Literatura científica selecionada sobre o tema "Radical hydroxyl. Chlore. Ozone"
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Artigos de revistas sobre o assunto "Radical hydroxyl. Chlore. Ozone"
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Ye, Miaomiao, Tuqiao Zhang, Zhiwei Zhu, Yan Zhang e Yiping Zhang. "Photodegradation of 4-chloronitrobenzene in the presence of aqueous titania suspensions in different gas atmospheres". Water Science and Technology 64, n.º 7 (1 de outubro de 2011): 1466–72. http://dx.doi.org/10.2166/wst.2011.531.
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The photocatalytic degradation of 4-chloronitrobenzene (4-CNB) was carried out using Degussa P25 TiO2 as photocatalyst in three different gas atmospheres: nitrogen, oxygen, and ozone. The total organic carbon (TOC) and inorganic anions including chloride, nitrite, and nitrate anions were measured to monitor the mineralization processes, while the degradation of 4-CNB and the formation of intermediates were followed by liquid chromatography–mass spectrometry (LC/MS). Results showed that the photocatalytic efficiency followed the order of TiO2/UV/N2 < TiO2/UV/O2 < TiO2/UV/O3, which was further proved by evaluating the reaction activities using electron paramagnetic resonance (EPR) spin trapping technique. Chlorine atom, nitro group and hydrogen atom of the benzene ring could be displaced by hydroxyl radical (•OH) leading to the formation of chloride, nitrite (III) anions and a variety of phenols, then the nitrite (III) anions were further oxidized to nitrate (V) anions. 4-Nitrophenol and 5-chloro-2-nitrophenol were identified and quantified in both of the TiO2/UV/N2 and TiO2/UV/O2 processes while no aromatic intermediates were monitored in the process of TiO2/UV/O3.
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Cho, Min, Hyenmi Chung e Jeyong Yoon. "Disinfection of Water Containing Natural Organic Matter by Using Ozone-Initiated Radical Reactions". Applied and Environmental Microbiology 69, n.º 4 (abril de 2003): 2284–91. http://dx.doi.org/10.1128/aem.69.4.2284-2291.2003.
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ABSTRACT Ozone is widely used to disinfect drinking water and wastewater due to its strong biocidal oxidizing properties. Recently, it was reported that hydroxyl radicals (·OH), resulting from ozone decomposition, play a significant role in microbial inactivation when Bacillus subtilis endospores were used as the test microorganisms in pH controlled distilled water. However, it is not yet known how natural organic matter (NOM), which is ubiquitous in sources of drinking water, affects this process of disinfection by ozone-initiated radical reactions. Two types of water matrix were considered for this study. One is water containing humic acid, which is commercially available. The other is water from the Han River. This study reported that hydroxyl radicals, initiated by the ozone chain reaction, were significantly effective at B. subtilis endospore inactivation in water containing NOM, as well as in pH-controlled distilled water. The type of NOM and the pH have a considerable effect on the percentage of disinfection by hydroxyl radicals, which ranged from 20 to 50%. In addition, the theoretical C̅T value of hydroxyl radicals for 2-log B. subtilis removal was estimated to be about 2.4 × 104 times smaller than that of ozone, assuming that there is no synergistic activity between ozone and hydroxyl radicals.
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Jung, Jong Tae, Jong Oh Kim, Bum Gun Kwon e Dong Ha Song. "Removal of Refractory Organic Compounds Using Peroxy Radical and Ozone Reaction in Aqueous Solution". Materials Science Forum 569 (janeiro de 2008): 33–36. http://dx.doi.org/10.4028/www.scientific.net/msf.569.33.
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This study was conducted to evaluate the treatment performance of the system using peroxy radical/ozone reaction for refractory organic compounds removal in aqueous solution. The effect of initial humic acid concentration was conducted under the conditions of humic acid concentration 10 mg/L, 30 mg/L, 50 mg/L and 100 mg/L. Reaction rate constant (k) in 30 mg/L of humic acid concentration was higher than that of humic acid concentration 10 mg/L, 50 mg/L amd 100 mg/L. However, it decreased over the range of 30 mg/L of humic acid concentration due to the action of internal filter of humic acid itself. Reaction rate constant (k) in the initial 20 minute of reaction time was accelerated by decreasing hydraulic retention time (HRT). This may be ascribed to increase the reaction time between peroxy radical and ozone. pH is a key for both ozone stability and TiO2 surface property in aqueous solution. Reaction rate constant (k) of acid solution on pH variation was smaller compared to that of neutral or basic circumstances because ozone decomposes easily into hydroxyl radicals in neutral or basic solution. At reaction rate constant (k) for humic acid degradation in each unit process, peroxy radical/ozone combined system was higher than that of ozone only due to the effective production of hydroxyl radical. An obvious difference between ozone and peroxy radical/ozone is the consequence of hydroxyl radical produced by the reaction of ozone molecules and peroxy radicals.
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Beltrán, Fernando J., Manuel Checa, Javier Rivas e Juan F. García-Araya. "Modeling the Mineralization Kinetics of Visible Led Graphene Oxide/Titania Photocatalytic Ozonation of an Urban Wastewater Containing Pharmaceutical Compounds". Catalysts 10, n.º 11 (30 de outubro de 2020): 1256. http://dx.doi.org/10.3390/catal10111256.
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In a water ozonation process, dissolved organics undergo two reactions at least: direct ozone attack and oxidation with hydroxyl radicals generated from the ozone decomposition. In the particular case of urban wastewater contaminated with pharmaceuticals, competition between these two reactions can be studied through application of gas–liquid reaction kinetics. However, there is a lack in literature about kinetic modeling of ozone processes in water specially in photocatalytic ozonation. In this work, lumped reactions of ozone and hydroxyl radicals with total organic carbon have been proposed. Urban wastewater containing a mixture of eight pharmaceutical compounds has been used to establish the kinetic model that simulates the mineralization process. The kinetic model is based on a mechanism of free radical and molecular reactions and the knowledge of mass transfer, chemical reaction rate constants, and radiation transfer data. According to the model, both single ozonation and photocatalytic ozonation present two distinct reaction periods characterized by the absence and presence of dissolved ozone. In the first period (less than 10 min), pharmaceuticals mainly disappear by direct ozone reactions and TOC variation due to these compounds has been modeled according to gas–liquid reaction kinetics through a lumped ozone-pharmaceutical TOC fast second order reaction. The corresponding rate constant of this reaction was found to change with time from 3 × 105 to 200 M−1 s−1 with Hatta values higher than 0.3. In the second period (nearly 5 h), competition between direct and hydroxyl radical reactions takes place and a kinetic model based on a direct and free radical reaction mechanism is proposed. Main influencing parameters to be known were: Direct ozone reaction rate constant, catalyst quantum yield, and hydroxyl radical scavengers. The first two take values of 0.5 M−1 s−1 and 5 × 10−4 mol·photon−1, respectively, while a fraction of TOC between 10% and 90% that changes with time was found to possess hydroxyl radical scavenger nature.
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Tootchi, L., R. Seth, S. Tabe e P. Yang. "Transformation products of pharmaceutically active compounds during drinking water ozonation". Water Supply 13, n.º 6 (12 de setembro de 2013): 1576–82. http://dx.doi.org/10.2166/ws.2013.172.
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Ozonation and ozone-based advanced oxidation processes have been shown to be effective in the oxidation of several pharmaceutically active compounds (PhACs) routinely detected in surface waters. Under typical operating conditions of these processes, most of the parent compound oxidized is expected to lead to the formation of transformation products (TPs). For a target ozone exposure, the resulting hydroxyl radical exposure depends on the water matrix or process chosen (e.g. peroxone) which in turn may influence the degradation pathway and the TPs formed. This study was undertaken to examine the expected impact that varying ozone and hydroxyl radical exposures may have on TP formation from the oxidation of PhACs during typical drinking water ozonation. Two representative PhACs were selected for the study. Carbamazepine was chosen to represent PhACs with a fast reaction rate with ozone (kO3 > 104 M−1 s−1) and bezafibrate was chosen to represent PhACs with a slow to moderate reaction rate with ozone (kO3 < 104 M−1 s−1). The results show that under varying ozone and hydroxyl exposure scenarios examined, the major oxidation pathway for the parent compound was dominated by reaction with ozone for carbamazepine while for bezafibrate it varied.
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Vel Leitner, Nathalie Karpel, e Babak Roshani. "Kinetic of benzotriazole oxidation by ozone and hydroxyl radical". Water Research 44, n.º 6 (março de 2010): 2058–66. http://dx.doi.org/10.1016/j.watres.2009.12.018.
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Spanggord, Ronald J., David Yao e Theodore Mill. "Kinetics of Aminodinitrotoluene Oxidations with Ozone and Hydroxyl Radical". Environmental Science & Technology 34, n.º 3 (fevereiro de 2000): 450–54. http://dx.doi.org/10.1021/es990189i.
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Azrague, K., S. W. Osterhus e J. G. Biomorgi. "Degradation of pCBA by catalytic ozonation in natural water". Water Science and Technology 59, n.º 6 (1 de março de 2009): 1209–17. http://dx.doi.org/10.2166/wst.2009.078.
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The catalytic effect of commercially available ceramic Raschig rings versus stainless steel rings (known to be oxidant resistant) at different water qualities, for the decomposition of ozone and the hydroxyl radical formation have been investigated by using an ozone bubble column. Para-chlorobenzoic acid (pCBA) has been used as a model pollutant since it has been reported to be an ideal compound for ozone AOP studies because it displays slow reaction rates with ozone, but rapid oxidation kinetics with the OH radical. While the ozone was quite stable when the stainless steel rings were used as a packing media, the ceramic media enhanced the decomposition of the ozone. Nevertheless, the water quality was found to significantly affect the ozone stability. Indeed, in addition to high pH, both NOM and TIC lowered the ozone concentration in the system. When considering the degradation of pCBA, the ceramic packing rings, as high pH and NOM, increases its rate constant which is correlated to the higher decomposition of ozone and consequently to higher formation of hydroxyl radicals. In contrast, TIC decreased the degradation rate of pCBA even if it decomposes the ozone which is due to its scavenging effect.
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Utsumi, Hideo, Sang-Kuk Han e Kazuhiro Ichikawa. "Enhancement of hydroxyl radical generation by phenols and their reaction intermediates during ozonation". Water Science and Technology 38, n.º 6 (1 de setembro de 1998): 147–54. http://dx.doi.org/10.2166/wst.1998.0247.
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Generation of hydroxyl radicals, one of the major active species in ozonation of water was directly observed with a spin-trapping/electron spin resonance (ESR) technique using 5,5-dimethyl-1-pyrrolineN-oxide (DMPO) as a spin-trapping reagent. Hydroxyl radical were trapped with DMPO as a stable radical, DMPO-OH. Eighty μM of ozone produced 1.08 X 10-6M of DMPO-OH, indicating that 1.4% of •OH is trapped with DMPO. Generation rate of DMPO-OH was determined by ESR/stopped-flow measurement. Phenol derivatives increased the amount and generation rate of DMPO-OH, indicating that phenol derivatives enhance •OH generation during ozonation of water. Ozonation of 2,3-, 2,5-, 2,6-dichlorophenol gave an ESR spectra of triplet lines whose peak height ratio were 1:2:1. ESR parameters of the triplet lines agreed with those of the corresponding dichloro-psemiquinone radical. Ozonation of 2,4,5- and 2,4,6-trichlorophenol gave the same spectra as those of 2,5- and 2,6-dichlorophenol, respectively, indicating that a chlorine group in p-position is substituted with a hydroxy group during ozonation. Amounts of the radical increased in an ozone-concentration dependent manner and were inhibited by addition of hydroxyl radical scavengers. These results suggest that p-semiquinone radicals are generated from the chlorophenols by hydroxyl radicals during ozonation. The p-semiquinone radicals were at least partly responsible for enhancements of DMPO-OH generation.
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Mutseyekwa, Michael Emmanuel, Şifa Doğan e Saltuk Pirgalıoğlu. "Ozonation for the removal of bisphenol A". Water Science and Technology 76, n.º 10 (2 de agosto de 2017): 2764–75. http://dx.doi.org/10.2166/wst.2017.446.
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Abstract The mechanism of byproduct formation and oxidation pathway of bisphenol A (BPA) during ozonation process have been compared under acidic, neutral and alkaline conditions at an applied ozone dose of 5.3 mg·L−1 min−1. Alkaline conditions promoted the fastest removal and the pseudo first-order reaction rate constant was calculated as 0.15 min−1. Complete removal under alkaline conditions (after 30 minutes of reaction time) was achieved with 1.59 mg ozone per mg BPA and 52% mineralization was achieved at 6.04 mg ozone application per mg total organic carbon (after 90 minutes of reaction time). Hydroxyl radical dominated degradation pathway (pH 10) resulted with opening of ring-structured products into Heptanoic acid, methyl ester. Sixty per cent BPA removal occurred under acidic conditions where the ozone was dominant and formation of Cyclohexene-1-carboxylic acid, ethyl ester, Benzaldehyde, 4-hydroxy-3,5-dimethyl- and 2-Phenylbenzoquinone were evidenced. Despite the fact that complete removal was achieved under neutral conditions, mineralization was not remarkable and both hydroxyl radical and ozone-based degradation pattern was evidenced after the treatment.
Teses / dissertações sobre o assunto "Radical hydroxyl. Chlore. Ozone"
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Hamdi, El Najjar Nasma. "Cinétiques et mécanismes d'oxydation de composés pharmaceutiques par le chlore, l'ozone et les radicaux hydroxyle". Thesis, Poitiers, 2012. http://www.theses.fr/2012POIT2264/document.
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La présence dans les eaux de composés pharmaceutiques constitue de nos jours une préoccupation croissante. Une grande variété de composés pharmaceutiques a récemment été mise en évidence dans les eaux de surface. La chloration, l'ozonation et l'oxydation radicalaire sont fréquemment employés au cours de la filière de traitement des eaux pour leurs propriétés désinfectante et oxydante. Toutefois, des sous-produits d'oxydation peuvent être rémanents. Dans ce contexte, il est important de connaître la réactivité de ces procédés oxydants sur ces composés. Pour cela, l'étude de l'effet du chlore, de l'ozone et des radicaux HO• sur trois composés pharmaceutiques couramment utilisés (le métronidazole, le paracétamol et la lévofloxacine) a été menée. Dans un premier temps, une étude cinétique a été menée à 20°C qui a conduit à la détermination de constantes cinétiques. Pour chaque composé, une dégradation plus ou moins rapide a été observée suivant le procédé d'oxydation employé. Afin de prévoir le devenir des composés pharmaceutiques au niveau des étapes d'oxydation, une modélisation de la dégradation de chacun des composés pharmaceutiques (pour différentes concentrations en oxydant, temps de contact et qualités de l'eau) a été estimée. Dans un second temps, de nombreux sous-produits ont été identifiés par LC/MS et LC/MS/MS et des mécanismesréactionnels ont été proposés. Enfin, un suivi de la toxicité (suivi de l'inhibition de la luminescence de Vibrio fisheri) a été entrepris et comparé avec l'évolution des sous-produits d'oxydation. Une augmentation de la toxicité a été observée pour les premiers taux de traitement pour chaque oxydant et composé pharmaceutique testésRecently, the presence of pharmaceuticals in the aquatic environment has been reported as an emerging environmental issue. Actually, numerous pharmaceuticals have been detected in surface waters. Chlorination, ozonation and oxidation by hydroxyl radicals are widely used in water treatment due to their disinfectant and oxidation properties. However, these oxidationprocesses can induce refractory transformation products. In this context, the objective of this work was to study the fate of three commonly used pharmaceuticals (metronidazole, paracetamol and levofloxacin) during oxidation with chlorine, ozone and hydroxyl radicals. First, a kinetic study was conducted at pH 7.2 and 20°C and rate constants were determined. For each pharmaceutical, different rates of degradation were observed depending on oxidation process. To better assess pharmaceutical removal under water treatment conditions, an estimation of pharmaceutical removal under several oxidation conditions (i.e.oxidant concentrations, contact time, water quality) was undertaken. In a second part, numerous transformation products were identified by LC/MS and LC/MS/MS and reactional pathways were suggested. Finally, monitoring of the toxicity (luminescence inhibition of Vibrio fisheri) were performed and compared to the formation of by-products. An increase in toxicity was observed for each oxidation process and pharmaceutical tested for the smallest oxidant doses
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Fakih, Mariam. "Réactivité atmosphérique des principaux produits d'oxydation de première génération des monoterpènes". Electronic Thesis or Diss., Reims, 2024. http://www.theses.fr/2024REIMS010.
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Les monoterpènes sont des composés organiques volatils biogéniques (COVB) largement émis dans l'atmosphère par les forêts et les cultures végétales, représentant ainsi des acteurs significatifs de la chimie atmosphérique. Leur réactivité importante envers les oxydants atmosphériques a fait sujet de plusieurs études dans la littérature. Cependant, leurs produits de première génération d’oxydation sont moins évalués et pourraient expliquer en partie la réactivité manquante ainsi que la sous-estimation de la formation des AOS par les modèles. Dans ce contexte, cette étude vise à comprendre la réactivité atmosphérique de cinq COVB (nopinone, myrténal, kétolimonène, caronaldéhyde, et limononaldéhyde) qui sont des produits de première génération de l’oxydation des α et β-pinène et du limonène. Ce travail porte sur l’étude des processus de dégradation en déterminant la cinétique et le mécanisme des réactions d'oxydation des COVB visés par le radical OH, le chlore et l’ozone, ainsi que leur potentielle de photolyse au travers de l’étude de leurs spectres d’absorption UV-Vis. Pour ce faire, les réactions d'oxydation des cinq produits de première génération d’oxydation de monoterpènes ont été étudiées en chambre de simulation atmosphérique couplée à différentes techniques analytiques (FTIR, SPME-GC/MS, PTR-MS-ToF).L’étude spectroscopique se concentre sur la détermination des spectres d’absorption UV-visible des cinq composés dans le domaine 200-400 nm à une température de 353 ± 2 K, et à une pression inférieure à la pression de vapeur saturante du COVB. Les spectres montrent une large bande d'absorption située entre 240 et 370 nm, correspondant à la bande n-π* du groupement carbonyle. L'absorption significative de ces composés au-delà de 290 nm suggère qu’ils sont susceptibles d'être décomposés par photolyse en quelques heures au minimum.Les études cinétiques en température réalisées dans cette thèse concernent la réaction (COV+ OH) pour le nopinone, le myrténal, le kétolimonène et le limononaldehdye, la réaction (COV + Cl) pour le nopinone, le myrténal et le kétolimonène et la réaction d’ozonolyse pour le kétolimonène, le myrténal et le limononaldéhyde. Les expériences ont été menées soit en utilisant la méthode cinétique relative ou la méthode cinétique absolue dans le domaine de température 298 – 353 K et à pression atmosphérique. Les résultats cinétiques obtenus ont permis de calculer les durées de vie atmosphérique de ces composés. Leur persistance atmosphérique ne dépasse pas une journée. Ces durées de vie montrent globalement que la principale voie d’élimination des composés étudiés est liée à leur réaction avec les radicaux OH avec une concurrence importante en région côtière des radicaux Cl. Par ailleurs, les études cinétiques en température ont mis en évidence une tendance générale positive avec l'augmentation de la température vis à vis des radicaux OH et de l’ozone et négative avec le chlore.Enfin des études mécanistiques d’ozonolyse concernant l’ozonolyse du kétolimonène, myrténal et limononaldéhyde ont été élaborées. Ces études consistent à suivre l’évolution temporelle des réactifs ainsi que leur produit de formation. Ces données nous ont permis d’extraire le taux de formation des produits formés lors des processus d’ozonolyse. En se basant sur ces résultats des mécanismes réactionnels d’ozonolyse du kétolimonène, myrténal et limononaldéhyde sont proposésMonoterpenes are biogenic volatile organic compounds (BVOCs) widely emitted into the atmosphere by forests and plant crops, thus representing significant players in atmospheric chemistry. Their high reactivity towards atmospheric oxidants has been the subject of several studies in the literature. However, their first-generation oxidation products are less evaluated, and could partly explain the missing reactivity and the underestimation of AOS formation by models. In this context, this study aims to understand the atmospheric reactivity of five VOCBs (nopinone, myrtenal, ketolimonene, caronaldehyde, and limononaldehyde) that are first-generation oxidation products of α- and β-pinene and limonene. This work focuses on the study of degradation processes by determining the kinetics and mechanism of oxidation reactions of the targeted BVOCs by the OH radical, chlorine and ozone, as well as their potential photolysis through the study of their UV-Vis absorption spectra. To this end, the oxidation reactions of five first-generation monoterpene oxidation products were studied in an atmospheric simulation chamber coupled with various analytical techniques (FTIR, SPME-GC/MS, PTR-MS-ToF).The spectroscopic study focused on determining the UV-visible absorption spectra of the five compounds in the 200-400 nm range at a temperature of 353 ± 2 K, and at a pressure below the saturation vapor pressure of COVB. The spectra show a broad absorption band between 240 and 370 nm, corresponding to the n-π* band of the carbonyl group. The significant absorption of these compounds above 290 nm suggests that they are likely to be removed by photolysis in at least a few hours.The temperature kinetic studies carried out in this thesis concern the (VOC+ OH) reaction for nopinone, myrtenal, ketolimonene and limononaldehdye, the (VOC + Cl) reaction for nopinone, myrtenal and ketolimonene and the ozonolysis reaction for ketolimonene, myrtenal and limononaldehyde. Experiments were carried out using either the relative or the absolute kinetic method in the temperature range 298 - 353 K and at atmospheric pressure. The kinetic results obtained made it possible to calculate the atmospheric lifetimes of these compounds. Their atmospheric persistence does not exceed one day. Overall, these lifetimes show that the main route of elimination for the compounds studied is through their reaction with OH radicals, with significant competition in coastal regions from Cl radicals. The study also revealed a generally positive trend for OH radicals and ozone with increasing temperature, and a negative trend for chlorine.Finally, mechanistic ozonolysis studies of ketolimonene, myrtenal and limononaldehyde were carried out. These studies consist of monitoring the temporal evolution of the reagents as well as the reaction product. These data allowed us to extract the formation rate of the products formed during ozonolysis processes. Based on these results, reaction mechanisms of ozonolysis of ketolimonene, myrtenal and limononaldehyde are proposed
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Park, Ji Ho. "Experimantal and theoretical studies of isoprene oxidation initiated by hydroxyl radical". Texas A&M University, 2004. http://hdl.handle.net/1969.1/1343.
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Isoprene (2-methyl-1,3-butadiene) is the most abundant non-methane
hydrocarbon mostly emitted from the trees and its oxidation by hydroxyl radical
contributes significantly to the tropospheric ozone production. We investigate the
development of a detailed predictive mechanism for isoprene oxidation using both
theory and experiment. We have identified a novel cyclization pathway for the radicals
formed by hydroxy radical (OH) addition to the inner carbons of isoprene. The pathway
predicted that C5 carbonyl compounds are produced, and it may also provide information
on the preference of sites for OH addition. The nitrite/nitrate isomerization is directly
related to the competition between ozone production and radical termination and was
investigated using variational RRKM theory coupled with the master equation. We find
that the dominant fate of the β-hydroxy alkoxy radicals produced from the dissociation
reaction of nitrite is a prompt dissociation, whereas δ-hydroxy radicals isomerize to form
dihydroxy radicals. We have performed experiments using laser photolysis (LP)/ laserinduced
fluorescence (LIF) spectroscopy to study the initial addition reaction of the
hydroxyl radical to isoprene. The overall reaction rates were estimated from experiments
conducted at various pressures and temperatures. The determined Arrhenius rates are
k∞(T) = (3.49±0.46)x10-11exp(366±40)/T molecule-1 cm3 s-1 and k∞(T) = (3.58±0.18)x10-
11exp(356±18)/T molecule-1 cm3 s-1, for the OH and OD addition reactions, respectively.
Isoprene oxidation in the presence of O2 and NO was studied and, based on simulations
to OH cycling curves, we determined a value of (9.0±3.0)x10-12 molecule-1 cm3 s-1 for
the overall reaction rate constant of hydroxy peroxy radical with NO at 298 K. We report
a rate constant for O2 addition to the hydroxy alkyl radical of (2.3±2.0)x10-12 molecule-1
cm3 s-1 at 298 K. We find little generation of OH from the OD initiated oxidation of
isoprene, and no significant differences in OH and OD cycling, which suggests that the
H-shift isomerization is the major pathway for δ-hydroxy alkoxy radicals in agreement
with theoretical predictions.
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Ragnar, Martin. "On the importance of radical formation in ozone bleaching". Doctoral thesis, Stockholm, 2000. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3042.
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Pillar-Little, Elizabeth A. "MECHANISMS OF HETEROGENEOUS OXIDATIONS AT MODEL AEROSOL INTERFACES BY OZONE AND HYDROXYL RADICALS". UKnowledge, 2017. http://uknowledge.uky.edu/chemistry_etds/80.
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Atmospheric aerosols play an important role in climate by scattering and absorbing radiation and by serving as cloud condensation nuclei. An aerosol’s optical or nucleation properties are driven by its chemical composition. Chemical aging of aerosols by atmospheric oxidants, such as ozone, alters the physiochemical properties of aerosol to become more hygroscopic, light absorbing, and viscous during transport. However the mechanism of these transformations is poorly understood. While ozone is a protective and beneficial atmospheric gas in the stratosphere, it is a potent greenhouse gas in the troposphere that traps heat near the Earth’s surface. It also impacts human heath by irritating the respiratory tract and exacerbating cardiovascular diseases. Additionally, ozone can alter the ecosystem through oxidizing plant foliage which can lead to deforestation and crop losses as well. Both gases and aerosols in the troposphere can react with ozone directly and indirectly with hydroxyl radicals. While daytime aging is thought to be primarily driven by photochemical processes and hydroxyl radicals, ozone is thought to be a key player in nighttime or dark aging processes that can alter the physicochemical properties of aerosols. Measured concentrations of trace gases and aged aerosol components in the field are higher than values predicted based on laboratory studies and computer simulations. Consequently, new experimental approaches are needed to narrow the gaps between observations and mechanistic understandings.
In this dissertation, a plume of microdroplets was generated by pneumatically assisted aerosolization and then exposed to a flow of ozone before entering a mass spectrometer. This surface-specific technique allowed for the real-time analysis of reaction products and intermediates at the air-water interface. This work explores the in situ oxidation of iodide, a component of sea spray aerosols, by 0.05 – 13.00 ppmv ozone to explore how heterogeneous oxidation could enhance the production of reactive iodide species. Methods to study the reaction channels and intermediates were also established to not only determine a mechanism of iodide oxidation by ozone, but to enable the study of more complex systems. The developed approach was then applied to examine the oxidation of catechol and its substituted cousins, a family of compounds selected to model biomass burning and combustion emissions, at the air-water interface. While literature suggested that the primary mechanism of catechol oxidation by ozone would be the cleavage of the C1-C2 bond, it was determined that this was only a minor pathway. An indirect oxidation channel dominated heterogeneous processes at the air-water interface, giving rise to hydroxyl and semiquinone radicals that recombine to produce polyhydroxylated aromatics and quinones. This new mechanism of aging represents an overlooked channel by which brown, light-absorbing carbon aerosols are produced in the atmosphere.
In addition, the work investigates how reactions on solid particulate aerosols proceed under variable relative humidity. Thin films were developed alongside a novel flow-through reactor to study of how aerosols are transformed by ozone and hydroxyl radicals when exposed to 50 ppbv - 800 ppmv of ozone. This system was employed to probe how catechol reacts with ozone under variable relative humidity. Further work was undertaken to model the adsorption process at the air-solid interface under variable humidity, permitting the estimation of the reactive uptake of ozone by the film at concentrations (50-200 ppbv) seen in rural and urban areas. Together, these results provide an increased understanding of how heterogeneous oxidation of aerosols contributes to aerosol aging processes as well as free radical production in the troposphere.
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Wagner, Alec Thomas. "Fundamental Studies of Two Important Atmospheric Oxidants, Ozone and Hydroxyl Radical, Reacting with Model Organic Surfaces". Thesis, Virginia Tech, 2012. http://hdl.handle.net/10919/45093.
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Heterogeneous reactions between gas-phase oxidants and particulate-phase organic compounds impact many important atmospheric chemical processes. For example, little is known about the reaction dynamics of gaseous oxidants with organic compounds found in the atmosphere. The first step of the reaction between gaseous ozone and solid pentacene was investigated using Reflection Absorption Infrared Spectroscopy (RAIRS). Ozone was found to add to pentacene non-selectively and form a range of products after heavy ozone exposure. The rate limiting step had an activation energy of 17 kJ/mol, which is consistent with the findings of previous ozone oxidation studies for the cleavage of a carbon-carbon double bond. Unfortunately the products could not be used to distinguish between probable reaction mechanisms.
Hydroxyl radicals (•OH) play a major role processing atmospheric hydrocarbons. Due to their short lifetimes, not much is known about the dynamics of the first steps of •OH reactions. To investigate these reactions, a rotational state-selector was constructed to filter a molecular beam of •OH for reaction dynamics investigations with organic surfaces. The rotational state-selector was designed to leverage the linear Stark effect to pass only suitable molecules in a particular rotational state and block the flow of any other atoms, molecules and ions in a molecular beam. The state-selector was validated and used to positively deflect molecular beams of methyl iodide and D₂O via the linear Stark effect. Future studies with the rotational state-selector will investigate the initial steps of •OH reactions with solid organic compounds.Master of Science
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Kuhlmann, Rolf von. "Tropospheric photochemistry of ozone, its precursors and the hydroxyl radical a 3d-modeling study considering non-methane hydrocarbons /". [S.l.] : [s.n.], 2001. http://ArchiMeD.uni-mainz.de/pub/2001/0141/diss.pdf.
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Murray, Lee Thomas. "Factors Controlling Variability in the Oxidative Capacity of the Troposphere on Interannual to Interglacial Time Scales". Thesis, Harvard University, 2013. http://dissertations.umi.com/gsas.harvard:11034.
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This thesis explores the natural forces controlling variability of the tropospheric oxidants on interannual to glacial-interglacial time scales. The oxidants (primarily OH and ozone) determine the lifetime of many trace gases of human interest, including air pollutants and long-lived greenhouse gases such as methane. The oxidants respond to meteorological conditions, precursor emissions (natural and anthropogenic), and surface and overhead stratospheric boundary conditions, all of which have changed since the Last Glacial Maximum (LGM; ~21ka). This dissertation first examines in mechanistic detail the effect of variability in the lightning source of nitrogen oxides \((NO_x)\) precursors on interannual variability (IAV) of the oxidants in the recent past. An optimized technique is presented to constrain the lightning \(NO_x\) source in the GEOS-Chem global chemical transport model (CTM) to time-varying satellite data from the Lightning Imaging Sensor. This constraint improves the ability of the CTM to reproduce observed IAV in 9-year (1998-2006) hindcasts of tropical ozone and OH. IAV in ozone and OH is more sensitive to lightning than to biomass burning, despite greater IAV in \(NO_x\) from the latter source. The sensitivity of OH to lightning reflects positive chemical feedbacks on ozone production, \(HO_x\) recycling, and loss frequencies. This dissertation next introduces an offline-coupled climate-biosphere-chemistry framework for determining oxidant levels at and since the LGM. Detailed simulations of tropospheric composition are performed by GEOS-Chem driven by meteorological fields from the GISS ModelE general circulation model, land cover from the BIOME4-TG global terrestrial equilibrium vegetation model, and fire emissions from the LMfire model. Time slice simulations are presented for the present day, preindustrial, and two different possible representations of the LGM climate. Sensitivity of the results to uncertainty in lightning and biomass burning emissions is tested. Though well-buffered, all simulations find net reduced oxidative capacities relative to the present day. The most important parameters for controlling tropospheric oxidants over glacial-interglacial periods are changes in overhead ozone, tropospheric \(H_2O\), and lightning. The results are discussed in the context of the ice-core record, particularly for methane.Engineering and Applied Sciences
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Coeur, Cécile. "Contribution à la mesure des émissions biogéniques du pourtour méditerranéen : étude des artefacts analytiques de certains terpènes et de la réactivité de l'acétate de bornyle avec le radical hydroxyl". Université Joseph Fourier (Grenoble ; 1971-2015), 1997. http://www.theses.fr/1997GRE10103.
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La vegetation emet des quantites importantes de composes organiques volatils dans l'atmosphere. Ces composes ont un role sur la chimie tropospherique, en particulier dans la formation d'ozone. L'objectif de ce travail est d'apporter, par des etudes au laboratoire et sur sites naturels, de nouvelles donnees sur les terpenoides. Au laboratoire, nous avons observe la decomposition de certains terpenes a la surface d'adsorbants solides, avec et sans ozone. Dans les experiences sans ozone, les produits de degradation identifies sont des terpenes et des aromatiques. Nous avons suggere le role d'impuretes metalliques pour expliquer cet artefact. Par ailleurs, nous avons etudie la reaction en phase gazeuse de l'acetate de bornyle avec le radical hydroxyle. La constante determinee est k = (13. 9 0. 5) x 10#-#1#2 cm#3 molecule#-#1. S#-#1. Les produits de degradation identifies sont le bicyclo2. 2. 1-heptan-2-one-1,7,7-trimethyle, le bicyclo2. 2. 1-heptan-2-one-5-acetyloxy-4,7,7-trimethyle et le bicyclo2. 2. 1-heptan-2,3-dione-6-acetyloxy-1,7,7-trimethyle. Sur site naturel, notre etude a porte sur le quercus pubescens et le quercus ilex. Leurs taux d'emission ont ete correles aux parametres environnementaux (temperature, ensoleillement) et physiologiques (assimilation de co#2, transpiration), ainsi qu'a l'algorithme d'emission g93. Ce modele decrit tres bien les emissions du quercus ilex, mais il tend a sous-estimer celui du quercus pubescens. En outre, pendant cette campagne, nous avons releve des hauts niveaux d'ozone (> 90 ppbv). Ces concentrations ont ete attribuees au transport a plus ou moins longue distance de masses d'air riches en ozone, plutot qu'a une production photochimique locale.
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Lendar, Maria. "Dégradation atmosphérique d’une série d’alcools, d’esters et de l’hexafluoroisobutène". Thesis, Orléans, 2012. http://www.theses.fr/2012ORLE2042/document.
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Cette thèse présente le devenir atmosphérique de trois alcools saturés CH3(CH2)4OH, CH3CH2CH2CH(OH)CH3 et (C2H5)2CHOH, de trois esters CH3CH2CH2C(O)OC2H5, CH3CH2C(O)OC2H5 et CH3CH2C(O)OCH2CH2CH3 ainsi que d’un HFC insaturé (CF3)2C=CH2 avec OH et Cl. La constante de vitesse de la réaction avec OH de ces composés a été déterminée en fonction de la température (253 – 373 K), en utilisant la technique Photolyse Laser Pulsée couplée à la Fluorescence Induite par Laser (PLP-FIL). La constante de vitesse de la réaction de OH et de Cl avec les alcools, les esters et l’hexafluoroisobutène (HFIB) a été également déterminée à température ambiante en utilisant la chambre de simulation atmosphérique. Pour la réaction du radical OH avec le HFC et de l’atome Cl avec les esters et le HFC, il s’agit d’une première détermination des constantes de vitesse. Les constantes de vitesse obtenues sont comparées à la littérature, la réactivité des alcools et des esters a été discutée. Enfin, le calcul des durées de vie de ces composés ainsi que la recherche de leurs produits éventuels ont permis d’évaluer l’impact atmosphérique de ces composés sur l’environnementIn this thesis we report the atmospheric fate of three saturated alcohols: CH3(CH2)4OH, CH3CH2CH2CH(OH)CH3 and (C2H5)2CHOH, three esters: CH3CH2CH2C(O)OC2H5, CH3CH2COOC2H5 and CH3CH2COOCH2CH2CH3 and an unsaturated HFC with OH radicals and Cl atoms. The rate coefficients of OH reactions with these compounds have been measured over the temperature range 253 – 373 K, using the Pulsed Laser Photolysis – Laser Induced Fluorescence technique (PLP-LIF). Moreover the rate coefficients of OH and Cl reactions with alcohols, esters and hexafluoroisobutene (HFIB) have been determined at room temperature, using smog chambers. For the reaction of OH radicals with HFIB and Cl atoms with esters and HFIB, the rate coefficients obtained in this study present the first determination. The results have been compared with the literature and the reactivity of the compounds has been discussed. Finally, the atmospheric lifetimes of these compounds have been determined and the OH oxidation products have been identified, which allows us to estimate the atmospheric impact of these compounds
Capítulos de livros sobre o assunto "Radical hydroxyl. Chlore. Ozone"
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Hjorth, J., G. Ottobrini, F. Cappellani, G. Restelli, H. Stangl e C. Lohse. "Hydroxyl Radical Concentration in Ambient Air Estimated from C13O16 Oxidation". In Atmospheric Ozone, 725–29. Dordrecht: Springer Netherlands, 1985. http://dx.doi.org/10.1007/978-94-009-5313-0_142.
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Bell, David M., Manuela Cirtog, Jean-François Doussin, Hendrik Fuchs, Jan Illmann, Amalia Muñoz, Iulia Patroescu-Klotz, Bénédicte Picquet-Varrault, Mila Ródenas e Harald Saathoff. "Preparation of Experiments: Addition and In Situ Production of Trace Gases and Oxidants in the Gas Phase". In A Practical Guide to Atmospheric Simulation Chambers, 129–61. Cham: Springer International Publishing, 2023. http://dx.doi.org/10.1007/978-3-031-22277-1_4.
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AbstractPreparation of the air mixture used in chamber experiments requires typically the injection of trace gases into a bath gas. In this chapter, recommendations and standard protocols are given to achieve quantitative injections of gaseous, liquid or solid species. Various methods to produce ozone, nitrate radicals and hydroxyl radicals are discussed. Short-lived oxidants need to be produced during the experiment inside the chamber from pre-cursor species. Because highly reactive oxidants like hydroxyl radicals are challenging to detect an alternative method for the quantification of radical concentrations using trace molecules is described.
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Prinn, R. G. "Ozone, Hydroxyl Radical, and Oxidative Capacity". In Treatise on Geochemistry, 1–19. Elsevier, 2003. http://dx.doi.org/10.1016/b0-08-043751-6/04140-2.
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Prinn, R. G. "Ozone, Hydroxyl Radical, and Oxidative Capacity". In Treatise on Geochemistry, 1–18. Elsevier, 2014. http://dx.doi.org/10.1016/b978-0-08-095975-7.00401-0.
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Calvert, Jack G., John J. Orlando, William R. Stockwell e Timothy J. Wallington. "The Hydroxyl Radical and Its Role in Ozone Formation". In The Mechanisms of Reactions Influencing Atmospheric Ozone. Oxford University Press, 2015. http://dx.doi.org/10.1093/oso/9780190233020.003.0007.
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Although the HO radical is present in the sunlight-irradiated troposphere at very low concentrations, only about 106 molecules cm−3, it is the most important trace component in our atmosphere. It is a highly reactive transient species and is responsible for initiating the oxidation of the majority of organic compounds in the troposphere. It initiates the chain reactions that produce ozone. All the saturated, H-atom containing molecules react with HO through abstraction of an H atom. In the case of the simplest alkane, methane, reaction (1) leads to the formation of a water molecule and an alkyl (CH3) radical: . . . HO + CH4 → H2O + CH3 (1) . . . The CH3 radical released into the oxygen-rich atmosphere quickly adds O2 to give the methyl peroxy radical in reaction (2), which in NO-containing atmospheres can react to form NO2, and an alkoxy radical, CH3O, in reaction (3). In turn, this radical reacts with O2 to give an HO2 radical and a molecule of formaldehyde in (4). An HO radical can be regenerated as the HO2 molecule oxidizes NO to NO2 in (5), and the chain of events, reactions (1) through (5), leads to ozone generation through the photolysis of the NO2 molecule in reactions (6) and (7): . . . CH3 + O2 → CH3O2 (2) . . . . . . CH3O2 + NO → CH3O + NO2 (3) . . . . . . CH3O + O2 → HO2 + CH2O (4) . . . HO2 + NO → HO + NO2 (5) . . . . . . NO2 + hν → O + NO (6) . . . . . . O + O2 (+ M) → O3 (+ M) (7) . . . Methane is the least reactive of the alkanes with HO. Urban atmospheres contain a complex mixture of the more reactive larger alkanes (RH). The number of different possible geometric isomers and stereoisomers of the alkanes that can be formed by association of C and H atoms is astounding (Calvert et al., 2008). For example, there are more than a thousand structurally different molecules of molecular formula C12H26, more than a million C20H22, more than a billion of formula C25H52, and more than a trillion possible different isomers of molecular formula C31H64.
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Basumatary, Moumita, Shilpa Neog, Srutishree Sarma, Nand Kishor Gour e Ramesh Chandra Deka. "A REVIEW ON PERVASIVE ATMOSPHERIC CHEMISTRY OF VOLATILE ORGANIC ACIDS". In Futuristic Trends in Chemical Material Sciences & Nano Technology Volume 3 Book 15, 89–102. Iterative International Publishers, Selfypage Developers Pvt Ltd, 2024. http://dx.doi.org/10.58532/v3becs15p4ch5.
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Emissions of volatile organic acids can cause detrimental impact on the air quality as well as risk to human health and environment. These organic acids are found all through the troposphere at high level concentration in the ppb range. In the forested and rural regions, divergent study reveals strong variations in volatile organic acids concentration, with a considerable decrease from summer to winter. The atmospheric sources of volatile organic acids comprise of mainly emissions from biogenic, anthropogenic and precursors photochemical transformation in the gaseous, particulate and aqueous phases. We also appraise the predominant sources of volatile organic acids, principal sinks of such compounds and their benefaction to tropospheric concentration for various environments. At the tropospheric level, these organic compounds are initiated with the atmospheric oxidants like hydroxyl (OH) radicals, ozone (O3) molecules, nitrate (NO3) radicals, chlorine (Cl) atoms and play a significant role in the lower region of the troposphere. In this review, moreover, the mechanism, kinetics and atmospheric lifetime of the tropospheric reactions of both the biogenic as well as anthropogenic organic acids are bestowed and discussed succinctly.
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Calvert, Jack G., John J. Orlando, William R. Stockwell e Timothy J. Wallington. "Mechanisms of Ozone Reactions in the Troposphere". In The Mechanisms of Reactions Influencing Atmospheric Ozone. Oxford University Press, 2015. http://dx.doi.org/10.1093/oso/9780190233020.003.0005.
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In Chapter I, we identified the origin of stratospheric ozone and its role in limiting the short wavelengths of sunlight reaching the Earth. We also saw the importance of trace impurities of NOx and hydrocarbons in the development of tropospheric ozone. In this chapter, we review and evaluate the chemical reactions of ozone that create the important hydroxyl (HO) radical. It is the photodecomposition of tropospheric ozone that is the major source of the important HO radical, and it is the HO radical that initiates the destruction of most of the reactive trace gases that are emitted into the atmosphere. Ozone also serves as a major reactant for removal of the alkenes and other reactive unsaturated compounds, and, in this chapter, we review and evaluate the rate coefficients and mechanisms of these reactions and the expected products that result from them. The reactions that generate oxygen atoms in their first excited electronic state, O(1D) atoms, and ultimately HO radicals within the atmosphere are initiated through ozone photodecomposition: . . . O3 (X1A1) + hν → O(1D) + O2(a1Δg) (I) . . . . . . → O(1D) + O2(X3Σ–g) (II) . . . A fraction of the O(1D) atoms formed in the reactions (I) and (II) react with water molecules to generate HO radicals in reaction (1) and a larger fraction are deactivated by collisions with N2 and O2 molecules to form ground state O(3P) atoms in reaction (2): . . . O(1D) + H2O → HO + HO (1) . . . . . . O(1D) + M (N2, O2) → O(3P) + M (N2, O2) (2) . . . The competition between H2O and other air molecules (N2, O2) for reaction with O(1D) atoms results in HO generation being dependent on relative humidity. Rate coefficients for reaction of O(1D) with H2O, N2, and O2 at 298 K (in units of 10−10 cm3 molecule−1 s−1) recommended by the International Union of Pure and Applied Chemistry (IUPAC) panel are 2.14, 0.31, and 0.40, respectively (Atkinson et al., 2004). To better understand the factors that control HO formation, we will review ozone photochemistry, its cross sections, quantum yields of its major photodecomposition modes, and its photolysis frequencies under varied atmospheric conditions.
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VanLoon, Gary W., e Stephen J. Duffy. "Tropospheric chemistry—smog". In Environmental Chemistry. Oxford University Press, 2017. http://dx.doi.org/10.1093/hesc/9780198749974.003.0006.
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This chapter features the events and chemical processes that lead to the formation of smog. It defines what smog is before identifying the different types of smog and the chemical compounds and climatic conditions that lead to their formation. It also analyses the chemistry of photochemical smog production and introduces the hydroxyl radical as the species central to the process. The chapter outlines the key reaction sequence for oxidation of volatile organic compounds (VOCs). It explores the emission concerns connected with different types of internal combustion engines, fuel types and additives, catalytic converters, and control of specific pollutants, such as carbon monoxide, VOCs, nitrogen oxides, and ozone.
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Harrison, Roy M. "Chemistry of the Troposphere". In Pollution: Causes, Effects and Control, 182–203. The Royal Society of Chemistry, 2013. http://dx.doi.org/10.1039/bk9781849736480-00182.
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The concept of pollutant cycling in the atmosphere is introduced in this chapter and the basic determinants of atmospheric lifetime and concentration variability described. The hydroxyl radical is central to atmospheric chemistry and its formation pathways are discussed leading into a description of the formation chemistry and behaviour of tropospheric ozone. A subsequent description of other atmospheric oxidants (peroxyacetylnitrate and oxides of nitrogen) is followed by a consideration of the sources and sinks of atmospheric acids and bases. Amongst the most important constituents in the atmosphere in relation to human health and climate regulation are atmospheric aerosols whose typical composition and formation pathways are outlined. Finally, the inter-relationships between pollutants, environmental effects and impacts in relation to climate, eco-systems and human health are presented.
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Calvert, J. G., R. Atkinson, J. A. Kerr, S. Madronich, G. K. Moortgat, T. J. Wallington, e G. Yarwood. "Summary". In The Mechanisms Of Atmospheric Oxidation Of The Alkenes, 422–29. Oxford University PressNew York, NY, 2000. http://dx.doi.org/10.1093/oso/9780195131772.003.0010.
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Abstract When alkenes are released into the atmosphere of a city during the day, they react quickly (within hours), largely with hydroxyl radical (OH), and somewhat more slowly with nitrate radical (N03) and ozone (03). When released at night, alkenes react largely with N03 or 03, with lifetimes of the order of days. Alkenes (as well as alkanes and aromatic hydrocarbons) react with OH radicals to form peroxy radicals that initiate chain reactions in which NO is oxidized to N02, N02 is photodissociated [N02 + hv (>-. < 430 nm) —s+ 0(3 P) + NO], and03 is formed from the 0-atoms produced [02 + 0(3 P) + (N2/02)---+03 + (N2/02)]. Although the alkenes constitute only about 7% of the non-methane hydrocarbons (NMHC) in the early morning urban atmosphere of Los Angeles, they account for about 27% of the species reacting with OH, and about 19% of the maximum incremental reactivity (MIR). In the Boston atmosphere in the morning, alkenes account for 10% of NMHCs, 24% of the species reacting with OH, and 18% of the MIR. Alkenes are one of the most important classes of hydrocarbons in promoting 03 and smog formation in urban environments.
Trabalhos de conferências sobre o assunto "Radical hydroxyl. Chlore. Ozone"
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Hudgens, Jeffrey W., Jeffrey L. Brum, Russell D. Johnson e David V. Dearden. "Structure Matters: Detection of Difluoromethyl and Difluoroethyl Radicals by Resonance Enhanced Multiphoton Ionization Spectroscopy". In Laser Applications to Chemical Analysis. Washington, D.C.: Optica Publishing Group, 1994. http://dx.doi.org/10.1364/laca.1994.fa.4.
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The link between anthropogenic chlorofluorocarbon (CFC) release and stratospheric ozone depletion now appears well established. Several fluorinated methanes and ethanes are among the hydrofluorocarbons (HFCs) currently being investigated as replacements for the chlorine containing congeners that have traditionally found use as refrigerants, fire extinguishers, and in more specialized applications. In recent years significant effort has focused on the tropospheric degradation pathways available to HFCs initiated by H atom abstraction by a hydroxyl radical. For alternate CFC's the generic initiating reactions are: Although an impressive amount of mechanistic and kinetic information concerning these pathways has been gathered recently, much remains to be learned about the fluorinated methyl and ethyl radicals which represent the first intermediates of the degradation process.
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Li Sen e S. Ishikawa. "Hydroxyl radical rinse water technology using ozone ultrasonic ultraviolet and TiO2". In 2011 International Symposium on Water Resource and Environmental Protection (ISWREP). IEEE, 2011. http://dx.doi.org/10.1109/iswrep.2011.5893254.
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Reichle, Henry G. "A Multi-Level Tropospheric Carbon Monoxide Correlation Radiometer for Eos". In Optical Remote Sensing of the Atmosphere. Washington, D.C.: Optica Publishing Group, 1990. http://dx.doi.org/10.1364/orsa.1990.mb5.
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Carbon monoxide (CO) is a key player in the chemistry of the troposphere. It is, by far, the largest sink for the hydroxyl (OH) radical, which is the oxidizer of all reduced species in the atmosphere. In addition, chemical processes involving CO produce tropospheric ozone (O3). The sources of CO are about equally divided between anthropogenic sources (combustion of fossil fuels and biomass) and natural sources (oxidation of isoprene, methane, and other hydrocarbons). Recently, increases in the mixing ratio of CO have been observed. The increasing level of CO will have direct effects on the OH level with resulting long term effects both on tropospheric ozone production and on climate through the reduced destruction of greenhouse gases like methane.
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Saif, Babak N., Bernard D. Seery, Jacob Khurgin e Colin Wood. "Generation of Far Infrared Radiation Using Compositionally-Asymmetric Multiple Quantum Well Waveguides". In Quantum Optoelectronics. Washington, D.C.: Optica Publishing Group, 1995. http://dx.doi.org/10.1364/qo.1995.qthe15.
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NASA's Earth and space science missions have motivated the investigation of methods to produce coherent radiation in the 1-3 terahertz (THz) spectral region, corresponding to 100-150 μm wavelength, for use as local oscillator sources in high resolution laser heterodyne spectrometers. Scientific applications of this technology include measurements of the hydroxyl radical (OH) at 2.5 THz in Earth's upper atmosphere, which is important because of its role in the destruction of ozone. In addition, astrophysicists are interested in spectroscopy of the interstellar molecular cloud in this previously unexplored region of the electromagnetic spectrum. However, these measurements nessitate a space-based instrument because the lower atmosphere is largely opaque in this spectral region.
Relatórios de organizações sobre o assunto "Radical hydroxyl. Chlore. Ozone"
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Atherton, C. S. Predicting tropospheric ozone and hydroxyl radical in a global, three-dimensional, chemistry, transport, and deposition model. Office of Scientific and Technical Information (OSTI), janeiro de 1995. http://dx.doi.org/10.2172/130611.
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