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  • Articles  (163)
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  • 1
    Electronic Resource
    Electronic Resource
    The mobilities of NO+(CH3CN)n cluster ions (n=0–3) drifting in helium and in helium–acetonitrile mixtures (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 105 (1996), S. 10398-10409 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The mobilities of NO+(CH3CN)n cluster ions (n=0–3) drifting in helium and in mixtures of helium and acetonitrile (CH3CN) are measured in a flow-drift tube. The mobilities in helium decrease with cluster size [the mobility at zero field, K(0)0, is 22.4±0.5 cm2 V−1 s−1 for NO+, 12.3±0.3 cm2 V−1 s−1 for NO+(CH3CN), 8.2±0.2 cm2 V−1 s−1 for NO+(CH3CN)2 and 7.5±0.5 cm2 V−1 s−1 for NO+(CH3CN)3] and depend only weakly on the characteristic parameter E/N (electric field strength divided by the number density of the buffer gas). The size dependence is explained in terms of the geometric cross sections of the different cluster ions. The rate constants for the various cluster formation and dissociation reactions have also been determined in order to rule out the possibility that reactions occurring in the drift region influence the measurements in the mixtures. Since high pressures of acetonitrile are required to form NO+(CH3CN)2 and NO+(CH3CN)3, the mobilities of these ions are found to be dependent on the acetonitrile concentration, as a result of anomalously small mobilities of these ions in acetonitrile [K(0)0=0.041±0.004 cm2 V−1 s−1 for NO+(CH3CN)2 and 0.044±0.004 cm2 V−1 s−1 for NO+(CH3CN)3]. These values are at least an order of magnitude smaller than any previously reported ion mobility, which can be partly explained by the large ion-permanent dipole interaction between the cluster ions and acetonitrile. The remaining discrepancies may be the result of momentum transfer outside the capture cross section, dipole–dipole interactions, ligand exchange, the formation of long-lived collision complexes or the transfer of kinetic energy into internal energy of the cluster ion and the acetonitrile molecule. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.472968
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  • 2
    Electronic Resource
    Electronic Resource
    Vibrational enhancement of the charge transfer rate constant of N+2(v=0–4) with Kr at thermal energies (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 105 (1996), S. 5455-5466 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The charge transfer reaction of N+2(v=0–4)+Kr→N2+Kr+ is studied at thermal energy as a function of vibrational excitation in the reactant ion. The selected-ion flow tube technique coupled with laser-induced fluorescence detection is used to measure the vibrationally state specific rate constants. A dramatic vibrational enhancement is observed; measured rate constants are 1.0 (±0.6)×10−12, 2.8 (±0.3)×10−12, 2.1 (±0.2)×10−11, 5.1 (±0.2)×10−11, and 8.3 (±0.4)×10−11 cm3 molecule−1 s−1 for v=0, 1, 2, 3 and 4, respectively. Mass spectrometric kinetics experiments are also performed to confirm that vibrational relaxation, N+2(v)+Kr→N+2(v′〈v)+Kr, is a negligible process. The charge transfer for v=0 is extremely slow in spite of the large exothermicity (e.g., 0.915 eV for the production of N2(v′=0)+Kr+(2P1/2) states), yet the reaction is enhanced when the apparent energy mismatch is greater for the vibrationally excited reactant. A simple model is proposed to explain the experimental results at thermal energies ((very-much-less-than)1 eV). The model assumes that only the most energy-resonant exothermic transitions, N+2(v)+Kr→N2(v+3)+Kr+(2P1/2), occur within the duration of the ion–molecule collision complex and that the charge transfer takes place with probabilities governed by the corresponding Franck–Condon factors. However, the Franck–Condon factors are modified by a trial displacement of 0.02 A(ring) to account for the changes in vibrational wave functions of N+2 and N2 during a close approach of the (N2–Kr)+ pair; this method gives an excellent description of the experimental results. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.472386
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  • 3
    Electronic Resource
    Electronic Resource
    Mobility and formation kinetics of NH4+(NH3)n cluster ions (n=0–3) in helium and helium/ammonia mixtures (1997)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 106 (1997), S. 530-538 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: NH4+(NH3)n (n=0–3) cluster ions are produced in a field-free flow tube section of a selected ion flow–drift tube (SIFDT) apparatus. Cluster ion mobilities are measured in mixtures of He and NH3 and used to obtain the individual mobilities in helium and in ammonia by applying Blanc's law to the mixtures. Mobilities of the cluster ions are also measured in pure helium by producing the ions in the ion source of a flowing afterglow, selected ion flow–drift tube apparatus (FA-SIFDT). The measurements in pure helium compare well with the mobilities in helium obtained by applying Blanc's law to the mixtures. The zero field mobilities of the cluster ions in helium are 22.1±0.4 cm2 V−1 s−1 for NH4+, 16.6±0.4 cm2 V−1 s−1 for NH4+(NH3), 12.2±0.4 cm2 V−1 s−1 for NH4+(NH3)2, and 12.1±0.4 cm2 V−1 s−1 for NH4+(NH3)3. The decrease with increasing size of the cluster can be explained in terms of the sizes of the geometric cross sections. The zero-field mobilities in NH3 are 0.94±0.35 cm2 V−1 s−1 for NH4+, 0.83±0.22 cm2 V−1 s−1 for NH4+(NH3), 0.50±0.27 cm2 V−1 s−1 for NH4+(NH3)2, and 0.25±0.20 cm2 V−1 s−1 for NH4+(NH3)3. The small values of the mobilities in these polar gas systems are understood in terms of the strong ion–dipole interactions. Calculated mobilities in NH3 are obtained by computing the collision cross section with the ion–dipole interactions taken into account; the results compare well with the measurements for NH4+ and NH4+(NH3). However, the measured mobilities of the larger cluster ions are smaller than the computed values. The discrepancies may be due to several factors including dipole–dipole interactions, ligand exchange reactions, formation of long-lived quasibound complexes, and efficient transfer of kinetic energy into internal energy of the cluster ion and the ammonia molecules. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.473964
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  • 4
    Electronic Resource
    Electronic Resource
    The mobilities of ions and cluster ions drifting in polar gases (1997)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 106 (1997), S. 5937-5942 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The mobility of ions drifting in polar gases is explored both theoretically and experimentally. New experimental results are presented for (i) NO+ ions drifting in H2O (the reduced zero-field mobility K0(0) is 0.66±0.07 cm2 V−1 s−1), (ii) H3O+(H2O)3 ions drifting in H2O (K0(0)=0.43±0.06 cm2 V−1 s−1), and (iii) NO+(CH3COCH3)n ions (n=2,3) drifting in CH3COCH3 (K0(0)=0.041 ±0.010 cm2 V−1 s−1 for n=2 and K0(0)=0.050±0.015 cm2 V−1 s−1 for n=3). A number of theoretical models for ion mobilities in polar gases are described. The models are compared with the available experimental data and a reasonable agreement is obtained. For larger cluster ions the measured mobilities are considerably smaller than the calculated values. Some possible reasons for the discrepancies are discussed, including momentum transfer outside the capture cross section, dipole–dipole interactions, ligand exchange, inelastic collisions, and the validity of Blanc's law. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.473609
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  • 5
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    Chemical data quantify Deepwater Horizon hydrocarbon flow rate and environmental distribution (2012)
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © The Author(s), 2011. This is the author's version of the work. It is posted here by permission of National Academy of Sciences for personal use, not for redistribution. The definitive version was published in Proceedings of the National Academy of Sciences of the United States of America (2012), doi:10.1073/pnas.1110564109.
    Description: Detailed airborne, surface, and subsurface chemical measurements, primarily obtained in May and June 2010, are used to quantify initial hydrocarbon compositions along different transport pathways – in deep subsurface plumes, in the initial surface slick, and in the atmosphere – during the Deepwater Horizon (DWH) oil spill. Atmospheric measurements are consistent with a limited area of surfacing oil, with implications for leaked hydrocarbon mass transport and oil drop size distributions. The chemical data further suggest relatively little variation in leaking hydrocarbon composition over time. While readily soluble hydrocarbons made up ~25% of the leaking mixture by mass, subsurface chemical data show these compounds made up ~69% of the deep plume mass; only ~31% of deep plume mass was initially transported in the form of trapped oil droplets. Mass flows along individual transport pathways are also derived from atmospheric and subsurface chemical data. Subsurface hydrocarbon composition, dissolved oxygen, and dispersant data are used to provide a new assessment of release of hydrocarbons from the leaking well. We use the chemical measurements to estimate that (7.8±1.9) x106 kg of hydrocarbons leaked on June 10, 2010, directly accounting for roughly three-quarters of the total leaked mass on that day. The average environmental release rate of (10.1 ± 2.0) x106 kg/day derived using atmospheric and subsurface chemical data agrees within uncertainties with the official average leak rate of (10.2 ± 1.0) x106 kg/day derived using physical and optical methods.
    Description: This research was supported by the National Science Foundation through grants to D. Blake (AGS-1049952), J. Kessler (OCE-1042650 and OCE-0849246), D. Valentine (OCE-1042097 and OCE-0961725), E. Kujawinski (OCE-1045811), and R. Camilli (OCE-1043976), by U.S. Coast Guard contract to R. Camilli (Contract HSCG3210CR0020), and by U.S. Department of Energy grant to D. Valentine (DE- NT0005667). The August, September, and October research cruises were funded by NOAA through a contract with Consolidated Safety Services, Incorporated. The NOAA P-3 oil spill survey flights were funded in part by NOAA and in part by a U.S. Coast Guard Pollution Removal Funding Authorization to NOAA.
    Repository Name: Woods Hole Open Access Server
    Type: Preprint
    Format: application/pdf
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  • 6
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    Highly functionalized organic nitrates in the southeast United States: Contribution to secondary organic aerosol and reactive nitrogen budgets (2016)
    National Academy of Sciences
    Details
    Publication Date: 2016-01-25
    Description: Speciated particle-phase organic nitrates (pONs) were quantified using online chemical ionization MS during June and July of 2013 in rural Alabama as part of the Southern Oxidant and Aerosol Study. A large fraction of pONs is highly functionalized, possessing between six and eight oxygen atoms within each carbon number group, and is not the common first generation alkyl nitrates previously reported. Using calibrations for isoprene hydroxynitrates and the measured molecular compositions, we estimate that pONs account for 3% and 8% of total submicrometer organic aerosol mass, on average, during the day and night, respectively. Each of the isoprene- and monoterpenes-derived groups exhibited a strong diel trend consistent with the emission patterns of likely biogenic hydrocarbon precursors. An observationally constrained diel box model can replicate the observed pON assuming that pONs (i) are produced in the gas phase and rapidly establish gas–particle equilibrium and (ii) have a short particle-phase lifetime (∼2–4 h). Such dynamic behavior has significant implications for the production and phase partitioning of pONs, organic aerosol mass, and reactive nitrogen speciation in a forested environment.
    Print ISSN: 0027-8424
    Electronic ISSN: 1091-6490
    Topics: Biology , Medicine , Natural Sciences in General
    Published by National Academy of Sciences
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  • 7
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    Continued emissions of carbon tetrachloride from the United States nearly two decades after its phaseout for dispersive uses (2016)
    National Academy of Sciences
    Details
    Publication Date: 2016-02-29
    Description: National-scale emissions of carbon tetrachloride (CCl4) are derived based on inverse modeling of atmospheric observations at multiple sites across the United States from the National Oceanic and Atmospheric Administration’s flask air sampling network. We estimate an annual average US emission of 4.0 (2.0–6.5) Gg CCl4 y−1 during 2008–2012, which is almost two orders of magnitude larger than reported to the US Environmental Protection Agency (EPA) Toxics Release Inventory (TRI) (mean of 0.06 Gg y−1) but only 8% (3–22%) of global CCl4 emissions during these years. Emissive regions identified by the observations and consistently shown in all inversion results include the Gulf Coast states, the San Francisco Bay Area in California, and the Denver area in Colorado. Both the observation-derived emissions and the US EPA TRI identified Texas and Louisiana as the largest contributors, accounting for one- to two-thirds of the US national total CCl4 emission during 2008–2012. These results are qualitatively consistent with multiple aircraft and ship surveys conducted in earlier years, which suggested significant enhancements in atmospheric mole fractions measured near Houston and surrounding areas. Furthermore, the emission distribution derived for CCl4 throughout the United States is more consistent with the distribution of industrial activities included in the TRI than with the distribution of other potential CCl4 sources such as uncapped landfills or activities related to population density (e.g., use of chlorine-containing bleach).
    Print ISSN: 0027-8424
    Electronic ISSN: 1091-6490
    Topics: Biology , Medicine , Natural Sciences in General
    Published by National Academy of Sciences
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  • 8
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    Monoterpenes are the largest source of summertime organic aerosol in the southeastern United States (2018)
    National Academy of Sciences
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    Publication Date: 2018-02-12
    Description: The chemical complexity of atmospheric organic aerosol (OA) has caused substantial uncertainties in understanding its origins and environmental impacts. Here, we provide constraints on OA origins through compositional characterization with molecular-level details. Our results suggest that secondary OA (SOA) from monoterpene oxidation accounts for approximately half of summertime fine OA in Centreville, AL, a forested area in the southeastern United States influenced by anthropogenic pollution. We find that different chemical processes involving nitrogen oxides, during days and nights, play a central role in determining the mass of monoterpene SOA produced. These findings elucidate the strong anthropogenic–biogenic interaction affecting ambient aerosol in the southeastern United States and point out the importance of reducing anthropogenic emissions, especially under a changing climate, where biogenic emissions will likely keep increasing.
    Print ISSN: 0027-8424
    Electronic ISSN: 1091-6490
    Topics: Biology , Medicine , Natural Sciences in General
    Published by National Academy of Sciences
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  • 9
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    Anthropogenic enhancements to production of highly oxygenated molecules from autoxidation (2019)
    National Academy of Sciences
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    Publication Date: 2019-03-18
    Description: Atmospheric oxidation of natural and anthropogenic volatile organic compounds (VOCs) leads to secondary organic aerosol (SOA), which constitutes a major and often dominant component of atmospheric fine particulate matter (PM2.5). Recent work demonstrates that rapid autoxidation of organic peroxy radicals (RO2) formed during VOC oxidation results in highly oxygenated organic molecules (HOM) that efficiently form SOA. As NOxemissions decrease, the chemical regime of the atmosphere changes to one in which RO2autoxidation becomes increasingly important, potentially increasing PM2.5, while oxidant availability driving RO2formation rates simultaneously declines, possibly slowing regional PM2.5formation. Using a suite of in situ aircraft observations and laboratory studies of HOM, together with a detailed molecular mechanism, we show that although autoxidation in an archetypal biogenic VOC system becomes more competitive as NOxdecreases, absolute HOM production rates decrease due to oxidant reductions, leading to an overall positive coupling between anthropogenic NOxand localized biogenic SOA from autoxidation. This effect is observed in the Atlanta, Georgia, urban plume where HOM is enhanced in the presence of elevated NO, and predictions for Guangzhou, China, where increasing HOM-RO2production coincides with increases in NO from 1990 to 2010. These results suggest added benefits to PM2.5abatement strategies come with NOxemission reductions and have implications for aerosol–climate interactions due to changes in global SOA resulting from NOxinteractions since the preindustrial era.
    Print ISSN: 0027-8424
    Electronic ISSN: 1091-6490
    Topics: Biology , Medicine , Natural Sciences in General
    Published by National Academy of Sciences
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  • 10
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    Organic Aerosols in the Earth’s Atmosphere (2009)
    American Chemical Society
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    Publication Date: 2009-10-15
    Print ISSN: 0013-936X
    Electronic ISSN: 1520-5851
    Topics: Chemistry and Pharmacology , Energy, Environment Protection, Nuclear Power Engineering
    Published by American Chemical Society
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