A modeling study of the nighttime radical chemistry in the lower continental troposphere: 1. Development of a detailed chemical mechanism including nighttime chemistry

2001 ◽  
Vol 106 (D9) ◽  
pp. 9959-9990 ◽  
Author(s):  
Isabelle Bey ◽  
Bernard Aumont ◽  
Gérard Toupance
Keyword(s):  
Chemical Mechanism ◽  
Radical Chemistry ◽  
Nighttime Chemistry ◽  
Detailed Chemical ◽  
Modeling Study

3D CFD Modeling of a Biodiesel-Fueled Diesel Engine Based on a Detailed Chemical Mechanism

2012 ◽  
Author(s):  
Junfeng Yang ◽  
Monica Johansson ◽  
Chitralkumar Naik ◽  
Karthik Puduppakkam ◽  
Valeri Golovitchev ◽  
...  
Keyword(s):  
Diesel Engine ◽  
Chemical Mechanism ◽  
Cfd Modeling ◽  
Detailed Chemical

Detailed chemical mechanism of the phase transition in nano-SrTiO3 perovskite with visible luminescence

2020 ◽  
Vol 120 ◽  
pp. 108125
Author(s):  
Sonali Mehra ◽  
Swati Bishnoi ◽  
Lalit Goswami ◽  
Govind Gupta ◽  
Avanish Kumar Srivastava ◽  
...  
Keyword(s):  
Phase Transition ◽  
Chemical Mechanism ◽  
Visible Luminescence ◽  
Detailed Chemical

scholarly journals Air-snowpack exchange of bromine, ozone and mercury in the springtime Arctic simulated by the 1-D model PHANTAS – Part 1: In-snow bromine activation and its impact on ozone

2013 ◽  
Vol 13 (8) ◽  
pp. 20341-20418 ◽  
Author(s):  
K. Toyota ◽  
J. C. McConnell ◽  
R. M. Staebler ◽  
A. P. Dastoor
Keyword(s):  
Boundary Layer ◽  
Aqueous Phase ◽  
Ambient Air ◽  
Atmospheric Mercury ◽  
Chemical Mechanism ◽  
The Arctic ◽  
Radical Chemistry ◽  
Ozone Loss ◽  
Key Species ◽  
Reactive Trace Gases

Abstract. To provide a theoretical framework towards better understanding of ozone depletion events (ODEs) and atmospheric mercury depletion events (AMDEs) in the polar boundary layer, we have developed a one-dimensional model that simulates multiphase chemistry and transport of trace constituents from porous snowpack and through the atmospheric boundary layer (ABL) as a unified system. In this paper, we describe a general configuration of the model and the results of simulations related to reactive bromine release from the snowpack and ODEs during the Arctic spring. The model employs a chemical mechanism adapted from the one previously used for the simulation of multiphase halogen chemistry involving deliquesced sea-salt aerosols in the marine boundary layer. A common set of aqueous-phase reactions describe chemistry both in the liquid-like (or brine) layer on the grain surface of the snowpack and in "haze" aerosols mainly composed of sulfate in the atmosphere. The process of highly soluble/reactive trace gases, whether entering the snowpack from the atmosphere or formed via gas-phase chemistry in the snowpack interstitial air (SIA), is simulated by the uptake on brine-covered snow grains and subsequent reactions in the aqueous phase while being traveled vertically within the SIA. A "bromine explosion", by which, in a conventional definition, HOBr formed in the ambient air is deposited and then converted heterogeneously to Br2, is a dominant process of reactive bromine formation in the top 1 mm (or less) layer of the snowpack. Deeper in the snowpack, HOBr formed within the SIA leads to an in-snow bromine explosion, but a significant fraction of Br2 is also produced via aqueous radical chemistry in the brine on the surface of the snow grains. These top- and deeper-layer productions of Br2 both contribute to the Br2 release into the atmosphere, but the deeper-layer production is found to be more important for the net outflux of reactive bromine. Although ozone is removed via bromine chemistry, it is also among the key species that control both the conventional and in-snow bromine explosions. On the other hand, aqueous-phase radical chemistry initiated by photolytic OH formation in the liquid-like layer is also a significant contributor to the in-snow source of Br2 and can operate without ozone, whereas the delivery of Br2 to the atmosphere becomes much smaller after ozone is depleted. Catalytic ozone loss via bromine radicals occurs more rapidly in the SIA than in the ambient air, giving rise to apparent dry deposition velocities for ozone from the air to the snow on the order of 10−3 cm s-1 under sunlight. Overall, however, the depletion of ozone in the system is caused predominantly by ozone loss in the ambient air. Increasing depth of the turbulent ABL under windy conditions will delay the build-up of reactive bromine and the resultant loss of ozone, while leading to the higher column amount of BrO in the atmosphere. If moderately saline and acidic snowpack is as prevalent as assumed in our model runs on sea ice during the spring, the shallow, stable ABL under calm weather conditions may undergo persistent ODEs without substantial contributions from blowing/drifting snow and wind-pumping mechanisms, whereas the column densities of BrO in the ABL will likely remain too low during the course of such events to be detected unambiguously by satellite nadir measurements.

Comprehensive Detailed Chemical Kinetic Modeling Study of Toluene Oxidation

2011 ◽  
Vol 25 (11) ◽  
pp. 4915-4936 ◽  
Author(s):  
W. K. Metcalfe ◽  
S. Dooley ◽  
F. L. Dryer
Keyword(s):  
Kinetic Modeling ◽  
Chemical Kinetic ◽  
Toluene Oxidation ◽  
Detailed Chemical ◽  
Modeling Study

scholarly journals An experimental and detailed chemical kinetic modeling study of hydrogen and syngas mixture oxidation at elevated pressures

2013 ◽  
Vol 160 (6) ◽  
pp. 995-1011 ◽  
Author(s):  
Alan Kéromnès ◽  
Wayne K. Metcalfe ◽  
Karl A. Heufer ◽  
Nicola Donohoe ◽  
Apurba K. Das ◽  
...  
Keyword(s):  
Kinetic Modeling ◽  
Chemical Kinetic ◽  
Elevated Pressures ◽  
Detailed Chemical ◽  
Modeling Study

scholarly journals Oxidative capacity and radical chemistry in the polluted atmosphere of Hong Kong and Pearl River Delta region: analysis of a severe photochemical smog episode

2016 ◽  
Author(s):  
Likun Xue ◽  
Rongrong Gu ◽  
Tao Wang ◽  
Xinfeng Wang ◽  
Sandra Saunders ◽  
...  
Keyword(s):  
Hong Kong ◽  
Pearl River Delta ◽  
Oxidative Capacity ◽  
River Delta ◽  
Chemical Mechanism ◽  
Solar Irradiation ◽  
Pearl River ◽  
Photochemical Smog ◽  
Radical Chemistry ◽  
Polluted Atmosphere

Abstract. We analyze a multi-day photochemical smog episode to understand the oxidative capacity and radical chemistry of the polluted atmosphere in Hong Kong and the Pearl River Delta (PRD) region. A photochemical box model based on the Master Chemical Mechanism (MCM v3.2) is constrained by an intensive set of field observations to elucidate the budgets of ROX (ROX=OH+HO2+RO2) and NO3 radicals. Highly abundant radical precursors (i.e., O3, HONO and carbonyls), nitrogen oxides (NOX) and volatile organic compounds (VOCs) facilitate strong production and efficient recycling of ROX radicals. The OH reactivity is dominated by oxygenated VOCs (OVOCs), followed by aromatics, alkenes and alkanes. Photolysis of OVOCs (except for formaldehyde) is the dominant primary source of ROX with an average daytime contribution of 47 %. HONO photolysis is the largest contributor to OH and the second most significant source (19 %) of ROX. Other considerable ROX sources include O3 photolysis (11 %), formaldehyde photolysis (10 %), and ozonolysis reactions of unsaturated VOCs (6.2 %). In one case when solar irradiation was attenuated by the high aerosol loadings, NO3 became an important oxidant and the NO3-initiated VOC oxidation presented another significant ROX source (6.2 %) even during daytime. Sensitivity studies show that controlling aromatics is the most efficient way to reduce the atmospheric oxidative capacity and mitigate photochemical pollution in Hong Kong. This study suggests the possible impacts of daytime NO3 chemistry in polluted atmospheres under conditions with the co-existence of abundant O3, NO2, VOCs and aerosols, and also provides new insights into the radical chemistry that essentially drives the formation of photochemical smog in Hong Kong and the PRD region.

Characteristics of Methanol Hydrothermal Combustion: Detailed Chemical Kinetics Coupled with Simple Flow Modeling Study

2017 ◽  
Vol 56 (18) ◽  
pp. 5469-5478 ◽  
Author(s):  
Mengmeng Ren ◽  
Shuzhong Wang ◽  
Jie Zhang ◽  
Yang Guo ◽  
Donghai Xu ◽  
...  
Keyword(s):  
Chemical Kinetics ◽  
Flow Modeling ◽  
Detailed Chemical Kinetics ◽  
Simple Flow ◽  
Detailed Chemical ◽  
Modeling Study

scholarly journals Air-snowpack exchange of bromine, ozone and mercury in the springtime Arctic simulated by the 1-D model PHANTAS – Part 2: Mercury and its speciation

2013 ◽  
Vol 13 (8) ◽  
pp. 22151-22220 ◽  
Author(s):  
K. Toyota ◽  
A. P. Dastoor ◽  
A. Ryzhkov
Keyword(s):  
Boundary Layer ◽  
Temperature Dependence ◽  
Ozone Depletion ◽  
Ambient Air ◽  
Companion Paper ◽  
Atmospheric Mercury ◽  
Chemical Mechanism ◽  
The Arctic ◽  
Radical Chemistry ◽  
Trace Constituents

Abstract. Atmospheric mercury depletion events (AMDEs) refer to a recurring depletion of mercury in the springtime Arctic (and Antarctic) boundary layer, occurring, in general, concurrently with ozone depletion events (ODEs). To close some of the knowledge gaps in the physical and chemical mechanisms of AMDEs and ODEs, we have developed a one-dimensional model that simulates multiphase chemistry and transport of trace constituents throughout porous snowpack and in the overlying atmospheric boundary layer (ABL). Building on the model reported in a companion paper (Part 1: In-snow bromine activation and its impact on ozone), we have expanded the chemical mechanism to include the reactions of mercury in the gas- and aqueous-phases with temperature dependence of rate and equilibrium constants accounted for wherever possible. Thus the model allows us to study the chemical and physical processes taking place during ODEs and AMDEs within a single framework where two-way interactions between the snowpack and the atmosphere are simulated in a detailed, process-oriented manner. Model runs are conducted for meteorological and chemical conditions representing the springtime Arctic ABL loaded with "haze" sulfate aerosols and the underlying saline snowpack laid on sea ice. Using recent updates for the Hg + Br ⇄ HgBr reaction kinetics, we show that the rate and magnitude of photochemical loss of gaseous elemental mercury (GEM) during AMDEs exhibit a strong dependence on the choice of reaction(s) of HgBr subsequent to its formation. At 253 K, the temperature that is presumably low enough for bromine radical chemistry to cause prominent AMDEs as indicated from field observations, the parallel occurrence of AMDEs and ODEs is simulated if the reaction HgBr + BrO is assumed to produce a thermally stable intermediate, Hg(OBr)Br, at the same rate constant as the reaction HgBr + Br. On the contrary, the simulated depletion of atmospheric mercury is notably diminished by not allowing the former reaction to occur in the model. Similarly to ozone (reported in the companion paper), GEM is destroyed via bromine radical chemistry more vigorously in the snowpack interstitial air than in the ambient air. However, the impact of such in-snow sink of GEM is found to be often masked by the re-emissions of GEM from the snow following the photo-reduction of Hg(II) deposited from the atmosphere. Gaseous oxidized mercury (GOM) formed in the ambient air is found to undergo fast "dry deposition" to the snowpack by being trapped on the snow grains in the top ~ 1 mm layer. We hypothesize that liquid-like layers on the surface of snow grains are connected to create a network throughout the snowpack, thereby facilitating the vertical diffusion of trace constituents trapped on the snow grains at much greater rates than one would expect inside solid ice crystals. Nonetheless, on the timescale of a week simulated in this study, the signal of atmospheric deposition does not extend notably below the top few centimeters of the snowpack. We propose and show that particulate-bound mercury (PBM) is produced mainly as HgBr42− by taking up GOM into bromide-enriched aerosols after ozone is significantly depleted in the air mass. In the Arctic, "haze" aerosols may thus retain PBM in ozone-depleted air masses, allowing the airborne transport of oxidized mercury from the area of its production farther than in the form of GOM. Temperature dependence of thermodynamic constants calculated in this study for Henry's law and aqueous-phase halide complex formation of Hg(II) species is a critical factor for this proposition, calling for experimental verification. The proposed mechanism may explain a major part of changes in the GOM-PBM partitioning with seasons, air temperature and the concurrent progress of ozone depletion as observed in the high Arctic. The net deposition of mercury to the surface snow is shown to increase with the thickness of the turbulent ABL and to correspond well with the column amount of BrO in the atmosphere.

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