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1. Comparison of Airborne Reactive Nitrogen Measurements During WINTER

   https://doi.org/10.1029/2019JD030700  

   Sparks, Tamara L.; Ebben, Carlena J.; Wooldridge, Paul J.; Lopez‐Hilfiker, Felipe D.; Lee, Ben H.; Thornton, Joel A.; McDuffie, Erin E.; Fibiger, Dorothy L.; Brown, Steven S.; Montzka, Denise D.; et al (October 2019, Journal of Geophysical Research: Atmospheres)

   Abstract We present a comparison of instruments measuring nitrogen oxide species from an aircraft during the 2015 Wintertime INvestigation of Transport, Emissions, and Reactivity (WINTER) campaign over the northeast United States. Instrument techniques compared here include chemiluminescence (CL), thermal dissociation laser‐induced fluorescence (TD‐LIF), cavity ring‐down spectroscopy (CRDS), high‐resolution time of flight, iodide‐adduct chemical ionization mass spectrometry (I^‐CIMS), and aerosol mass spectrometry. Species investigated include NO₂, NO, total nitrogen oxides (NO_y), N₂O₅, ClNO₂, and HNO₃. Particulate‐phase nitrate is also included for comparisons of HNO₃and NO_y. Instruments generally agreed within reported uncertainties, with individual flights sometimes showing much better agreement than the data set taken as a whole, due to flight‐to‐flight slope changes. NO measured by CRDS and CL showed an average relative slope of 1.16 ± 0.01 across all flights, which is outside of combined uncertainties. The source of the error was not identified. For NO₂measured by CRDS and TD‐LIF the average was 1.02 ± 0.00; for NO_ymeasured by CRDS and CL the average was 1.01 ± 0.00; and for N₂O₅measured by CRDS and I^‐CIMS the average was 0.89 ± 0.01. NO_ybudget closure to within 20% is demonstrated. We observe nonlinearity in NO₂and NO_ycorrelations at concentrations above ~30 ppbv that may be related to the NO discrepancy noted above. For ClNO₂there were significant differences between I^‐CIMS and TD‐LIF, potentially due in part to the temperature used for thermal dissociation. Although the fraction of particulate nitrate measured by the TD‐LIF is not well characterized, it improves comparisons to include particulate measurements. 

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2. Multiphase Reactive Bromine Chemistry during Late Spring in the Arctic: Measurements of Gases, Particles, and Snow

   https://doi.org/10.1021/acsearthspacechem.2c00189  

   Jeong, Daun; McNamara, Stephen M.; Barget, Anna J.; Raso, Angela R.; Upchurch, Lucia M.; Thanekar, Sham; Quinn, Patricia K.; Simpson, William R.; Fuentes, Jose D.; Shepson, Paul B.; et al (December 2022, ACS Earth and Space Chemistry)
3. Parahydrogen‐Induced Hyperpolarization of Gases

   https://doi.org/10.1002/anie.201915306  

   Kovtunov, Kirill_V; Koptyug, Igor_V; Fekete, Marianna; Duckett, Simon_B; Theis, Thomas; Joalland, Baptiste; Chekmenev, Eduard_Y (August 2020, Angewandte Chemie International Edition)

   Abstract Imaging of gases is a major challenge for any modality including MRI. NMR and MRI signals are directly proportional to the nuclear spin density and the degree of alignment of nuclear spins with applied static magnetic field, which is called nuclear spin polarization. The level of nuclear spin polarization is typically very low, i.e., one hundred thousandth of the potential maximum at 1.5 T and a physiologically relevant temperature. As a result, MRI typically focusses on imaging highly concentrated tissue water. Hyperpolarization methods transiently increase nuclear spin polarizations up to unity, yielding corresponding gains in MRI signal level of several orders of magnitude that enable the 3D imaging of dilute biomolecules including gases. Parahydrogen‐induced polarization is a fast, highly scalable, and low‐cost hyperpolarization technique. The focus of this Minireview is to highlight selected advances in the field of parahydrogen‐induced polarization for the production of hyperpolarized compounds, which can be potentially employed as inhalable contrast agents. 

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4. Airborne transmission of respiratory viruses

   https://doi.org/10.1126/science.abd9149  

   Wang, Chia C.; Prather, Kimberly A.; Sznitman, Josué; Jimenez, Jose L.; Lakdawala, Seema S.; Tufekci, Zeynep; Marr, Linsey C. (August 2021, Science)

   The COVID-19 pandemic has revealed critical knowledge gaps in our understanding of and a need to update the traditional view of transmission pathways for respiratory viruses. The long-standing definitions of droplet and airborne transmission do not account for the mechanisms by which virus-laden respiratory droplets and aerosols travel through the air and lead to infection. In this Review, we discuss current evidence regarding the transmission of respiratory viruses by aerosols—how they are generated, transported, and deposited, as well as the factors affecting the relative contributions of droplet-spray deposition versus aerosol inhalation as modes of transmission. Improved understanding of aerosol transmission brought about by studies of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection requires a reevaluation of the major transmission pathways for other respiratory viruses, which will allow better-informed controls to reduce airborne transmission. 

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5. Anisotropic thermalization of dilute dipolar gases

   https://doi.org/10.1103/PhysRevA.103.063320  

   Wang, Reuben R.; Bohn, John L. (June 2021, Physical Review A)

   null (Ed.)