More Like this

1. ClNO 2 Yields From Aircraft Measurements During the 2015 WINTER Campaign and Critical Evaluation of the Current Parameterization

   https://doi.org/10.1029/2018JD029358  

   McDuffie, Erin E. ; Fibiger, Dorothy L. ; Dubé, William P. ; Lopez Hilfiker, Felipe ; Lee, Ben H. ; Jaeglé, Lyatt ; Guo, Hongyu ; Weber, Rodney J. ; Reeves, J. Michael ; Weinheimer, Andrew J. ; et al ( November 2018 , Journal of Geophysical Research: Atmospheres)

   Nitryl chloride (ClNO₂) plays an important role in the budget and distribution of tropospheric oxidants, halogens, and reactive nitrogen species. ClNO₂is formed from the heterogeneous uptake and reaction of dinitrogen pentoxide (N₂O₅) on chloride‐containing aerosol, with a production yield,ϕ(ClNO₂), defined as the moles of ClNO₂produced relative to N₂O₅lost. Theϕ(ClNO₂) has been increasingly incorporated into 3‐D chemical models where it is parameterized based on laboratory‐derived kinetics and currently accepted aqueous‐phase formation mechanism. This parameterization modelsϕ(ClNO₂) as a function of the aerosol chloride to water molar ratio. Box model simulations of night flights during the 2015 Wintertime INvestigation of Transport, Emissions, and Reactivity (WINTER) aircraft campaign derived 3,425 individualϕ(ClNO₂) values with a median of 0.138 and range of 0.003 to 1. Comparison of the box model median to those predicted by two other field‐basedϕ(ClNO₂) derivation methods agreed within a factor of 1.3, within the uncertainties of each method. In contrast, the box model median was 75–84% lower than predictions from the laboratory‐based parameterization (i.e., [parameterization − box model]/parameterization). An evaluation of factors influencing this difference reveals a positive dependence ofϕ(ClNO₂) on aerosol water, opposite to the currently parameterized trend. Additional factors may include aqueous‐phase competition reactions for the nitronium ion intermediate and/or direct ClNO₂loss mechanisms. Further laboratory studies of ClNO₂formation and the impacts of aerosol water, sulfate, organics, and ClNO₂aqueous‐phase reactions are required to elucidate and quantify these processes on ambient aerosol, critical for the development of a robustϕ(ClNO₂) parameterization.

    

   more » « less
2. Observational Constraints on the Formation of Cl 2 From the Reactive Uptake of ClNO 2 on Aerosols in the Polluted Marine Boundary Layer

   https://doi.org/10.1029/2019JD030627  

   Haskins, Jessica D. ; Lee, Ben H. ; Lopez‐Hilifiker, Felipe D. ; Peng, Qiaoyun ; Jaeglé, Lyatt ; Reeves, J. Michael ; Schroder, Jason C. ; Campuzano‐Jost, Pedro ; Fibiger, Dorothy ; McDuffie, Erin E. ; et al ( August 2019 , Journal of Geophysical Research: Atmospheres)

   We use observations from the 2015 Wintertime Investigation of Transport, Emissions, and Reactivity (WINTER) aircraft campaign to constrain the proposed mechanism of Cl₂production from ClNO₂reaction in acidic particles. To reproduce Cl₂concentrations observed during WINTER with a chemical box model that includes ClNO₂reactive uptake to form Cl₂, the model required the ClNO₂reaction probability, γ (ClNO₂), to range from 6 × 10⁻⁶to 7 × 10⁻⁵, with a mean value of 2.3 × 10⁻⁵(±1.8 × 10⁻⁵). These field‐determined γ (ClNO₂) are more than an order of magnitude lower than those determined in previous laboratory experiments on acidic surfaces, even when calculated particle pH is ≤2. We hypothesize this is because thick salt films in the laboratory enhanced the reactive uptake ClNO₂compared to that which would occur in submicron aerosol particles. Using the reacto‐diffusive length‐scale framework, we show that the field and laboratory observations can be reconciled if the net aqueous‐phase reaction rate constant for ClNO₂(aq) + Cl^‐(aq) in acidic particles is on the order of 10⁴s⁻¹. We show that wet particle diameter and particulate chloride mass together explain 90% of the observed variance in the box model‐derived γ (ClNO₂), implying that the availability of chloride and particle volume limit the efficiency of the reaction. Despite a much lower conversion of ClNO₂into Cl₂, this mechanism can still be responsible for the nocturnal formation of 10–20 pptv of Cl₂in polluted regions, yielding an atmospherically relevant concentration of Cl atoms the following morning.

    

   more » « less
3. 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)

   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.

    

   more » « less
4. Reactive uptake of N 2 O 5 by atmospheric aerosol is dominated by interfacial processes

   https://doi.org/10.1126/science.abd7716  

   Galib, Mirza ; Limmer, David T. ( February 2021 , Science)

   Nitrogen oxides are removed from the troposphere through the reactive uptake of N₂O₅into aqueous aerosol. This process is thought to occur within the bulk of an aerosol, through solvation and subsequent hydrolysis. However, this perspective is difficult to reconcile with field measurements and cannot be verified directly because of the fast reaction kinetics of N₂O₅. Here, we use molecular simulations, including reactive potentials and importance sampling, to study the uptake of N₂O₅into an aqueous aerosol. Rather than being mediated by the bulk, uptake is dominated by interfacial processes due to facile hydrolysis at the liquid-vapor interface and competitive reevaporation. With this molecular information, we propose an alternative interfacial reactive uptake model consistent with existing experimental observations.

    

   more » « less
5. The Chemistry Mechanism in the Community Earth System Model Version 2 (CESM2)

   https://doi.org/10.1029/2019MS001882  

   Emmons, Louisa K. ; Schwantes, Rebecca H. ; Orlando, John J. ; Tyndall, Geoff ; Kinnison, Douglas ; Lamarque, Jean‐François ; Marsh, Daniel ; Mills, Michael J. ; Tilmes, Simone ; Bardeen, Charles ; et al ( April 2020 , Journal of Advances in Modeling Earth Systems)

   The Community Earth System Model version 2 (CESM2) includes a detailed representation of chemistry throughout the atmosphere in the Community Atmosphere Model with chemistry and Whole Atmosphere Community Climate Model configurations. These model configurations use the Model for Ozone and Related chemical Tracers (MOZART) family of chemical mechanisms, covering the troposphere, stratosphere, mesosphere, and lower thermosphere. The new MOZART tropospheric chemistry scheme (T1) has a number of updates over the previous version (MOZART‐4) in CESM, including improvements to the oxidation of isoprene and terpenes, organic nitrate speciation, and aromatic speciation and oxidation and thus improved representation of ozone and secondary organic aerosol precursors. An evaluation of the present‐day simulations of CESM2 being provided for Climate Model Intercomparison Project round 6 (CMIP6) is presented. These simulations, using the anthropogenic and biomass burning emissions from the inventories specified for CMIP6, as well as online calculation of emissions of biogenic compounds, lightning NO, dust, and sea salt, indicate an underestimate of anthropogenic emissions of a variety of compounds, including carbon monoxide and hydrocarbons. The simulation of surface ozone in the southeast United States is improved over previous model versions, largely due to the improved representation of reactive nitrogen and organic nitrate compounds resulting in a lower ozone production rate than in CESM1 but still overestimates observations in summer. The simulation of tropospheric ozone agrees well with ozonesonde observations in many parts of the globe. The comparison of NO_xand PAN to aircraft observations indicates the model simulates the nitrogen budget well.

    

   more » « less