On the role of heterogeneous reactions in aluminum combustion

2016 ◽  
Vol 168 ◽  
pp. 378-392 ◽  
Author(s):  
Julien Glorian ◽  
Stany Gallier ◽  
Laurent Catoire
Keyword(s):  
Heterogeneous Reactions ◽  
Aluminum Combustion

scholarly journals The significant contribution of HONO to secondary pollutants during a severe winter pollution event in southern China

2019 ◽  
Vol 19 (1) ◽  
pp. 1-14 ◽  
Author(s):  
Xiao Fu ◽  
Tao Wang ◽  
Li Zhang ◽  
Qinyi Li ◽  
Zhe Wang ◽  
...  
Keyword(s):  
Southern China ◽  
Heterogeneous Reactions ◽  
Severe Winter ◽  
Peak Enhancement ◽  
Key Species ◽  
Secondary Pollutants ◽  
Light Effects ◽  
Haze Formation ◽  
The Pearl River

Abstract. Nitrous acid (HONO) can strongly affect atmospheric photochemistry in polluted regions through the production of hydroxyl radicals (OHs). In January 2017, a severe pollution episode occurred in the Pearl River Delta (PRD) of China, with maximum hourly PM2.5, ozone, and HONO levels reaching 400 µg m−3, 150 ppb, and 8 ppb, respectively, at a suburban site. The present study investigated the sources and processes generating such high HONO concentrations and the role of HONO chemistry in this severe winter episode. Four recently reported HONO sources were added to the Community Multiscale Air Quality (CMAQ) model, including RH-dependent (relative humidity) and light-enhancing effects on heterogeneous reactions, photolysis of particulate nitrate in the atmosphere, and photolysis of HNO3 and nitrate on surfaces. The revised model reproduced the observed HONO and significantly improved its performance for O3 and PM2.5. The model simulations showed that the heterogeneous generation on surfaces (with RH and light effects) was the largest contributor (72 %) to the predicted HONO concentrations, with the RH-enhancing effects more significant at nighttime and the light-enhancing effects more important in the daytime. The photolysis of total nitrate in the atmosphere and deposited on surfaces was the dominant HONO source during noon and afternoon, contributing above 50 % of the simulated HONO. The HONO photolysis was the dominant contributor to HOx production in this episode. With all HONO sources, the daytime average O3 at the Heshan site was increased by 24 ppb (or 70 %), compared to the simulation results without any HONO sources. Moreover, the simulated mean concentrations of TNO3 (HNO3+ fine particle NO3-) at the Heshan site, which was the key species for this haze formation, increased by about 17 µg m−3 (67 %) due to the HONO chemistry, and the peak enhancement reached 55 µg m−3. This study highlights the key role of HONO chemistry in the formation of winter haze in a subtropical environment.

Ubiquity of ClNO2 in the urban boundary layer of Calgary, Alberta, Canada

2016 ◽  
Vol 94 (4) ◽  
pp. 414-423 ◽  
Author(s):  
Levi H. Mielke ◽  
Amanda Furgeson ◽  
Charles A. Odame-Ankrah ◽  
Hans D. Osthoff
Keyword(s):  
Chlorine Atom ◽  
Urban Environments ◽  
Heterogeneous Reactions ◽  
Ionization Mass ◽  
Mixing Ratios ◽  
Nitryl Chloride ◽  
Reservoir Species ◽  
Intermittent Measurements ◽  
Oxidation Of No

The role of nitryl chloride (ClNO2) as a nocturnal nitrogen oxide reservoir species and chlorine atom precursor is well established for polluted coastal areas, but its role at midcontinental locations is less clear. In this paper, intermittent measurements over the course of several seasons of ClNO2 mixing ratios by iodide ion chemical ionization mass spectrometry in Calgary, Alberta, Canada, are presented. Mixing ratios were highly variable between nights and seasons and depended on the abundances of precursors and meteorological conditions. The lowest ClNO2 mixing ratios (nocturnal maximum of 30 parts per trillion by volume (pptv)) were observed in the summer, rationalized by losses of the nitrate radical (NO3) that were more efficient than in the other months. Higher ClNO2 mixing ratios (up to 330 pptv) were observed in the winter and spring months but varied between nights. In the fall, ClNO2 mixing ratios increased from night to night following the application of salt to roads. The ClNO2 yield relative to the amount of NO3 produced from oxidation of NO2 by O3 ranged from 0.1% to 4.5% (10th and 90th percentiles, median 1.0%). The ClNO2 yield relative to N2O5 consumed by heterogeneous reactions was estimated using a time-integrated box model and ranged from 0.5% to 12.1% (10th and 90th percentiles, median 3.4%). The ubiquity of ClNO2 implies that the chlorine atom needs to be considered as an oxidant in high-latitude urban environments in winter.

scholarly journals Bringing Service Interactions Into Focus: Prevention- Versus Promotion-Focused Customers’ Sensitivity to Employee Display Authenticity

2020 ◽  
pp. 109467052090441 ◽  
Author(s):  
Andreas T. Lechner ◽  
Frank Mathmann
Keyword(s):  
Regulatory Focus ◽  
Service Performance ◽  
Heterogeneous Reactions ◽  
Employee Behavior ◽  
Negative Effects ◽  
Frontline Employee ◽  
Conditional Effect ◽  
Emotion Displays ◽  
Dyadic Field

Despite growing managerial interest in frontline employee behavior, and in display authenticity specifically, customers’ heterogeneous reactions to authentic displays have received little scholarly attention. Drawing on emotion as social information theory, we investigate the role of motivational orientations (i.e., regulatory focus) in customer reactions to authentic displays. The findings show that inauthentic displays have stronger negative effects on service performance for prevention-focused than for promotion-focused customers. A dyadic field study details these effects in terms of tipping, and three experiments provide further evidence by experimentally manipulating authenticity and regulatory focus. The conditional effect of authenticity on service performance also is mediated by inferred deception. Specifically, prevention-focused customers interpret inauthentic emotion displays as more deceptive than promotion-focused customers do. Managers should prime customers’ promotion focus using marketing communications before the service delivery when inauthentic displays are likely as well as consider customers’ regulatory focus when designing authenticity training for employees.

The rôle of diffusion during catalysis by colloidal metals and similar substances.

1905 ◽  
Vol 74 (497-506) ◽  
pp. 356-369 ◽  
Author(s):  
Henry J. S. Sand ◽  
John Henry Poynting
Keyword(s):  
Chemical Reactions ◽  
Chemical Equilibrium ◽  
Heterogeneous Systems ◽  
Heterogeneous Reactions ◽  
Diffusion And Convection ◽  
Two Phases ◽  
Special Instance ◽  
Kinetics Of

In a paper on reaction-velocities in heterogeneous systems, Nernst has recently put forward the view that all chemical reactions taking place on the boundary of two phases proceed to equilibrium practically instantaneously, and that the velocities actually observed are simply those with which diffusion and convection renew the reacting material at the boundary. As a special instance of heterogeneous reactions, he mentions catalytic decompositions due to finely divided particles, such as colloidal metals, and he believes it probable that the kinetics of these reactions can be deduced from the assumption that chemical equilibrium remains permanently established on the surface of the particles.

scholarly journals Evaluating evidence for Cl sources and oxidation chemistry in a coastal, urban environment

2013 ◽  
Vol 13 (5) ◽  
pp. 13685-13720 ◽  
Author(s):  
C. J. Young ◽  
R. A. Washenfelder ◽  
P. M. Edwards ◽  
D. D. Parrish ◽  
J. B. Gilman ◽  
...  
Keyword(s):  
Los Angeles ◽  
Recent Observation ◽  
Heterogeneous Reactions ◽  
Tropospheric Chemistry ◽  
Chemical Mechanism ◽  
Production Model ◽  
Atmospheric Oxidation ◽  
The Arctic ◽  
Oh Radicals

Abstract. The role of chlorine atoms (Cl) in atmospheric oxidation was traditionally thought to be limited to the marine boundary layer, where they are produced through heterogeneous reactions involving sea salt. However, recent observation of photolytic Cl precursors (ClNO2 and Cl2) formed from anthropogenic pollution has expanded the potential importance of Cl to include coastal and continental urban areas. Measurements of ClNO2 in Los Angeles during CalNex showed it to be an important primary (first generation) radical source. Ratios of volatile organic compounds (VOCs) have been proposed as a sensitive method to quantify Cl oxidation, but have shown little evidence for a significant role of Cl outside of the Arctic. We used a box model with the Master Chemical Mechanism (MCM v3.2) chemistry scheme, constrained by observations in Los Angeles, to examine the Cl-sensitivity of the most commonly used VOC ratios (i-butane, n-butane, and propane) as a function of NOx and secondary radical production. Model results indicated these and faster reacting VOC tracer ratios could not detect the influence of Cl unless the sustained ratio of OH to Cl was below 200. However, the model results also show that secondary (second generation) OH production resulting from Cl oxidation of VOCs is strongly influenced by NOx, and that this effect can obscure the importance of Cl as a primary oxidant. Calculated concentrations of Cl showed a maximum in mid-morning due to a photolytic source from ClNO2 and loss primarily to reactions with VOCs. The OH to Cl ratio was below 200 for approximately three hours in the morning, but Cl oxidation was not evident from the measured ratios of VOCs. Instead, model simulations show that secondary OH production causes VOC ratios to follow the values expected for OH oxidation despite the significant input of primary Cl from ClNO2 photolysis in the morning. Despite the prevalence of secondary OH as an oxidant in Los Angeles, Cl may play an important role in tropospheric chemistry. The reactivity of Cl in Los Angeles during CalNex was more than an order of magnitude larger than that of OH. In addition, because of its reactivity toward different classes of VOCs and its greater propensity to participate in chain propagation rather than sink reactions, Cl atoms have a different impact on regional atmospheric oxidation than do OH radicals.

Reactive Radicals on Reactive Surfaces: Heterogeneous Processes in Catalysis and Environmental Pollution Control

2005 ◽  
Vol 30 (3) ◽  
pp. 145-213 ◽  
Author(s):  
Christopher J. Rhodes
Keyword(s):  
Pollution Control ◽  
Surface Defects ◽  
Practical Investigations ◽  
Heterogeneous Reactions ◽  
Molecular Surface ◽  
Spin Resonance ◽  
Heterogeneous Processes ◽  
Tunnelling Microscopy ◽  
Reactive Radicals

Many reactions that occur on solid surfaces are mediated by free radicals. A review is presented of both mechanistic and practical investigations in relation to catalysis and environmental applications. The review begins with actual imaging of surface adsorbed reactive radicals using scanning tunnelling microscopy (STM), and then discusses a range of examples, mainly as underpinned by electron spin resonance (ESR) measurements. Included are surface defects and their reactions, studies of the redox behaviour of zeolites, and the use of radicals adsorbed in zeolites as molecular surface probes of diffusion and reactivity within these important materials. Photocatalysis, mainly using TiO2-based materials, is reviewed both from the fundamental perspective and in terms of some practical examples relating to pollution control. Other reactive oxide surfaces are considered, including silica, and the nature of paramagnetic centres that may be induced thereon by a variety of activation procedures. Evidence is presented for the formation of radical species during heterogeneous reactions on metal surfaces. Finally, the role of free radical generation in creating and modifying polymer and nanomolecular systems is discussed, and the health implications of the ability of some solids such as quartz to generate reactive oxygen radicals in contact with biological media.

Mandelic acid and phenyllactic acid “Reaction Sets” for exploring the kinetics and mechanism of oxidations by hydrous manganese oxide (HMO)

2019 ◽  
Vol 21 (6) ◽  
pp. 1038-1051
Author(s):  
Xiaomeng Xia ◽  
Alan T. Stone
Keyword(s):  
Physicochemical Properties ◽  
Manganese Oxide ◽  
Mandelic Acid ◽  
Heterogeneous Reactions ◽  
Hydroxy Acids ◽  
Medium Effects ◽  
Phenyllactic Acid ◽  
Hydrous Manganese Oxide ◽  
Acid Reaction

Two hydroxy acids reaction sets are used to explore the kinetics, the role of physicochemical properties, and medium effects of the heterogeneous reactions on hydrous manganese oxide (HMO) surface.

scholarly journals The potential importance of frost flowers, recycling on snow, and open leads for Ozone Depletion Events

2007 ◽  
Vol 7 (2) ◽  
pp. 4521-4595 ◽  
Author(s):  
M. Piot ◽  
R. von Glasow
Keyword(s):  
Gas Phase ◽  
Ozone Depletion ◽  
Aerosol Deposition ◽  
Heterogeneous Reactions ◽  
The Arctic ◽  
Acid Uptake ◽  
Mixing Ratios ◽  
Haze Pollution ◽  
Frost Flowers

Abstract. We present model studies with the one-dimensional model MISTRA to investigate the potential role of frost flowers, recycling on snow, and open leads in the depletion of tropospheric ozone in the Arctic spring. In our model, we assumed frost flower aerosols to be the major source of bromine. We show that a major ozone depletion event can be satisfactorily reproduced only if the recycling on snow of deposited bromine into gas phase bromine is assumed. In the model, this cycling is more efficient than the bromine explosion process and maintains sufficiently high levels of bromine to deplete ozone down to few nmol mol−1 within four days. We assessed the influence of different surface combinations (open lead/frost flowers) on the chemistry in the model. Results showed noticeable modifications affecting the composition of aerosols and the deposition velocities. A model run with a series of coupled frost flower fields and open leads, separated by large areas of snow, showed results comparable with field observations. In addition, we studied the effects of modified temperature of either the frost flower field or the ambient airmass. A warmer frost flower field increases the relative humidity and the aerosol deposition rate. The deposition/re-emission process gains in importance, inducing more reactive bromine in the gas phase, and a stronger ozone depletion. A decrease of 1 K in airmass temperature shows in our model that the aerosol uptake capacities of all gas phase species substantially increases, leading to enhanced uptake of acids from the gas phase. Consequently, the so-called bromine explosion accelerated and O3 mixing ratios decreased. In our model representation, variations in wind speed affected the aerosol source function and influenced the amount of bromine in the atmosphere and thus the ozone depletion strength. Recent studies have suggested the important role of the precipitation of calcium carbonate (CaCO3) out of the brine layer for the possible acidification of the liquid phase by acid uptake. Our investigation showed that this precipitation is a crucial process for the timing of the bromine explosion in aerosols. Nevertheless, model runs with either 50% precipitation or complete precipitation displayed a relatively weak difference in ozone mixing ratios after four simulated days. By considering conditions typical for "Arctic Haze" pollution events at the start of the run we obtained a low pH in frost flower aerosols due to a greater mixing ratio of SO2, and a strong recycling efficiency via large aerosol number concentration. The aerosol acidification during a haze event most likely intensifies the ozone depletion strength and occurrence. The comparison between our modeled deposition on snow and sampled snow at Barrow (Alaska) shows that approximately 75% of deposited bromine may be re-emitted into the gas phase as Br2/BrCl. Among several non-halogen fluxes from the snow, model simulations showed that only HONO affects the chemistry. Finally, we investigated the release of Br2 potentially produced by heterogeneous reactions directly on frost flowers. In this case, we obtained unrealistic results of aerosol compositions and deposition rates on snow compared to observations in the Arctic.

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