Pacific along 2-day trajectories during CSET will be an invaluable resource for modeling studies of boundary layer cloud system evolution and its governing physical processes.
- Published
- 2020
4. Chemical feedbacks weaken the wintertime response of particulate sulfate and nitrate to emissions reductions over the eastern United States
- Author
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Joel A. Thornton, Jose L. Jimenez, Andrew J. Weinheimer, Felipe D. Lopez-Hilfiker, Lyatt Jaeglé, Rodney J. Weber, Ben H. Lee, Jason C. Schroder, Viral Shah, Steven S. Brown, Amy P. Sullivan, Teresa Campos, Meghan Stell, J. R. Green, Pedro Campuzano-Jost, Hongyu Guo, Denise D. Montzka, Marc N. Fiddler, and Solomon Bililign
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Multidisciplinary ,010504 meteorology & atmospheric sciences ,Chemical transport model ,Chemistry ,Fine particulate ,010501 environmental sciences ,Particulates ,01 natural sciences ,chemistry.chemical_compound ,Nitrate ,Environmental chemistry ,Physical Sciences ,Sulfate ,NOx ,0105 earth and related environmental sciences ,Particle fraction - Abstract
Sulfate ( S O 4 2 - ) and nitrate ( N O 3 - ) account for half of the fine particulate matter mass over the eastern United States. Their wintertime concentrations have changed little in the past decade despite considerable precursor emissions reductions. The reasons for this have remained unclear because detailed observations to constrain the wintertime gas–particle chemical system have been lacking. We use extensive airborne observations over the eastern United States from the 2015 Wintertime Investigation of Transport, Emissions, and Reactivity (WINTER) campaign; ground-based observations; and the GEOS-Chem chemical transport model to determine the controls on winter S O 4 2 - and N O 3 - . GEOS-Chem reproduces observed S O 4 2 - – N O 3 - – N H 4 + particulate concentrations (2.45 μg s m - 3 ) and composition ( S O 4 2 - : 47%; N O 3 - : 32%; N H 4 + : 21%) during WINTER. Only 18% of S O 2 emissions were regionally oxidized to S O 4 2 - during WINTER, limited by low [H2O2] and [OH]. Relatively acidic fine particulates (pH∼1.3) allow 45% of nitrate to partition to the particle phase. Using GEOS-Chem, we examine the impact of the 58% decrease in winter S O 2 emissions from 2007 to 2015 and find that the H2O2 limitation on S O 2 oxidation weakened, which increased the fraction of S O 2 emissions oxidizing to S O 4 2 - . Simultaneously, NOx emissions decreased by 35%, but the modeled N O 3 - particle fraction increased as fine particle acidity decreased. These feedbacks resulted in a 40% decrease of modeled [ S O 4 2 - ] and no change in [ N O 3 - ], as observed. Wintertime [ S O 4 2 - ] and [ N O 3 - ] are expected to change slowly between 2015 and 2023, unless S O 2 and NOx emissions decrease faster in the future than in the recent past.
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- 2018
5. Airborne observations of mercury emissions from the Chicago/Gary urban/industrial area during the 2013 NOMADSS campaign
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D. J. Knapp, Rebecca S. Hornbrook, Andrew J. Weinheimer, Lynne E. Gratz, Teresa Campos, Daniel M. Stechman, Lyatt Jaeglé, Mike Reeves, Eric C. Apel, Denise D. Montzka, Meghan Stell, Frank Flocke, J. L. Ambrose, Roy L. Mauldin, Christopher A. Cantrell, Geoffrey S. Tyndall, Noelle E. Selin, Nicola J. Blake, Christoph Knote, and Daniel A. Jaffe
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Hydrology ,Atmospheric Science ,geography ,geography.geographical_feature_category ,010504 meteorology & atmospheric sciences ,chemistry.chemical_element ,010501 environmental sciences ,Urban area ,Atmospheric sciences ,7. Clean energy ,01 natural sciences ,Nitrogen ,Plume ,Aerosol ,Mercury (element) ,chemistry.chemical_compound ,chemistry ,13. Climate action ,Environmental science ,Outflow ,Emission inventory ,Sulfur dioxide ,0105 earth and related environmental sciences ,General Environmental Science - Abstract
Atmospheric emissions from the Chicago/Gary urban/industrial area significantly enhance ambient mercury (Hg) concentrations and lead to increased levels of atmospheric Hg deposition within the Lake Michigan Basin. We use airborne observations collected over Lake Michigan during the 2013 Nitrogen, Oxidants, Mercury, and Aerosol Distributions, Sources, and Sinks (NOMADSS) campaign to quantify the outflow of total Hg (THg) emissions from the Chicago/Gary urban/industrial area. We use concurrent airborne measurements of THg, carbon monoxide (CO), nitrogen oxides (NOx = NO + NO2), and sulfur dioxide (SO2) to calculate measured enhancement ratios and to characterize Chicago/Gary emissions with respect to the 2011 U.S. EPA National Emissions Inventory. We determine the observed THg/CO enhancement ratio in outflow from Chicago/Gary to be 0.21 ± 0.09 × 10−6 mol mol−1 (ppqv/ppbv), which is comparable to observations reported for other major U.S. urban/industrial areas. We also employ the FLEXPART Lagrangian transport and dispersion model to simulate air mass transport during plume encounters and to compare our observations to inventoried emission ratios. We find that our observed THg/CO enhancement ratios are 63–67% greater than the transport-corrected emission ratios for the Chicago/Gary area. Our results suggest that there are many small emission sources that are not fully accounted for within the inventory, and/or that the re-emission of legacy Hg is a significant source of THg to the atmosphere in this region.
- Published
- 2016
6. Sources and Characteristics of Summertime Organic Aerosol in the Colorado Front Range: Perspective from Measurements and WRF-Chem Modeling
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Roya Bahreini, Ravan Ahmadov, Stu A. McKeen, Kennedy T. Vu, Justin H. Dingle, Eric C. Apel, Donald R. Blake, Nicola Blake, Teresa L. Campos, Chris Cantrell, Frank Flocke, Alan Fried, Jessica B. Gillman, Alan J. Hills, Rebecca S. Hornbrook, Greg Huey, Lisa Kaser, Brian M. Lerner, Roy L. Mauldin, Simone Meinardi, Denise D. Montzka, Dirk Richter, Jason R. Schroeder, Meghan Stell, David Tanner, James Walgea, Peter Weibring, and Andrew Weinheimer
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Climate Action ,Meteorology & Atmospheric Sciences - Abstract
Evolution of organic aerosol (OA) and their precursors in the boundary layer of Colorado Front Range during the Front Range Air Pollution and Photochemistry Éxperiment (FRAPPÉ, July–August 2014) was analyzed by in-situ measurements and chemical transport modeling. Measurements indicated significant production of secondary OA (SOA), with enhancement ratio of OA with respect to carbon monoxide (CO) reaching 0.068 ± 0.004 μg m−3 ppbv−1. At background mixing ratios of CO, up to ~ 2 μg m−3 background OA was observed, suggesting significant non-combustion contribution to OA in the Front Range. The mean concentration of OA in plumes with a high influence of oil and natural gas (O&G) emissions was ~ 40 % higher than in urban-influenced plumes. Positive matrix factorization confirmed a dominant contribution of secondary, oxygenated OA (OOA) in the boundary layer instead of fresh, hydrocarbon-like OA (HOA). Combinations of primary OA (POA) volatility assumptions, aging of semi-volatile species, and different emission estimates from the O&G sector were used in the Weather Research and Forecasting model, coupled with Chemistry (WRF-Chem) simulation scenarios. The assumption of semi-volatile POA resulted in greater than a factor of 10 lower POA concentrations compared to PMF-resolved HOA. Including a top-down modified O&G emissions resulted in substantially better agreements in modeled ethane, toluene, hydroxyl radical, and ozone compared to measurements in the high O&G-influenced plumes. By including emissions from the O&G sector using the top-down approach, it was estimated that the O&G sector contributed to
- Published
- 2018
7. Supplementary material to 'Sources and Characteristics of Summertime Organic Aerosol in the Colorado Front Range: Perspective from Measurements and WRF-Chem Modeling'
- Author
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Roya Bahreini, Ravan Ahmadov, Stu A. McKeen, Kennedy T. Vu, Justin H. Dingle, Eric C. Apel, Donald R. Blake, Nicola Blake, Teresa L. Campos, Chris Cantrell, Frank Flocke, Alan Fried, Jessica B. Gillman, Alan J. Hills, Rebecca S. Hornbrook, Greg Huey, Lisa Kaser, Brian M. Lerner, Roy L. Mauldin, Simone Meinardi, Denise D. Montzka, Dirk Richter, Jason R. Schroeder, Meghan Stell, David Tanner, James Walgea, Peter Weibring, and Andrew Weinheimer
- Published
- 2018
8. Supplementary material to 'Impacts of the Denver Cyclone on Regional Air Quality and Aerosol Formation in the Colorado Front Range during FRAPPÉ 2014'
- Author
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Kennedy T. Vu, Justin H. Dingle, Roya Bahreini, Patrick J. Reddy, Teresa L. Campos, Glenn S. Diskin, Alan Fried, Scott C. Herndon, Rebecca S. Hornbrook, Greg Huey, Lisa Kaser, Denise D. Montzka, John B. Nowak, Dirk Richter, Joseph R. Roscioli, Stephen Shertz, Meghan Stell, David Tanner, Geoff Tyndall, James Walega, Peter Weibring, Andrew J. Weinheimer, Gabriele Pfister, and Frank Flocke
- Published
- 2016
9. Impacts of the Denver Cyclone on Regional Air Quality and Aerosol Formation in the Colorado Front Range during FRAPPÉ 2014
- Author
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Kennedy T. Vu, Justin H. Dingle, Roya Bahreini, Patrick J. Reddy, Teresa L. Campos, Glenn S. Diskin, Alan Fried, Scott C. Herndon, Rebecca S. Hornbrook, Greg Huey, Lisa Kaser, Denise D. Montzka, John B. Nowak, Dirk Richter, Joseph R. Roscioli, Stephen Shertz, Meghan Stell, David Tanner, Geoff Tyndall, James Walega, Peter Weibring, Andrew J. Weinheimer, Gabriele Pfister, and Frank Flocke
- Abstract
We present airborne measurements made in the Colorado Front Range aboard the NSF C-130 aircraft during the 2014 Front Range Air Pollution and Photochemistry Éxperiment (FRAPPÉ) project. Data on trace gases, non-refractory sub-micron aerosol chemical constituents, and aerosol optical extinction (βext) at λ = 632 nm in the presence and absence of a surface mesoscale circulation pattern, called the Denver Cyclone, were analyzed in three study regions of the Front Range: In-Flow, Northern Front Range (NFR), and Denver Metropolitan (DM). Pronounced increases in mass concentrations of organics, nitrate, and sulfate in NFR and DM were observed during the cyclone episodes (27–28 July) compared to the non-cyclonic days (26 July, 02–03 August). Organics (OA) dominated the mass concentrations on all evaluated days, with a 45 % increase in OA on cyclone days across all three regions while the increase during the cyclone episode was up to ~ 80 % for DM, from 3.78 ± 1.55 µg sm−3 to 6.78 ± 1.78 µg sm−3, where sm−3 is the STP unit of volume of air. Average nitrate mass concentrations were 0.26 ± 0.27 µg sm−3 vs. 1.03 ± 0.74 µg sm−3 followed by sulfate with an average of 0.58 ± 0.23 µg sm−3 vs. 1.08 ± 0.73 µg sm−3 on non-cyclone vs. cyclonic days, respectively. In the most aged air masses (NOx/NOy
- Published
- 2016
10. Aerosol Optical Extinction during the Front Range Air Pollution and Photochemistry Éxperiment (FRAPPÉ) 2014 Summertime Field Campaign, Colorado U.S.A
- Author
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Justin H. Dingle, Kennedy Vu, Roya Bahreini, Eric C. Apel, Teresa L. Campos, Frank Flocke, Alan Fried, Scott Herndon, Alan J. Hills, Rebecca S. Hornbrook, Greg Huey, Lisa Kaser, Denise D. Montzka, John B. Nowak, Mike Reeves, Dirk Richter, Joseph R. Roscioli, Stephen Shertz, Meghan Stell, David Tanner, Geoff Tyndall, James Walega, Petter Weibring, and Andrew Weinheimer
- Abstract
Summertime aerosol optical extinction (βext) was measured in the Colorado Front Range and Denver Metropolitan Area as part of the Front Range Air Pollution and Photochemistry Experiment (FRAPPÉ) campaign during July–August 2014. An Aerodyne Cavity Attenuated Phase Shift particle light extinction monitor (CAPS-PMex) was deployed to measure dry, βext of submicron aerosols at λ = 632 nm at 1 Hz. Data from a suite of gas-phase instrumentation were used to interpret βext behavior under various categories of air masses and sources. Extinction enhancement ratios relative to CO (Δβext/ΔCO) were significantly increased in highly aged air masses compared to fresh air masses by 50–60 %. The resulting increase in Δβext/ΔCO under highly aged air masses was accompanied by formation of secondary organic aerosols (SOA). In addition, the impacts of aerosol composition on βext in air masses under the influence of urban, natural oil and gas operations (O&G), and agriculture and livestock operations were evaluated. Estimated non-refractory mass extinction efficiency (MEE) values for different air mass types ranged from 1.83–3.30 m2 g−1, with the minimum and maximum values observed in agriculture and urban + O&G influenced air masses, respectively. The mass distribution for organic, nitrate, and sulfate aerosols presented distinct profiles in different air mass types. During Aug. 11–12, regional influence of a biomass burning event was observed, increasing the background βext by 10–15 Mm−1 and the estimated MEE and Δβext/ΔCO values in the Front Range.
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- 2016
11. Supplementary material to 'Aerosol Optical Extinction during the Front Range Air Pollution and Photochemistry Éxperiment (FRAPPÉ) 2014 Summertime Field Campaign, Colorado U.S.A.'
- Author
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Justin H. Dingle, Kennedy Vu, Roya Bahreini, Eric C. Apel, Teresa L. Campos, Frank Flocke, Alan Fried, Scott Herndon, Alan J. Hills, Rebecca S. Hornbrook, Greg Huey, Lisa Kaser, Denise D. Montzka, John B. Nowak, Mike Reeves, Dirk Richter, Joseph R. Roscioli, Stephen Shertz, Meghan Stell, David Tanner, Geoff Tyndall, James Walega, Petter Weibring, and Andrew Weinheimer
- Published
- 2016
12. Oxidation of mercury by bromine in the subtropical Pacific free troposphere
- Author
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Lyatt Jaeglé, Nicola J. Blake, Shaojie Song, Frank Flocke, Lynne E. Gratz, J. L. Ambrose, Xianliang Zhou, Viral Shah, Rebecca S. Hornbrook, Geoffrey S. Tyndall, D. J. Knapp, Catalina Tsai, Andrew J. Weinheimer, Samuel R. Hall, Meghan Stell, Denise D. Montzka, Eric C. Apel, Daniel M. Stechman, Mike Reeves, Noelle E. Selin, Daniel A. Jaffe, Max Spolaor, James Festa, Jochen Stutz, and Teresa Campos
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Bromine ,010504 meteorology & atmospheric sciences ,chemistry.chemical_element ,North Pacific High ,010501 environmental sciences ,Atmospheric sciences ,01 natural sciences ,Nitrogen ,Mercury (element) ,Tropospheric ozone depletion events ,Trace gas ,Aerosol ,Troposphere ,Geophysics ,chemistry ,13. Climate action ,General Earth and Planetary Sciences ,Environmental science ,0105 earth and related environmental sciences - Abstract
Mercury is a global toxin that can be introduced to ecosystems through atmospheric deposition. Mercury oxidation is thought to occur in the free troposphere by bromine radicals, but direct observational evidence for this process is currently unavailable. During the 2013 Nitrogen, Oxidants, Mercury and Aerosol Distributions, Sources and Sinks campaign, we measured enhanced oxidized mercury and bromine monoxide in a free tropospheric air mass over Texas. We use trace gas measurements, air mass back trajectories, and a chemical box model to confirm the origin and chemical history of the sampled air mass. We find the presence of elevated oxidized mercury to be consistent with oxidation of elemental mercury by bromine atoms in this subsiding upper tropospheric air mass within the subtropical Pacific High, where dry atmospheric conditions are conducive to oxidized mercury accumulation. Our results support the role of bromine as the dominant oxidant of mercury in the upper troposphere.
- Published
- 2015
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